DAQ-2024-012072

P R E P A R E D B Y

Utah Department of Environmental Quality
Utah Division of Air Quality

Overview
On August 3, 2018, the U.S. Environmental Protection Agency (EPA) designated Utah’s
Northern Wasatch Front (NWF) as a marginal nonattainment area (NAA) for the 2015
National Ambient Air Quality Standard (NAAQS) for 8-hour ozone concentrations.1 On
November 7, 2022, the EPA finalized the reclassification of the NWF NAA from marginal
to moderate status since the area failed to attain the standard by the marginal
attainment date.2 Monitoring data from 2021 through 2023 indicate that the NWF NAA
did not attain the standard by the moderate attainment date of August 3, 2024, and as
a result is subject to reclassification to serious nonattainment status.

1 83 Fed. Reg. 25,776 (June 4, 2018).
2 87 Fed. Reg. 60,897 (Oct. 7, 2022).
Section 179B(b) of the Clean Air Act (CAA) states,“ Notwithstanding any other
provision of law, any State that establishes to the satisfaction of the Administrator
that, with respect to an ozone nonattainment area in such State, such State would
have attained the national ambient air quality standard for ozone by the applicable
attainment date, but for emissions emanating from outside of the United States, shall
not be subject to the provisions of section 7511(a)(2) or (5)3 of this title or section
7511d4 of this title.”5 This provision is known as an international transport
demonstration and allows a state to show that international emissions are responsible
for the exceedances of the standard, which would not have occurred in absence of
these emissions. As noted in the preambles of both the 2008 6 and 2015 7 ozone
implementation rules, section 179B does not prohibit non-international border states
from submitting a demonstration. However, guidance by the EPA states that
demonstrations from states that do not directly share an international border will
require additional technical rigor compared to international border areas.8
Section 179B has two mechanisms to demonstrate that international contributions
impact a NAA’s ability to attain or maintain a NAAQS. A state may demonstrate
independent of a State Implementation Plan (SIP) revision that a NAA would have
attained the standard at a past attainment date but for the presence of international

3 CAA, Section 181(a)(2) or (5).
4 Id., Section 185.
5 42 U.S.C. § 7509a(b).
6 Implementation of the 2008 National Ambient Air Quality Standards for Ozone: State Implementation
Plan Requirements, 80 Fed. Reg. 12,264, 12,294 (March 6, 2015)(“The EPA has historically evaluated
these demonstrations on a case-by-case basis, based on the individual circumstances. The EPA does
not believe this provision is restricted to areas adjoining international borders.”).
7 Implementation of the 2015 National Ambient Air Quality Standards for Ozone: NAA State
Implementation Plan Requirements, 83 Fed. Reg. 62,998, 63,010 (Dec. 6, 2018)(“. . . we are not adopting
any geographic limitation on the use of CAA section 179B for purposes of the 2015 ozone NAAQS. We are
instead clarifying that a demonstration prepared under CAA section 179B could consider emissions
emanating from North American or intercontinental sources and is not restricted to areas adjoining
international borders, consistent with the approach articulated in the preamble of the 2008 Ozone
NAAQS SIP Requirements Rule.”)(emphasis added).
8 Guidance on the Preparation of Clean Air Act Section 179B Demonstrations for NAAs Affected by
International Transport of Emissions at 6 (Dec. 2020) (179B Demonstrations Guidance), available at
draft_179b_guidance-final_draft_for_posting.pdf.
emissions, known as a retrospective 179B(b) demonstration, and thus should not be
advanced in nonattainment classifications.9 Conversely, a state may demonstrate as
part of a SIP revision that a NAA will attain the standard by a future attainment date,
but for the presence of international emissions. This is known as a prospective 179B(a)
demonstration. 10
On May 28, 2021, the Utah Division of Air Quality (UDAQ) submitted to the EPA for
consideration a retrospective 179B(b) demonstration for the NWF NAA for the marginal
attainment date of August 3, 2021.11 In the demonstration, the UDAQ provided three
separate analyses examining international contributions including a synoptic weather
analysis, Hybrid Single–Particle Lagrangian Integrated Trajectory (HYSPLIT)12
backward dispersion modeling, and photochemical modeling results performed by a
third party showing that the area would have attained the standard by the marginal
attainment date, but for the presence of international contributions.
Upon publication of the Determination of Attainment by the Attainment Date (DAAD),
the EPA disapproved Utah’s demonstration and subsequently reclassified the area as
a moderate NAA.13 The EPA cited four primary reasons for its disapproval including: 1) a
lack of technical information; 2) a divergence in interpretation of section 179B
including the importance of the proportion of local versus international contributions;
3) a failure to demonstrate sufficient implementation of feasible emission reduction
measures; and 4) the presence of a nearby NAA that attained the standard despite
the presence of international contributions.14 It is important to note that all four of the

9 42 U.S.C. § 7509a(b)-(d); see also 179B Demonstrations Guidance at 15-18.
10 42 U.S.C. § 7509a(a); see also 179B Demonstrations Guidance at 12-15.
11 Retrospective 179B(b) Demonstration for Utah’s Northern Wasatch Front Ozone NAA. May 28, 2021.
DAQP-048-21.
12 https://www.ready.noaa.gov/HYSPLIT.php
13 87 Fed. Reg. 60,897.
14 Technical Support Document (TSD): Northern Wasatch Front (NWF), Utah: Failure to Attain the 2015
Ozone National Ambient Air Quality Standard by the Attainment Date; Reclassification and Disapproval
of International Emission Demonstration, Docket Id. No. EPA-HQ-OAR-2021-0742-0043 (Jan. 2022)
(179B NWF TSD).
points made by the EPA in the denial of Utah’s original 179B(b) demonstration are
based on EPA’s guidance, and not on any provisions in the CAA.
Additionally, the UDAQ included a prospective 179B(a) demonstration in the moderate
ozone SIP revisions for the NWF NAA, which was submitted to the EPA in September of
2023.15 However, as the EPA has not yet finalized the DAAD for reclassification from
moderate to serious designations, nor has the EPA made any final determinations on
the associated SIP revision, the outcome of that demonstration is unknown at the time
of the submission of this demonstration. Additionally, an approved prospective
179B(a) demonstration, as included within the moderate SIP revision, would not
prevent the area from being reclassified to a more stringent designations if the area
later failed to attain the standard. The prospective demonstration only pertains to the
approvability of the SIP.
In anticipation of the upcoming DAAD reclassifying NAA’s from moderate to serious
status, the UDAQ has developed a Section 179B(b) retrospective demonstration
(APPENDIX I), using an updated and improved photochemical modeling, which shows
that the NWF NAA attained the 2015 8-hour ozone NAAQS by the attainment date of
August 3, 2024, but for the presence of international emissions. Beyond the modeling
demonstration contained in APPENDIX I, this document addresses each of EPA's
reasons for denying Utah’s previous 179B(b) demonstration.

15 Utah State Implementation Plan, Section IX.D.11: 2015 Ozone NAAQS Northern Wasatch Front
Moderate Nonattainment Area. https://documents.deq.utah.gov/airquality/planning/DAQ-2023-
011344.pdf.

Demonstration Results
The full 179B(b) modeling demonstration is provided in APPENDIX I, including:
1) A conceptual model;
2) precursor and ozone trends;
3) transport analysis;
4) modeling and source apportionment; and
5) results and conclusions.
The results included here are a high-level summary of the findings. For more details
including detailed methods, modeling, technical, and model performance evaluation
statistics, please refer to APPENDIX I.
Conceptual Model
The conceptual model includes a detailed description of the physical and
topographical features of the NWF NAA, a detailed analysis of the meteorological and
atmospheric conditions during ozone exceedance episodes, as well as a description
of a well-developed conceptual model of intercontinental transport between Asia and
North America. The conceptual model details how the unique and complex topography
of the NWF NAA plays a central role in driving contributions from international
anthropogenic emissions, noting that the high mountain ranges throughout north-
central Utah enhance vertical circulations that expose the elevated basin to
background mid- and upper-tropospheric air that is often laden with foreign pollution
during the summer ozone season.
The conceptual model found that ozone exceedance days in the NWF are associated
with deep tropospheric high pressure with strong sinking motion leading to higher
temperatures, drier air, and a suppression of boundary layer mixing. This in turn is
associated with strong and deep sinking air through at least the lowest 10 km of the
atmosphere. This sinking air brings mid-level internationally influenced ozone toward
the surface where it can be mixed to the surface within the midday boundary layer.
Therefore, the atmosphere over the NWF NAA represents an area that experiences a
consistent maximum impact from the phenomenon of international transport from
Asia which raises background ozone concentrations given the climatological presence
of summertime high pressure over the western US and the elevated terrain.
Precursor and Ozone Trends
The precursor emissions and ozone trends analysis highlights the substantial amount
of emission reductions achieved throughout the NWF NAA, as well as the disconnect
observed between decreasing emissions and observed atmospheric ozone
concentrations, likely driven in part due to the increasing influence of wildfire in the
western U.S (Figure 1, and APPENDIX I Figures 17 and 18).
This analysis found that annual anthropogenic NOx emissions have decreased by 23%
and VOC emissions have decreased by 33% throughout the four county NAA from 2017
to 2020. This is consistent with the daily emission reductions as reported in the recent
moderate SIP revision.16 These emission reductions are driven by the vast array of
emission reduction strategies adopted by the state of Utah, including thirty NOx and
VOC administrative rules,17 as well as policies at the federal level including Tier III fuel
standards which were voluntarily adopted in Utah, and Tier III engine standards.

16 Utah State Implementation Plan, Section IX.D.11: 2015 Ozone NAAQS Northern Wasatch Front
Moderate Nonattainment Area. https://documents.deq.utah.gov/airquality/planning/DAQ-2023-
011344.pdf.
17 See Utah Administrative Rules: R307-211, R307-230, R307-303, R307-304, R307-328, R307-335, R307-
341, R307-342, R307-343, R307-344, R307-345, R307-346, R307-347, R307-348, R307-349, R307-350,
R307-351, R307-352, R307-353, R307-354, R307-355, R307-356, R307-357, R307-361, R307-230, R307-
356, R307-302, R307-313, R307-315, and R307-316.

Figure 1: Comparison of NWF peak ozone DV trend and triennial anthropogenic NOx and VOC precursor
emissions over the four NAA counties from 2011 to 2020 (emission years are centered on 3-year design
value periods).
Transport Analysis
HYSPLIT back trajectory analysis was used to explore the origins of air parcels that
arrived in the NWF area via long range transport on ozone exceedance days from 2021
to 2023. This analysis found that 29 of the 33 ensembles (88%) performed indicate air
parcel origins reaching toward or over Asia or passing over Mexico. This demonstrates
that international emissions from both Asia and Mexico are present on exceedance
days in the NWF NAA, and contributes to exceeding the standard.
Modeling and Source Apportionment
Results from source apportionment photochemical modeling show consistent
international anthropogenic contributions to the NWF (6 to 7%) with evidence for
larger contributions that scale with locally elevated ozone events (Figure 2, APPENDIX I
Figures 24 and 25). This agrees with the conceptual model that the very same
meteorological processes that lead to local buildup of pollution within the NWF (high
pressure subsidence with capping inversion, stagnation, higher temperature, and
increased emissions) also enhance mid-tropospheric pollution transport into the NWF.
Therefore, the contributions of international anthropogenic emissions are elevated on
exceedance days due to the high-pressure subsidence of the lowest 10 km of the
atmosphere.

Figure 2: Time series of simulated contributions to MDA8 ozone at the Hawthorne monitor site
demonstrating international anthropogenic contributions.
Results and Conclusions
When international anthropogenic contributions are accounted for, the model-
projected 2023 NWF Design Values (DV) (from 2017 DVs) show attainment of the 2015
ozone NAAQS at all sites by a large margin by the attainment date (Table 1, APPENDIX I
Tables 6 and 7). These results are consistent with previous source apportionment
analyses for the area.18,19 The removal of international anthropogenic contributions

18 Clean Air Act 179B(b) Demonstration, Northern Wasatch Front Ozone Nonattainment Area
(05/05/2021). https://documents.deq.utah.gov/air-quality/planning/air-quality-policy/DAQ-2021-
005764.pdf.
19 Utah State Implementation Plan, 2015 Ozone NAAQS Northern Wasatch Front Moderate
Nonattainment Area, Section IX Part D.11. https://documents.deq.utah.gov/airquality/planning/DAQ-
2023-011344.pdf.
from measured 2023 DVs adjusted for wildfire-impacted exceedance days in 2021-
2023 leads to attainment of the 2015 ozone NAAQS at all sites by a larger margin.
Table 1: Observed 2023 DVs (3-year average of 2021-2023 4th high MDA8 ozone) and RRF determined modeled ozone
concentrations without (2023 DV) and with international anthropogenic contributions removed (Future DV IA Adjusted). All sites
with international anthropogenic emissions removed demonstrate meeting the 70 ppb standard. *Represents a 2023 DV adjusted
for impacts of wildfire smoke (see APPENDIX I Section 5.5.2 and APPENDIX II for details).
Site County 2023 DV (ppb) RRF Future DV IA Adjusted (ppb)
Bountiful Davis 76 0.932 70
Hawthorne Salt Lake 75 0.934 70
Herriman Salt Lake 75 0.942 70
Erda Tooele 71 0.933 66
Harrisville Weber 72 0.931 67
Copper View Salt Lake 75* 0.944 70
Rose Park Salt Lake 74 0.936 69

Conclusions
In its document overviewing the disapproval of Utah’s first retrospective 179B(b)
demonstration, EPA cited a lack of “sufficient technical information”20 to support the
modeled conclusions including: a lack of emission data, observations, and
meteorological analyses. Further, EPA noted that the model UDAQ relied on for its
submission did not demonstrate adequate model performance to creditably
determine the influence of international contributions in the NAAs ability to attain the
standard.21
The 179B(b) demonstration provided here builds on the wealth of information included
within the most recent moderate SIP revision for the NWF NAA,22 as well as an
improved photochemical model (APPENDIX I). This includes detailed information on the
underlying emission inventories (APPENDIX I, Section 3), modeled and observed
concentrations (APPENDIX I, Section 5), and meteorological and conceptual model
(APPENDIX I, Section 2).23 The improved modeling also conforms with EPA’s modeling
performance metrics (APPENDIX I, Section 5.3). Thus, the analysis and conclusions
provided in this 179B(b) demonstration fulfill the technical requirements EPA noted in
Utah's first submission, and conclusively identifies the role international emissions
play in the NWF NAA’s ability to attain the 2015 NAAQS for ozone by the attainment
date.
Beyond the lack of technical information cited by EPA in its disapproval of Utah’s
179B(b) demonstration, EPA also noted that the state’s demonstration diverged from
EPA’s interpretation of criteria for a successful demonstration in several ways.24 EPA

20 179B NWF.
21 Id.
22 Utah State Implementation Plan, Section IX.D.11: 2015 Ozone NAAQS Northern Wasatch Front
Moderate Nonattainment Area. https://documents.deq.utah.gov/airquality/planning/DAQ-2023-
011344.pdf.
23 Meteorological Modeling for Wasatch FrontO3 SIP. Technical Support Documentation and Model
Performance Evaluation.
24 179B NWF TSD at 2-3.
noted that the state did not demonstrate that international transport is significantly
different on ozone exceedance days compared to non-exceedance days and that
international contributions appear to contribute less than local ozone production, and
that ozone on exceedance days in the NWF NAA is likely predominantly due to local
contributions.25
As shown in Figure 2 (more details in APPENDIX I Figure 24), this demonstration has
identified that international anthropogenic emissions contribute to 7.2% of ozone in
NWF NAA on exceedance days. As further demonstrated by Figure 2, international
emissions represent a significant contribution to the NAA relative to ozone
attributable to anthropogenic emissions within the NAA, and thus emissions which
this SIP can regulate. For instance, when averaging all exceedance days throughout
the modeling episode, anthropogenic emissions within the 4km domain contribute to
just 24.5% of modeled ozone. However, contributions from international
anthropogenic emissions account for 6.5% of the modeled ozone concentrations
during the same period.
Regardless of the amount of contribution on any given exceedance or non-
exceedance day, it is vital to acknowledge that the CAA makes no reference to a
proportional requirement of local vs. international contributions. On the contrary, the
plain language of the CAA states that an area should be granted regulatory relief if the
NAA “would have attained the national ambient air quality standard for ozone by the
applicable attainment date, but for emissions emanating from outside of the United
States.”26 The interpretation that a 179B(b) demonstration is only approvable when it
demonstrates that “ there is a large international contribution relative to the domestic
contribution and whether there are larger international contributions on exceedance
days compared to non-exceedance days”27 contradicts the statutory language.

25 Id. at 3.
26 42 U.S.C. § 7509a(b)(emphasis added).
27 Technical Support Document (TSD): Northern Wasatch Front (NWF), Utah: Failure to Attain the 2015
Ozone National Ambient Air Quality Standard by the Attainment Date; Reclassification and Disapproval
of International Emission Demonstration, Docket Id. No. EPA-HQ-OAR-2021-0742-0043 (Jan. 2022)
(179B NWF TSD).
The EPA further explains in its disapproval of Utah’s 179B(b) submission that the state
failed to adequately demonstrate that all “feasible” emission reduction strategies had
been implemented.28 As noted in the ozone implementation rules,29 emission
reduction strategies implemented as part of ozone SIPs are to be reasonably available
(i.e., Reasonably Available Control Technologies (RACT)30 or Reasonably Available
Control Measures (RACM)31), and thus feasible controls in the context of ozone
reductions strategies should be held to a comparable standard. While section 179B
makes no specific mention of the requirement for implementation of feasible controls,
sections 4 and 5 of the state’s most recent SIP revision clearly demonstrate that the
state of Utah has implemented an exhaustive list of VOC and NOx emission reduction
strategies throughout the NAA embodied in the thirty administrative rules as a result
of ongoing and past SIPs, many of which go beyond what would be considered
reasonably available.32 Beyond the emission reduction measures implemented to date,
the UDAQ has identified additional emission reduction controls and strategies as
outlined in Sections 4, 5 and 7 of its most recent SIP revision,33 many of which have
been determined to be ”beyond-RACT” measures. These emission reductions will be
implemented in the coming years and serve as further evidence that the state has
implemented feasible controls, and thus the contributions of international emissions
should be considered when determining attainment. Taken together, the efforts by
the state to reduce emissions through the adoption of RACT and RACM requirements
serves to demonstrate that the state has adopted all feasible measures that could be
implemented prior to the attainment date.
It is important to note that, much like demonstrating proportional international vs. local
contributions, the CAA does not require RACM or “feasible” control requirements for
an approvable demonstration. The test for meeting the criteria of a 179B

28 Id. at 3.
29 83 Fed. Reg. 62,998.
30 42 U.S.C. § 7511a(b)(2).
31 40 C.F.R. § 51.1112.
32 Utah State Implementation Plan, Section IX.D.11: 2015 Ozone NAAQS Northern Wasatch Front
Moderate Nonattainment Area. https://documents.deq.utah.gov/airquality/planning/DAQ-2023-
011344.pdf.
33 Id.
demonstration in the CAA is simply whether or not the area has attained the standard
by the relevant attainment date, but for the presence of international emissions.
Therefore, the availability of emission reduction measures that cannot be
implemented prior to the attainment date are irrelevant as they serve no role in
advancing the date of attainment. If an area can demonstrate attainment by the
attainment date, regardless of the presence of international emissions, additional
emission reduction measures are not required, as the area has demonstrated meeting
the standard. As the state of Utah has demonstrated that the NWF NAA has attained
the standard, requiring further emission reductions beyond the attainment date is
contrary to the CAA, irrelevant, and arbitrary.
Lastly, in its disapproval of Utah’s 179B(b) demonstration EPA argued that the
presence of a nearby ozone NAA, the Southern Wasatch Front (SWF) which attained
the standard by the marginal attainment date, is evidence that the NWF NAA can
attain the current standard despite the presence of international emissions. However,
in the same document, EPA demonstrates that the SWF has an order of magnitude
lower anthropogenic NOx emissions and almost a third of the anthropogenic VOC
emissions when compared to the NWF.34 To this point, the SWF has approximately 1.2
million fewer residents than the NWF and a substantially different industrial sector.
While the SWF did attain the 2015 ozone NAAQS by the marginal attainment date of
August 3, 2021, it did so by just 1.0 ppb, and has subsequently exceeded this
standard.35 The fact that a bordering NAA, with fewer residents, lower emissions, and a
substantially different industrial make-up, is marginally attaining the standard further
demonstrates why it is critical that the presence of international emissions be
appropriately acknowledged as regulatorily significant. Unless it is the intent of the
EPA to suggest that the NWF NAA must reduce NOx and VOC emissions to levels similar
to that of the SWF, which is impossible given the lack of reasonably available control
options as demonstrated in sections 4 and 5 of the state’s most recent moderate SIP
revision,36 the attainment status of the SWF is irrelevant. In fact, comparisons

34 179B NWF TSD at 14, Tables 2 and 3.4
35 87 Fed. Reg. 60,897 (Oct. 7, 2022) Table 1 at 60,899.
36 Utah State Implementation Plan, Section IX.D.11: 2015 Ozone NAAQS Northern Wasatch Front
Moderate Nonattainment Area. https://documents.deq.utah.gov/airquality/planning/DAQ-2023-
011344.pdf.
between two substantially different NAAs, both of which are facing the Intermountain
West’s regionally specific challenges in addressing ozone, only further supports that
international emissions are regulatorily significant to the region. Thus, section 179B is
an appropriate mechanism to provide regulatory flexibility to NAAs within this unique
geographic region.

APPENDIX I: 179B(b) Modeling Demonstration
Prepared for:
Utah Department of Environmental Quality
Division of Air Quality
195 N 1950 W
Salt Lake City, UT 84116

Prepared by:
Ramboll
7250 Redwood Blvd., Suite 105
Novato, California 94945

November 2024
1940107280

Clean Air Act §179B Demonstration
for the Northern Wasatch Front
Ozone Nonattainment Area

Ramboll – Clean Air Act §179B Demonstration for the Northern Wasatch Front Ozone Nonattainment Area
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Contents
1.0 Overview ......................................................................................................... 1
1.1 Introduction ............................................................................................... 1
1.2 Report Organization ..................................................................................... 2
1.3 Summary ................................................................................................... 2
2.0 Conceptual Model ............................................................................................ 5
2.1 The Northern Wasatch Front Airshed.............................................................. 5
2.2 Ozone Air Quality ........................................................................................ 5
2.3 Exceedances during the 2021-2023 DV Period ................................................ 7
2.4 Conditions Associated with Ozone Exceedances ............................................... 9
2.4.1 Local Meteorology ............................................................................. 9
2.4.2 Temperature and Wind Profiles ......................................................... 12
2.4.3 Surface Synoptic Analysis ................................................................. 14
2.4.4 Upper Air Synoptic Analysis .............................................................. 16
2.4.5 International Transport .................................................................... 17
3.0 Precursor and Ozone Trends .......................................................................... 21
4.0 Transport Analysis ......................................................................................... 25
5.0 Modeling to Quantify International Contribution ........................................... 30
5.1 EPA Recommended Ozone Design Value Projection Procedure ......................... 30
5.2 Source Apportionment Modeling .................................................................. 31
5.2.1 Model Configuration ......................................................................... 32
5.2.2 Model Results ................................................................................. 33
5.3 Model Performance Evaluation .................................................................... 39
5.3.1 Time Series of MDA8 Ozone at Select Sites ......................................... 39
5.3.2 Statistical Performance Metrics for MDA8 Ozone .................................. 39
5.3.3 Spatial Plots of 1-hour Ozone ............................................................ 44
6.0 Conclusions ................................................................................................... 45
7.0 References ..................................................................................................... 47
TABLES
Table 1. 2017 and 2020 annual anthropogenic emissions inventory by major sector over
Salt Lake, Davis, Weber and Tooele Counties. ............................................ 21
Table 2. NWF ozone exceedance days in 2021-2023 analyzed with HYSPLIT back
trajectories. ........................................................................................... 25
Table 3. CAMx source apportionment groups.......................................................... 32
Table 4. Baseline 2017 design values (BDV), projected 2023 future design values (FDV),
simulated IA contributions, and adjusted future design values (FDV adj) with IA
removed. .............................................................................................. 37
Table 5. As in Table 4 except with BDV based on adjusted 2017 DVs according to the
UDAQ SIP exclusion of wild-fire impacted days (UDAQ, 2023; Table 68). ...... 37
Ramboll – Clean Air Act §179B Demonstration for the Northern Wasatch Front Ozone Nonattainment Area
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Table 6. As in Table 4 except showing actual 2023 DVs (3-year average of 2021-2023
4th high MDA8 ozone) reported by EPA10, and RRF determined from the SMAT-
calculated ratio of modeled ozone concentrations without and with IA
contributions. ........................................................................................ 38
Table 7. As in Table 6 except showing adjusted 2023 DVs (3-year average of 2021-2023
4th high MDA8 ozone) by removing wildfire impact days at Copperview
(highlighted). ........................................................................................ 39
Table 8. Performance statistics for MDA8 ozone at sites within the NWF NAA on all days
of the modeling episode. ......................................................................... 43
Table 9. Performance statistics for MDA8 ozone at sites within the NWF NAA on high
days (observed MDA8 > 60 ppb). ............................................................. 43
Table 10. Performance statistics for MDA8 ozone at regional background sites
surrounding the NWF NAA on all days of the modeling episode. ................... 43
Table 11. Performance statistics for MDA8 ozone at regional background sites
surrounding the NWF NAA on high days (observed MDA8 > 60 ppb). ............ 43
FIGURES
Figure 1. Ozone monitoring sites within the NWF NAA. ............................................... 6
Figure 2. Trends in annual 4th-high MDA8 ozone among NWF monitoring sites from 2010
to 2023. .................................................................................................. 7
Figure 3. Number of ozone exceedance days in 2021 through 2023 at each of the current
NWF ozone monitors. ................................................................................ 8
Figure 4. Annual 4th highest MDA8 ozone in 2021 through 2023 at each of the current
NWF ozone monitors. ................................................................................ 8
Figure 5. Average MDA8 ozone and average daily maximum 1-hour NOx by day of week,
for exceedance and non-exceedance days during May-September, 2021-2023. 9
Figure 6. Scatter plots of MDA8 ozone concentrations versus meteorological variables at
the Hawthorne monitoring site on May through September days of 2021-2023:
daily maximum wind speed (top left), daily maximum temperature (top right),
daily mean relative humidity (bottom left), and daily mean mixing height from
a ceilometer instrument (bottom right). .................................................... 10
Figure 7. Wind rose plots for hourly speed and direction at the Hawthorne monitoring
site during 6 AM to noon on May through September days of 2021-2023: all
days (left) and ozone exceedance days (right). .......................................... 11
Figure 8. Scatter plots of MDA8 ozone concentrations versus meteorological variables at
the Bountiful Viewmont monitoring site on May through September days of
2021-2023: daily maximum wind speed (top left), daily maximum temperature
(top right), and daily mean relative humidity (bottom left). ......................... 11
Figure 9. Wind rose plots for hourly speed and direction at the Bountiful Viewmont
monitoring site during 6 AM to noon on May through September days of 2021-
2023: all days (left) and ozone exceedance days (right). ............................ 12
Figure 10. Composite and average Salt Lake City radiosonde profiles of temperature (red),
dewpoint (green), and winds (shown as wind barbs) at 00 UTC (6 PM MDT) on
all non-smoke ozone exceedances days during 2021-2023. ......................... 13
Figure 11. Average Salt Lake City radiosonde profiles of temperature (red), dewpoint
(green), and winds (shown as wind barbs) at 00 UTC (6 PM MDT) on all ozone
exceedances days (solid), all non-smoke ozone exceedances days (dotted), and
all non-exceedance days (dashed) during May-September 2021-2023. ......... 14
Ramboll – Clean Air Act §179B Demonstration for the Northern Wasatch Front Ozone Nonattainment Area
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Figure 12. Surface synoptic analysis on August 31, 2022, 00 UTC, representing conditions
favorable for ozone exceedances in the NWF area of Utah. .......................... 15
Figure 13. Mid-tropospheric (500 mb) synoptic analysis on August 31, 2022 00 UTC
representing conditions favorable for ozone exceedances in the NWF area of
Utah. .................................................................................................... 17
Figure 14. Schematic conceptual model of pollutant transport from Asia to North America
(from HTAP, 2010). Blue text on left refers to Asian continental boundary layer
processes, red text along bottom refers to low level transport, and black/white
text along top and right refers to high altitude transport. ............................ 18
Figure 15. Examples of modeled surface background ozone (ppb) from Baker et al. (2015;
left) showing July 2011 average US background from the CAMx regional
photochemical model, and from Zhang et al. (2020; right) showing tracked
ozone from Asia on May 24, 2017 from the AM4 global model. ..................... 19
Figure 16. Results from Baker et al. (2015) showing examples of US background ozone
contribution (ppb) from the western CAMx boundary and from three sets of
vertical model layers; boundary layer (left), mid troposphere (middle),
stratosphere (right). ............................................................................... 19
Figure 17. Comparison of NWF peak ozone DV trend and triennial anthropogenic NOx and
VOC precursor emissions over the four NAA counties from 2011 to 2020
(emission years are centered on 3-year design value periods). .................... 22
Figure 18. As in Figure 17, but with a revised ozone DV trendline reflecting the removal of
the 2021 4th high MDA8 ozone from the 3-year DV calculations due to the
large frequency of possible wildfire impacts during that year. ...................... 22
Figure 19. Trends in 2011-2023 June-August percentiles for 1-hour NOx concentration at
Hawthorne (top left) and Bountiful (top right), and for daily non-methane
organic compound (NMOC) concentrations at Bountiful (bottom). ................. 24
Figure 20. Location and extent of the 10 initiation points for HYSPLIT back trajectories. . 26
Figure 21. Examples of ensemble trajectory plots initiated on 4 specific NWF exceedance
days in 2021-20023 that represent 4 types of transport patterns. ................ 27
Figure 22. Heat map representation of 10-day transport of air parcels that arrive on NWF
exceedance days in 2021 – 2023. ............................................................ 29
Figure 23. Heat map representation of air parcel trajectory points 7-10 days upstream
prior to arriving on NWF exceedance days in 2021 – 2023. .......................... 29
Figure 24. Time series of simulated contributions to MDA8 ozone at the Hawthorne
monitor site (top panel), and average contributions on all days and high ozone
days. .................................................................................................... 34
Figure 25. Time series of simulated contributions to MDA8 ozone at the Bountiful
Viewmont monitor site (top panel), and average contributions on all days and
high ozone days. .................................................................................... 35
Figure 26. Spatial distribution of modeled MDA8 ozone (top left) and contributions from
OSAT source groups over the 4 km UDAQ modeling domain, averaged over the
top 10 high modeled ozone days at the Hawthorne site. .............................. 36
Figure 27. Time series of observed (grey) and simulated (red) MDA8 ozone at (top to
bottom) Bountiful, Hawthorne, Erda, and Herriman. ................................... 40
Figure 28. Time series of observed (grey) and simulated (red) MDA8 ozone at Joe Neal in
Las Vegas. ............................................................................................ 41
Figure 29. Time series of observed (grey) and simulated (red) MDA8 ozone at (top to
bottom) Great Basin, Canyonlands, and Dinosaur National Monument. ......... 42
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Figure 30. Isopleth plots of simulated hourly ozone within the 1.33 km modeling grid at 3
PM during July 13-15 when monitored ozone was high. ............................... 44

APPENDICES
Appendix A Example HYSPLIT control file for Aug 16, 2023, 2000 m initiation height, NWF
box, southeast corner initiation point
Appendix B Plots of HYSPLIT 10-day ensemble trajectories from each of 33 NWF ozone
exceedance days in 2021 – 2023
Appendix C Isopleth plots of hourly ozone (at 0, 6, 9, 12, 15, 18 local time) over the 1.33
km modeling grid with hourly observations overlaid on the high observed ozone
days of July 13-15

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1.0 Overview
This report documents data analyses and modeling that support a Clean Air Act (CAA) §179B(b) retrospective demonstration to the US Environmental Protection Agency (EPA) for
the Northern Wasatch Front (NWF) Moderate Ozone Nonattainment Area (NAA) in north-
central Utah. This demonstration shows that the NWF NAA would have attained the 2015
ozone National Ambient Air Quality Standard (NAAQS) by the moderate attainment date of
August 3, 2024 “but for” contributions from international sources.
1.1 Introduction
On October 26, 2015, the EPA revised the primary (health-based) and secondary (welfare-
based) ozone (O3) NAAQS from 0.075 to 0.070 parts per million by volume (ppm) (Federal
Register, 2015). The statistical form of the NAAQS is defined as the 3-year average of
annual 4th highest daily maximum 8-hour average (MDA8) ozone concentration. This is referred to as the “design value” (DV). The EPA designates nonattainment areas based on DVs that exceed 0.070 ppm (or 70.9 parts per billion37, ppb) based on certified, quality-
assured air quality monitoring data.
Areas along the Wasatch Front in north-central Utah experience episodically high ozone
levels during summer months when MDA8 ozone measurements often exceed 70 ppb. The
NWF NAA, which covers all of Salt Lake and Davis Counties and portions of Weber and Tooele Counties, is currently designated a moderate ozone nonattainment area for the 2015 8-hour ozone standard based on exceeding DVs through 2020. DV exceedances have continued through 2023 and thus the area will be bumped up to serious nonattainment later
in 2024/25 with an attainment date of August 2026. Serious nonattainment areas are
subject to stricter emissions reporting/permitting levels and additional control measure
requirements.
In the State Implementation Plan (SIP) addressing the moderate designation, the Utah Division of Air Quality (UDAQ, 2023) report results from photochemical source apportionment modeling. That modeling shows minor ozone contributions derived from local controllable emissions within the NWF relative to consistently substantial contributions
from regional emissions among neighbor states and foreign sources. UDAQ’s findings are
consistent with a summary by the EPA (2015) and a preliminary modeling study by Ramboll
(2021a) that show most of the ozone in the Wasatch Front results from the combination of
natural and foreign anthropogenic emissions.
The CAA provides some regulatory flexibility for nonattainment areas impacted by foreign contributions if they fail to attain despite reasonable efforts to control local emissions.
According to Section 179B of the Act, a State may develop a technical demonstration
showing that the nonattainment area would attain the ozone standard “but for” the
contribution from international emissions. As stated in its 179B demonstration guidance
(EPA, 2020; pages 5-6), “… EPA has twice affirmed in recent years its interpretation that this provision is not restricted to areas adjoining international borders [citing preambles to the 2015 and 2008 ozone NAAQS implementation rules] … Domestic O3 air quality can be
affected by sources of emissions located across US borders in Canada and Mexico, and
under certain circumstances, from sources in other continents.” EPA guidance goes on to

37 Appendix U to 40 CFR Part 50 (Section 3, paragraph (e)) requires the design value to be reported in ppm with additional digits to the right of the third
decimal place truncated.
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state, “… technical demonstrations for non-border areas may involve additional technical rigor and resources compared to demonstrations for border areas.” However, EPA provides
no additional guidance for non-border nonattainment areas beyond specific and less
relevant examples drawn from historical demonstration for areas along the US-Mexico
border.
In a previous retrospective §179B(b) demonstration looking back at the 2020 marginal attainment year (UDAQ, 2021), and a prospective §179B(a) demonstration included in the SIP looking forward to the 2023 moderate attainment year (UDAQ, 2023), both employing
detailed photochemical modeling following EPA’s guidance (EPA, 2018; 2020), UDAQ shows
that the NWF would attain the ozone NAAQS in the absence of international anthropogenic
(IA) contributions. UDAQ is submitting to EPA this updated retrospective demonstration for
the 2023 NWF moderate attainment year before the bump up to the serious classification.
This demonstration addresses the elements listed in EPA’s 179B guidance (EPA, 2020) to the extent feasible for this non-border nonattainment area.
1.2 Report Organization
This section presents historical context and summarizes results from this NWF NAA 179B(b)
demonstration. Section 2 provides a description of the NWF airshed, recent DVs for each monitoring site, a conceptual model of meteorological conditions that generally lead to ozone exceedances, and a conceptual model of intercontinental transport as summarized by the EPA. Section 3 presents an emissions analysis, tabulating current annual ozone
precursor emissions and comparing trends in emissions and measured ozone and precursor
concentrations at NWF monitors. Section 4 presents a meteorological transport analysis
based on air parcel trajectories on all exceedance days during the 2021-2023 moderate
attainment period. Section 5 summarizes photochemical modeling and ozone source apportionment results that substantiate the evidence for IA contributions to NWF ozone exceedances.
1.3 Summary
The following lines of evidence demonstrate that the NWF NAA would have attained the
2015 ozone NAAQS by the moderate attainment date of August 3, 2023 but for global international anthropogenic contributions.
• Physical setting (Section 2): The NWF is a highly urbanized and industrial area that
rests at the foot of the Wasatch Mountains and adjacent to the Great Salt Lake, features
that exacerbate airmass pooling (stagnation) and local recirculation under strong
capping inversions and contribute to degraded air quality. Furthermore, the high
mountain ranges throughout north-central Utah enhance vertical circulations that expose
the elevated basin to background mid- and upper-tropospheric air that is often laden with foreign pollution during the summer ozone season.
• Conceptual Model of Ozone Episodes (Section 2): The NWF has continued to
exceed past and current ozone standards at most monitors within the NAA, with large
site-to-site interannual variability but a slightly increasing site-averaged trendline,
despite combined state and federal regulatory actions to reduce emissions. Ozone
exceedance frequencies and concentrations during the summer of 2021 were anomalously high, likely due to a heavy influence from record-breaking wildfire activity throughout the western US. During ozone exceedances wind speed is low, temperature is high, relative humidity is low, and mixing heights are suppressed. All of these
features are consistent with locally stagnant conditions associated with a
sinking/compressing warm air mass within a deep dome of high pressure centered over
the western US, which suppresses vertical mixing and cloud formation. High
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temperatures lead to increased emission rates for biogenic and evaporative processes, along with higher chemical oxidation rates.
• Intercontinental transport (Section 2): As a summer phenomenon, ozone episodes
coincide with the seasonal western North American circulation pattern known as the
Mexican Monsoon, which brings humid air northward from Mexico into the Great Basin
states during July and August. This establishes a common transport corridor for pollutants emitted in Mexico to rapidly reach the NWF. However, there is another common transport pattern linking Asia to the western US. As summarized in EPA’s 179B
guidance document and in published literature, persistent global circulation patterns
establish a direct transport route in the mid- to upper troposphere that brings pollutant-
laden air to North America within days to weeks. Sinking air within a high pressure
dome over the western US brings transported ozone and precursors toward the surface,
while complex topography enhances vertical circulations, and thus high-altitude locations throughout the western US experience the greatest ozone impacts from intercontinental transport. This transport mechanism is especially persistent throughout
the summer season. Moreover, a recent multi-decadal trend analysis through 2021
indicates that free tropospheric ozone over western North America continues to increase
despite a decreasing trend in boundary layer ozone, affirming vertically different sources
and mechanisms.
• Emission and concentration trends (Section 3): Despite years of success in reducing precursor emissions and ambient concentrations of nitrogen oxides (NOx) and
volatile organic compounds (VOC), the region faces significant challenges in meeting the
ozone standard. These regionally specific challenges include significantly elevated
background ozone levels related to increasing instances and contributions of emissions
from wildfire events as well as both interstate and international transport. According to UDAQ reported triennial emission inventories for the NWF counties, nitrogen oxide (NOx) and volatile organic compound (VOC) emissions have decreased by roughly half (46% and 55%, respectively) between 2011 and 2020, and these reductions are consistent
with summer season ambient NOx and VOC concentration measurements over the same
period. However, NWF ozone DVs have increased at a rate of just under a half ppb per
year. UDAQ estimates that NOx and VOC emissions will continue to decrease into the
future as local and federal control measures continue to take effect.
• Trajectory analyses (Section 4): Upstream air parcel transport pathways arriving in the NWF on exceedance days during 2021-2023 were analyzed using the HYSPLIT
trajectory model. Most ozone exceedance days were analyzed except those noted with
medium and heavy smoke impacts (as reported by UDAQ), resulting in a set of 33
exceedance days. Four types of distinct transport patterns were subjectively identified
with 29 of the 33 trajectory days (88%) indicating air parcel origins reaching
toward/over Asia (40%) or passing over Mexico (48%).
• Source apportionment modeling (Section 5): Results from source apportionment photochemical modeling show consistent international anthropogenic contributions to
the NWF (6 to 7%) with evidence for larger contributions that scale with locally elevated
ozone events. This agrees with our conceptual model that the very same meteorological
processes that lead to local buildup of pollution within the NWF (high pressure
subsidence with capping inversion, stagnation, higher temperature, and increased emissions) also enhance mid-tropospheric pollution transport into the NWF area. With the removal of the international anthropogenic contributions, the model-projected 2023
NWF DVs (from 2017 DVs) attain the 2015 ozone NAAQS at all sites by a large margin.
These results are consistent with previous source apportionment analyses for the area
(UDAQ, 2021; 2023). The removal of international anthropogenic contributions from
measured 2023 DVs leads to attainment of the 2015 ozone NAAQS at all sites except at
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Copperview. Exclusion of wildfire smoke-impacted days in 2021 only at Copperview are sufficient to show attainment without international anthropogenic contributions.
Based on these results, international anthropogenic emissions contribute to ozone
exceedances in the NWF NAA, and the area would have attained the 2015 ozone NAAQS by
the marginal attainment date of August 3, 2023 but for that contribution.

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2.0 Conceptual Model
The conceptual model developed here characterizes the environmental factors that lead to high summertime ozone events in the NWF nonattainment area. It includes information
regarding ozone concentration and precursor emission patterns, local versus regional
meteorology/transport, and wildfire influences. A “synoptic” meteorological analysis using
surface and upper air weather maps during 2021-2023 exceedance days frames the local
and large scale conditions and features that set up during high ozone events. This section also includes a well-developed conceptual model of intercontinental transport between Asia and North America, as summarized in EPA’s 179B Guidance document (EPA, 2020) and
published literature.
2.1 The Northern Wasatch Front Airshed
As documented in the moderate ozone SIP (UDAQ, 2023), the boundaries for the NWF NAA include three valleys that are part of the Intermountain West’s basin and range geological province (Figure 1): the Salt Lake Valley, the North Salt Lake Valley, and the Tooele Valley.
The majority of the approximately 1.8 million residents within the NWF NAA reside in the
two Salt Lake Valleys situated along the base of the Wasatch Mountains. All three areas
consist of a variety of complex topography including low and broad valleys bordered by
steep mountain terrain and the Great Salt Lake. The average elevation of the three valleys is 4,327 feet above sea level with the bordering Wasatch Mountains rising to elevations over 11,000 feet. The area experiences a summer continental climate with hot and dry summers dominated by persistent high-pressure systems spanning much of the Intermountain West.
The relatively high baseline elevation, coupled with its warm and dry climate, and its
prominent location in the Intermountain West, results in a naturally high contribution of
background ozone in the NWF NAA during the typical summer ozone season (Jaffe et al.,
2018).
2.2 Ozone Air Quality
The UDAQ operates a network of continuous ambient air monitors that meet standardized
EPA requirements. The monitors collect data for five NAAQS criteria pollutants including:
sulfur dioxide (SO2), carbon monoxide (CO), ozone (O3), nitrogen dioxide (NO2) and
particulate matter (PM10 and PM2.5). In addition, UDAQ operates four continuous gas
chromatographs for the collection and analysis of VOC concentrations under the Photochemical Assessment Monitoring Station (PAMS) program. PAMS sites are required for
enhanced monitoring of ozone precursor chemicals in areas with populations over 1,000,000
and with nonattainment designations of moderate and above. Utah has also established a
comprehensive meteorological monitoring network to supply data for modeling activities,
including measurements of temperature, relative humidity, wind speed, and wind direction.
With respect to ozone, UDAQ’s monitoring network consists of eleven active regulatory sites, including three historic sites (Harrisville, Hawthorne, Bountiful) that help provide context for the extent and length of UDAQs monitoring network (Figure 1). The PAMS
monitor is co-located with the Hawthorne site in Salt Lake County. UDAQ measures the
following parameters at that site: ozone, carbonyls, meteorological parameters
(temperature, wind speed/direction, pressure, relative humidity, precipitation, mixing layer
height, solar radiation), speciated VOC, true NO2, NO, and total oxidized nitrogen (NOy).

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Figure 1. Ozone monitoring sites within the NWF NAA.

Figure 2 shows trends in monitored annual fourth-high MDA8 ozone for the past 14 years.
For clarity, 2021-2023 values at two of the newest sites, Inland Port and AMC/Utah Tech
Center, are not shown but report ozone levels consistent with Lake Park. Despite combined
state and federal regulatory actions to reduce emissions in the NWF, the area has continued to exceed past and current ozone standards at most monitors within the NAA. Overall, the data exhibit a slightly increasing site-averaged trendline over the period (~0.1 ppb/year,
not plotted). Ozone during the summer of 2021 was anomalously high, likely due to a
heavy influence from record-breaking wildfire activity throughout the western US. If that
year is removed, the site-averaged ozone trendline in Figure 2 is practically flat (-0.02
ppb/year, not shown) but with very low correlation due to large interannual variability.
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Figure 2. Trends in annual 4th-high MDA8 ozone among NWF monitoring sites from 2010 to 2023.
2.3 Exceedances during the 2021-2023 DV Period
The three years spanning 2021-2023 comprise the 2023 DV period and thus represent
conditions during the latest monitoring period that failed to attain the 2015 ozone NAAQS by the moderate attainment date. Figure 3 presents the number ozone exceedance days each year and at each of the current NWF ozone monitors. The number of exceedance days
associated with potential impacts from western US wildfires is highlighted by the grey bars,
as determined by UDAQ 38 who identified smoke-impacted days using a two-factor
methodology involving surface monitoring of PM2.5 concentrations and satellite imagery.
First, 24-hour PM2.5 concentration data were used to identify elevated levels potentially due
to wildfire smoke, followed by the use of NOAA’s Hazard Mapping System (HMS) to confirm the presence of smoke plumes over monitoring sites. A day was flagged as smoke-
impacted if PM2.5 levels exceeded one standard deviation above the monthly mean, and the
presence of a smoke plume was detected in HMS. Ozone exceedance dates were then
noted with no, light, medium, and heavy smoke impacts. This is similar to a methodology
that was developed and employed in a UDAQ-funded project led by Jaffe et al. (2023).
Disregarding smoke days, the typical number of exceedances range up to 10 per year. The least frequent exceedances occur at Erda in Tooele County, well west of the NWF urbanized basin and separated by a substantial ridge. The most consistently frequent exceedances
occur at Bountiful/Viewmont, north of central Salt Lake City. Other frequent exceedances of
5 or more occur at the newer sites: Inland Port, Near Road, and Utah Tech Center. The
number of exceedances associated with smoke days is a significant feature in 2021, which
increases the frequencies by factors of 3 to 6. These exceedances days are pervasive across the entire monitoring network, even at Erda, indicating a widespread impact separate from local source influences. In other years, there are only 1 to 2 exceedances associated
with smoke days, which illustrates just how much of an outlier 2021 is with respect to
wildfire smoke.

38 UDAQ provided a list of 2021-2023 ozone exceedance dates noting light, medium, and heavy smoke impacts.
60
65
70
75
80
85
90
2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 2023
pp
b
4th-high MDA8 Ozone
Bountiful Copperview Hawthorne Rose Park
Herriman Lake Park Near Road Tooele #3
Erda Harrisville Ogden NAAQS
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Figure 3. Number of ozone exceedance days in 2021 through 2023 at each of
the current NWF ozone monitors.
Figure 4 presents the 4th highest MDA8 ozone concentrations each year and at each of the current NWF ozone monitors (all days considered). Despite differences in exceedance
frequencies (Figure 3), most sites reach or exceed the 70 ppb standard in all three years,
showing how ozone is an area-wide problem. Significantly higher 4th-high ozone occurs in
2021 and again this indicates that fire smoke not only increased exceedance frequencies but
also ozone levels as well. This is consistent with findings from the 2022 Salt Lake Regional Smoke, Ozone, and Aerosol (SAMOZA) Study that showed highly reactive VOC in fire smoke can enhance local ozone production by 5-10 ppb (Jaffe et al., 2023, 2024).

Figure 4. Annual 4th highest MDA8 ozone in 2021 through 2023 at each of the
current NWF ozone monitors.

0
5
10
15
20
25
30
Bountiful #2 Copperview Erda Harrisville Hawthorne Herriman #3 Inland Port Lake Park Near Road Rose Park Utah
TechnicalCenter
Number of Ozone Exceedances During 2023 DV Period
Smoke Day Exceedances 2021 2022 2023
0
10
20
30
40
50
60
70
80
90
100
Bountiful #2Copperview Erda Harrisville Hawthorne Herriman #3 Inland Port Lake Park Near Road Rose Park UtahTechnicalCenter
pp
m
H4MDA8 Ozone
2021 2022 2023 2015 NAAQS (70 ppb)
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Figure 5 presents an analysis of NOx and ozone at the Hawthorne monitor by day of week during the 2021-2023 ozone seasons (May-September). Considering the more robust
number of non-exceedance days, average daily maximum 1-hour NOx concentrations are
notably lower on weekends, but there is very little ozone variation other than a hint of
higher weekend ozone on Friday through Sunday. Other studies report similar findings
(Jaffe et al., 2022, 2023, 2024). The weekend ozone signal suggests a slight NOx-disbenefit condition at that site, where under NOx-rich conditions higher mid-week NOx can inhibit ozone projection while lower weekend NOx eases that inhibition. On exceedance
days, however, there is no clear ozone pattern in NOx or ozone by day of week. This is
likely related to the small number of exceedances occurring on each day of the week (from
1 to 6 over the 2021-2023 period) when daily meteorological and emissions variations, as
well as intermittent wildfire influences, are not sufficiently averaged out. Nevertheless,
exceedance day ozone levels tend to correlate with NOx levels by day of week, indicating ozone sensitivity to NOx.

Figure 5. Average MDA8 ozone and average daily maximum 1-hour NOx by day
of week, for exceedance and non-exceedance days during May-September, 2021-2023.
2.4 Conditions Associated with Ozone Exceedances
2.4.1 Local Meteorology
Figure 6 compares daily MDA8 ozone concentrations against four key meteorological
variables measured at the Hawthorne monitoring site during all days of May through
September, 2021-2023. The variables include daily maximum wind speed, daily maximum temperature, daily mean relative humidity, and daily mean mixing height reported by a ceilometer instrument. Presented as scatter plots, Figure 6 captures the cluster of
meteorological conditions that are prevalent during ozone exceedance days (red dots) over
the past 3 years comprising the attainment year DV period. Figure 7 presents wind roses at
Hawthorne for the same period. Wind roses show the frequency distributions for the
0
10
20
30
40
50
60
70
80
90
Sun Mon Tue Wed Thu Fri Sat
pp
b
Hawthorne 2021-2023, May-September
Non-exceedance MDA8 ozone Non-exceedance daily max NOx
Exceedance MDA8 ozone Exceedance daily max NOx
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combination of wind speed (radially) and direction (azimuthally); the frequencies shown in Figure 7 were developed from the ozone production hours 6 AM to noon. Separate roses
are shown for all May-September days and only for exceedance days. Similar scatter and
wind rose plots from the Bountiful Viewmont monitoring site are shown in Figures 8 and 9
(note mixing height is not reported at this site).

Figure 6. Scatter plots of MDA8 ozone concentrations versus meteorological variables at the Hawthorne monitoring site on May through September days of 2021-2023: daily maximum wind speed (top left), daily maximum temperature (top right), daily mean relative humidity (bottom left), and daily mean mixing
height from a ceilometer instrument (bottom right).

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Figure 7. Wind rose plots for hourly speed and direction at the Hawthorne
monitoring site during 6 AM to noon on May through September days of 2021-
2023: all days (left) and ozone exceedance days (right).

Figure 8. Scatter plots of MDA8 ozone concentrations versus meteorological variables at the Bountiful Viewmont monitoring site on May through September
days of 2021-2023: daily maximum wind speed (top left), daily maximum
temperature (top right), and daily mean relative humidity (bottom left).
20
30
40
50
60
70
80
90
2 4 6 8 10 12 14 16 18
MD
A
8

O
z
o
n
e

[
p
p
b
]
Daily Maximum Hourly Windspeed [knots]
Daily Maximum Wind Speed
Non-Exceedance Day
Exceedance Day
70 ppb NAAQS
2021-2023, May -Septemberat Bountiful Viewmont 20
30
40
50
60
70
80
90
45 55 65 75 85 95 105 115 125
MD
A
8

O
z
o
n
e

[
p
p
b
]
Degrees Fahrenheit
Daily Maximum Temperature
Non-Exceedance Day
Exceedance Day
70 ppb NAAQS
2021-2023, May -Septemberat Bountiful Viewmont
20
30
40
50
60
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90
0 10 20 30 40 50 60 70 80 90 100
MD
A
8

O
z
o
n
e

[
p
p
b
]
Percent
Daily Mean Relative Humidity
Non-Exceedance Day
Exceedance Day
70 ppb NAAQS
2021-2023, May -Septemberat Bountiful Viewmont
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Figure 9. Wind rose plots for hourly speed and direction at the Bountiful
Viewmont monitoring site during 6 AM to noon on May through September days of
2021-2023: all days (left) and ozone exceedance days (right).
Meteorological patterns recorded at both Hawthorne and Bountiful Viewmont are very
similar. As expected during ozone exceedances, wind speed is low (mostly <6 knots or 3
m/s), temperature is high (mostly >90 °F), relative humidity is low (<40%), and mixing
heights at Hawthorne are suppressed (mostly <1000 m). All of these features are consistent with locally stagnant conditions associated with a sinking/compressing air mass within a deep dome of high pressure centered over the western US. Sinking motions warm the atmosphere and suppress vertical mixing and cloud formation. High temperatures lead
to increased emission rates for biogenic and evaporative processes, along with higher
chemical oxidation rates. Winds reflect the dominant local forcings such as lake/land and
mountain/valley circulations on all summer days. The morning wind roses on exceedance
days confirm the dominance of low wind speeds with more focused southerly directional distributions during the morning hours, indicating flow moving from the valley towards the Great Salt Lake.
These wind patterns are consistent with results from the 2022 SAMOZA study (Jaffe et al.,
2024). Based on 12-hour back trajectory data, Jaffe report that the most frequent wind
directions during the mornings of 2015-2022 ozone exceedance days were from the
southeast to south directions. That means precursor airmass trajectories coming from the
south traverse the highly populated areas of Salt Lake and Utah counties (~2 million population) during the ozone production period before arriving at the high ozone monitoring sites in north-central NWF. Whereas the wind roses indicate similar directional patterns on
all versus exceedance days, the main difference on exceedance days is the predominance of
lower wind speeds, less ventilation from shallower mixing, and warm temperatures.
Therefore, ozone exceedance days are associated with subtle stagnating changes in local
meteorology.
2.4.2 Temperature and Wind Profiles
Figure 10 presents a composite of vertical temperature, dewpoint, and wind profiles on all 2021-2023 non-smoke impacted ozone exceedance days as measured by radiosonde
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balloon soundings launched from Salt Lake City International Airport. Each individual profile represents a balloon ascent at 00 GMT (6 PM MDT), where altitude is represented by
atmospheric pressure (in units of hectopascals or hPa). The bottom of the plot at 1000 hPa
represents sea level, while the top of the plot at 100 hPa is equivalent to ~15 km (50,000
ft) above sea level. The average temperature and dewpoint are plotted in bold. Only the
average wind profile is shown on the right, where each symbol represents the direction from which the wind is blowing with speed indicated by the barbs in knots (one full barb signifies 10 knots, half barbs are 5 knots).

Figure 10. Composite and average Salt Lake City radiosonde profiles of
temperature (red), dewpoint (green), and winds (shown as wind barbs) at 00 UTC (6 PM MDT) on all non-smoke ozone exceedances days during 2021-2023.

The high altitude of Salt Lake Valley is apparent by the profiles starting at around 860 hPa
(~1,360 m or ~4,500 ft above sea level). The average surface temperature exceeds 30°C
(86°F) and the profile indicates adiabatic (well-mixed) conditions in the late afternoon extending to around 700 mb or roughly 1,600 m (5,200 ft) above the valley floor. The
average wind profile also indicates mixing heights reaching 700 mb as indicated by the
sharp change in direction in the mean profile. Unlike temperature, the dewpoint profiles
exhibit large variability indicating a wide range of atmospheric humidity day-to-day.
Figure 11 compares the average temperature, dewpoint, and wind profiles on non-smoke
exceedance days (as in Figure 10), all exceedance days, and all May-September non-exceedance days during May-September 2021-2023. Exceedance days are substantially warmer than non-exceedance days throughout the troposphere (~200 mb, ~12,000 m or
39,000 ft), and the entire warmer troposphere is deeper as indicated by the higher
temperature transition to isothermal in the stratosphere. Non-smoke exceedance days are
just slightly warmer than all exceedance days, but those differences are likely not
statistically significant. The average non-exceedance day temperature profile indicates
deeper mixing to about 600 mb (2,800 m or 9,200 ft above the valley floor). All exceedance days also tend to be drier as shown by lower dewpoint, although non-smoke exceedances are slightly more humid. These patterns indicate that ozone exceedance days
are always associated with deep tropospheric high pressure with strong sinking/compressive
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motion leading to higher temperatures, drier air, and a suppression of boundary layer mixing.

Figure 11. Average Salt Lake City radiosonde profiles of temperature (red), dewpoint (green), and winds (shown as wind barbs) at 00 UTC (6 PM MDT) on all ozone exceedances days (solid), all non-smoke ozone exceedances days (dotted), and all non-exceedance days (dashed) during May-September 2021-2023.
2.4.3 Surface Synoptic Analysis
This section presents a qualitative overview of the regional surface meteorological
conditions that are associated with ozone exceedance events in north-central Utah. This
summary is based on a “synoptic” review of surface weather maps for every day in each
month when at least one exceedance date occurred: June through September 2021, June through September 2022, and May through August 2023. The maps are produced at the scale of the contiguous US and archived by the National Weather Service’s Weather
Prediction Center.39
As expected, ozone exceedances usually occur during periods of higher surface pressure.
As discussed in Section 2.4.1, high-pressure systems are associated with sinking motion.
This action brings mid-tropospheric ozone down toward the surface over long distances, inhibits convection and cloud development, and creates conditions favorable for air stagnation at the surface. Additionally, since air warms during compressive sinking motion,
days with higher pressure are also associated with warmer temperatures, leading to both
increased biogenic and evaporative emissions and increased reaction rates. It is noted that
warm and dry conditions associated with high surface pressure are typical of the summer
climatology of the area. Therefore, many days in the record experience these conditions in the absence of ozone exceedances. Outside of other regional influences such as wildfire activity, however, locally-generated ozone exceedance days are always associated with high
pressure, high temperatures, and low winds.

39 https://www.wpc.ncep.noaa.gov/archives/web_pages/sfc/sfc_archive.php.
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Figure 12 shows a representative example of surface conditions during a non-smoke impacted ozone exceedance event on August 31, 2022 at 00 UTC (6 PM MDT on August 30).
The maps include sea level pressure contours (isobars), locations of fronts and troughs, and
meteorological variables recorded at a sample of surface stations (temperature, dewpoint,
wind barbs, and pressure). High pressure was dominant throughout the Intermountain
West, stretching from western Canada southward into Arizona and New Mexico. Pressure was unusually high for the season, although given the elevation of the Intermountain West, extrapolated sea-level pressure should be treated with some caution. Light or calm winds
are noted at the surface stations in Utah and the surrounding states. Conditions are hot
and dry, as typified by reports of 91°F temperature and 36°F dewpoint at Milford, UT. The
temperature, dewpoint, and wind observations are consistent with the exceedance day
values displayed in Figures 6 and 8. Fire-influenced exceedances days are found to be
noticeably cooler, however. For example, during July 2021 the extensive wildfire activity
provided a large source of ozone precursors, but either the smoke obscured sunlight which moderated daily maximum temperatures, and/or local conditions on those days would not have been sufficient in isolation to produce exceedance ozone levels.

Figure 12. Surface synoptic analysis on August 31, 2022, 00 UTC, representing conditions favorable for ozone exceedances in the NWF area of Utah.

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2.4.4 Upper Air Synoptic Analysis
This section presents a similar qualitative overview of the regional upper air meteorological
conditions that are associated with ozone exceedance events in north-central Utah. This
summary is based on a “synoptic” review of mid-tropospheric (5.5-6 km) weather maps for
the same set of days in 2021-2023 that were reviewed in Section 2.4.3. The maps are
produced at the scale of most of North America and archived by the National Weather
Service’s Weather Prediction Center.40 Similar synoptic patterns associated with ozone exceedance days are found aloft and at the surface. The patterns in pressure, wind, and temperature aloft are more prominent than those found at the surface and less influenced
by surface topology.
Figure 13 shows a representative example of conditions at the 500 mb pressure level on
August 31, 2022 at 00 UTC (6 PM MDT on August 30). Note that in this case, the map
presents contours of geopotential height of the 500 mb pressure level above sea level,
plotted as dekameters (dkm). Regions of high or low height on these maps are analogous to regions of high or low pressure in the surface analyses. Similar observational data for temperature, dewpoint, and wind barbs are also plotted from radiosonde balloon profile
measurements. A very strong and wide ridge of anomalously high geopotential heights was
present across the western two-thirds of the US. The axis of the ridge extended from
western Canada through Arizona and New Mexico, aligned with the surface pressure ridge.
The clockwise circulation around the ridge was rather weak for this altitude (5-15 knots). Stronger wind speeds were present to the north and east, across southern Canada and the Great Lakes, where the gradients in geopotential height were stronger.
The 500 mb pressure surface map is shown as a representative example, but similar
patterns of high geopotential heights and low wind speeds associated with surface ozone
exceedance days also hold true for data reviewed at other levels, including 700 mb (~3 km)
and 300 mb (~9 km). These ridging patterns indicate that locally-generated ozone
exceedances in Utah are always associated with strong and deep sinking air through at least the lowest 10 km of the atmosphere. Sinking air brings down mid-level ozone toward the
surface where it can be mixed to the surface within the midday boundary layer.

40 https://www.wpc.ncep.noaa.gov/archives/web_pages/sfc/sfc_archive.php.
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Figure 13. Mid-tropospheric (500 mb) synoptic analysis on August 31, 2022 00
UTC representing conditions favorable for ozone exceedances in the NWF area of
Utah.
2.4.5 International Transport
It is first important to define the term “background ozone.” Historically, it has been used generically to mean ozone formed outside the area of concern (e.g., a basin/airshed, region,
or the entire US) and so it’s specific meaning changes according to context. From a policy
or regulatory standpoint, background ozone often refers to the uncontrollable fraction
entering and impinging on the area of concern. In the context of domestic air pollution,
background ozone includes all domestic and global natural sources (biogenic, stratospheric,
natural fires, lightning, etc.) and foreign anthropogenic or IA sources (industrial/ commercial, transportation, residential, agricultural fires, etc.).
EPA’s synthesis of relevant literature, including scientific reviews presented by EPA (2015)
and Jaffe et al. (2018), consistently shows that international pollutants arrive in the US from
both diffuse and distinct plume transport. This distinction is important because while plume
impacts can result in relatively discrete events at specific locations, the diffuse aspect of
background ozone leads to a more seasonally homogenous and long-term contribution to pollution levels over wide areas of the western US. At high-altitude western US sites, modeled background ozone correlates with total ground-level ozone, implying that the
background drives day-to-day variations in observed ozone (Fiore et al., 2014 [see their
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Figure 8]; Lefohn et al., 2014; Huang et al., 2015), although Dolwick et al. (2015) note that the fractional background contribution is typically less for the highest modeled values.
As a summer phenomenon, ozone episodes coincide with the seasonal western North
American circulation pattern known as the Mexican Monsoon. This lower-level atmospheric
flow pattern brings humid air northward from Mexico into the Great Basin states during July
and August. This establishes a common transport corridor for pollutants emitted in Mexico to rapidly reach the NWF. However, there is another common transport pattern in the mid-to upper atmosphere linking Asia to the western US.
This remainder of this section presents a conceptual model of intercontinental ozone
transport from Asia. The transport mechanism described here is based on a summary of
current scientific understanding as presented in EPA’s 179B guidance document (EPA,
2020). Seasonally persistent global circulation patterns establish a direct transport route
within the upper troposphere that brings pollutant-laden air from Asia to North America within days to weeks (Figure 14). Over eastern Asia, a persistent low-pressure trough lofts air and associated pollutants to the upper troposphere. While rapidly transported across the
Pacific, the chemical lifetimes of ozone and peroxyacetyl nitrate (PAN, an ozone precursor)
increase because low temperatures minimize destruction (Jiang et al., 2016). Sinking air
within the persistent high pressure dome over the western US brings transported ozone and
PAN toward the surface, while complex topography and deep boundary layer mixing enhances vertical transport (Zaveri et al., 1995). Thus, high-altitude locations throughout the western US experience the greatest ozone impacts from intercontinental transport. This
transport mechanism is especially persistent throughout the summer season.

Figure 14. Schematic conceptual model of pollutant transport from Asia to North
America (from HTAP, 2010). Blue text on left refers to Asian continental boundary layer processes, red text along bottom refers to low level transport, and black/white text along top and right refers to high altitude transport.

Baker et al. (2015) and Zhang et al. (2020) employed different modeling techniques that
assessed and confirmed the importance of deep vertical transport of global ozone from the
middle and upper troposphere to the western US. Interestingly, both studies referenced
above show that summer surface background ozone in the western US often peaks over Utah as a result of sinking motion from the mid-troposphere (Figures 15 and 16) and
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circulations induced by the high topography. This pattern is consistent with other literature (Langford et al., 2017; Mathur et al., 2022) that state some of the highest U.S. background
ozone occurs in Nevada and Utah.

Figure 15. Examples of modeled surface background ozone (ppb) from Baker et
al. (2015; left) showing July 2011 average US background from the CAMx regional
photochemical model, and from Zhang et al. (2020; right) showing tracked ozone from Asia on May 24, 2017 from the AM4 global model.

Figure 16. Results from Baker et al. (2015) showing examples of US background ozone contribution (ppb) from the western CAMx boundary and from three sets of
vertical model layers; boundary layer (left), mid troposphere (middle),
stratosphere (right).
EPA 179B guidance also summarizes extensive research linking decadal increases in Asian emissions to intercontinental transport. During the 1990s and 2000s, Asian NOx emissions
increased quickly (van der A et al., 2017) along with transported ozone (Verstraeten et al.,
2015; Lin et al., 2017). Numerous other studies (EPA, 2015 and references therein; Huang,
et al., 2017; Nopmongcol et al., 2017) have estimated resulting ozone transport to North
America up through 2010. While Jaffe et al. (2018) present a consensus from the literature that Asian transport had peaked around 2010, a recent multi-decadal trend analysis through 2021 (Chang et al., 2023, and references therein) indicates that free tropospheric ozone
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over western North America continues to increase despite a decreasing trend in boundary layer ozone, affirming vertically different sources and mechanisms.
In summary, there is overwhelming evidence from more than a decade of scientific
literature that transport of ozone from Asia has raised background ozone levels in the
western US, particularly in high elevation areas exposed to enhanced vertical circulations
from complex terrain. According to numerous modeling analyses presented in the literature, the atmosphere over Utah represents an area of consistently maximum impact from this phenomenon given climatological presence of summertime high pressure over the
western US and the elevated terrain.

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3.0 Precursor and Ozone Trends
Table 1 lists the two most recent annual anthropogenic NOx and VOC emissions inventories by major sector over the entirety of the four NAA Counties (Salt Lake, Davis, Weber and
Tooele) as reported by UDAQ (2024a,b). The largest contributors to NOx emissions include
on-road and nonroad vehicles and point sources. The largest contributors to VOC emissions
include area (non-point) sectors and on-road vehicles. Remarkable emission reductions are
estimated to have occurred in the intervening three years between these inventories (-23% and -33% for NOx and VOC, respectively) across all sectors except for area source NOx. Vehicle and area emissions are the largest drivers of these reductions.
Table 1. 2017 and 2020 annual anthropogenic emissions inventory by major sector over Salt Lake, Davis, Weber and Tooele Counties.

2017 2020 % Difference
NOx (tpy) VOC (ty) NOx (tpy) VOC (tpy) NOx VOC
Area 2,621 21,143 5,320 12,438 103% -41%
Nonroad 8,381 4,730 4,287 3,895 -49% -18%
On-road 19,576 9,043 12,187 6,356 -38% -30%
Point Source 8,691 4,228 8,254 3,367 -5% -20%
Total 39,270 39,145 30,048 26,057 -23% -33%
Figure 17 compares trends in anthropogenic precursor emissions and the NWF maximum DV
over the past decade. Annual NOx and VOC emissions represent sums over the entirety of
the four NAA counties as reported by UDAQ for the triennial National Emissions Inventories
(NEI; EPA, 2024a) in 2011, 2014, 2017, and 2020. Reductions in anthropogenic NOx and
VOC have followed each other in lockstep over this period, with an overall reduction of roughly half (46% for NOx, 55% for VOC) or ~3000 TPY per year. Reductions have been primarily achieved among the motor vehicle sectors. Over the same period, the maximum
DV has increased from the low 70’s to upper 70’s ppb at a rate of just under a half ppb per
year. As mentioned in Section 2.2, the large number of ozone exceedances recorded in
2021 may have been related to wildfire influences and may have impacted recent DVs and
the overall trendline. However, when removing 2021 4th high MDA8 values entirely from
the running 3-year DV calculations, the 2010-2023 DV trend remains positive at 0.2 ppb/year (Figure 18).
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Figure 17. Comparison of NWF peak ozone DV trend and triennial anthropogenic
NOx and VOC precursor emissions over the four NAA counties from 2011 to 2020
(emission years are centered on 3-year design value periods).

Figure 18. As in Figure 17, but with a revised ozone DV trendline reflecting the removal of the 2021 4th high MDA8 ozone from the 3-year DV calculations due to the large frequency of possible wildfire impacts during that year.

Besides increased wildfire activity related to the western US “megadrought” over the past decade, another possible cause for increasing ozone may involve the transition from locally VOC-limited (relatively NOx-rich) conditions in the basin to more NOx-limited conditions.
Under VOC-limited conditions, daily ozone production efficiency can be inhibited by NOx. As
NOx slope = -2650 tpy/year
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NOx emissions decrease, the ozone inhibition relaxes and ozone production efficiency increases (a “NOx disbenefit” response). This may have been a contributing factor to the
ozone trend over the past decade. Further NOx reductions will ultimately lead to NOx-
limited conditions and reverse the positive ozone trend. The effect of transitioning from a
predominantly VOC-limited to NOx-limited environment is supported by recent monitoring
at Hawthorne that shows ozone production in central Salt Lake City area forming in a VOC-limited chemical environment with evidence for a transition to NOx-limited conditions during high ozone events, especially when influenced by VOC from wildfires (Jaffe et al., 2023,
2024). Definitive observational evidence on current NWF ozone sensitivity is confounded by
the complex mix of emission sources and meteorology that lead to site-to-site differences in
ozone levels and response to reductions.
Periodic area-wide anthropogenic emission inventories do not necessarily reflect ambient
conditions at specific exceeding monitors because they represent best estimates at the time of their development yet are subject to large uncertainty. Inventories are developed somewhat independently year-to-year and estimates often change substantially with the
use of updated models and methodologies, emission factors, activity profiles, and
assumptions. Furthermore, biogenic emissions and sources outside the nonattainment area
(e.g., fires) can contribute substantially to ambient concentrations. Therefore, it is also
important to evaluate trends in measured ambient NOx and VOC concentrations.
Figure 19 shows 2011-2023 trends for summer (June-August) 1-hour NOx percentiles at Hawthorne and Bountiful monitoring sites, as well as for every-sixth day daily
measurements of non-methane organic compounds (NMOC, similar to VOC) at Bountiful.
NMOC concentrations are presented as parts per billion as carbon (ppbC). The analysis
focuses on the 90th percentile trends as representative of poor air quality episodes,
recognizing that high precursor concentrations over the entire summer may not be entirely associated with high ozone events.
At Hawthorne, the 90th percentile NOx decreased by 15 ppb over the 2011-2023 period (54%) with a linear trendline of -1.2 ppb/year (not shown). At Bountiful, the 90th percentile
NOx exhibits a more variable pattern with a period of higher NOx during 2013-2017 and
lower NOx afterwards. The trendline is nearly flat over the entire period but since 2014 90th
percentile NOx has reduced 9 ppb (39%, linear trend line of -0.9 ppb/year). These ambient
NOx reductions are consistent with the four-county anthropogenic emission trend of 46% shown in Figure 17. The NMOC percentiles at Bountiful exhibit a variable pattern over the period ranging mostly within 100-250 ppbC, but with shallow decreasing trendlines for all three percentiles ranging from -3.5 to -7.6 ppbC/year (20-35% over 2011-2023). The
NMOC concentration trendlines partially reflect the downward 4-county VOC emission trends
over the same period (55%). It is important to note that biogenic emissions set a VOC floor
above zero but at a small fraction of concentrations shown in Figure 19.
Ozone represents a unique challenge in the Intermountain West. Despite years of success in reducing precursor emissions and ambient concentrations of NOx and VOCs, the region still faces significant and unique challenges in meeting ambient ozone concentration health-
based standards. These regionally specific challenges include significantly elevated
background ozone levels (Jaffe et al., 2018) related to increasing instances and
contributions of emissions from wildfire events (Jaffe et al., 2023, 2024) as well as both
interstate and international transport (Langford et al., 2017).

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Figure 19. Trends in 2011-2023 June-August percentiles for 1-hour NOx
concentration at Hawthorne (top left) and Bountiful (top right), and for daily non-
methane organic compound (NMOC) concentrations at Bountiful (bottom).

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4.0 Transport Analysis
This section presents the results of a HYSPLIT41 back trajectory analysis that explores the origins of air parcels that arrived in the NWF area via long range transport on ozone
exceedance days during 2021 – 2023. Most ozone exceedance days during this period were
analyzed except those noted with medium and heavy smoke impacts (as reported by
UDAQ); i.e., only those days not impacted by smoke or impacted by light smoke were
evaluated. No trajectory analyses could be calculated for 2 exceedance days (6/12/2021 and 7/7/2023) due to uncorrectable errors reported by HYSPLIT. This resulted in a total of 33 exceedance days analyzed (Table 2).
Table 2. NWF ozone exceedance days in 2021-2023 analyzed with HYSPLIT back trajectories.
2021 2022 2023
6/4/2021 6/8/2022 5/20/2023
6/21/2021 7/12/2022 7/8/2023
7/8/2021 7/20/2022 7/20/2023
7/15/2021 7/21/2022 7/25/2023
7/16/2021 7/22/2022 8/9/2023
7/17/2021 7/23/2022 8/14/2023
7/20/2021 8/4/2022 8/15/2023
7/21/2021 8/9/2022 8/16/2023
7/22/2021 8/31/2022
7/29/2021 9/3/2022
7/30/2021 9/7/2022
7/31/2021
8/1/2021
9/15/2021

While helpful in understanding general air pathways upwind of a receptor area over a
limited timeframe, the HYSPLIT model includes some inherent limitations (Fleming et al., 2012; Stein et al, 2015). First, HYSPLIT back trajectories estimate the path of a single air parcel and do not account for diffusion or dispersion of air within that parcel. Diffusion is the
microscopic phenomenon of random molecular motions and dispersion is a macroscopic
phenomenon due to turbulence or atmospheric flow patterns below resolved scales. Both
effects tend to mix and spread the constituents of an air parcel over time and space.
Second, HYSPLIT can provide useful information regarding approximate upwind transport, but uncertainties associated with each individual parcel back-trajectory can be substantial. Uncertainties are associated with omission of dispersion and diffusion processes, and
reliance on modeled meteorological data with spatial averaging over grid cells and discrete
(rather than continuous) modeled time steps.

41 https://www.ready.noaa.gov/HYSPLIT.php
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Third, considering an ensemble of back-trajectories released at different locations and times, rather than a single parcel back-trajectory, is generally preferable since the
divergence of an ensemble reflects dispersion patterns associated with resolved
meteorology, but also elucidate the uncertainties associated with single back-trajectories.
Depending on how the ensemble is structured, different sensitivities are explored, and
although the ensemble does not estimate true uncertainties it highlights potential variability and reduces the tendency to interpret a single back-trajectory as an absolute path and assign source-receptor relationship.
For these reasons, ensemble HYSPLIT back-trajectory runs were performed by defining
trajectory initiation (ending) points at the center and corners of a 3-D box covering the NWF
airshed and centered on the Hawthorne monitor site (40.73°N, 111.87°W). The corners of
the box were offset from Hawthorne by ±0.25° in each direction. The area roughly covers the size of the NWF NAA (Figure 20) and is sufficiently large that it contains multiple (estimated 15-25) meteorological data points in the NAM12 dataset (described below). The
ending heights at each of the five coordinates were set at 1,000 and 2,000 m above ground
(AGL). These elevated heights were selected to be within the upper portion of the
atmospheric boundary layer during midday and afternoon hours. Two initiation times per
day were specified that coincide with the typical period of rapid ozone formation (12 PM) and deep boundary layer with well-mixed conditions in the afternoon (3 PM). With this ensemble configuration, 20 HYSPLIT trajectories per exceedance day were initiated.

Figure 20. Location and extent of the 10 initiation points for HYSPLIT back
trajectories.

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The duration for all HYSPLIT back trajectories was set to 10 days to assess long range transport. To drive the trajectory calculations, we selected the NAM12 analyses42 (a North
American 12 km spatial resolution product) as it was the highest resolution meteorological
dataset that was feasible to use.43 High spatial resolution is important for this analysis since
the NWF area has complex terrain that would not be well represented by lower resolution
products. In addition to the NAM12, HYSPLIT was run in a nested grid mode employing the GFS analyses44 (a global 0.25-degree spatial resolution product) when the trajectories exited the NAM12 domain. HYSPLIT includes the capability to automatically switch
meteorological analyses/grids for calculations such as these. A sample HYSPLIT control file
is shown in the Appendix A. The isentropic vertical velocity option was employed as it best
represents three-dimensional synoptic-scale flow and is not subject to discretization and
numerical uncertainties related to model-calculated vertical velocities. The vertical velocity
option is set in the fifth line of the HYSPLIT control file, and the number 2 corresponds to isentropic.
Figure 21 shows examples of 10-day ensemble trajectories initiated on four different NWF
exceedance days. Each hourly trajectory point is color-coded according to altitude. These
four days characterize four distinct transport patterns that we have subjectively identified
from all 33 exceedance day ensembles (provided in Appendix B). As described below, 29 of
the 33 ensembles (88%) indicate air parcel origins reaching toward/over Asia (40%) or passing over Mexico (48%).

Figure 21. Examples of ensemble trajectory plots initiated on 4 specific NWF exceedance days in 2021-20023 that represent 4 types of transport patterns.

42 https://www.ncei.noaa.gov/access/metadata/landing-page/bin/iso?id=gov.noaa.ncdc:C00630 43 HRRR 3km data was impractical due to dataset size.
44 https://www.ncei.noaa.gov/products/weather-climate-models/global-forecast
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The upper left ensemble shows transport primarily from the west within 4000 – 6000 m
altitude (mid-troposphere) and has generally consistent trajectories for all 20 instances in
the ensemble. This pattern shows strong mid-level westerlies with 10-day origins nearing
east Asia. Nine of the 33 exceedance day ensembles (27%) were similar to this pattern.
The upper right ensemble is similar but exhibits more variation and includes some trajectories that extend much greater distances and at higher altitudes (>8000 m). This pattern shows stronger mid- and upper-level westerlies with upper-tropospheric subsidence
over Asia and 10-day origins from east/central Asia. Four of 33 exceedance day ensembles
(12%) were similar to this pattern.
The lower left ensemble shows an altogether different transport pattern with origins from
Mexico, the Gulf of Mexico, and the southern US within an anti-cyclonic flow pattern. This
pattern shows monsoonal southerly to southeasterly flow passing over the entirety of northern Mexico under the influence of central US high pressure. This was the most common pattern, with 16 of 33 exceedance day ensembles (48%) similar to this pattern.
The lower right ensemble also shows transport from the west, but the trajectories are
shorter in length, extending over the eastern Pacific Ocean. This pattern shows weaker
transport and subsidence within the broad eastern Pacific sub-tropical high pressure dome,
indicating general western US stagnation. Four of 33 exceedance day ensembles (12%) were similar to this pattern.
Figure 22 shows a heat map that shows the aggregate frequency of all 10-day ensemble
trajectory points from all 33 NWF ozone exceedance days. The heat map was developed by
defining a 2-degree grid mesh over the analysis region and summing the number of back
trajectory points that fall into each cell. Since all the back trajectories were initiated from
the 3-D NWF box, the highest concentration of points is in that area. However, this type of map makes it easy to discern the regions that are most frequently upwind of the NWF area prior to high ozone days (within 10 days). Obviously, air parcel trajectories extend farther beyond the 10-day limit analyzed here. But uncertainties related to errors in the technique
and data make such extended trajectory calculations and analyses less reliable.
Figure 23 is a similar heat map but showing only the frequency of ensemble trajectory
points on the last four days (i.e., days 7-10) to focus on parcel origins. Large frequencies
occur over the western US, Mexico, the Pacific Ocean and Asia. High frequencies also extend into the south-central US, indicating a common circulation pattern around a central US high pressure system.
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Figure 22. Heat map representation of 10-day transport of air parcels that arrive
on NWF exceedance days in 2021 – 2023.

Figure 23. Heat map representation of air parcel trajectory points 7-10 days upstream prior to arriving on NWF exceedance days in 2021 – 2023.

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5.0 Modeling to Quantify International Contribution
In its State Implementation Plan (SIP) addressing the NWF moderate nonattainment designation, UDAQ (2023) employed the Comprehensive Air quality Model with extensions
(CAMx: Ramboll, 2022a) to simulate ozone air quality during the 2017 base year and to
project monitored ozone levels to the 2023 attainment year. UDAQ also used the CAMx
Ozone Source Apportionment Technology (OSAT) to quantify local, regional, and
international/global ozone contributions in the NWF NAA. OSAT results were consistent with a summary by EPA (2015) and a preliminary modeling study by Ramboll (2021a) that showed most of the ozone in the Wasatch Front results from sources outside of Utah and
from global background, i.e. the combination of natural and international anthropogenic
emissions.
For this demonstration, Ramboll carefully considered options to update the source
apportionment analysis using newer modeling datasets that explicitly simulate an ozone
season during the 2021-2023 moderate attainment period. EPA is developing a new US modeling platform for the year 2022 but a beta version is not expected until late 2024 at the earliest. The schedule for submitting this demonstration for State and EPA review prior
to nonattainment bump-up precluded the use of the EPA 2022 platform, as well as the
creation and evaluation of a more recent high-resolution modeling platform specific to
north-central Utah.
By necessity, Ramboll revisited UDAQ’s 2017/23 CAMx modeling platform for this demonstration. We recognize that this approach is not ideal as it represents meteorology and air quality conditions during the June-July period of the 2017 base year and does not
directly address specific ozone exceedance events during the 2021-2023 attainment period.
The approach therefore assumes that the summer of 2017 adequately characterizes typical
air quality events that have occurred in the more recent years. The new OSAT application
described here included an updated CAMx model version.
5.1 EPA Recommended Ozone Design Value Projection Procedure
EPA (2018) modeling guidance details procedures on using base and future year modeling
results to project future year ozone DVs – referred to as a “modeled attainment test”. EPA
has developed the Software for Model Attainment Test - Community Edition (SMAT-CE; EPA,
2024b) that codifies the recommended procedures.
The SMAT-CE procedure is outlined in Chapter 4 of EPA’s modeling guidance (EPA, 2018, pages 99-110). PGM output for the base and future year is used in a relative sense to scale the base year ozone DV (DVB) to the future year ozone DV (DVF) at each monitoring site.
The model-derived Relative Response Factor (RRF) is defined individually at each monitoring
site as the ratio of average future MDA8 ozone concentration (O3FY) to the average base
MDA8 ozone concentrations (O3BY), where the average is over the same set of several
modeled high ozone days. This is expressed mathematically below:
DVF = DVB x RRF
RRF = ∑(O3FY) / ∑(O3BY)

The site-specific DVB is defined as the three-year average ozone DV centered on the base
modeling year. As each year’s DV is itself defined as the three-year average of the 4th
highest MDA8 ozone concentration each year (H4MDA8), the DVB is thus based on 5 years
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of H4MDA8 ozone concentrations centered on the base year, such that the central year is weighted by a factor of 3/5, the 2nd and 4th years are weighted by a factor of 2/5, and the
1st and 5th years are weighted by a factor of 1/5. This approach is EPA’s way to account for
interannual variability affecting DVs in and around the base year.
The NWF NAA modeled base year is 2017 so the DVB at each site is defined from three
years of ozone DVs as follows:
DVB2017 = (DV2015-2017 + DV2016-2018 + DV2017-2019) / 3 or DVB2017 = (H4MDA82015 + 2xH4MDA82016 + 3xH4MDA82017 + 2xH4MDA82018 + H4MDA82019) / 5

The RRF is determined from maximum MDA8 ozone concentrations near each monitor, averaged over 10 days with the highest base year modeled MDA8 ozone concentrations.
Near the Monitor: This means that the highest modeled base year MDA8 ozone is selected
from one of a 3x3 array of grid cells centered on the monitor. The future year MDA8 ozone
is selected from the same grid cell of the 3x3 array.
10 Highest Base Year MDA8 Ozone Days: Modeled MDA8 ozone concentrations are
averaged over 10 days with the highest base year modeled ozone concentrations near the monitor, provided MDA8 ozone on the chosen days are each ≥60 ppb. If there are less than 10 days meeting this criterion, then only the days meeting this criterion are used in the
average, provided there are at least 5 days available for the RRF calculation. If there are
less than 5 days meeting this criterion, EPA recommends that RRFs not be calculated for the
given site and the regional EPA office should be consulted if the site is an important high DV
site.
5.2 Source Apportionment Modeling
The UDAQ modeling platform consists of a set of three nested grids, with the largest domain
covering the western US at 12 km resolution and the finest resolution covering the NWF
NAA at 1.33 km resolution. The modeling period extends from late June through July of
2017. The modeling system includes requisite three-dimensional meteorological fields for
all grids developed using the Weather Research and Forecasting (WRF) model (Skamarock et al., 2019), as well as all anthropogenic, biogenic, and fire emission inventories within the domain developed using the Sparse Matrix Operator Kernel Emissions (SMOKE) processing
system (CMAS, 2024). Three-dimensional initial/boundary conditions (IC/BC) for the
master domain were developed from Ramboll’s application of the GEOS-Chem global
chemistry model (Ramboll, 2021). The GEOS-Chem runs included: (1) a full representation
of ozone, PM, and precursors from the entire globe, and (2) a scenario in which all IA emissions were removed. For the OSAT run, UDAQ used time- and space-resolved BC concentration differences between the two global model scenarios to track the IA
contributions to total simulated ozone at NWF monitors.
We reran UDAQ’s 2017/23 CAMx/OSAT modeling system with a few modifications. First, we
applied a more recent public-released version of CAMx (v7.3), which includes bug fixes,
minor stability and performance enhancements, as well as chemistry upgrades unrelated to this project (Ramboll, 2022a). We retained specific modifications that UDAQ introduced in v7.1 to account for higher surface albedos associated with salt flats and playas. Third, we
reduced the number of OSAT sources and regions tracked to just those needed for this
analysis, thereby decreasing model runtimes and produced data volumes.
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5.2.1 Model Configuration
CAMx v7.3 simulated ozone formation in the NWF NAA for base year 2017 and future year
2023 emission scenarios. The Carbon Bond version 6 revision 5 (CB6r5h) gas-phase
chemical mechanism, which includes the full suite of halogen chemistry, was selected to be
as consistent as possible with UDAQ SIP modeling chemistry.
OSAT uses reactive tracers assigned to each selected source group and region to determine
precursor and ozone contributions across the modeling domain. These reactive tracers operate in parallel to the host photochemical grid model, accessing the model’s transport, dispersion, chemistry, and deposition algorithms. There are 10 reactive tracers used to
track ozone formation for each user-defined source group (i):
VOCi VOC emissions
NITi Nitric oxide (NO) and nitrous acid (HONO) emissions
RGNi Nitrogen dioxide (NO2), nitrate radical (NO3), and dinitrogen pentoxide (N2O5)
TPNi Peroxyacetyl nitrate (PAN), analogues of PAN, and peroxynitric acid (PNA) NTRi Organic nitrates (RNO3) HN3i Gaseous nitric acid (HNO3)
O3Ni Ozone formed under NOx sensitive conditions
O3Vi Ozone formed under VOC sensitive conditions
OONi Odd oxygen in NO2 formed from O3Ni
OOVi Odd oxygen in NO2 formed from O3Vi
At each time step and grid cell where ozone is formed, OSAT determines whether the ozone
formation is more VOC-sensitive or NOx-sensitive and apportions the ozone formed to
source groups based on the relative contribution of the limiting precursor to the total
precursor (e.g., to VOCi/ ∑VOCi under VOC sensitive conditions). Applying OSAT for 2023
future year simulations allows us to quantify IA impacts on simulated MDA8 ozone and
future year DVs. Emission groups defined in Table 3 were tracked by OSAT. This is a consolidated list of 25 emission groups and two IC/BC groups in UDAQ SIP modeling, yet sufficient to track the IA contributions along with anthropogenic, natural, and fire sources.
OSAT tracked two source apportionment IC and BC groups: one group represents IA ozone
and precursors and the other represents global natural and US emissions within the 12 km
CAMx domain that are transported into the 4 km domain. Only one geographic region was
applied in OSAT, namely the entire 4 km Utah and 1.33 km NWF grids.
Table 3. CAMx source apportionment groups.
OSAT Group ID Group Name Description
1 Anthropogenic All anthropogenic emissions within the 4 km grid
2 Biogenic All biogenic emissions within the 4 km grid
3 Fire + Lightning Wildfire, agricultural, and prescribed fires, and lightning
emissions within the 4 km grid
IC/BC 1 International
Anthropogenic
Non-US anthropogenic emissions estimated based on 12 km CAMx 2023 base case and zero-out GEOS-Chem
simulations
IC/BC 2 Global Natural + US Anthropogenic
Global natural emissions plus US biogenic and anthropogenic emissions from outside the 4 km grid, based on 12 km CAMx 2023 base case and zero-out GEOS-Chem simulations
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5.2.2 Model Results
The 2023 OSAT results were extracted at the locations of Hawthorne and Bountiful
monitoring sites from 1.33 km grid output files. Raw hourly ozone tracer and cumulative
ozone concentrations were post-processed to MDA8 ozone each day; i.e., the unique 8-hour
period defining total MDA8 ozone at each grid cell on each day was used to time-average all
ozone tracers. Results were then compiled into an Excel spreadsheet where the source
apportionment contributions to daily MDA8 ozone concentrations can be visualized. The top panels in Figures 24 and 25 present “landscape” time series (as stacked area plots) of source contributions to 2023 MDA8 ozone at the Hawthorne and Bountiful monitoring sites,
respectively, over June 26th to July 31st. The bottom panels in Figures 24 and 25 present IA
and other source group contributions to average MDA8 ozone over several groups of days.
Following the UDAQ SIP methodology, we define high ozone days as modeled MDA8 ozone
≥60 ppb.
The time series plots indicate that at both sites, daily IA contributions to MDA8 (light green) exhibited little variation with a standard deviation of 1.6 ppb, compared to the contributions
from other sectors with standard deviations greater than 2.2 ppb. IA contributions to MDA8
ranged between 5 and 8 ppb at the beginning of the analysis period and decreased to a
lower range of 2 to 4 ppb starting around July 8th. Over the top 10 highest modeled ozone
days, IA contributed an average of 5.1 ppb (7%) to MDA8 ozone at Hawthorne, consistent with the UDAQ SIP assessment of 4.5 ppb. Average IA contributions to MDA8 ozone on lower ozone days were noticeably smaller. The IA contribution to MDA8 ozone at the
Bountiful site followed very similar trends.
Figure 26 presents the spatial distribution of modeled MDA8 ozone concentrations and the
contributions from each of the OSAT source groups over the entire 4 km UDAQ modeling
domain. These plots represent the average over the top ten highest modeled days at
Hawthorne. IA contributions range from 3 to 6 ppb throughout the domain, with the highest contributions over northern Utah. The widespread and relatively homogeneous ozone distribution shows the regional nature of IA contributions. The only other OSAT
group exhibiting such features is the global natural background+US contribution with a
range of 35 to 40 ppb. More localized contributions result from biogenic (where there are
high levels of urban NOx) and anthropogenic sources. Contributions from the combination
of fires and lightning NOx (according to 2017 base year emission estimates) are negligible
at less than 1 ppb.
The UDAQ SIP source apportionment modeling shows generally similar results, yet the total MDA8 ozone time series (i.e., sum of all contributions) differ somewhat from the figures
below and UDAQ reports much larger contributions from lightning NOx (0-10 ppb over the
modeling period, 2-4 ppb average). Ramboll could not replicate UDAQ’s total ozone time
series, which we’ve mutually determined is caused by different methods to post-process
hourly model output to MDA8 form. Additionally, UDAQ used CAMx v7.1 for the SIP whereas Ramboll used CAMx v7.3 for this 179B demonstration. Ramboll discovered code bugs in the v7.1 OSAT routines that read the new three-dimensional input emission file
format, which included the lightning NOx files prepared by UDAQ. As an initial workaround
for v7.1, Ramboll regenerated lightning NOx inputs as point sources using UDAQ’s CAMx
meteorological input files. The code bugs have since been resolved in v7.3, although
Ramboll has continued to use the lightning NOx inputs as point sources. As a result of
these changes, contributions from lightning NOx in combination with occasional minor fire activity within the domain are reduced to a much more realistic level below 1 ppb.

Ramboll – Clean Air Act §179B Demonstration for the Northern Wasatch Front Ozone Nonattainment Area
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Figure 24. Time series of simulated contributions to MDA8 ozone at the Hawthorne monitor site (top panel), and average contributions on all days and high ozone days.
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38.5(63.1%)Global Natural + Non-UT US Antho
4.1 (6.8%)
Inter.
Anthro.
5.2(8.5%) Biogenic
13.0(21.3%) 4-km Anthropogenic
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39.5(58.8%)Global Natural + Non-UT US Antho
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16.5 (24.5%) 4-km Anthropogenic
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37.1(70.6%)Global Natural + Non-UT US Antho
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HAWTHORNE
Ramboll – Clean Air Act §179B Demonstration for the Northern Wasatch Front Ozone Nonattainment Area
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Figure 25. Time series of simulated contributions to MDA8 ozone at the Bountiful
Viewmont monitor site (top panel), and average contributions on all days and high ozone days.

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Global Natural + NonUtah US Anthropogenic International Anthropogenic 4-km Anthropogenic
Biogenic Fire+Lighting MDA8 >= 60ppb
38.1(63.6%)Global Natural + Non-UT US Antho
4.1 (6.9%)
Inter. …
5.1(8.5%) Biogenic
12.4(20.7%) 4-km Anthropogenic
0.2(0.3%) Fire, Lighting
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Ramboll – Clean Air Act §179B Demonstration for the Northern Wasatch Front Ozone Nonattainment Area
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Figure 26. Spatial distribution of modeled MDA8 ozone (top left) and
contributions from OSAT source groups over the 4 km UDAQ modeling domain, averaged over the top 10 high modeled ozone days at the Hawthorne site.

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To quantify IA impacts on 2023 projected DVs, we applied SMAT-CE v2.1 with the most current monitoring database from EPA containing 2002-2020 4th high MDA8 ozone for all
official sites operating in NWF. The SMAT-CE configuration followed the UDAQ SIP SMAT
configuration as described above and in the respective SIP TSD 45. EPA’s guidance includes
some flexibility to modify the recommended ozone DV projection procedure such as
accounting for “exceptional event like” days (i.e., days that might not qualify as official exceptional events like wild-fire impacted days). Following this guidance, the UDAQ SIP determined 2023 DVs for the three highest monitors in the NWF (e.g., Hawthorne, Bountiful
and Herriman) from the standard 2017 DVs and from adjusted 2017 DVs excluding wildfire
smoke-impacted ozone exceedance days (UDAQ, 2023). We report results below using
those same two sets of 2017 DVs for consistency.
Table 4 shows projected 2023 future DVs with (FDV) and without IA (FDV_adj) contributions
projected from the standard 2017 monitored ozone DVs. Simulated IA contributions to FDV at all sites are significant and removing those contributions would bring all sites into attainment. When using UDAQ’s adjusted (no-fire) 2017 ozone DVs (Table 5), projected
2023 FDV values are consistently lower by 1 to 2 ppb for the three highest sites and while
simulated IA impacts are similar.
Table 4. Baseline 2017 design values (BDV), projected 2023 future design
values (FDV), simulated IA contributions, and adjusted future design values (FDV adj) with IA removed.
Site Site ID County BDV
(ppb)
FDV
(ppb)
IA
(ppb)
FDV_adj
(ppb)
Bountiful 490110004 Davis 76 74 5.00 69
Hawthorne 490353006 Salt Lake 76 74 4.89 69
Herriman 490353013 Salt Lake 76 73 4.30 68
Erda 490450004 Tooele 73 70 4.69 65
Harrisville 490571003 Weber 72 70 4.89 65

Table 5. As in Table 4 except with BDV based on adjusted 2017 DVs according to the UDAQ SIP exclusion of wild-fire impacted days (UDAQ, 2023; Table 68).
Site Site ID County Adjusted BDV (ppb) FDV (ppb) IA (ppb)
FDV_adj
(ppb)
Bountiful 490110004 Davis 75 72 5.00 67
Hawthorne 490353006 Salt Lake 75 72 4.90 67
Herriman 490353013 Salt Lake 74 71 4.10 67
Erda 490450004 Tooele 73 70 4.69 65
Harrisville 490571003 Weber 72 70 4.89 65
Since modeled 2023 DV projections are lower than actual monitored 2023 DVs, we also used OSAT IA results to scale EPA’s reported 2023 DVs46 to reflect removal of IA contributions (Table 6). The 2023 DVs in Table 6 reflect the actual monitored 3-year

45 https://documents.deq.utah.gov/air-quality/planning/DAQ-2023-001838.pdf 46 EPA 2023 Design Value Reports; available at https://www.epa.gov/system/files/documents/2024-
06/o3_designvalues_2021_2023_final_06_04_24.xlsx
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average of the 4th highest concentration from 2021, 2023, and 2023, and thus represent the observed concentrations from within the NAA scaled accordingly based on modeled IA
contributions. Note there are more active NWF sites that report ozone DVs in 2023 than in
2017. The RRF listed in Table 6 is determined using SMAT-CE according to the ratio of
averaged modeled ozone concentrations with and without IA contributions. All sites except
Copperview are below the NAAQS with IA removed.
Table 6. As in Table 4 except showing actual 2023 DVs (3-year average of 2021-2023 4th high MDA8 ozone) reported by EPA10, and RRF determined from the SMAT-calculated ratio of modeled ozone concentrations without and with IA contributions.
Site Site ID County 2023 DV (ppb) RRF FDV_adj (ppb)
Bountiful 490110004 Davis 76 0.932 70
Hawthorne 490353006 Salt Lake 75 0.934 70
Herriman 490353013 Salt Lake 75 0.942 70
Erda 490450004 Tooele 71 0.933 66
Harrisville 490571003 Weber 72 0.931 67
Copperview 490352005 Salt Lake 77 0.944 72
Rose Park 490353010 Salt Lake 74 0.936 69

The 2023 DVs in Table 6 are determined using all MDA8 ozone days in 2021 through 2023.
As described in Section 2 and shown in Table 2, numerous exceedance days were associated
with the presence of wildfire smoke, especially in 2021. UDAQ adjusted the 2023 DV values
at the Copperview monitor to remove days influenced by wildfire smoke. Specifically, UDAQ
selected wildfire smoke impacted dates in 2021-2023 based on their two factor screening
tool, and weighed which of those screened dates would be most defensible as exceedance ozone events due to wildfire smoke emissions. The process involved flagging wildfire smoke dates with 24-hour PM2.5 measurements exceeding 15 µg/m3. This PM2.5 threshold is
somewhat subjective but was determined to provide dates with the most convincing
argument for wildfire smoke impacts. Wildfire smoke dates were then excluded from the
yearly ranked monitored MDA8 ozone at Copperview, and a new 4th high MDA8 was
calculated for each year. As a result, the top 5 ozone dates in 2021 were removed and the 2021 4th high MDA8 ozone decreased from 86 to 80 ppb. The 4th high MDA8 ozone values in 2022 and 2023 were unaffected. The adjusted 4th high MDA8 values were then averaged over 2021-2023 to determine the fire-adjusted 2023 DV (Table 7).
By applying the same RRF values listed in Table 6 to the fire-adjusted 2023 Copperview DV
listed in Table 7, all monitors are reduced below the 2015 ozone NAAQS when IA
contributions are removed.

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Table 7. As in Table 6 except showing adjusted 2023 DVs (3-year average of 2021-2023 4th high MDA8 ozone) by removing wildfire impact days at Copperview (highlighted).
Site Site ID County 2023 DV (ppb) RRF FDV_adj (ppb)
Bountiful 490110004 Davis 76 0.932 70
Hawthorne 490353006 Salt Lake 75 0.934 70
Herriman 490353013 Salt Lake 75 0.942 70
Erda 490450004 Tooele 71 0.933 66
Harrisville 490571003 Weber 72 0.931 67
Copperview 490352005 Salt Lake 75 0.944 70
Rose Park 490353010 Salt Lake 74 0.936 69

5.3 Model Performance Evaluation
5.3.1 Time Series of MDA8 Ozone at Select Sites
Figure 27 compares time series of simulated and observed MDA8 ozone at monitoring sites
within the NWF NAA. Results are very similar to those shown in the Moderate Ozone SIP,
with a pervasive under prediction tendency on most days while generally following observed
inter-daily variations and trends. As a point of comparison, Figure 28 shows time series at one of the historical peak monitors in Las Vegas (Joe Neal), where the model simulates MDA8 ozone rather well in contrast to the NWF and regional background sites. Figure 29
shows similar time series for regional background ozone sites at Great Basin National Park,
Canyonlands National Park, and Dinosaur National Monument. Ozone is consistently under
predicted at these sites early in the period. This contradicts results at Gothic in the
Moderate Ozone SIP, which showed generally good performance in replicating high-altitude ozone over the Colorado Rockies. Under predictions at these regional sites surrounding the NWF NAA suggest that natural global background ozone or international anthropogenic
contributions are not well characterized by the boundary conditions, that regional fires or
biogenic emissions are not well characterized within the modeling domain, or some
combination of all factors.
5.3.2 Statistical Performance Metrics for MDA8 Ozone
Consistent with the Moderate Ozone SIP, the following statistical metrics for MDA8 ozone
performance were calculated to quantify model-observation agreement: mean bias (MB, ppb), mean error (ME, ppb), normalized mean bias (NMB, %), normalized mean error (NME, %), and Pearson correlation (R, unitless). These metrics were calculated using the
Atmospheric Model Evaluation Tool (AMET version 1.4).
A summary of site-specific performance statistics for all modeled days and high ozone days
(observed MDA8 > 60 ppb) are listed in Tables 8 and 9 for sites within the NWF NAA, and in
Table 10 and 11 for the three regional background sites. NWF statistics are consistent with those cited in the Moderate Ozone SIP. Regional background results are consistent with the NWF statistics, showing relatively large negative biases. These performance metrics
indicate that the model performs toward the outer range of typical statistical results (15%
NMB, 25% NME) given by the criteria benchmarks of Emery et al. (2016). UDAQ has
attributed some of the performance under predictions to variable cloud cover, which WRF
did not simulate completely.
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Figure 27. Time series of observed (grey) and simulated (red) MDA8 ozone at (top to bottom) Bountiful, Hawthorne, Erda, and Herriman.
Ramboll – Clean Air Act §179B Demonstration for the Northern Wasatch Front Ozone Nonattainment Area
41

Figure 27 (concluded). Time series of observed (grey) and simulated (red)
MDA8 ozone at (top to bottom) Harrisville and Ogden.

Figure 28. Time series of observed (grey) and simulated (red) MDA8 ozone at
Joe Neal in Las Vegas.

Ramboll – Clean Air Act §179B Demonstration for the Northern Wasatch Front Ozone Nonattainment Area
42

Figure 29. Time series of observed (grey) and simulated (red) MDA8 ozone at
(top to bottom) Great Basin, Canyonlands, and Dinosaur National Monument.

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43
Table 8. Performance statistics for MDA8 ozone at sites within the NWF NAA on all days of the modeling episode.
Site Name MB (ppb) ME (ppb) NMB (%) NME (%) R
Bountiful -7.8 9.1 -11.9 13.9 0.76
Hawthorne -7.6 9.2 -11.6 14.0 0.78
Erda -9.4 10.7 -14.9 16.9 0.69
Herriman -10.5 10.8 -16.2 16.7 0.63
Harrisville -9.8 10.2 -15.5 16.1 0.74
Ogden -8.0 9.4 -12.6 14.8 0.68

Table 9. Performance statistics for MDA8 ozone at sites within the NWF NAA
on high days (observed MDA8 > 60 ppb).
Site Name MB (ppb) ME (ppb) NMB (%) NME (%) R
Bountiful -7.6 9.2 -10.8 13.2 0.43
Hawthorne -6.6 8.7 -9.5 12.4 0.43
Erda -10.3 11.3 -15.0 16.5 0.48
Herriman -10.7 10.7 -15.6 15.6 0.33
Harrisville -9.8 10.4 -14.4 15.3 0.31
Ogden -7.6 9.3 -11.1 13.7 0.26

Table 10. Performance statistics for MDA8 ozone at regional background sites surrounding the NWF NAA on all days of the modeling episode.
Site Name MB (ppb) ME (ppb) NMB (%) NME (%) R
Great Basin -7.6 8.6 -14.4 16.3 0.60
Canyonlands -3.7 7.0 -6.8 12.7 0.50
Dinosaur NM -4.1 6.4 -7.3 11.5 0.49

Table 11. Performance statistics for MDA8 ozone at regional background sites surrounding the NWF NAA on high days (observed MDA8 > 60 ppb).
Site Name MB (ppb) ME (ppb) NMB (%) NME (%) R
Great Basin -13.0 13.0 -20.9 20.9 0.28
Canyonlands -14.4 14.4 -22.8 22.8 0.36
Dinosaur NM -6.6 7.0 -10.7 11.3 0.45

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44
5.3.3 Spatial Plots of 1-hour Ozone
Figure 30 presents spatial isopleth plots of simulated ozone within the 1.33 km modeling
grid at 3 PM during July 13-15 when monitored ozone was high. Each figure overlays small
circles at locations of monitoring sites using the same color spectrum as the isopleths to
compare observed and simulated ozone patterns. Plots at additional hours during this
period are provided in Appendix C. Figure 30 and Appendix C show that the model
simulates the daily spatial evolution of ozone well during this 3-day period, from low ozone overnight, especially in NOx-rich urban areas and along major arterials, to high ozone exceeding the standard throughout the NWF NAA. Patterns at 3 PM on July 13 are well
simulated, while patterns on July 14 tend to be over predicted in Weber County and under
predicted in southern Salt Lake and Utah Counties. Ozone on the afternoon of July 15 is
under predicted in Salt Lake and Davis Counties but well simulated elsewhere.

Figure 30. Isopleth plots of simulated hourly ozone within the 1.33 km modeling grid at 3 PM during July 13-15 when monitored ozone was high.

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45
6.0 Conclusions
The following lines of evidence demonstrate that the NWF NAA would have attained the 2015 ozone NAAQS by the moderate attainment date of August 3, 2023 but for global
international anthropogenic contributions.
• Physical setting (Section 2): The NWF is a highly urbanized and industrial area that
rests at the foot of the Wasatch Mountains and adjacent to the Great Salt Lake, features
that exacerbate airmass pooling (stagnation) and local recirculation under strong capping inversions and contribute to degraded air quality. Furthermore, the high mountain ranges throughout north-central Utah enhance vertical circulations that expose
the elevated basin to background mid- and upper-tropospheric air that is often laden
with foreign pollution during the summer ozone season.
• Conceptual Model of Ozone Episodes (Section 2): The NWF has continued to
exceed past and current ozone standards at most monitors within the NAA, with large
site-to-site interannual variability but a slightly increasing site-averaged trendline, despite combined state and federal regulatory actions to reduce emissions. Ozone exceedance frequencies and concentrations during the summer of 2021 were
anomalously high, likely due to a heavy influence from record-breaking wildfire activity
throughout the western US. During ozone exceedances wind speed is low, temperature
is high, relative humidity is low, and mixing heights are suppressed. All of these
features are consistent with locally stagnant conditions associated with a sinking/compressing warm air mass within a deep dome of high pressure centered over the western US, which suppresses vertical mixing and cloud formation. High
temperatures lead to increased emission rates for biogenic and evaporative processes,
along with higher chemical oxidation rates.
• Intercontinental transport (Section 2): As a summer phenomenon, ozone episodes
coincide with the seasonal western North American circulation pattern known as the Mexican Monsoon, which brings humid air northward from Mexico into the Great Basin states during July and August. This establishes a common transport corridor for pollutants emitted in Mexico to rapidly reach the NWF. However, there is another
common transport pattern linking Asia to the western US. As summarized in EPA’s 179B
guidance document and in published literature, persistent global circulation patterns
establish a direct transport route in the mid- to upper troposphere that brings pollutant-
laden air to North America within days to weeks. Sinking air within a high pressure dome over the western US brings transported ozone and precursors toward the surface, while complex topography enhances vertical circulations, and thus high-altitude
locations throughout the western US experience the greatest ozone impacts from
intercontinental transport. This transport mechanism is especially persistent throughout
the summer season. Moreover, a recent multi-decadal trend analysis through 2021
indicates that free tropospheric ozone over western North America continues to increase
despite a decreasing trend in boundary layer ozone, affirming vertically different sources and mechanisms.
• Emission and concentration trends (Section 3): Despite years of success in
reducing precursor emissions and ambient concentrations of nitrogen oxides (NOx) and
volatile organic compounds (VOC), the region faces significant challenges in meeting the
ozone standard. These regionally specific challenges include significantly elevated
background ozone levels related to increasing instances and contributions of emissions from wildfire events as well as both interstate and international transport. According to UDAQ reported triennial emission inventories for the NWF counties, nitrogen oxide (NOx)
and volatile organic compound (VOC) emissions have decreased by roughly half (46%
and 55%, respectively) between 2011 and 2020, and these reductions are consistent
Ramboll – Clean Air Act §179B Demonstration for the Northern Wasatch Front Ozone Nonattainment Area
46
with summer season ambient NOx and VOC concentration measurements over the same period. However, NWF ozone DVs have increased at a rate of just under a half ppb per
year. UDAQ estimates that NOx and VOC emissions will continue to decrease into the
future as local and federal control measures continue to take effect.
• Trajectory analyses (Section 4): Upstream air parcel transport pathways arriving in
the NWF on exceedance days during 2021-2023 were analyzed using the HYSPLIT trajectory model. Most ozone exceedance days were analyzed except those noted with medium and heavy smoke impacts (as reported by UDAQ), resulting in a set of 33
exceedance days. Four types of distinct transport patterns were subjectively identified
with 29 of the 33 trajectory days (88%) indicating air parcel origins reaching
toward/over Asia (40%) or passing over Mexico (48%).
• Source apportionment modeling (Section 5): Results from source apportionment
photochemical modeling show consistent international anthropogenic contributions to the NWF (6 to 7%) with evidence for larger contributions that scale with locally elevated ozone events. This agrees with our conceptual model that the very same meteorological
processes that lead to local buildup of pollution within the NWF (high pressure
subsidence with capping inversion, stagnation, higher temperature, and increased
emissions) also enhance mid-tropospheric pollution transport into the NWF area. With
the removal of the international anthropogenic contributions, the model-projected 2023 NWF DVs (from 2017 DVs) attain the 2015 ozone NAAQS at all sites by a large margin. These results are consistent with previous source apportionment analyses for the area
(UDAQ, 2021; 2023). The removal of international anthropogenic contributions from
measured 2023 DVs leads to attainment of the 2015 ozone NAAQS at all sites except at
Copperview. Exclusion of wildfire smoke-impacted days in 2021 only at Copperview are
sufficient to show attainment without international anthropogenic contributions. Based on these results, international anthropogenic emissions contribute to ozone exceedances in the NWF NAA, and the area would have attained the 2015 ozone NAAQS by the marginal attainment date of August 3, 2023 but for that contribution.

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Ramboll – Clean Air Act §179B Demonstration for the Northern Wasatch Front Ozone Nonattainment Area

APPENDIX A

Example HYSPLIT control file for Aug 16, 2023, 2000 m initiation
height, NWF box, southeast corner initiation point

Ramboll – Clean Air Act §179B Demonstration for the Northern Wasatch Front Ozone Nonattainment Area
A-1
Appendix A Example HYSPLIT control file for Aug 16,
2023, 2000 m initiation height, NWF box, southeast
corner initiation point
2024 08 16 22 1
40.486389 -111.622222 2000
-240
2 15500 2 11
../metdata/namsa/
20230816_hysplit.t00z.namsa ../metdata/namsa/ 20230815_hysplit.t00z.namsa
../metdata/namsa/
20230814_hysplit.t00z.namsa
../metdata/namsa/ 20230813_hysplit.t00z.namsa ../metdata/namsa/
20230812_hysplit.t00z.namsa
../metdata/namsa/
20230811_hysplit.t00z.namsa ../metdata/namsa/
20230810_hysplit.t00z.namsa
../metdata/namsa/
20230809_hysplit.t00z.namsa ../metdata/namsa/ 20230808_hysplit.t00z.namsa
../metdata/namsa/
20230807_hysplit.t00z.namsa ../metdata/namsa/ 20230806_hysplit.t00z.namsa ../metdata/gfs/
20230816_gfs0p25
../metdata/gfs/ 20230815_gfs0p25 ../metdata/gfs/
20230814_gfs0p25
../metdata/gfs/
20230813_gfs0p25 ../metdata/gfs/
20230812_gfs0p25
../metdata/gfs/
20230811_gfs0p25 ../metdata/gfs/ 20230810_gfs0p25
../metdata/gfs/
20230809_gfs0p25
../metdata/gfs/ 20230808_gfs0p25 ../metdata/gfs/
20230807_gfs0p25
../metdata/gfs/ 20230806_gfs0p25 ./hysplit_output_2000/
hysplit.se.20230816.15.2000m.240.bt
~

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APPENDIX B

Plots of HYSPLIT 10-day ensemble trajectories from each of 33 NWF
ozone exceedance days in 2021 – 2023

Ramboll – Clean Air Act §179B Demonstration for the Northern Wasatch Front Ozone Nonattainment Area
B-1
Appendix B Plots of HYSPLIT 10-day ensemble
trajectories from each of 33 NWF ozone exceedance
days in 2021 – 2023
Ramboll – Clean Air Act §179B Demonstration for the Northern Wasatch Front Ozone Nonattainment Area
B-2
Ramboll – Clean Air Act §179B Demonstration for the Northern Wasatch Front Ozone Nonattainment Area
B-3
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B-4
Ramboll – Clean Air Act §179B Demonstration for the Northern Wasatch Front Ozone Nonattainment Area
B-5
Ramboll – Clean Air Act §179B Demonstration for the Northern Wasatch Front Ozone Nonattainment Area
B-6
Ramboll – Clean Air Act §179B Demonstration for the Northern Wasatch Front Ozone Nonattainment Area
B-7
Ramboll – Clean Air Act §179B Demonstration for the Northern Wasatch Front Ozone Nonattainment Area
B-8
Ramboll – Clean Air Act §179B Demonstration for the Northern Wasatch Front Ozone Nonattainment Area
B-9
Ramboll – Clean Air Act §179B Demonstration for the Northern Wasatch Front Ozone Nonattainment Area
B-10
Ramboll – Clean Air Act §179B Demonstration for the Northern Wasatch Front Ozone Nonattainment Area
B-11
Ramboll – Clean Air Act §179B Demonstration for the Northern Wasatch Front Ozone Nonattainment Area
B-12
Ramboll – Clean Air Act §179B Demonstration for the Northern Wasatch Front Ozone Nonattainment Area
B-13
Ramboll – Clean Air Act §179B Demonstration for the Northern Wasatch Front Ozone Nonattainment Area
B-14
Ramboll – Clean Air Act §179B Demonstration for the Northern Wasatch Front Ozone Nonattainment Area
B-15
Ramboll – Clean Air Act §179B Demonstration for the Northern Wasatch Front Ozone Nonattainment Area
B-16

Ramboll – Clean Air Act §179B Demonstration for the Northern Wasatch Front Ozone Nonattainment Area
B-17

Ramboll – Clean Air Act §179B Demonstration for the Northern Wasatch Front Ozone Nonattainment Area

APPENDIX C

Isopleth plots of hourly ozone (at 0, 6, 9, 12, 15, 18 local time) over
the 1.33 km modeling grid with hourly observations overlaid on the
high observed ozone days of July 13-15

Appendix C Isopleth plots of hourly ozone (at 0, 6, 9, 12,
15, 18 local time) over the 1.33 km modeling grid with
hourly observations overlaid on the high observed ozone
days of July 13-15

APPENDIX II: Exceptional Events and Data Modification
Demonstration
ANALYSES IN SUPPORT OF
EXCEPTIONAL EVENT FLAGGING AND
EXCLUSION FROM MODELING
FOR THE WEIGHT OF
EVIDENCE ANALYSIS

Supporting the
Clean Air Act §179B Demonstration
for the Northern Wasatch Front
Ozone Nonattainment Area

November 2024

Table of Contents
1 Introduction ........................................................................................................................................ 21
1.1 Overview of Events ..................................................................................................................... 21
1.2 Significance and Justification ...................................................................................................... 27
2 Regional Description ........................................................................................................................... 32
2.1 Monitor Overview ....................................................................................................................... 32
2.2 Summertime Climatology and Geography .................................................................................. 33
2.3 Wasatch Front Ozone Climatological Characteristics ................................................................. 36
2.3.1 Characteristics of Non-Flagged High Ozone Events (Non-Events) ...................................... 36
2.3.2 Characteristics of Flagged Wildfire Impacted High Ozone Concentration Events .............. 39
3 Flagging Wildfire Smoke Event Criteria ............................................................................................... 41
3.1 Flagging Methodology ................................................................................................................ 41
4 Conceptual Overview and Narrative ................................................................................................... 43
4.1 Conceptual Model and Clear Causal Relationship: Smoke Event July 12, 2021 ............................... 44
4.1.1 Wildfire Conditions: July 12, 2021 ...................................................................................... 44
4.1.2 Meteorological Conditions .................................................................................................. 49
4.1.3 Wildfire Smoke: Remote Sensing and Ground-Based Analysis ........................................... 57
4.1.4 HYSPLIT: Wildfire Smoke Transport to CV Monitor ............................................................ 71
4.1.5 Wildfire Smoke Emissions and Ozone Exceedance: Clear Causal Relationship .................. 78
4.1.5.1 Surface Smoke Observations and Historical Monitor Comparison ................................. 79
4.1.5.2 Event and non-event Ozone ........................................................................................... 82
4.1.5.3 Wildfire Smoke and Ozone Formation: NOx and VOCs .................................................. 86
4.2 Conceptual Model and Clear Causal Relationship: Smoke Event July 24, 2021 ......................... 90
4.2.1 Wildfire Conditions: July 24, 2021 ...................................................................................... 90
4.2.2 Meteorological Conditions .................................................................................................. 95
4.2.3 Wildfire Smoke: Remote Sensing and Ground-Based Analysis ......................................... 102
4.2.4 HYSPLIT: Wildfire Smoke Transport to CV Monitor .......................................................... 113

4.2.5 Wildfire Smoke Emissions and Ozone Exceedance: Clear Causal Relationship ................ 117
4.2.5.1 Surface Smoke Observations and Historical Monitor Comparison ............................... 117
4.2.5.2 Event and non-event Ozone ......................................................................................... 120
4.2.5.3 Wildfire Smoke and Ozone Formation: NOx and VOCs ................................................ 124
4.3 Conceptual Model and Clear Causal Relationship: Smoke August 7-8, 2021 ........................... 128
4.3.1 Wildfire Conditions: August 7-8, 2021 .............................................................................. 128
4.3.2 Meteorological Conditions ................................................................................................ 134
4.3.3 Wildfire Smoke: Remote Sensing and Ground-Based Analysis ......................................... 146
4.3.4 HYSPLIT: Wildfire Smoke Transport to CV Monitor .......................................................... 168
4.3.5 Wildfire Smoke Emissions and Ozone Exceedance: Clear Causal Relationship ................ 175
4.3.5.1 Surface Smoke Observations and Historical Monitor Comparison ............................... 175
4.3.5.2 Event and non-event Ozone ......................................................................................... 178
4.3.5.3 Wildfire Smoke and Ozone Formation: NOx and VOCs ................................................ 182
4.4 Conceptual Model and Clear Causal Relationship: Smoke Event August 16, 2021 .................. 187
4.4.1 Wildfire Conditions: August 16, 2021 ............................................................................... 187
4.4.2 Meteorological Conditions ................................................................................................ 192
4.4.3 Wildfire Smoke: Remote Sensing and Ground-Based Analysis ......................................... 199
4.4.4 HYSPLIT: Wildfire Smoke Transport to CV Monitor .......................................................... 209
4.4.5 Wildfire Smoke Emissions and Ozone Exceedance: Clear Causal Relationship ................ 214
4.4.5.1 Surface Smoke Observations and Historical Monitor Comparison ............................... 214
4.4.5.2 Event and non-event Ozone ......................................................................................... 217
4.4.5.3 Wildfire Smoke and Ozone Formation: NOx and VOCs ................................................ 221
5 Summary ........................................................................................................................................... 225
6 Data Exclusion and Adjusted BDV ..................................................................................................... 226
7 References ........................................................................................................................................ 228

Figures
Figure 1 - HMS Smoke Plume Extent .......................................................................................................... 23
Figure 2 - HMS Cumulative Smoke Days ..................................................................................................... 23
Figure 3 - Smoke Density Fraction at CV ..................................................................................................... 24
Figure 4 - NWF Non-Attainment Area ......................................................................................................... 25
Figure 5 - EPA EE DV Tool: No EE Exclusions ............................................................................................... 30
Figure 6 - EPA EE DV Tool: EE Exclusions .................................................................................................... 31
Figure 7 - Salt Lake Valley and UDAQ Monitor Locations ........................................................................... 33
Figure 8 - NCEP Reanalysis Mean 1000-500 mb Thickness Composites ..................................................... 34
Figure 9 - KSLC Wind Roses: Summer Climatology ..................................................................................... 35
Figure 10 - Diurnal Wind Patterns SLV ........................................................................................................ 36
Figure 11 - SLV Historical MD8A Ozone Exceedance Day Trends ............................................................... 37
Figure 12 - SLV Ozone Daily AQI Historic Trend .......................................................................................... 38
Figure 13 - Western U.S. Drought Monitor: July 2021 ................................................................................ 44
Figure 14 - NCEP Reanalysis Average 500 mb GPH: June 1- July 12, 2021 ................................................. 45
Figure 15 - PRISM June 2021 Precipitation Anomalies ............................................................................... 46
Figure 16 - PRISM June 2021 Temperature Anomalies............................................................................... 46
Figure 17 – WFPI: July 12, 2021 .................................................................................................................. 47
Figure 18 - WFIGS Wildfire Perimeters: July 12, 2021 ................................................................................ 48
Figure 19 - CV Meteogram: July 12, 2021 ................................................................................................... 50
Figure 20 - NCEP Reanalysis Average 500 mb GPH: July 12, 2021 .............................................................. 51
Figure 21 - NOAA SPC 500 mb and 700 mb Upper Air Charts: July 12, 2021.............................................. 52
Figure 22 - GFS Analyzed 500 mb GPH and Winds: July 12, 2021 .............................................................. 53
Figure 23 - NOAA SPC 500 mb Heights and Vorticity: July 12, 2021 ........................................................... 54
Figure 24 - WPC Surface Analysis: July 12, 2021 ......................................................................................... 55
Figure 25 - NOAA SPC Surface Pressure Chart: July 12, 2021 ..................................................................... 56

Figure 26 - KSLC Radiosonde Soundings: July 12, 2021 .............................................................................. 57
Figure 27 - FIRMS Map: July 12, 2021 ......................................................................................................... 60
Figure 28 - GOES East True Color and GFS 500 mb Heights and Winds: July 12, 2021 ............................... 61
Figure 29 - GOES West True Color: Western CONUS July 12, 2021 ............................................................ 62
Figure 30 - GOES East True Color: Utah July 12, 2021 ................................................................................ 63
Figure 31 - GOES West AOD: July 12, 2021 ................................................................................................. 64
Figure 32 - HMS Smoke Fields and WFIGS Wildfire Perimeters: July 12, 2021........................................... 65
Figure 33 - HMS Smoke Field: Utah July 12, 2021 ...................................................................................... 66
Figure 34 - HRRR Smoke VIS and NSFC Smoke: July 12, 2021..................................................................... 67
Figure 35 - BlueSky Dispersion Analysis: July 12, 2021 ............................................................................... 68
Figure 36 - AERONET Level 2 AOD: July 2021 ............................................................................................. 69
Figure 37 - AERONET Level 2 AOD: July 12, 2021 ....................................................................................... 70
Figure 38 - MESOWEST WBBS Camera Images: July 12, 2021 .................................................................... 71
Figure 39 - HYSPLIT 72-hr Ensemble Backward Traj: July 12, 2021 15Z ...................................................... 74
Figure 40 - HYSPLIT 72-hr Backward Frequency Traj: July 12, 2021 15Z .................................................... 75
Figure 41 - Sugar Fire, CA; HYSPLIT 48-hr Forward Ensemble and Frequency Traj: July 10-12, 2021 15Z . 76
Figure 42 - Bootleg Fire, OR; HYSPLIT 72-hr Forward Ensemble and Frequency Traj: July 9-12, 2021 21Z 77
Figure 43 - Lava Fire, CA; HYSPLIT 72-hr Forward Ensemble and Frequency Traj: July 9-12, 2021 15Z ..... 78
Figure 44 - CV Hourly PM2.5: July 12, 2021 ................................................................................................ 80
Figure 45 - CV Monitored 24-hr PM2.5 and MD8A Ozone: July 12, 2021 .................................................. 81
Figure 46 - Hourly Brown Carbon (BrC) Concentrations: July 12, 2021 ...................................................... 81
Figure 47 - MD8A Ozone 2019-2023 at CV Monitor ................................................................................... 83
Figure 48 - Non-Event and Event MD8A Ozone: NWF 2016-2023 .............................................................. 84
Figure 49 - Non-Event and Event Average Hourly Diurnal Ozone at CV Monitor: : July 12, 2021 .............. 85
Figure 50 - Flagged Event Hourly Ozone vs. Average Hourly Diurnal Ozone at CV Monitor (2016-2021): :
July 12, 2021 ............................................................................................................................................... 85
Figure 51 - HW Average Daily VOCs: Jul-Aug .............................................................................................. 87
Figure 52 - HW Average Daily TNMOC: Jul-Aug 2021 ................................................................................. 88
Figure 53 – Event vs. Non-Event: Average Daily VOCs at HW: July 12, 2021.............................................. 88
Figure 54 – Event vs. Non-Event: Average Hourly Diurnal Total VOCs, TNMOC, and NOx: July 12, 2021 .. 89

Figure 55 – Event vs. Comparable MET: Hourly VOCs, NOx, and Ozone at HW and CV: July 12, 2021 ..... 90
Figure 56 - Western U.S. Drought Monitor: July 2021 ................................................................................ 91
Figure 57 - NCEP Reanalysis Average 500 mb GPH: July 24, 2021 .............................................................. 92
Figure 58 - PRISM July 2021 Precipitation Anomalies ................................................................................ 93
Figure 59 - PRISM July 2021 Temperature Anomalies ................................................................................ 93
Figure 60 – WFPI: July 24, 2021 .................................................................................................................. 94
Figure 61 - WFIGS Wildfire Perimeters: July 24, 2021 ................................................................................ 95
Figure 62 - NCEP Reanalysis Average 500 mb GPH: July 24, 2021 .............................................................. 97
Figure 63 - NOAA SPC 500 mb and 700 mb Upper Air Charts: July 24, 2021.............................................. 98
Figure 64 - GFS Analyzed 500 mb GPH and Winds: July 24, 2021 .............................................................. 99
Figure 65 - WPC Surface Analysis: July 24, 2021 ....................................................................................... 100
Figure 66 - KSLC Radiosonde Soundings: July 24, 2021 ............................................................................ 101
Figure 67 - CV Meteogram: July 24, 2021 ................................................................................................ 102
Figure 68 - FIRMS Map: July 24, 2021 ....................................................................................................... 104
Figure 69 - GOES West True Color: Western CONUS July 24, 2021 ........................................................... 105
Figure 70 - GOES East True Color and GFS 500 mb Heights and Winds: July 24, 2021 ............................. 106
Figure 71 - GOES East True Color: Utah July 24, 2021 .............................................................................. 107
Figure 72 – GOES West AOD Composite 18-21Z: July 24, 2021 ................................................................ 108
Figure 73 - HMS Smoke Fields and WFIGS Wildfire Perimeters: July 24, 2021......................................... 109
Figure 74 - HRRR Smoke VIS and NSFC Smoke: July 24, 2021................................................................... 110
Figure 75 - BlueSky Dispersion Analysis: July 24, 2021 ............................................................................. 111
Figure 76 – AERONET Level 2 AOD: July 2021 ........................................................................................... 112
Figure 77 - AERONET Level 2 AOD: July 24, 2021 ..................................................................................... 113
Figure 78 - HYSPLIT 72-hr Ensemble and Frequency Backward Traj: July 24, 2021 23Z ........................... 115
Figure 79 – Tamarack Fire; HYSPLIT 72-hr Forward Ensemble and Frequency Traj: July 22-24, 2021 12Z
.................................................................................................................................................................. 116
Figure 80 - Dixie Fire; HYSPLIT 72-hr Forward Ensemble and Frequency Traj: July 22-24, 2021 12Z ....... 117
Figure 81 - CV Hourly PM2.5: July 24, 2021 .............................................................................................. 118
Figure 82 - CV Monitored 24-hr PM2.5 and MD8A Ozone: July 24, 2021 ................................................ 119
Figure 83 - Hourly Brown Carbon (BrC) Concentrations: July 24, 2021 .................................................... 119

Figure 84 - MD8A Ozone 2019-2023 at CV Monitor ................................................................................. 121
Figure 85 - Non-Event and Event MD8A Ozone: NWF 2016-2023 ............................................................ 122
Figure 86 - Non-Event and Event Average Hourly Diurnal MD8A Ozone at CV Monitor .......................... 123
Figure 87 - Flagged Event Hourly Ozone vs. Average Hourly Diurnal MD8A Ozone at CV Monitor: 2016-
2021 .......................................................................................................................................................... 123
Figure 88 - HW Average Daily VOCs: Jul-Aug ............................................................................................ 125
Figure 89 - HW Average Daily TNMOC: Jul-Aug 2021 ............................................................................... 126
Figure 90 - Event vs. Non-Event: Average Daily VOCs at HW: July 24, 2021 ............................................ 126
Figure 91 - Event vs. Non-Event: Average Hourly Diurnal Total VOCs, TNMOC, and NOx: July 24, 2021 127
Figure 92 - Event vs. Comparable MET: Hourly VOCs, NOx, and Ozone at HW and CV: July 24, 2021 .... 128
Figure 93 - Western U.S. Drought Monitor: August 2021 ........................................................................ 129
Figure 94 - NCEP Reanalysis Average 500 mb GPH: July 1 – August 8, 2021 ............................................ 130
Figure 95 - PRISM July 2021 Precipitation Anomalies .............................................................................. 130
Figure 96 - PRISM July 2021 Temperature Anomalies .............................................................................. 131
Figure 97 - WFPI Forecast: August 7-8, 2021 ............................................................................................ 132
Figure 98 - WFIGS Wildfire Perimeters: August 7-8, 2021 ........................................................................ 133
Figure 99 - CV Meteogram: August 7-8, 2021 ........................................................................................... 136
Figure 100 - NCEP Reanalysis Average 500 mb GPH: August 7-8, 2021 ................................................... 137
Figure 101 - NOAA SPC 500 mb Upper Air Charts: August 7-8, 2021 ....................................................... 138
Figure 102 - NOAA SPC 500 mb Upper Air Charts: Zoomed August 7-8, 2021 ......................................... 139
Figure 103 - NOAA SPC 700 mb Upper Air Charts: August 7-8, 2021 ....................................................... 140
Figure 104 - NOAA SPC 700 mb Upper Air Charts: Zoomed August 7-8, 2021 ......................................... 141
Figure 105 - GFS Analyzed 500 mb GPH and Winds: August 7-8, 2021 .................................................... 142
Figure 106 - WPC Surface Analysis: August 6-8, 2021 .............................................................................. 143
Figure 107 - NOAA SPC Surface Pressure and Chart: August 6, 2021 ....................................................... 144
Figure 108 - NOAA SPC Surface Pressure Chart: August 8, 2021 .............................................................. 145
Figure 109 - KSLC Radiosonde Soundings: August 7-8, 2021 .................................................................... 146
Figure 110 - FIRMS Map: August 6, 2021 .................................................................................................. 148
Figure 111 - FIRMS Map: August 7, 2021 .................................................................................................. 149
Figure 112 - FIRMS Map: August 8, 2021 .................................................................................................. 150

Figure 113 - GOES-East TrueColor Imagery with 500 mb GPH and Winds: August 6, 2021 ..................... 151
Figure 114 - GOES-East TrueColor Imagery with 500 mb GPH and Winds: August 7, 2021 ..................... 152
Figure 115 - GOES-East TrueColor Imagery with 500 mb GPH and Winds: August 8, 2021 ..................... 153
Figure 116 – Smoke vs. Smoke Free Conditions: GOES East True Color - Utah August 7-8, 2021 ............ 154
Figure 117 - GOES-West TrueColor Imagery with Surface PM2.5: August 7, 2021 .................................. 155
Figure 118 - GOES-West TrueColor Imagery with Surface PM2.5: August 8, 2021 .................................. 156
Figure 119 - GOES-West AOD Composite 15-18Z: August 7, 2021 ........................................................... 157
Figure 120 - GOES-West AOD Composite 15-18Z: August 8, 2021 ........................................................... 158
Figure 121 - HMS Smoke Fields and WFIGS Wildfire Perimeters: August 7, 2021 ................................... 159
Figure 122 - HMS Smoke Fields and WFIGS Wildfire Perimeters: August 8, 2021 ................................... 160
Figure 123 - HRRR Smoke VIS and NSFC Smoke: August 7, 2021 ............................................................. 161
Figure 124 - HRRR Smoke VIS and NSFC Smoke: August 8, 2021 ............................................................. 162
Figure 125 - BlueSky Dispersion Analysis: August 7-8, 2021 .................................................................... 163
Figure 126 - AERONET Level 2 AOD: August, 2021 ................................................................................... 164
Figure 127 - AERONET Level 2 AOD: August 6, 2021 ................................................................................ 165
Figure 128 - AERONET Level 2 AOD: August 7, 2021 ................................................................................ 166
Figure 129 - AERONET Level 2 AOD: August 8, 2021 ................................................................................ 167
Figure 130 - MESOWEST WBB Camera Images: August 6-8, 2021 ........................................................... 168
Figure 131 - HYSPLIT 60-hr Ensemble Backward and Frequency Traj: August 7, 2021 21Z ..................... 171
Figure 132 - HYSPLIT 60-hr Ensemble Backward and Frequency Traj: August 8, 21Z .............................. 172
Figure 133 – Dixie and Bootleg Fires; HYSPLIT 48-hr Ensemble Forward Traj: August 7, 15Z and 18Z .... 173
Figure 134 – Antelope and Bootleg Fires; HYSPLIT 72-hr and 48-hr Ensemble Forward Traj: August 8, 15Z
.................................................................................................................................................................. 174
Figure 135 – Dixie and Bootleg Fires; HYSPLIT 48-hr and 60-hr Ensemble Forward Traj: August 7, 15Z and
August 8, 18Z ............................................................................................................................................ 175
Figure 136 – CV Hourly PM2.5: August 7-8, 2021 ..................................................................................... 176
Figure 137 - CV Monitored 24-hr PM2.5 and MD8A Ozone: August 7-8, 2021 ........................................ 177
Figure 138 - Hourly Brown Carbon (BrC) Concentrations: August 7-8 2021 ............................................ 177
Figure 139 - MD8A Ozone 2019-2023 at CV Monitor ............................................................................... 179
Figure 140 - Non-Event and Event MD8A Ozone: NWF 2016-2023 .......................................................... 180
Figure 141 - Non-Event and Event Average Hourly Diurnal MD8A Ozone at CV Monitor: August 7-8 .... 181

Figure 142 - Flagged Event Hourly Ozone vs. Average Hourly Diurnal MD8A Ozone at CV Monitor 2016-
2021: August 7-8 ....................................................................................................................................... 181
Figure 143 - HW Average Daily VOCs: Jul-Aug .......................................................................................... 183
Figure 144 - HW Average Daily TNMOC: Jul-Aug 2021 ............................................................................. 184
Figure 145 – Event vs. Non-Event: Average Daily VOCs at HW ................................................................ 184
Figure 146 – Event vs. Non-Event: Average Hourly Diurnal Total VOCs, TNMOC, and NOx: August 7-8 . 185
Figure 147 – Event vs. Comparable MET: Hourly VOCs, NOx, and Ozone at HW and CV: August 7-8 ..... 186
Figure 148 - Western U.S. Drought Monitor: August 2021 ...................................................................... 187
Figure 149 - NCEP Reanalysis Average 500 mb GPH: August 16, 2021 ..................................................... 188
Figure 150 - PRISM July 2021 Precipitation Anomalies ............................................................................ 189
Figure 151 - PRISM July 2021 Temperature Anomalies ............................................................................ 189
Figure 152 – WFPI: August 16, 2021 ......................................................................................................... 190
Figure 153 - WFIGS Wildfire Perimeters: August 16, 2021 ....................................................................... 191
Figure 154 - NCEP Reanalysis Average 500 mb GPH: August 16, 2021 ..................................................... 194
Figure 155 - NOAA SPC 500 mb and 700 mb Upper Air Charts: August 16, 2021 .................................... 195
Figure 156 - GFS Analyzed 500 mb GPH and Winds: August 16, 2021 ..................................................... 196
Figure 157 - CV Meteogram: August 16, 2021 .......................................................................................... 197
Figure 158 - WPC Surface Analysis: August 16, 2021................................................................................ 198
Figure 159 - KSLC Radiosonde Soundings: August 16, 2021 ..................................................................... 199
Figure 160 - FIRMS Map: August 16, 2021 ................................................................................................ 201
Figure 161 - GOES West True Color: Western CONUS August 16, 2021 ................................................... 202
Figure 162 - GOES East True Color and GFS 500 mb Heights and Winds: August 16, 2021 ..................... 203
Figure 163 - GOES East True Color: Utah August 16, 2021 ....................................................................... 204
Figure 164 - GOES West AOD Composite 18-21Z: August 16, 2021 ......................................................... 205
Figure 165 - HMS Smoke Fields and WFIGS Wildfire Perimeters: August 16, 2021 ................................. 206
Figure 166 - HRRR Smoke VIS and NSFC Smoke: August 16, 2021 ........................................................... 207
Figure 167 – BlueSky Dispersion Analysis: August 16, 2021 ..................................................................... 208
Figure 168 - MESOWEST WBB Camera: August 16, 2021 ......................................................................... 209
Figure 169 - HYSPLIT 72-hr Ensemble Backward & Frequency Trajectories: August 16th, 2021 23Z ...... 211
Figure 170 – Lick Creek, ID Fire; HYSPLIT 72-hr Ensemble Forward & 48-hr Frequency Trajectories: August
14-17, 2021 ............................................................................................................................................... 212

Figure 171 - Trail Creek & Alder Creek, MT Fires; HYSPLIT 48-hr Ensemble Forward & Frequency
Trajectories Fires: August 14-17, 2021 ..................................................................................................... 213
Figure 172 – Boundary, ID Fire; HYSPLIT 48-hr Ensemble Forward & 60-hr Frequency Trajectories Fires:
August 14-18, 2021 ................................................................................................................................... 214
Figure 173 - CV Hourly PM2.5: August 16, 2021 ....................................................................................... 215
Figure 174 - CV Monitored 24-hr PM2.5 and MD8A Ozone: August 16, 2021 ......................................... 216
Figure 175 - Hourly Brown Carbon (BrC) Concentrations: August 16, 2021 ............................................. 216
Figure 176 - MD8A Ozone 2019-2023 at CV Monitor: August 16, 2021 ................................................... 218
Figure 177 - Non-Event and Event MD8A Ozone: NWF 2016-2023 .......................................................... 219
Figure 178 - Non-Event and Event Average Hourly Diurnal MD8A Ozone at CV Monitor: August 16, 2021
.................................................................................................................................................................. 220
Figure 179 - Flagged Event Hourly Ozone vs. Average Hourly Diurnal MD8A Ozone at CV Monitor (2016-
2021): August 16, 2021 ............................................................................................................................. 220
Figure 180 - HW Average Daily VOCs: Jul-Aug .......................................................................................... 222
Figure 181 - HW Average Daily TNMOC: Jul-Aug 2021 ............................................................................. 223
Figure 182 - Event vs. Non-Event: Average Daily VOCs at HW: August 16, 2021 ..................................... 223
Figure 183 - Event vs. Non-Event: Average Hourly Diurnal Total VOCs, TNMOC, and NOx: August 16, 2021
.................................................................................................................................................................. 224
Figure 184 - Event vs. Comparable MET: Hourly VOCs, NOx, and Ozone at HW and CV: August 16, 2021
.................................................................................................................................................................. 225

Tables
Table 1 - Flagged EE Events ......................................................................................................................... 25
Table 2 – Flagged EE Wildfire Smoke Source Information .......................................................................... 26
Table 3 - Ranked MD8A Ozone at CV With and Without EE Exclusions ..................................................... 29
Table 4 - Adjusted CV 2021 4th High MD8A ............................................................................................... 31
Table 5 - CV Monitor Details ....................................................................................................................... 33
Table 6 - KSLC Climate Averages ................................................................................................................. 34
Table 7 – Non-Event MD8A Ozone Exceedance: Surface Meteorological Conditions................................ 37
Table 8 - Event and Non-Event CV MD8A Ozone ........................................................................................ 40
Table 9 – Flagged Event MD8A Ozone Exceedance: Surface Meteorological Conditions .......................... 40
Table 10 - Potential Wildfire Smoke Sources: July 12, 2021 ....................................................................... 48
Table 11 – Average Brown Carbon (BrC) Concentrations: July 2019-2023................................................. 82
Table 12 - Top 10 CV POR Ranked MD8A (2018-2024) ............................................................................... 83
Table 13 – Potential Wildfire Smoke Sources: July 24, 2021 ...................................................................... 95
Table 14 - Average Brown Carbon (BrC) Concentrations July 2019-2023: July 24, 2021 ......................... 120
Table 15 - Top 10 CV POR Ranked MD8A (2018-2024) ............................................................................. 121
Table 16 - Potential Wildfire Smoke Sources: August 7-8, 2021 .............................................................. 133
Table 17 - Average Brown Carbon (BrC) Concentrations July 2019-2023: August 7-8 2021 .................... 178
Table 18 - Top 10 CV POR Ranked MD8A (2018-2024) ............................................................................. 180
Table 19 - Potential Wildfire Smoke Sources: August 16, 2021 ................................................................ 191
Table 20 - Average Brown Carbon (BrC) Concentrations July 2019-2023: August 16, 2021 .................... 217
Table 21 - Top 10 CV POR Ranked MD8A (2018-2024): August 16, 2021 ................................................. 218
Table 22 – Copperview Data Exclusion: New 4th Max MD8A 2021 ........................................................... 227
Table 23 – DV Flagged Data Excluded ....................................................................................................... 228

Analysis in Support of Exceptional Event
Flagging and Exclusion from 179B
Demonstration for the Weight of Evidence
Analysis
Introduction
During the period July through August of 2021, numerous medium to large sized wildfires burned
across the western U.S (e.g. California, Oregon, Washington, and Idaho), leading to large aggregate smoke
plumes spilling into Utah. In total, nearly 50 days monitored by the Utah Division of Air Quality (UDAQ)
were impacted by some level of smoke emissions across northern Utah. The dense smoke plumes caused
multiple exceedances of the 24-hour PM2.5 NAAQS as well as coincident exceedances of the MD8A Ozone
NAAQS at many UDAQ monitors. While many monitors were affected by high particulate concentrations
and emissions from wildfire smoke in the summer of 2021, the Copperview (CV) UDAQ site was most
significantly impacted. In total, more than 15 ozone exceedances at the CV monitor were impacted by
wildfire smoke in the summer of 2021, but due to time constraints UDAQ only focuses on a few selected
heavy smoke impacted exceedance events in this demonstration. UDAQ has identified four separate
contiguous events between July and August of 2021 that had ozone concentrations that were heavily
impacted by wildfire smoke emissions at the CV monitor and are considered exceptionally abnormal
compared to historical conditions. These events and surrounding circumstances were evaluated by UDAQ
and have been deemed atypical. Given the gravity of smoke emission impacts on ozone, UDAQ suggests
these events should be excluded from design value calculations within the 179B modeling demonstration.
UDAQ has identified that ozone concentrations exceeding the NAAQS on July 12, July 24, August
7 & 8, and August 16, 2021 qualify as wildfire smoke impacted ozone exceedances. The purpose of this
document is to provide technical documentation supporting a concurrence and petition to the Regional
Administrator for Region 8 of the U.S. Environmental Protection Agency (EPA) for the exceptional event
flagging, proceeding data modification, and exclusion of the aforementioned wildfire smoke impacted
ozone exceedances (July 12, July 24, August 7-8, and August 16) from the 2021-2023 Average 3-year
(2021-2023) design value (DV) used within the 179B modeling demonstration. The following subsections
include a brief overview and regulatory significance of the wildfire smoke impacted high-concentration
events excluded from 2021-2023 Average DV calculation as a part of Weight of Evidence analysis for the
179B demonstration.

Overview of Events
The wildfire season of 2021 was severe and extensive, creating significant and far-reaching
deleterious impacts across the Western U.S. and the CONUS (Figure 31). Many areas experienced
prolonged periods of wildfire smoke and extremely poor air quality, including northern Utah. Figure 32

shows the number of smoke days analyzed by the Hazard Mapping System (HMS)47 across the U.S., with
Utah averaging more than 80 smoke days in 2021. The unprecedented nature of the wildfire season
brought numerous waves of wildfire smoke across northern Utah and the CV monitor, totaling 635 hours48
of smoke over the season. The fraction of light, medium, and heavy smoke hours at the CV monitor is
given in Figure 33, with nearly half of the total smoke hours analyzed being medium to heavy density.
During the months of July and August, the CV monitor was particularly impacted by wildfire smoke
plumes. These plumes were often a conglomeration of smoke from multiple wildfires across the Western
U.S., making for dense aggregate plume masses of smoke.
On July 12, July 24, August 7-8, and August 16, 2021, high ozone concentrations were observed
across the Northern Wasatch Front Nonattainment area (Figure 34), with five ozone MD8A exceedances
of the 2015 NAAQS (> 70 ppb) measured at Copperview (CV) as shown in Table 12. These ozone
exceedances are considered significant and were due to the presence of wildfire smoke transported over
the Wasatch Front from a number of different fire complexes in California, Oregon, Washington, and
Idaho outlined in Table 13. In Table 13, the fire size of each flagged event date is given for the potential
wildfire smoke sources. It is noteworthy that no single wildfire was the sole contributor to the flagged EE
events at CV, but rather a combination of multiple wildfire smoke sources. Wildfire smoke sources on
flagged dates were determined from forward and backward HYSPLIT trajectories, which will be detailed
further in Section 0. Additionally, the selected flagged dates exhibit elevated concentrations of particulate
matter (PM2.5), which are shown to be well above average, and 98th percentile concentrations for the
CV monitor (Table 12). The PM2.5 concentrations on the flagged dates, along with enhanced ozone values,
are atypical when compared to historical concentrations and are considered consequential for certain
determinations.
The wildfire smoke emissions on flagged EE days contained a mixture of PM2.5 and other
emissions, including ozone itself - formed from photochemical reactions within the aged smoke plumes -
and ozone precursors. These ozone precursors include nitrogen oxides (NOx) and volatile organic
compounds (VOCs), which were both major contributors to ozone formation during the specified high
ozone events. The presence of wildfire smoke from each of these high ozone events was flagged due to
observed elevated tracer concentrations of PM2.5, CO, and black/brown carbon, which will be detailed
further in the following sections. Additionally, observed VOC species related to wildfire smoke emissions
were also observed, supporting the flagging of these dates.

47 Hazard Mapping System Smoke product can be found at: https://www.ospo.noaa.gov/products/land/hms.html#stats-smoke
48 HMS smoke statistics can be found at: https://globalfires.earthengine.app/view/hms-smoke

Figure 31 - HMS Smoke Plume Extent

Figure 31. Smoke plume extent (km²) over North America by month as analyzed by HMS in 2021 compared
to the long-term average (Period of Record (POR) 2006-2022). The observed plume sizes in 2021 were
significantly above the POR normal.

Figure 32 - HMS Cumulative Smoke Days

Figure 32. Cumulative number of smoke days analyzed by HMS across the CONUS in 2021. Utah averaged
about 80 smoke days, with the CV monitor observing 88 smoke days.

Figure 33 - Smoke Density Fraction at CV

Figure 33. Fraction of total (635 hours) light, medium, and heavy smoke hours at the CV monitoring site
in 202149. Slightly less than half of the smoke observed at CV was considered medium to heavy.

49 Cumulative smoke duration statistics can be found at: https://globalfires.earthengine.app/view/hms-smoke

Figure 34 - NWF Non-Attainment Area

Figure 34. The Northern Wasatch Front 8-hour Ozone (2015 Standard) Nonattainment area boundary
(black solid line) and the location of the UDAQ Copperview monitor (yellow star).

Table 12 - Flagged EE Events
Event
Date
Event
Type
AQS
Flag
Monitor AQS
ID and POC
Monitor
Name
MD8A
ozone
(ppb)
24hr PM2.5
(µg/m3)
98th Percentile
PM2.5 (µg/m3) Notes
7/12/21 Wildfire IF
490352005 -
POC 3
Copperview
(SLAMS) 96 27.3 17.8
2021 EE flagged
wildfire
7/24/21 Wildfire IF
490352005 -
POC 3
Copperview
(SLAMS) 83 26.2 17.8
2021 EE flagged
wildfire
8/7/21 Wildfire IF
490352005 -
POC 3
Copperview
(SLAMS) 89 42.8 26.2
2021 EE flagged
wildfire

Event
Date
Event
Type
AQS
Flag
Monitor AQS
ID and POC
Monitor
Name
MD8A
ozone
(ppb)
24hr PM2.5
(µg/m3)
98th Percentile
PM2.5 (µg/m3) Notes
8/8/21 Wildfire IF
490352005 -
POC 3
Copperview
(SLAMS) 87 49.5 26.2
2021 EE flagged
wildfire
8/16/21 Wildfire IF
490352005 -
POC 3
Copperview
(SLAMS) 86 48.4 26.2
2021 EE flagged
wildfire
Table 12. MD8A ozone, 24hr PM2.5, and the site specific 98th percentile PM2.550 (based on the lesser
value of either (a) the most recent 5-year month specific 98th percentile for 24-hour PM2.5 data, or (b)
the minimum annual 98th percentile for 24-hour PM2.5 data for the most recent 5-year period with R and
I Fire flags excluded51) observed at the Copperview (CV) monitor. The MD8A ozone data is flagged as
wildfire impacted (IF) Exceptional Event and excluded from the 2021-2023 Average 3-year DV.

Table 13 – Flagged EE Wildfire Smoke Source Information
Event Date
CV - 490352005 Wildfire Details Event
Type
MD8A ozone (ppb) & 24-hr PM2.5 (µg/m3) Smoke Sources (potential) Fire Size (Event - acres) Regional
7/12/2021 96; 27.3
Sugar fire/Beckwourth Complex, CA 61252
✔
Lava, CA 26162
Bootleg fire, OR 150812
Lick Creek fire, OR 55055
Snake River Complex, ID 54407
7/24/2021 83; 26.2
Dixie fire, CA 167430
✔ Sugar fire/Beckwourth Complex, CA 105670
Tamarack fire, CA/NV 59112
Bootleg fire, OR 400389

50 EPA PM2.5 Tiering Tool: https://www.epa.gov/air-quality-analysis/pm25-tiering-tool-exceptional-events-analysis
51 EPA PM2.5 Tiering Guidance: https://www.epa.gov/system/files/documents/2024-04/final-pm-fire-tiering-4-30-24.pdf

Event Date
CV - 490352005 Wildfire Details Event
Type
MD8A ozone (ppb) & 24-hr PM2.5 (µg/m3) Smoke Sources (potential) Fire Size
(Event - acres) Regional
8/7-
8/8/2021 89; 42.8 87; 49.5
Dixie fire, CA 434813
✔
Haypress (River Complex) fire, CA 23121
Monument fire, CA 44317
Mcfarland fire, CA 30093
Antelope fire, CA 41410
Tamarack fire, CA/NV 68696
Bootleg fire, OR 413765
Lick Creek fire, OR 80421
Snake River Complex, ID 109444
Black Butte Complex, OR 8612
Elbow Creek fire, OR 22960
8/16/2021 86; 48.4
Dixie fire, CA 570211
✔
Haypress (River Complex) fire, CA 41031
Monument fire, CA 85076
Mcfarland fire, CA 43708
Antelope fire, CA 53864
Tamarack fire, CA/NV 68637
Lick Creek fire, OR 80421
Schneider Springs fire, WA 16516
Snake River Complex, ID 10944
Trail Creek, MT 37412
Alder Creek, MT 13011
Dixie, ID 43344
Summit Trail, OR 29205
Rough Patch Complex, OR 12280
Bedrock fire, OR 10850
Jack fire, OR 23647
425-Smith (Devils Knob Cpx), OR 7766
Gales (Middle Fork Complex), OR 9253
Table 13. Wildfire smoke source information for each flagged event period requested for exclusion, with
the list of potential wildfire smoke sources contributing to smoke emissions at CV (identified from forward
and backward HYSPLIT trajectories) and the approximate size of the fires in acres52 on the date of the
event. The corresponding MD8A ozone and 24-hour PM2.5 concentrations are given for each event day.

Significance and Justification
The EPA states in the “Additional Methods, Determinations, and Analyses to Modify Air Quality
Data Beyond Exceptional Events (Clarification Memo on Data Modification)”53 memorandum there are
determinations and analyses not covered by the Exceptional Events Rule (i.e., not included in the list of

52 Dataset of U.S. IMSR found at: https://research.fs.usda.gov/treesearch/67197
53 Additional Methods, Determinations, and Analyses to Modify Air Quality Data Beyond Exceptional Events (Clarification Memo
on Data Modification). Available on EPA’s web page at: https://www.epa.gov/sites/default/files/2019-
04/documents/clarification_memo_on_data_modification_methods.pdf

covered regulatory actions) that also rely on ambient air quality monitoring data that may have been
influenced by atypical, extreme, or unrepresentative events. In such events, independent determinations
and analyses covered by other regulatory programs (not exceptional events) are allowed to be made when
regarding mechanisms for possible monitoring data exclusion, selection, or adjustment. Specifically,
monitoring data exclusion, selection, or adjustment may qualify for determinations and analyses by
meeting two main requirements:

1. Ambient air data are not representative per other applicable EPA rules/guidance (i.e., 40 CFR Part
58 requirements and relevant guidance).
2. Ambient data are not representative to characterize background concentrations or base period
concentrations in accordance with the EPA Guideline, which may impact a determinative value in
a past or projected time period. Situations could include removal of air quality monitoring data
that apply to characterizing background contributions for NAAQS compliance demonstrations
under PSD and transportation conformity, and to developing alternative current and future year
design values for SIP modeling in attainment demonstrations.

The five flagged wildfire smoke impacted ozone exceedances of the NAAQS at CV (Table 12) are
not representative of ozone background or base period concentrations, and without exclusion, impact
base and projected future design values within SIP and other modeling attainment demonstrations.
UDAQ’s flagged wildfire smoke impacted ozone exceedances meet the qualifying requirements to
proceed with a monitoring data modification and exclusion analysis. Therefore, as promulgated by EPA’s
Guideline on Air Quality Models (“Guideline”; see 40 CFR Part 51, Appendix W)54, the appropriate types
of determination or analysis to justify a monitoring data modification and exclusion includes:

1. Estimating base and future year design values for ozone and PM2.5 SIP attainment
demonstration.
2. Determining whether a SIP satisfies CAA 110(a)(2)(D)(i)(I).

Utilizing the provisions set forth in the Clarification Memo on Data Modification, Table 14 exhibits
how the CV monitoring data is modified by excluding the five flagged wildfire EE dates in Table 12 - Flagged
EE Events. The exclusion of the flagged EE dates alters the ranked 4th high ozone in 2021 at CV. UDAQ
employed the EPA’s Exceptional Event Design Value Tool55 to determine the regulatory significance of
excluding the flagged EE days. As shown in Figure 35 and Figure 36, the EPA Design Value Tool reveals
that excluding the flagged EE dates (Table 14) modifies the 4th high ozone value from 86 ppb (8/16/2021)
to 80 ppb (7/10/2021). Furthermore, the modified 2021 4th high ozone with the exclusions of EE dates
drives the 3-year average (2021-2023) ozone DV from 77 ppb to 75 ppb. The results of the data exclusion

54 40 CFR Part 51, Appendix W is available online at: https://www.epa.gov/sites/default/files/2020-09/documents/appw_17.pdf
55 EPA’s Exceptional Events Design Value Tool found at: https://www.epa.gov/air-quality-analysis/exceptional-events-design-
value-tool

and modification, using the EPA’s Design Value Tool, is summarized in Table 15 and described in more
detail in Section 6.
The procedure for monitoring data exclusion, selection, or adjustment, given the types of
determination and analysis mentioned previously, involves following EPA’s recommendations detailed in
Section 8.3.2 c.ii. and d., and Section 8.3.3 d. of the Guideline. UDAQ follows the suggested EPA analysis
and procedures to support monitor data modification and exclusion, by presenting air quality along with
meteorological, HYSPLIT trajectory-dispersion, and satellite analysis in the sections below. The analysis
demonstrates the impact of wildfire smoke on high ozone concentrations and provides justification for
data exclusion at the CV monitoring station. In order to estimate the modeled year design values for the
179B demonstration, the 2021-2023 Average 3-year DV and 179B modeled year design value (FDV) are
recalculated by excluding the flagged MD8A ozone exceedances. The preceding analysis and estimates of
the adjusted DV and FDV are explained in more detail in Section 4.

Table 14 - Ranked MD8A Ozone at CV With and Without EE Exclusions
Old Rank New Rank Date CV MD8A (ppb) Smoke Flag PM2.5 (µg/m3)
1 - 7/12/2021 96 SMOKE 27.3
2 - 8/8/2021 89 SMOKE 42.8
3 - 8/7/2021 87 SMOKE 49.5
4 - 8/16/2021 86 SMOKE 48.4
5 1 9/8/2021 85 SMOKE 23.4
6 2 8/4/2021 85 SMOKE 22.4
7 3 7/11/2021 84 SMOKE 31
8 - 7/24/2021 83 SMOKE 26.2
9 4 7/10/2021 80 SMOKE 19.8
10 5 8/29/2021 79 SMOKE 24.3
Table 14. Ranked MD8A ozone concentrations (ppb) at CV for 2021 without EE flagged exclusions (old
rank) and with EE flagged exclusions (new rank). Old 4th high MD8A ozone without EE flagged exclusions

outlined in red. Flagged EE wildfire dates are highlighted in red and the new 4th high MD8A ozone with
EE flagged exclusions highlighted in green.
Figure 35 - EPA EE DV Tool: No EE Exclusions

Figure 35. Output from EPA’s Exceptional Event Design Value Tool56, with no data exclusions (generated
on Oct. 10, 2024)

56 EPA’s Exceptional Events Design Value Tool found at: https://www.epa.gov/air-quality-analysis/exceptional-events-design-
value-tool

Figure 36 - EPA EE DV Tool: EE Exclusions

Figure 36. Output from EPA’s Exceptional Event Design Value Tool57, with data exclusions from July 12,
July 24, August 7-8, and August 16, 2021 (generated on Oct. 10, 2024)

Table 15 - Adjusted CV 2021 4th High MD8A
Date MD8A ozone
Old 4th Max 2021 8/16/2021 86
New 4th Max 2021 7/10/2021 80
Old 3-year DV 77
New 3-year DV 75
Table 4. Old 2021 CV 4th high MD8A ozone and new 4th high MD8A ozone after flagged wildfire EE
exclusions.

57 EPA’s Exceptional Events Design Value Tool found at: https://www.epa.gov/air-quality-analysis/exceptional-events-design-
value-tool

Regional Description
Monitor Overview
In this document, the analysis focuses on the monitor data modification and exclusion from the
CV monitor for the selected dates listed in Table 12 - Flagged EE Events. The CV monitor is located in the
south-central portion of the Salt Lake Valley (SLV), Utah, which lies at the eastern edge of the Great Basin
and Range and within the north-south oriented Wasatch Front Urban Corridor. As the main population
center of Utah, the Wasatch Front comprises more than two thirds of Utah’s population, with the SLV
contributing 1.1 million people to the area. A diverse range of environments and topography characterize
the Wasatch Front and SLV, ranging from high desert, playa, wetlands, semiarid foothills, sub-alpine
forests, and alpine environments. The SLV is bounded by the Oquirrh Mountains and Great Salt Lake (GSL)
to the west and north, respectively, and the Wasatch Mountains to the east. The valley sits at roughly
4300 ft ASL, with the surrounding mountains rising more than 5000-6000 ft above the valley floor. This
gives the SLV a bathtub or bowl shape, which creates unique and challenging conditions for air quality. A
closer inspection of the SLV is given in Figure 37, with UDAQ monitors. Due to difficult air quality issues,
the EPA designated a large portion of the Wasatch Front as the 8-hour ozone (2015 standard) Moderate
Northern Wasatch Front (NWF) Nonattainment area (Figure 34). The CV monitor sits in the southern
portion of the NWF Nonattainment region in an area characterized as a mix between suburban/urban.
Monitored species and details for the CV station are given in Table 16.

Figure 37 - Salt Lake Valley and UDAQ Monitor Locations

Figure 37. Map of the Salt Lake Valley with the location of the Copperview (CV) monitor (yellow star) and
surrounding UDAQ monitors (red circles) marked.

Table 16 - CV Monitor Details
AIRS Code
Site
Code Site Name
Start
Year
End
Year ozone CO
PM2.5
hourly
PM2.5
24hr NO2 Lat Lon
490352005 CV Copperview 2018 present X X X X X 40.6 -111.89
Table 16 - CV Monitor Details.
Summertime Climatology and Geography
The SLV is characterized by a semiarid/steppe climate, with cold wet winters and hot dry
summers. During the summer, the large-scale weather (synoptic) pattern over Utah is dominated by
upper-level ridging or high pressure as seen in Figure 38. This synoptic pattern creates relatively benign
and quiescent conditions across the Wasatch Front, with deep planetary boundary layer mixed layers, hot

temperatures, weak surface and mid-level winds, and dry conditions. In Table 17, the average daily high
temperatures and precipitation are given for Salt Lake City, which is deemed a representative location for
summertime climate along the Wasatch Front. Generally, most precipitation during the summer is
attributed to late spring (June) mid-latitude cyclones or afternoon thunderstorms during the monsoon
season (July-August).

Figure 38 - NCEP Reanalysis Mean 1000-500 mb Thickness Composites

Figure 38 - NCEP Reanalysis Mean 1000-500 mb Thickness Composites. Mean 1000-500 mb thickness
composites for Jun, Jul, and Aug (1991-2020 Climatology). Warmer colors indicate higher thicknesses and
higher pressure on average, with a relatively persistent upper-level ridge axis evident across western
CONUS for the months Jun-Aug.

Table 17 - KSLC Climate Averages

Table 17. Averages for high and low temperature, and precipitation between the months June-September
at Salt Lake City International Airport (KSLC).

Besides creating hot and dry conditions, the characteristic summertime upper-level pattern forms
a conducive environment for the transport of wildfire smoke from local and distant sources into Utah.
This is due to the clockwise and relatively weak winds around a ridge of high pressure, which tend to
accumulate and swirl wildfire smoke from across the western United States into Utah. The pattern
frequently creates periods of diffuse and dense wildfire smoke being advected over the Wasatch Front,
with elevated smoke layers often mixed down to the surface due to the characteristic deep mixed layers
and subsidence under an upper level ridge.
The geography of the Wasatch Front is characterized as complex topography, with the valley areas
of highest population density bounded by the Great Salt Lake on the north and west and the Wasatch
Mountains on the east. This geographical setup creates a unique and complex lake-valley-mountain
climate and weather system. Mesoscale and thermally driven winds, including mountain, canyon, and
valley-lake breezes, dominate the summertime wind climatology. Often, these types of complex
topographical winds occur on a diurnal periodicity, and are fairly consistent under calm and quiescent
synoptic weather conditions. A wind climatology summary is given in Figure 39 in the form of wind roses
for Salt Lake City International Airport (KSLC). The wind rose in Figure 39 demonstrates the consistent
nature of the diurnal lake (daytime N-NW winds) and valley breeze (nighttime S-SE winds) in the Salt Lake
Valley during the summer months. Only under strong synoptic forcing does the lake breeze not occur,
which is rarer given the typical benign summer climate. An example of the thermally driven daytime (lake)
and nighttime (valley) breeze is given in Figure 40.

Figure 39 - KSLC Wind Roses: Summer Climatology

Figure 39. KSLC Jun-Sept wind rose composite (1991-2020 Climatology) broken down by day and night
periods. Left: Wind during the period 2100-1000 MDT, representing the nighttime valley winds (S-SE).
Right: Wind during the period 1000-2100 MDT, representing the daytime lake breeze (N-NW).

Figure 40 - Diurnal Wind Patterns SLV

Figure 40. Conceptual diagram of the left: daytime N-NW lake breeze (1000-2000 MST) and right:
nighttime S-SE valley breeze (2100-0900 MST).

Wasatch Front Ozone Climatological Characteristics
Characteristics of Non-Flagged High Ozone Events (Non-Events)
Anthropogenic emissions contributing to ozone formation in SLV are comprised of volatile organic
compounds (VOCs) and oxides of nitrogen (NOx). The main sources of NOx and VOC emissions include
mobile sources (cars, trucks, locomotives, off-road equipment) along with stationary and area sources
that include industrial processes, and consumer products. Transportation and population-driven sources
dominate the anthropogenic emissions. However, large point sources, including oil/gas refining and pit
mining operations, also contribute large amounts of VOCs and NOx. Over the past several decades, VOC
and NOx emissions have decreased significantly in the SLV. As seen in Figure 41 - SLV Historical MD8A
Ozone Exceedance Day Trends, this reduction has directly translated into fewer days above the 2015
ozone NAAQs 8-hour ozone standard compared to the past. These significant improvements occurred
despite increases in population, vehicle activity, and economic development.
Previous research has characterized ozone formation sensitivity in SLV airshed on non-impacted
wildfire smoke days in terms of NOx to VOC ratios and weekend to weekday ozone and NOx analysis (e.g.
Gonzalez et al., 2024). Studies have revealed that the SLV airshed generally resides within a transitional
to slightly VOC limited regime, meaning that ozone formation has the potential to be sensitive to both
increases/decreases in NOx and VOC emissions but at times can be more responsive to VOC emissions
depending on the location in the valley (e.g. Gonzalez et al., 2024; Jaffe et al., 2024). Other research has
noted that ozone production rates in the SLV for both smoke influenced and non-event days demonstrates
a strong sensitivity to VOC concentrations and less sensitivity to NOx (Jaffe et al., 2024).
The typical summertime high ozone season for the Wasatch Front area is marked between June
and September when increased incident solar radiation along with clear skies and hot temperatures aid
in ozone formation (Figure 42 - SLV Ozone Daily AQI Historic Trend). In particular, the meteorological
conditions favoring elevated ozone concentrations along the Wasatch Front are known to occur under
upper-level ridges/domes of high pressure, which create a stagnant environment with decreased emission
dispersion, deep vertical mixed layers, weak surface and mid-level winds, and increased surface
temperatures. These conditions allow the buildup of ozone precursors (NOx and VOCs) and create the
optimal environment for ozone photochemistry. Additionally, thermally driven circulations arising from
the Great Salt Lake (GSL) and nearby mountains are noted to impact the formation of summertime ozone

(Doran et al., 2002; Zumpfe and Horel, 2007). Table 18 – Non-Event MD8A Ozone Exceedance: Surface
Meteorological Conditions provides the typical surface meteorological conditions characteristic of non-
event ozone exceedance days in the SLV, with non-event exceedance days having hot temperatures (mid
90s F), weak winds (< 5kts), dry conditions (low dewpoint/RH), and relatively clear skies (SW > ~700
W/m2).

Figure 41 - SLV Historical MD8A Ozone Exceedance Day Trends

Figure 41. a.) Average number of MD8A ozone exceedances 1990-2005 compared to 2006-2024, b.)
Cumulative number of MD8A ozone exceedances 1990-2005 compared to 2006-2024, and c.) Number of
MD8a ozone exceedances and AQI for the years 2000-2024.

Table 18 – Non-Event MD8A Ozone Exceedance: Surface Meteorological Conditions
Monitor
Avg Max
Temp (F)
Avg Wind
Speed (mph)
Avg Wind
Direction (deg)
Avg SW Radiation
(W/m)
Avg RH
(%)
O3
Exceedances
HW 96 4 251 900 18 44
CV 95 4 199 691 26 37
Table 18. Non-event MD8A exceedance days (non-flagged wildfire event) average surface meteorological
conditions during ozone formation hours (1000-1800 MST) at the controlling SLV Hawthorne (HW)
monitor and CV monitor for the 5-year period 2019-2023 and 3-year period 2021-2023, respectively.

Figure 42 - SLV Ozone Daily AQI Historic Trend

Figure 42 - SLV Ozone Daily AQI Historic Trend. Ozone daily AQI values for 2000-2024. The focus of
elevated AQI values extends Jun-Sep, which is considered ozone season for the Wasatch Front.

Past research has attempted to outline the most common meteorological factors contributing to
high surface ozone concentrations across the western U.S. The presence of increased 500 hPa heights or
upper level ridging has been linked to increased ozone, particularly for areas of elevated terrain near
urban sources with high emissions of NO2 and other ozone precursors (Reddy and Pfister, 2016). Salt Lake
City was included in this study as one of the urban areas in elevated terrain, with high ozone events linked
to upper-level ridging and deep vertical mixing. The study concluded that “upper level ridges in the west
reduce westerlies at the surface and aloft and allow cyclic terrain-driven circulations to reduce transport
away from sources. Upper level ridges can also increase background concentrations within the ridge.
Ozone and NO2 concentrations build locally, and deeper vertical mixing in this region provides a potential
mechanism for recapture of ozone in layers aloft including urban plume residual layers, ozone from
thunderstorms, and ozone and precursors from smoke. Ozone precursors and reservoir species in large-
scale basin drainage flows can be brought back to source areas and nearby mountains by daytime,
thermally driven upslope flows. In addition, recirculation and local accumulation can allow precursors
with lower reactivities more time to contribute to local ozone” (Reddy and Pfister, 2016).
As mentioned in previous studies (e.g. Doran et al., 2002; Reddy and Pfister, 2016; Zumpfe and
Horel, 2007), the formation of ozone across the western U.S. is not only impacted by upper level ridging,
but also by complex topographical and thermally-driven wind systems. In particular, the diurnal lake-
valley breeze is noted as being a potential contributing factor to high ozone concentrations in Salt Lake

City during upper level ridging. Past research has attempted to explore the relationship between
summertime ozone concentrations along the Wasatch Front and complex topographical wind systems.
Specifically, UDAQ initiated the Great Salt Lake Summer Ozone Study (GSLSozoneS) in 2015 to explore
how summer ozone concentrations are influenced by the diurnal lake-valley breeze. The study showed
the Great Salt Lake can impact ozone concentrations along the Wasatch Front through several
mechanisms: 1) Lake-induced wind systems modulate the transport and exchange of background ozone
and ozone precursors between the lake and urban environments, with nocturnal land breezes from the
Wasatch Front towards the Lake transporting ozone precursors towards the Lake; and afternoon lake
breezes transporting at times air with higher ozone and precursor concentrations towards the Wasatch
Front while at other times advecting cleaner air into the urban corridor, and 2) Lake-modulated boundary-
layer depth affecting pollutant vertical mixing over the Lake and along the Wasatch Front (Horel et al.,
2016; Long, 2017). The interaction of the lake breeze and ozone formation is revealed to be a fairly
common phenomena between June-August, with the N-NW lake breeze from the GSL observed at KSLC
nearly 75-80% of dry days for the Period of Record (POR) 1948-2003 (Zumpfe and Horel, 2007). As
exhibited by Zumpfe and Horel (2007), the nearly consistent nature of the lake-valley breeze during the
summer makes it an integral component of the general meteorology and therefore the air quality
climatology of the Wasatch Front. This persistent occurrence of the lake-valley breeze and associated
transport is noted to impact ozone formation on a frequent basis as described by Horel et al. (2016).
Considering the above criteria, the main ingredients for a non-flagged high surface ozone concentration
event along the Wasatch Front include:
1. The presence of an upper-level ridge/high pressure system situated over western CONUS, creating
stagnant and clear conditions
2. A deep, well-mixed PBL
3. Weak surface winds out of the SW to NW and weak mid-level winds
4. Topographic and thermally driven wind systems such as the GSL lake-valley breeze. The diurnal nature
of these winds recirculates emissions back into source areas cyclically, which enhances the
accumulation and residence time of ozone precursor emissions.

Characteristics of Flagged Wildfire Impacted High Ozone Concentration Events
The core characteristics of the SLV airshed on flagged wildfire events are similar to non-events,
with anthropogenic NOx and VOC emissions contributing to ozone production. However, on flagged
wildfire event events, there are additional NOx and VOC emissions injected into the SLV by wildfire smoke.
These supplemental precursor emissions from wildfire smoke provide extra fuel for ozone formation,
subsequently leading to higher ozone concentrations than would be observed without the incorporation
of smoke into the valley airshed. This enhancement of ozone by wildfire smoke compared to non-wildfire
smoke events is shown in Table 19 - Event and Non-Event CV MD8A Ozone. On average, flagged wildfire
smoke ozone exceedance events have MD8A ozone concentrations 3-6 ppb above exceedance non-
events. Additionally, all non-exceedance wildfire smoke events are noted to have MD8A ozone
concentrations of about 7-8 ppb greater than all non-exceedance non-wildfire events (Table 19 - Event
and Non-Event CV MD8A Ozone). Research has shown that both higher NOx and VOC emissions are
observed in the presence of wildfire smoke, and that the inclusion of these emissions into an airshed can
create enhanced ozone formation (e.g. Jaffe et al., 2024; Ninneman and Jaffe, 2018).
High ozone concentration events flagged for wildfire smoke impacts over the Wasatch Front
contain many overlapping meteorological characteristics as non-flagged events. Findings from previous
research, investigating the link between high ozone and meteorology in Salt Lake City and across western
CONUS, make it evident that the meteorological conditions favorable for high ozone concentrations (e.g.

upper lever ridging, weak surface and mid-level winds, and occurrence of diurnal thermally driven winds)
are also favorable for the transport of wildfire smoke and subsequent impacts on surface ozone formation
(Reddy and Pfister, 2016; Zumpfe and Horel et al., 2016). Therefore, the common meteorological
conditions that influence non-flagged high ozone concentrations and those that contribute to flagged
wildfire impacts on ozone are often the same and not necessarily independent from one another.

Table 19 - Event and Non-Event CV MD8A Ozone
Monitor MD8A Non-Event
Exceedance
MD8A WF Event
Exceedance
MD8A Non-
Wildfire MD8A All WF
HW 74.8 78 56.2 63
CV 75 80.1 56.2 64.1
BV 75.2 77.6 56.6 63.2
H3 74.9 78.6 57.4 64.9
RP 75.5 77.8 56 62.4
Table 19. Average MD8A for Non-Event Exceedances, Wildfire Event Exceedances, Non-Wildfire, and for
all Wildfire days for the period 2019-2023 at UDAQ monitors within the Northern Wasatch Front NAA,
including Hawthorne (HW), Copperview (CV), Bountiful (BV), Herriman (H3), and Rose Park (RP).

Table 20 – Flagged Event MD8A Ozone Exceedance: Surface Meteorological Conditions
Monitor Avg Max
Temp (F)
Avg Wind
Speed (mph)
Avg Wind
Direction
(deg)
Avg SW
Radiation
(W/m)
Avg RH (%) O3
Exceedances
HW 95 3 233 721 20 19
CV 95 4 210 674 19 21
Table 20. Flagged Event MD8A exceedance days (wildfire events) average surface meteorological
conditions during ozone formation hours (1000-1800 MST) at the controlling SLV Hawthorne (HW)
monitor and CV monitor for the 5-year period 2019-2023 and 3-year period 2021-2023, respectively.

Wildfire season across the western U.S typically ranges between Jun-Oct when hot and dry
conditions and upper level ridging persist. These conditions create dry fuels and favorable fire weather
for wildfire formation. The clockwise winds around the upper level ridge allows the long-range transport
and accumulation of wildfire smoke from numerous fires across the western region. This type of transport
around an upper level ridge creates large areas of dense and diffuse smoke over the west and sometimes
the entire CONUS. As noted in previous works, under an upper level ridge a few factors can contribute to
wildfire smoke impacts on ozone formation. These factors can include the development of a deep vertical
mixed layer and subsidence under a ridge, which can provide a mechanism for the capture of elevated
ozone and precursors from wildfire smoke, and the stagnation and accumulation of ozone precursor
emissions at the surface (Reddy and Pfister, 2016; Horel et al., 2016). Other studies across the west have

also concluded that upper level ridging, leading to higher temperatures and less synoptic ventilation, was
the dominant meteorological setup during high ozone wildfire impacted days (Pan and Faloona, 2022).
Wildfires emit large amounts of primary pollutants including PM2.5, black/brown carbon, carbon
monoxide (CO) and ozone precursors, including NOx and large amounts of VOCs. The ozone precursors
are transported within the wildfire smoke plume downwind of the source and undergo various
photochemical reactions as the plume ages (Lindass et al., 2017). When the VOC rich wildfire smoke plume
is transported across urban areas and mixes with NOx rich urban air, ozone formation is enhanced and
high ozone concentrations can develop (Lu Xu et al., 2021). A number of observational studies have
indicated the link between increased surface ozone concentrations and arrival of wildfire smoke emissions
across urban areas. (e.g. Jaffe et al., 2008, Lu et al., 2016). During periods of upper level ridging, wildfire
smoke is frequently transported over the Wasatch Front from both in state and out of state sources.
Observational evidence from relatively recent studies (e.g. Horel et al., 2016; Long, 2017) has shown that
elevated ozone concentrations along the Wasatch Front coincide with large-scale ridging and the
presence of wildfire smoke. For example, Horel et al. (2016) observed high ozone concentrations that
exceeded the NAAQS in the Salt Lake Valley during the latter half of August 2015 as a result of both strong
ridging aloft and regional transport of wildfire smoke.
The magnitude of surface ozone enhancement by wildfire smoke is non-trivial and has significant
ramifications for air quality monitoring data. Studies that have quantified the impact of wildfire smoke on
surface ozone concentrations across the western U.S have shown wildfire smoke can increase ozone by
up to 5-10 ppb (Pan and Faloona, 2022, Lindaas et al., 2017). The increase of ozone commonly leads to
situations that would have been in compliance with the NAAQs if not for the contributing wildfire
emissions (Lindaas et al., 2017). Interestingly, Lindaas et al. (2017) revealed that enhancement of ozone
concentrations by wildfire smoke can occur independent of warmer temperatures or anomalous
meteorological conditions, meaning the influence of transport emissions from wildfire smoke has a
profound effect on surface ozone formation. Table 20 provides the typical surface meteorological
conditions characteristic of non-event ozone exceedance days in the SLV, with non-event exceedance
days having hot temperatures (mid 90s F), weak winds (< 5kts), dry conditions (low dewpoint/RH), and
relatively clear skies (SW ~700 W/m2).
Considering the above criteria, the main ingredients for a flagged wildfire smoke impacted high
surface ozone concentration event along the Wasatch Front include:
1. The presence of an upper-level ridge/high pressure system situated over western CONUS, aiding in
the transport of wildfire smoke from source areas to the Wasatch Front.
2. Weak surface and mid-level winds, creating stagnant conditions
3. Topographic and thermally driven winds, transporting smoke via canyon, valley, or lake-valley flows.
4. A deep PBL mixed layer, mixing wildfire smoke emissions from PBL residual layers or other elevated
layers to the surface
5. Enhanced surface concentrations of wildfire smoke tracers, including PM2.5, CO, and brown carbon,
marking the presence of smoke
Flagging Wildfire Smoke Event Criteria
Flagging Methodology
Numerous studies have shown observations of tracer concentrations are related to the influence
of wildfire smoke on surface ozone. Tracers, such as PM2.5, are relatively ubiquitous measurements taken
at air quality monitoring stations, with many sites having observations over an extended historical
timeframe. The commonality and typical long Period of Record (POR) of PM2.5 observations make it a

useful tool for distinguishing abnormal levels of particulate matter in the context of historical
concentrations. Therefore, PM2.5 historical average concentrations are often used as threshold criteria
to filter wildfire smoke events from non-smoke events. The use of satellite data and imagery as become
another important tool for determining smoke impacts at the surface and aloft.
To identify dates where surface monitoring sites were potentially influenced by wildfire smoke,
UDAQ employs air quality monitoring observations of PM2.5 at an hourly frequency as well as the National
Oceanic and Atmospheric Administration (NOAA) National Environmental Satellite, Data, and Information
Service (NESDIS) Hazard Mapping System (HMS) smoke product58 to distinguish the residence of wildfire
smoke over the Wasatch Front. Observations of PM2.5 concentrations at monitors can help indicate the
presence of wildfire smoke emissions at the surface. Additionally, the HMS smoke product is derived from
visible satellite imagery from seven satellites and provides information regarding whether a smoke plume
resides in the column overhead a monitor location (Ruminski et al. 2006).
By employing the combination of surface observations of PM2.5 and satellite derived smoke fields
(HMS smoke product) described previously, UDAQ filters dates with possible wildfire smoke impacts at a
monitoring location using a two-factor screening methodology. This methodology is based on a number
of previous studies investigating wildfire smoke impacts on air quality (e.g. Lee and Jaffe, 2024; Liu et al.
2016; Brey et al., 2018; Larsen et al. 2018; McClure and Jaffe, 2018; Preisler et al. 2015), with one such
study completed in the Salt Lake Valley in 2022-202359 (e.g. Lee and Jaffe, 2024). First, using shapefiles
containing satellite derived HMS smoke60 fields, deterministic spatial analysis is conducted using Python-
Shapely spatial analysis toolkit61 to determine if a monitor location (latitude/longitude) is bounded within
an HMS smoke-field polygon. If a monitor is contained within a smoke polygon, that day is noted to have
smoke present in the atmospheric column overhead and marked as an HMS smoke day. A monitor specific
baseline monthly 24-hour average PM2.5 concentration( 𝑃𝑃𝑃𝑃2.5���������𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚ℎ ) is then calculated for all non-HMS
smoke dates by excluding HMS smoke dates for each month of the wildfire season (May-October). Second,
monitored 24-hr PM2.5 concentrations (𝑃𝑃𝑃𝑃2.5���������24ℎ𝑟𝑟) are calculated for all days (HMS smoke and HMS
non-smoke). If the monitored 24-hr PM2.5 concentration exceeds one standard deviation above the
monitor specific baseline mean monthly 24-hour average PM2.5 concentration (𝑃𝑃𝑃𝑃2.5���������24ℎ𝑟𝑟 > 𝑃𝑃𝑃𝑃2.5���������𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚ℎ + σ), that date is noted for further inspection related to wildfire smoke impacts. The
motivation of using one standard deviation above the monthly mean PM2.5 as a flagging criterion is based
on previous research that has determined that one standard deviation (68th percentile) is a reasonable
and appropriate cutoff point for identifying dates with abnormal PM2.5 concentrations compared to
baseline variability (e.g. Lee and Jaffe, 2024; Brey et al., 2018). This two-factor screening process ensures
that biases and weaknesses in any one flagging method (e.g. satellite or surface observations) are
minimized (i.e. identification of a smoke plume overhead does not necessarily translate to elevated
ground-level PM2.5 concentrations or vice versa).

58 NESDIS Hazard Mapping System (HMS) can be found at: https://www.ospo.noaa.gov/Products/land/hms.html#0
59 SAMOZA report can be found at: https://deq.utah.gov/air-quality/the-salt-lake-regional-smoke-ozone-and-aerosol-study-
samoza
60 HMS smoke field datasets can be found at: https://www.ospo.noaa.gov/products/land/hms.html#data
61 Python Shapely documentation can be found at: https://shapely.readthedocs.io/en/stable/manual.html

Using the above HMS and PM2.5 criteria to detect the presence of wildfire smoke at UDAQ
monitors, the five dates shown in Table 12 - Flagged EE Events were identified as potential atypical wildfire
smoke impacted dates at the CV monitor. To further add confidence to the atypical date selection and
flag as Exceptional Events, the 24hr PM2.5 concentrations on each of these flagged dates were compared
to the monthly monitor specific Tier 2 PM2.5 threshold values listed in Table 12 - Flagged EE Events. These
threshold concentrations were formulated using EPA’s PM2.5 Tiering Tool for Exceptional Events62 and
EPA guidance which states:
“The tier thresholds are based on the lesser value of either (a) the most recent 5-year month specific 98th
percentile for 24-hour PM2.5 data, or (b) the minimum annual 98th percentile for 24- hour PM2.5 data
for the most recent 5-year period.”63
In this analysis, the Tier 2 threshold is delineated by the lowest 98th percentile PM2.5 within the
5-year period 2019-2023. While this PM2.5 Tiering analysis does not pertain specifically to ozone EE
tiering, it does provide some indication how heavily monitors were impacted by wildfire smoke and aids
in flagging EE dates impacted by wildfire emissions. All five of the flagged atypical events in this analysis
exceed the Tier 2 threshold PM2.5 concentrations (Table 12), adding to the justification that these dates
should be flagged as wildfire impacted EE’s. Additionally, based on 24hr surface PM2.5 concentrations at
the UDAQ monitor, a light (<10 µg/m3), medium (10-22 µg/m3), or heavy (>22 µg/m3) smoke density
rating was given to each flagged atypical event day. This PM2.5 smoke density scale was derived from
previous research, which investigated the differences in surface and satellite-based wildfire smoke density
detection (e.g. Fadadu et al. 2020; Vargo, 2020). In order to add further weight and trust in the atypical
event selection, dates were only selected where wildfire smoke was analyzed as both heavy from surface
PM2.5 and analyzed as heavy from the HMS smoke product. The combination of HMS, tiering threshold
comparison, and surface derived smoke density adds significant weight in the dates designated as flagged
as EE’s.
Conceptual Overview and Narrative
In this section, we provide a narrative conceptual model that describes the flagged wildfire smoke
events (Table 12) and how emissions from the wildfire smoke led to the ozone exceedances at the CV
monitor. A number of different analyses are given to elucidate the direct connection between wildfires
burning across the Western U.S. the summer of 2021 to the monitored flagged ozone exceedances at
Copperview. These analyses include, but are not limited to, a review the meteorological conditions that
characterize each flagged wildfire smoke impacted ozone event (July 12, July 24, August 7-8, and August
16, 2021), satellite data, HRRR Smoke, the HMS smoke product, forward and backwards HYSPLIT
trajectories, and analysis of surface PM2.5, brown carbon, VOC, and NOx emission trends to identify the
source areas of smoke and associated transport. In addition, the aforementioned tools and analysis will
provide the evidence and support the case for the presence of wildfire smoke at the CV monitor and
subsequent impact on surface ozone enhancement above the 2015 NAAQS of 70 ppb for the flagged dates
July 12, 24 and August 7-8 and 16, 2021.

62 EPA PM2.5 Tiering Tool: https://www.epa.gov/air-quality-analysis/pm25-tiering-tool-exceptional-events-analysis
63 EPA PM2.5 Tiering Guidance: https://www.epa.gov/system/files/documents/2024-04/final-pm-fire-tiering-4-30-24.pdf

4.1 Conceptual Model and Clear Causal Relationship: Smoke Event July
12, 2021
Wildfire Conditions: July 12, 2021
Due to a relatively benign synoptic pattern with persistent ridging events, the months prior to July
2021 were exceptionally dry and warm. This set the stage for abnormally dry and drought-stricken
conditions across the Western U.S. by the mid-summer of 2021 (Figure 43). Large scale ridging is shown
to have dominated across the Western CONUS the month preceding the July 12 flagged event (Figure 14).
This synoptic setup facilitated abnormally dry and hot conditions across the Western U.S. (Figure 45 and
Figure 46) leading up to the flagged EE date on July 12. In Figure 43, the U.S. Drought Monitor is given for
the Western U.S. for the second week of July, 2021, with a large portion of the West under Extreme to
Exceptional Drought (D3-D4) conditions. Given the extreme drought, wildfire fuels were primed for
ignition as shown by the high values of the Wildland Fire Potential Index (WFPI) in the West derived on
July 12, 2021 in Figure 47. In early July, 2021, these conditions led to high fire danger and various wildfires
burned across the Western U.S., with a number of large to medium sized fires noted to the west and north
of Utah in California, Oregon, Washington, and Idaho on July 12 (Figure 48). The major fires of concern
burning on July 12 are shown in Figure 48 and noted in Table 21. The National Interagency Coordination
Center Incident Management Situation Report on July 12, 2021 is provided in Appendix A.

Figure 43 - Western U.S. Drought Monitor: July 2021

Figure 43. Drought monitor for the Western U.S. derived for the seven-day period ending on July 13,
202164. Much of the West was under extreme to exceptional drought (D3-D4) at the time of the July 12
flagged EE event.
Figure 44 - NCEP Reanalysis Average 500 mb GPH: June 1- July 12, 2021

Figure 44. NCEP Reanalysis Average 500 mb Geopotential Heights65 for the period June 1 - July 12, 2021.
The presence of higher average 500 mb geopotential heights across the West indicate persistent ridging
in the month preceding July 12.

64 U.S. Drought Monitor can be found at: https://droughtmonitor.unl.edu/
65 NCEP Reanalysis Data can be found at: https://psl.noaa.gov/data/gridded/data.ncep.reanalysis.html

Figure 45 - PRISM June 2021 Precipitation Anomalies

Figure 45. PRISM precipitation anomalies66 for June 1-30, 2021. Well below normal precipitation was
observed across the Western U.S. in the month prior to the July 12 event.

Figure 46 - PRISM June 2021 Temperature Anomalies

Figure 46. PRISM daily mean temperature anomalies67 for June 1-30, 2021. Well above normal
temperatures were observed across the Western U.S. in the month prior to the July 12 event.

66 PRISM data can be found at: https://prism.oregonstate.edu/graphics/
67 PRISM data can be found at: https://prism.oregonstate.edu/graphics/

Figure 47 – WFPI: July 12, 2021

Figure 47. Wildland Fire Potential Index (WFPI) 68 for July 12, 2021. Many areas in the Western U.S.
exceeded WFPI values of > 100, indicating a high potential for wildfires on the flagged event date.

68 WFPI can be found at: https://firedanger.cr.usgs.gov/apps/staticmaps

Figure 48 - WFIGS Wildfire Perimeters: July 12, 2021

Figure 48. WFIGS Wildfire perimeters69 (> 10,000 acres) on July 12, 2021. Medium to large fires are
evident across the CA Sierras, central OR, NW ID, and SE WA.

Table 21 - Potential Wildfire Smoke Sources: July 12, 2021
Event Date Wildfire Smoke Sources (potential) Fire Size (Event - acres)
7/12/2021
Sugar fire/Beckwourth Complex, CA 61252
Lava, CA 26162
Bootleg fire, OR 150812

69 WFIGS Wildfire Perimeters can be found at: https://data-
nifc.opendata.arcgis.com/search?tags=historic_wildlandfire_opendata%2CCategory

Lick Creek fire, OR 55055
Snake River Complex, ID 54407
Table 21. List of potential wildfire smoke sources contributing to smoke emissions at CV (devised from
forward and backward HYSPLIT trajectories) and the approximate size of the fires in acres70 on July 12,
2021.

Meteorological Conditions
During the flagged event period of July 12, the large-scale synoptic pattern continued to feature an
established upper-level ridge across the Western U.S. (Figure 50). Figure 51 and Figure 52 shows the mid
to upper-level winds and geopotential heights on July 12, with the overall synoptic pattern characterized
by a large dome of high pressure centered over the Western U.S. The ridge axis extended roughly north-
south across the central Great Basin region, orienting the anticyclonic southwesterly to northwesterly mid
to upper-level winds across northern Utah (Figure 51). Residual convectively induced vorticity/energy
from upstream, progressed across Utah on July 12, bringing a shield of scattered mid to high-level clouds
and a few high based showers across the Wasatch Front (Figure 53 and Figure 54). At the surface, a
stationary front and a cold front were draped across southern Idaho and Wyoming, respectively (Figure
54). These frontal boundaries were associated with a surface high pressure over southern Canada and
Montana and a thermal low pressure centered over south-central CA and southern NV (Figure 55). Figure
55 shows the orientation of the high and low surface pressure gradients facilitated westerly flow from
northern CA across the Great Basin to Utah.
Soundings launched at KSLC on July 12 show a deep and well mixed planetary boundary layer
(PBL) up to about 700 mb (~3km AGL) and potentially extending up to 500 mb (~4.7km AGL) in the
afternoon (00Z) (Figure 56). A mid-level (700 mb) temperature of 18.6 C was observed on July 12, which
is well above the climatological mean (13.6 C)71, indicating the presence of a strong heat dome and the
potential for elevated surface temperatures. In Figure 56a, the vertical wind profile at 12z exhibits
southerly down-valley winds in the lowest layer of the atmosphere. Lower level winds in Figure 56b
suggest a mix of afternoon lake-land breeze and outflow winds from high based showers in the area, as
noted by the inverted “V” shape of the 00Z sounding profile and from satellite imagery in Figure 58.
Nonetheless, winds above 700 mb in both the 12Z and 00Z soundings are consistently out of the west as
also evidence in the mid and upper-level charts in Figure 51. The evolution and associated impacts of the
upper-level ridge and synoptic pattern is described in full detail in the National Weather Surface (NWS)
area forecast discussions (AFDs)72 for KSLC between July 10-12 (Appendix A). In general, the NWS AFDs
illuminate how the meteorological pattern influenced the transport of smoke into Utah. For example,
highlighted AFD text discussing the intrusion wildfire smoke into Utah on July 10-12 is given below:

“Area Forecast Discussion
National Weather Service Salt Lake City UT
405 AM MDT Sat Jul 10 2021

70 Dataset of U.S. IMSR found at: https://research.fs.usda.gov/treesearch/67197
71 NWS Sounding Climatology Information can be found at: https://www.spc.noaa.gov/exper/soundingclimov2/
72 Archived NWS AFDs can be found at: https://mesonet.agron.iastate.edu/wx/afos/list.phtml

“Increased smoke was readily apparent across northern Utah Friday (July 10) evening,
as wildfire smoke from California, Nevada and Oregon was advected into the region.
Northerly low-level flow behind a weak boundary aided in advecting near-surface smoke
into northern Utah. While smoke will persist across northern Utah today, it will be
slightly more apparent across central Utah as it continues to advect southward. HRRR
smoke model suggests near-surface smoke will once again thicken tonight and Sunday
(July 12) across much of northern and central Utah.73”
Surface sensible weather conditions in the SLV on July 12 reflected the upper-level environment.
In Figure 49, the observed temperature, winds, and moisture are given for a period centering on the
flagged event of July 12. The high temperature on July 12 was 103 F, with generally light surface winds <
5 kts and low relative humidity (RH). The measured incoming solar radiation at the CV site reveals periods
of clouds and clear conditions through the course of July 12 (Figure 49).
Figure 49 - CV Meteogram: July 12, 2021

Figure 49. Meteogram of observed sensible weather conditions at the CV monitor through the period July
10-14, centered on the flagged event date of July 12 (delineated by the red dashed lines). Hot
temperatures, low wind speeds, and low moisture as well as decreased solar radiation due to afternoon
clouds are noted on July 12.

73 Archived NWS AFD July 10, 2021 can be found at: https://mesonet.agron.iastate.edu/wx/afos/p.php?pil=AFDSLC&e=202107101005

Figure 50 - NCEP Reanalysis Average 500 mb GPH: July 12, 2021

Figure 50. NCEP Reanalysis Average 500 mb Geopotential Heights74 for the period July 11 - July 12, 2021.
The higher 500 mb geopotential heights centered across the Great Basin Region indicates a relatively
strong upper-level ridge.

74 NCEP Reanalysis Data can be found at: https://psl.noaa.gov/data/gridded/data.ncep.reanalysis.html

Figure 51 - NOAA SPC 500 mb and 700 mb Upper Air Charts: July 12, 2021

Figure 51. NOAA-Storm Prediction Center75 upper air charts for a.) 500 mb geopotential heights, winds,
and temperature, b.) 500 mb chart zoomed in over the West, c.) 700 mb geopotential heights, winds,
temperature, and relative humidity, and d.) 700 mb chart zoomed in over the West. Higher heights and
warmer temperatures at 500 and 700 mb indicate an upper-level ridge across the Western U.S. Flow from
700-500 mb is generally from the west which suggests winds were conducive for smoke transport from
wildfires in the northern CA Sierras and central OR.

75 NOAA-SPC Mesoscale Analysis Upper Air Charts can be found at: https://www.spc.noaa.gov/

Figure 52 - GFS Analyzed 500 mb GPH and Winds: July 12, 2021

Figure 52. GOES East True Color satellite imagery with overlaid analyzed GFS 500 mb geopotential heights
(m) and winds (kts) and the location of the CV monitor (yellow star) on July 12, 2021 at 1800Z zoomed
over a.) the CONUS and b.) Utah. A dome of high pressure resides across the Great Basin with westerly
upper-level winds across northern Utah. Clouds associated with remnant convectively induced energy
progressed across Utah.

Figure 53 - NOAA SPC 500 mb Heights and Vorticity: July 12, 2021

Figure 53. 500 mb heights and vorticity on July 12, 2021. Small positive vorticity lobes are present over
and near Utah, indicating upper-level cyclonic energy rotating through the region. These vorticity lobes
were associated with the formation of clouds within the smoke field over Utah on July 12.

Figure 54 - WPC Surface Analysis: July 12, 2021

Figure 54. NOAA-Weather Prediction Center (WPC)76 surface analysis and IR satellite imagery on July 12,
2021 at 1800Z zoomed over a.) North America and b.) the Western U.S. - defined red bounding box in a.).
The analyzed fronts show a stationary front draped across southern ID and a cold front across southern
Wyoming. A surface high pressure and thermal low are evident over the northern Great Plains and Mojave
Desert, respectively.

76 NOAA-WPC Surface Analysis Charts can be found at: https://www.wpc.ncep.noaa.gov/archives/web_pages/sfc/sfc_archive_maps.php

Figure 55 - NOAA SPC Surface Pressure Chart: July 12, 2021

Figure 55. NOAA-Storm Prediction Center77 surface pressure chart and winds (kts) on July 12, 2021 at
1900Z for a.) the CONUS and b.) zoomed in across the Western U.S. The juxtaposition of a thermal low to
southwest of Utah and a surface high to the northeast, created a pressure gradient conducive for westerly
surface winds from the northern CA Sierras to northern Utah.

77 NOAA-SPC Mesoscale Analysis Upper Air Charts can be found at: https://www.spc.noaa.gov/

Figure 56 - KSLC Radiosonde Soundings: July 12, 2021

Figure 56. Radiosonde soundings from KSLC on July 12, 2021 at a.) 12Z and b.) 00Z. An inverted “V” profile
with a deep well mixed PBL is evident in the 00Z sounding, with winds out of the west near and above 700
mb in both the morning and afternoon soundings. Winds at lower levels were a mix of diurnal and
mesoscale driven winds.
Wildfire Smoke: Remote Sensing and Ground-Based Analysis
It is apparent that the meteorological environment on July 12, 2021 was conducive for the
transport of air parcels from points west of Utah into the state at upper and lower levels of the
atmosphere. Visible satellite imagery reveals a large consolidated mass of smoke mixed with clouds
transported to the CV UDAQ monitor on July 12 (Figure 57 - Figure 60). In Figure 58, visible satellite
imagery merged with the analyzed 500 mb upper-level wind field exhibits the pattern of transport of

smoke from areas west around the upper-level ridge into northern Utah. Figure 59 and Figure 60a show
an enhanced depiction of the smoke extent and density from increased scattering of solar radiation in the
early morning when the sun angle was low. The opaque milky color in Figure 59 and Figure 60a is indicative
of heavy wildfire smoke, with the outline of the GSL only slightly visible through the thick smoke layer. In
Figure 60b, an example of what smoke free conditions over Utah is given. Revealed in the satellite
imagery, the synoptic meteorological pattern allowed the west to east transport and aggregation of
smoke plumes from numerous fires in California and Oregon around the upper-level ridge into Utah, while
the surface level environment allowed near-surface level smoke to be transported to Utah from the fires
in the northern Sierras of CA. Vertical temperature and wind profiles from soundings launched on July 12
reveal a deep PBL mixed layer in the SLV, suggesting that the capture and transport of smoke emissions
from aloft to the surface was possible (Figure 56).
We investigate satellite aerosol optical depth (AOD) and satellite HMS smoke field to distinguish
wildfire smoke density over Utah on July 12. Due to embedded clouds obscuring portions of the
atmospheric column, derived AOD is patchy across northern Utah on July 12. However, the analyzed AOD
does still provide information regarding smoke density when portions of the sky were cloud free (Figure
61). Where the AOD is analyzed, the dense smoke plume density is exhibited by high values of AOD
observed by the Multi-Angle Implementation of Atmospheric Correction (MAIAC) Land Aerosol Optical
Depth level 2 product78. In Figure 61, AOD values > 0.9 are present over the SLV, indicating dense wildfire
smoke in the atmospheric column. Synthesizing the remote sensing imagery and analysis into one
product, the HMS analyzed smoke fields show that medium to heavy dense smoke plumes converged
over the Northern Wasatch Front and the CV monitor from these fires on July 12 (Figure 62 and Figure
63). The summarization of smoke field characteristics observed by satellite imagery is given by the NOAA
NEDIS smoke narrative79 published on July 12, 2021 at 0001Z. The smoke discussion notes thick and dense
smoke across Utah from the wildfire activity in the Western U.S.:

“Monday, July 12, 2021
DESCRIPTIVE TEXT NARRATIVE FOR SMOKE/DUST OBSERVED IN SATELLITE IMAGERY THROUGH 0001Z July 13, 2021
SMOKE:
Western and Central United States...
A large region of moderate to thick density smoke attributed from wildfire activity in northern California, southern Oregon, southeastern
Washington, northern Idaho, and western Montana was observed over most of the Northern and Central Rockies as well as parts of the southwestern,
south central, north central and northwestern U.S. Thick density smoke was observed over portions of Southern, California, Nevada, Idaho, Montana, Wyoming, Utah, Colorado, Arizona, most of New Mexico, and parts of West Texas. Light density smoke was seen covering most of the western half of the U.S. from the ongoing wildfire activity.80”
A more detailed characterization of the magnitude and transport pattern of smoke from wildfires
across the West is given by the High-Rapid Refresh (HRRR) smoke model analysis in Figure 64. In Figure
64a, the July 12, 12Z initialized HRRR total column smoke density exhibits the extensive and dense shield
of smoke across the Western U.S. and Utah (> 150 μg/m²). Additionally, the total column smoke density

78 AOD satellite imagery found at: https://worldview.acom.ucar.edu/
79 NOAA NEDIS Smoke Narrative can be found at: https://www.ssd.noaa.gov/PS/FIRE/smoke.html
80 NOAA NEDIS Smoke Narrative can be found at: https://www.ssd.noaa.gov/PS/FIRE/smoke.html

reveals well defined heavy plumes originating from the Sugar, Lava, Bootleg, Lick Creek, and Snake River
Fire complexes (as seen in Figure 48 and Figure 57) being transported west to east around the upper-level
ridge centered over the Great Basin region. A closer inspection of HRRR smoke is given in Figure 64b,
showing dense surface level smoke (> 40 μg/m³) at the CV monitor on July 12. In Figure 65, the BlueSky
Smoke model81 outlines the smoke plumes originating from the fires across the West, ultimately forming
a conglomerate mass of smoke over the entire region. The relative magnitude of smoke plume densities
and transport pattern of smoke to the CV from the Sugar, Lava, Bootleg, and potentially to some extent
from the Lick Creek and Snake River fires (Figure 65).
The presence of wildfire smoke as noted by satellite imagery and HRRR smoke across the Wasatch
Front is corroborated by surface observations of the aerosol optical depth (AOD) from the Aerosol Robotic
Network (AERONET) (Figure 66 and Figure 67). A larger or thicker AOD signifies more
attenuation/scattering of incident solar radiation through the column of the atmosphere and can be
correlated with the presence of wildfire smoke. We utilize AERONET Level 2 AOD82 (Pre- and post-field
calibration applied, automatically cloud cleared and manually inspected83) observations from the
NEON_ONAQ site, which is located approximately 40 miles due SW (40.17759 N, 112.45244 W) of the CV
monitor. Figure 66 and Figure 67 shows AOD ranging from < 0.2 before July 9 to 0.8-1.5 July 11-12 when
the densest smoke plume arrived across northern Utah. The increase in AOD from July 9 to July 12 is due
to the increased transport of wildfire smoke across the area. For reference on clear days with no smoke,
AOD’s are < 0.1. The observed AOD on the days following July 12 shows a sharp decrease to values < 0.3,
indicating the dissipation and clearing of the smoke plume from the area. Observations from ground-
based cameras around the SLV further verify the presence of near surface smoke across the valley on July
12, 2021 (Figure 68). In Figure 68a and Figure 68d, the camera images from July 7 and July 14 represent
clear days free from wildfire smoke preceding and proceeding the flagged smoke event, respectively.
Images in Figure 68b and Figure 68c from the morning and afternoon July 12 show conditions during the
flagged smoke event, with reduced visibility due to wildfire smoke emissions within the SLV.

81 BlueSky Modeling Framework can be found at: https://tools.airfire.org/websky/v2/#status
82 AERONET AOD data can be found at: https://aeronet.gsfc.nasa.gov/cgi-bin/data_display_aod_v3
83 AERONET System description can be found at: https://aeronet.gsfc.nasa.gov/new_web/system_descriptions.html

Figure 57 - FIRMS Map: July 12, 2021

Figure 57. FIRMS Map84 with VIIRS S-NPP True Color Satellite imagery for July 12, 2021 overlaid with
satellite analyzed fire hotspots (red dots) and fire perimeter burned area (shaded light blue areas). A large
swath of medium to heavy smoke is evident across the Western U.S., with heavy smoke and a mix of
clouds present across Utah. Smoke plumes from the large fires in CA and OR are shown to be drifting to
the west into NV, ID, and UT. The large fires contributing to smoke transport over northern Utah are
labeled (e.g. Sugar, CA; Bootleg, OR; Lick Creek, WA; Snake River CPX, ID).

84 FIRMS Fire Map can be found at: https://firms.modaps.eosdis.nasa.gov/usfs/map/#d:24hrs;@-100.0,40.0,4.0z

Figure 58 - GOES East True Color and GFS 500 mb Heights and Winds: July 12, 2021

Figure 58. GOES East True Color satellite imagery with overlaid analyzed GFS 500 mb geopotential heights
(m) and winds (kts) and satellite analyzed wildfire hotspots (red circles) on July 12, 2021 at 1800Z. The
satellite imagery reveals a large swath of wildfire smoke across the Western and Central U.S. being
transported from fires located across the West by anticyclonic flow around the upper-level ridge centered
over the Great Basin. A shield of clouds is mixed within the smoke plume over Utah.

Figure 59 - GOES West True Color: Western CONUS July 12, 2021

Figure 59. GOES West True Color Satellite imagery85 on July 12, 2021 at 1400Z. The low sun angle at this
time of day reveals the widespread and dense nature of the smoke across the Western U.S. Utah in
particular is blanketed in heavy-dense wildfire smoke transported from fires in CA, OR, and potentially
WA and ID.

85 NOAA-Aerosol Watch Satellite imagery can be found at: https://www.star.nesdis.noaa.gov/smcd/spb/aq/AerosolWatch/

Figure 60 - GOES East True Color: Utah July 12, 2021

Figure 60. GOES East True Color satellite imagery on the event date a.) July 12, 2021 at 1500Z and on b.)
a non-smoke impacted date July 7, 2021 at 1500Z. On July 12, a plume wildfire smoke across Utah being
transported by anticyclonic flow around the upper-level ridge. In b.) key geographical landmarks are more
visible due to the smoke free skies.

Figure 61 - GOES West AOD: July 12, 2021

Figure 61. GOES West satellite derived Aerosol Optical Depth (AOD)86 on July 12, 2021 for a.) the Western
U.S., and b.) zoomed in over northern Utah. AOD values of 0.8-1 were observed over the SLV, indicating
the presence of dense wildfire smoke attenuating incoming solar radiation.

86 Aerosol Watch AOD product can be found at: https://www.star.nesdis.noaa.gov/smcd/spb/aq/AerosolWatch/index.php

Figure 62 - HMS Smoke Fields and WFIGS Wildfire Perimeters: July 12, 2021

Figure 62. HMS smoke fields87 with WFIGS Wildfire perimeters88 across the Western U.S. on July 12, 2021.
Smoke plumes are shown to be transported west to east from fires in CA, OR, and WA, creating medium
to heavy smoke plumes over Utah. Heavy smoke is analyzed above the CV monitor.

87 HMS Smoke Field data can be found at: https://www.ospo.noaa.gov/products/land/hms.html#0
88 WFIGS Wildfire Perimeters can be found at: https://data-
nifc.opendata.arcgis.com/search?tags=historic_wildlandfire_opendata%2CCategory

Figure 63 - HMS Smoke Field: Utah July 12, 2021

Figure 63. Same as in Figure 21 but also including satellite detected fire hot spots (purple dots) and
zoomed in and centered over Utah and the CV monitor (yellow star). The entirety of Utah was analyzed
to be under the influence of heavy wildfire smoke.

Figure 64 - HRRR Smoke VIS and NSFC Smoke: July 12, 2021

Figure 64. HRRR-NCEP smoke fields on July 12 at 12Z of a.) total column smoke (vertically integrated) over
the CONUS and b.) near-surface level smoke focused over Utah. Dense smoke was transported west to
east from fires in CA, OR, WA, and ID into Utah. Both vertically integrated and surface level smoke reveal
heavy-dense smoke over the CV monitor (yellow star).

Figure 65 - BlueSky Dispersion Analysis: July 12, 2021

Figure 65. BlueSky Daily Smoke Dispersion model run89 (GFS 0.5 deg and 0.15 deg dispersion) from July
13, 2021 at 00Z. Satellite analyzed fire hotspots are overlaid (red flames) along with the location of the
CV monitor (yellow star pin). A large swath of wildfire smoke is indicated across the Western U.S. and over
the CV monitor, with dense plumes evident from a few different fires west and north of Utah.

89 BlueSky Modeling Framework can be found at: https://tools.airfire.org/websky/v2/#status

Figure 66 - AERONET Level 2 AOD: July 2021

Figure 66. AERONET derived Level 2 AOD90 from the NEON_ONAQ site (40 miles SW of the CV monitor)
for the month of July 2021. Periods preceding, during, and after the flagged smoke event are noted, with
corresponding AOD. Increased AOD values, signaling the presence of wildfire smoke, are apparent on July
9-12 compared to preceding and proceeding dates.

90 AERONET AOD data can be found at: https://aeronet.gsfc.nasa.gov/cgi-bin/data_display_aod_v3

Figure 67 - AERONET Level 2 AOD: July 12, 2021

Figure 67. a.) AERONET derived Level 2 AOD91 from the NEON_ONAQ site (40 miles SW of the CV monitor)
on the flagged event date of July 12 and b.) Terra MODIS True Color satellite imagery on July 12 overlaid
with the NEON_ONAQ site location (orange circle) and CV monitor location (yellow star). AOD values 0.5-
1.1 on July 12 signal the presence of wildfire smoke. The wildfire smoke was slightly obscured by a patchy
cloud field as revealed in the satellite imagery.

91 AERONET AOD data can be found at: https://aeronet.gsfc.nasa.gov/cgi-bin/data_display_aod_v3

Figure 68 - MESOWEST WBBS Camera Images: July 12, 2021
Figure 68. MESOWEST WBBS camera images from a.) July 7 at 1855 MST, b.) July 11 at 1121 MST, c.) July
11 at 1430 MST, and d.) July 14 at 1252 MST. The camera is located on the University of Utah campus at
the north end of the SLV and faces to the south. Images a.) and b.) represent conditions expected on non-
smoke days, with images in b.) and c.) representing the conditions on the morning and afternoon of smoke
impacted date of July 12, 2021.

HYSPLIT: Wildfire Smoke Transport to CV Monitor
The July 12 flagged event was near the end of a five-day period of wildfire smoke that inundated
the SLV from July 9-13. Conditions leading up to the July 12 flagged event were characterized by multiple
waves of wildfire smoke, with the thickest smoke observed on July 11-12 across the SLV. In the previous
section, the orientation of the synoptic pattern suggests the transport of smoke plumes from the Sugar,
Bootleg, Lick Creek, and Snake River fires to the CV monitor was possible. To obtain a more detailed
representation of the possible transport paths and all potential smoke sources that contributed to the
observed wildfire smoke emissions on July 12 at the CV monitor, HYSPLIT multiple particle forward and
backward trajectory analysis was performed using GFS 0.25 deg model input. Multiple particle trajectories
were utilized in this analysis to more accurately simulate smoke dispersion from wildfires as single particle
trajectories are typically insufficient to represent smoke dispersion well. The GFS 0.25-degree model was
chosen due to its resolution and ability to provide a reliable representation of the synoptic meteorology.
Nevertheless, HYSPLIT modeled trajectories are analyzed with scrutiny and consideration due to potential
error within the modeled meteorological fields and in the trajectory calculations themselves. Trajectory
paths are therefore interpreted in a relative sense and are not taken as exact.

Parcel trajectory analysis was completed using various configurations of the HYSPLIT model to
determine source regions of wildfire smoke on July 12. The first two HYSPLIT model configurations chosen
were the backward ensemble and frequency trajectory options, with parcels starting at model derived
mid-boundary layer height (Figure 69 and Figure 70). The ensemble option allows 27-member trajectories
to be launched from the starting location (CV), where each member of the trajectory ensemble offsets
the meteorological data by one fixed grid factor (one meteorological grid point in the horizontal and 0.01
sigma units in the vertical). The frequency option starts a trajectory from a location and height every 6
hours and then sums the frequency that the trajectory passed over a grid cell before normalizing by either
the total number of trajectories or endpoints92. Both the ensemble and frequency trajectory approaches
were selected to reduce uncertainty in trajectory calculations that arise from errors in the meteorological
data that represent the wind field and in the parameterizations of physical93. Trajectory starting/ending
heights, where applicable, were chosen at the mid-boundary layer to provide information on air parcels
residing within the PBL mixed-layer and ultimately impacting the surface. The purpose of the frequency
and ensemble backward trajectories are to reveal the possible origins of air parcels and associated
trajectory paths that were present in the SLV on the flagged event date. Trajectory paths crossing or
starting from regions of active wildfires indicate the potential transport of wildfire smoke from these
locations to the SLV.
In Figure 69, 72-hour ensemble backward trajectories beginning at the CV monitor on July 12 at
15Z and integrated through July 8 05Z are shown. The HMS smoke fields and VIIRS analyzed wildfire
hotspots are also include in Figure 69 to help distinguish the potential source regions of wildfire smoke
that impacted the CV monitor. By selecting the ensemble configuration, a robust characterization of
potential source areas of air parcels arriving at various levels above the CV monitor on July 12 is given.
Figure 69 reveals multiple trajectories ending at CV on July 12 originated or passed over the Sugar, Lava,
and Bootleg fires. These trajectory paths are consistent with the west to east transport pattern around
the upper-level ridge by the mean synoptic environment identified in the previous section, and showcase
how multiple wildfires contributed to the smoke emissions observed on July 12 in the SLV. In Figure 70,
the 72-hour backward trajectory frequencies are provided, with areas of highest trajectory frequencies
corresponding to locations of active wildfires in northern CA, OR, WA, and ID. The frequency plot suggests
that the smoke plume over the CV monitor on July 12 was an aggregate smoke mass composed of smoke
sourced from multiple wildfire sources across the Western U.S. In general, frequency and ensemble
trajectories show air parcels mainly originating from: 1.) the Sugar and Lava fires in CA and 2.) the Bootleg
Fire in OR. There is also some indication from the frequency trajectories (Figure 70) that air parcels near
the Lick Creek and Snake River Complex fires in ID and WA, respectively, could have been incorporated
into the smoke plume that impacted the CV on July 12.
Investigation of smoke transport from the Sugar, Lava/Tennant, and Bootleg fires to the SLV
employs multi-particle forward ensemble and frequency HYSPLIT trajectories (Figure 71-Figure 73). The
integration periods for the forward trajectories was varied between 48-72 hours depending on the fire
and distance to the CV monitor, with trajectories starting at 1500 m AGL for all simulations to replicate
smoke lofted in the atmosphere due to plume rise. Additionally, the ensemble trajectory approach
launches particles at varying heights above the fire locations, which more realistically represents air
parcels at different levels within the rising smoke plume. In Figure 71, both the 48-hour forward ensemble
and frequency trajectories starting at the Sugar, CA fire reveal a well-defined west to east transport
pattern from the fire to the SLV over the period of July 10 to the morning of July 12. The Bootleg, OR and
Lava, CA fire resided a bit further north than the Sugar, CA fire, where the anticyclonic circulation around
the upper-level ridge shifted more westerly to southwesterly. In Figure 72 and Figure 73, the wide arcing

92 HYSPLIT Ensemble Trajectory info found at: https://www.ready.noaa.gov/hypub-bin/trajtype.pl?runtype=archive
93 HYSPLIT Trajectory Uncertainty can be found at: https://www.ready.noaa.gov/documents/Tutorial/html/ens_meteo.html

nature of the Bootleg and Lava forward ensemble and frequency trajectories exhibit the clockwise flow
around the upper-level ridge centered over the Great Basin (Figure 51a and Figure 52). The trajectories
were integrated over a 72-hour period from July 9 to July 12 to account for the longer transport time that
was needed for smoke to reach the SLV from these fires. In general, the forward trajectories from the
Bootleg and Lava fires show a transport path ending or progressing over the SLV on the flagged event date
of July 12 (Figure 72 and Figure 73).
The forward ensemble and frequency trajectory paths from the wildfires mentioned align well
with transport patterns outlined by backward trajectories from the CV monitor. Additionally, the spatial
variability, magnitude, and suggested plume transport from the satellite imagery and HRRR/BlueSky
modeled smoke dispersion output described in the previous section verifies well with the HYSPLIT forward
and backward trajectory analysis highlighted in this section. The corroboration of these analysis adds
confidence that wildfire smoke was transported to the CV monitor from regional wildfire highlighted in
Table 21 - Potential Wildfire Smoke Sources: July 12, 2021 during the period July 9-12.

Figure 69 - HYSPLIT 72-hr Ensemble Backward Traj: July 12, 2021 15Z

Figure 69. HYSPLIT 72-hr Ensemble Backward Trajectories starting at the CV monitor starting at mid-
boundary layer height on July 12, 2021 at 15Z. Trajectory paths indicate air parcels on the morning of July
12 were potentially sourced from the areas adjacent and over the Sugar, Lava, and Bootleg fires.

Figure 70 - HYSPLIT 72-hr Backward Frequency Traj: July 12, 2021 15Z

Figure 70. HYSPLIT 72-hr Backward Frequency Trajectories starting at the CV monitor starting at mid-
boundary layer height on July 12, 2021 at 15Z. Trajectories were launched at 6-hr intervals and calculated
for three days. Trajectory paths indicate air parcels on the morning of July 12 were potentially sourced
from the areas adjacent and over the Sugar, Lava, and Bootleg fires.

Figure 71 - Sugar Fire, CA; HYSPLIT 48-hr Forward Ensemble and Frequency Traj: July 10-12, 2021 15Z

Figure 71. HYSPLIT 48-hr Forward a.) Ensemble and b.) Frequency trajectories from the Sugar, CA fire
starting at 1500 m AGL on July 10, 2021 at 15Z. The trajectory paths suggest transport from the Sugar Fire
to CV (yellow star) by the morning of July 12.

Figure 72 - Bootleg Fire, OR; HYSPLIT 72-hr Forward Ensemble and Frequency Traj: July 9-12, 2021 21Z

Figure 72. HYSPLIT 72-hr Forward a.) Ensemble and b.) Frequency trajectories from the Bootleg, OR fire
starting at 3000 m AGL on July 9, 2021 at 21Z. The trajectory paths suggest transport from the Bootleg
Fire to CV (yellow star) by the afternoon of July 12.

Figure 73 - Lava Fire, CA; HYSPLIT 72-hr Forward Ensemble and Frequency Traj: July 9-12, 2021 15Z

Figure 73. HYSPLIT 72-hr Forward a.) Ensemble and b.) Frequency trajectories starting from the Lava fire
starting at 1500 m AGL on July 9, 2021 at 15Z. The trajectory paths suggest transport from the Bootleg
Fire to CV (yellow star) by the morning of July 12.
Wildfire Smoke Emissions and Ozone Exceedance: Clear Causal Relationship
The previous sections have outlined the evolution of wildfire and smoke activity across the
Western U.S. leading up to and on the flagged event date of July 12, 2021. Meteorological analysis,
satellite/surface imagery and products, and HYSPLIT trajectory analysis reveal a clear depiction of how
wildfire smoke was amassed from multiple large ongoing wildfires (e.g. Sugar, Lava, and Bootleg fires) and
advected via the mean wind field to the CV monitor. These analyses provide a comprehensive narrative

of how smoke emissions were sourced and transported from ongoing wildfire activity to the CV monitor,
and unequivocal evidence that smoke was present in the atmospheric column and at the surface on July
12.
In the following sections, we not only further ground-truth the analyzed smoke fields over CV but
also demonstrate the contribution of wildfire smoke to surface level emissions in the SLV. First, we verify
the presence and amount of wildfire smoke at the surface using tracer PM2.5, CO, and brown carbon
concentrations to provide incontrovertible evidence that wildfire smoke and associated emissions existed
at the surface-level of the SLV. Second, we characterize the potential contribution of smoke emissions to
enhanced ozone concentrations using NOx and VOC measurements. Observed ground level air quality
species related to smoke and ozone production are also compared in a historical context and against
typical conditions on non-event and wildfire impacted event days. This type of analysis delineates how
the wildfire impacted conditions of July 12 differed greatly from the non-event and average air quality
characteristics of the SLV air shed and ultimately contributed to the observed CV ozone exceedance.
Surface Smoke Observations and Historical Monitor Comparison
UDAQ CV monitor hourly and daily (24-hr average) PM2.5 observations indicate the progression of
surface particulate concentrations from clear conditions before July 7, to periods of wildfire smoke July
8-12, and to relatively clear conditions again on July 14 (Figure 75 and Figure 74). As seen in Figure 75, the
largely smoke free days preceding and following the July 8-12 smoke event (e.g. July 7 and July 14) saw
daytime PM2.5 hourly concentrations ranging 5-10 µg/m3. In comparison, during the smoke impacted
period the maximum hourly PM2.5 concentrations observed on July 11 and on the flagged event date of
July 12 ranged from 35-45 µg/m3 and 25-35 µg/m3, respectively, indicating that significant enhancement
of PM2.5 by wildfire smoke emissions occurred on July 11-12. Trends in the observed monitored daily
PM2.5 concentrations reveal a similar story of PM2.5 enhancement by wildfire smoke, with a daily PM2.5
value of 27.3 µg/m3 on July 12 and 4 µg/m3 and 5 µg/m3 on the relatively clear days of July 7 and July 14,
respectively. When compared to PM2.5 concentrations at CV over the 5-year period of 2019-2021, the
July 12 daily PM2.5 concentration (27.3 µg/m3) exceeds the 5-year month’s specific 24-hr PM2.5 98th
percentile94 value of 17.8 µg/m3 by nearly 10 µg/m3 (Figure 75). Figure 74 and Figure 75 displays the
marked departure of the monitored daily PM2.5 on the flagged event date from the 5-year (2019-2023)
month’s daily averages (excluding the fire year 2021), with 24-hr average PM2.5 observations on the July
12 event ~3-3.5 times larger than the typical values for this period.
Similar to the utility of PM2.5 as a tracer for wildfire smoke, brown carbon (BrC) has been shown
to be extremely useful for identifying biomass burning emissions. Any observational value (> 0 ng/m3) of
BrC signals the presence of smoke from some source of biomass burning. UDAQ has continuous
aethalometer observations of BrC dating back to 2017 at a number of sites around the northern Wasatch
Front Non-attainment area. The UDAQ aethalometers measure absorption of particulate matter on a filter
tape at seven wavelengths (or channels) ranging from the UV to infrared (370 - 950 nm). Since BrC coexists
with black carbon (BC), BrC observations are derived by finding the separation between the BC absorption
in channel 6 (880 nm) from channel 1 (370 nm). This differential between channels is commonly referred
to as the parameter delta-c (BrC). In Figure 76, delta-c concentrations are shown for a period surrounding
the July 12 flagged smoke event. Elevated concentrations of delta-c are observed during the smoke period
of July 8-13, peaking on July 11 and 12 (> 800-1000 ng/m3), and tapering to lower concentrations on the
clear smoke-free days of July 7 and 14 (< 150 ng/m3) (Figure 76). Because delta-c is an unambiguous
indicator of biomass burning, the enhanced delta-c observations on the flagged event date undisputedly
indicate the residence of surface-level wildfire smoke in the SLV on July 12. For reference, on days that

94 EPA PM2.5 Tiering Tool: https://www.epa.gov/air-quality-analysis/pm25-tiering-tool-exceptional-events-analysis

are considered smoke free average delta-c concentrations typically range 150-200 ng/m3 or less. Table 22
provides the average delta-c concentrations for the 5-year (2019-2023) month’s daily averages compared
to concentrations observed during the flagged event, with the observed delta-c on July 12 ~6 times larger
than average.
Figure 74 - CV Hourly PM2.5: July 12, 2021

Figure 74. Mon
itored
hourly PM2.5 concentrations at CV for the period July 8-16, 2021, centered on July 12 (vertical red line).
Increased hourly PM2.5 concentrations (~25-30 µg/m3) associated with the smoke is evident on July 12.

Figure 75 - CV Monitored 24-hr PM2.5 and MD8A Ozone: July 12, 2021

Figure 75. Daily (24-hr avg) PM2.5 (right axis) and MD8A ozone (left axis) observed at the CV monitor for
the period July 5-16, 2021, centered on the July 12 flagged event. Trends in daily PM2.5 and MD8A ozone
correspond well with each other, revealing the close connection between the presence of wildfire smoke
emissions and enhanced ozone formation.
Figure 76 - Hourly Brown Carbon (BrC) Concentrations: July 12, 2021

Figure 76. Monitored hourly BrC concentrations at CV for the period July 7-16, 2021, centered on July 12
(vertical dashed-red lines) from the Bountiful (BV), Inland Port (IP), and Lake Park (LP) UDAQ monitoring
sites. Increased hourly BrC concentrations (>800-1000 ng/m3) associated with smoke is evident on July
12.

Table 22 – Average Brown Carbon (BrC) Concentrations: July 2019-2023
Station 2019 2020 2021 2022 2023 Average July 12
Event Avg.
Bountiful 134 163 280 112 77 153 846
Inland Port -- -- 303 66 71 147 861
Lake Park -- -- 262 131 92 162 --
Table 22. 5-year month’s specific (July 2019-2023) average BrC concentrations from the Bountiful (BV),
Inland Port (IP), and Lake Park (LP) UDAQ monitoring sites, with the daily BrC concentration for the flagged
event day of July 12 also given.

Event and non-event Ozone
The presence of surface-level wildfire smoke at the CV monitor has been established in the prior
sections. Here, we show how the addition of wildfire smoke emissions into the SLV airshed caused the
ozone exceedance at the CV monitor. Daytime hourly ozone and PM2.5 concentrations trend closely
during the wildfire smoke impacted period of July 8-13 (Figure 74). Daily PM2.5 and MD8A ozone
concentrations also exhibit a close positive relationship, where the local MD8A ozone maximum
corresponds with the local maxima of PM2.5 (Figure 74). It has been established by prior studies that
PM2.5 can be used to indicate the potential magnitude of ozone enhancement by wildfire smoke.
Empirical relationships between PM2.5 and ozone concentrations reveal that surface ozone increases at
low to moderate PM2.5 concentrations up to 30-50 ppb before decreasing at higher PM2.5 levels (e.g.
Buysse et al. 2019; Ninneman and Jaffe, 2021). The negative relationship between high PM2.5
concentrations and ozone suggest that ozone production can be suppressed due to
backscattering/attenuation of solar radiation in dense smoke (high PM2.5), leading to reduced ozone
photochemistry near the surface. In the case of July 12, both hourly and daily observed PM2.5
concentrations were within the moderate range and correspond with PM2.5 concentrations that correlate
with ozone enhancement from wildfire smoke emissions (Figure 74).
The observed ozone concentrations on the July 12, 2021 flagged wildfire smoke event were
significantly elevated and notably anomalous. In Figure 77, the MD8A ozone at CV is given for the 5-year
period 2019-2023 to highlight monitored flagged wildfire smoke MD8A ozone relative to non-events.
Compared to the 5-year period MD8A ozone concentrations at CV, the MD8A value on July 12 of 96 ppb
is not only higher than the 98th and 99th MD8A percentile, but is also the highest MD8A observed in the
5-year period (Figure 77). Furthermore, the observed MD8A on July 12 is the highest ever recorded in the
complete historical POR CV has been operational (2018-2024), with almost all of the top 10 ranked MD8A
ozone at CV composed of other wildfire smoke flagged events (Table 23). To further quantify the distinct
difference in observed ozone on wildfire smoke events compared to non-events, mean MD8A and average
diurnal hourly ozone are given for non-event and wildfire smoke event days in Figure 78 and Figure 79,
respectively. On average, measured MD8A ozone at CV is 6-8 ppb higher on wildfire smoke event days
than on non-event days (Figure 78). Diurnal average hourly ozone reveals that the rate of ozone formation
(dO3/dt) is much greater on wildfire smoke event days than on non-event days (Figure 79). When the
hourly ozone trend from the flagged event of July 12 is compared with diurnal average hourly ozone
concentrations of non-event and wildfire events and across the 5-year period 2019-2023, it is evident that

the ozone formation rate on July 12 is significantly greater than what would be normally observed on non-
event days and has similar trend characteristics as on flagged wildfire event days (Figure 79).
Figure 77 - MD8A Ozone 2019-2023 at CV Monitor

Figure 77 - MD8A Ozone 2019-2023 at CV Monitor. MD8A ozone (ppb) at the CV monitor for the 5-year
period 2019-2023. Wildfire smoke flagged EE’s (red circles) (July 12 and 25, 2021; August 7-8 and 16, 2021)
and dates with flags for wildfire smoke (orange circles) are highlighted. The July 12 flagged EE is outlined,
showcasing the extremely high MD8A ozone observed on that date compared to the 5-year period.

Table 23 - Top 10 CV POR Ranked MD8A (2018-2024)
Rank CV MD8A Date
1 96 2021-07-12

2 89 2021-08-08
3 87 2021-08-07
4 86 2021-08-16
5 85 2021-08-04
6 85 2021-09-08
7 85 2020-08-21
8 84 2021-07-11
9 83 2021-07-24
10 82 2020-07-11
Table 23 - Top 10 CV POR Ranked MD8A (2018-2024). The top 10 ranked MD8A ozone at the CV monitor
for the operational POR (2018-2023). The wildfire smoke flagged EE of July 12 is the highest MD8A ever
recorded (highlighted red) at CV. Other flagged EE’s and wildfire impacted events compose almost all
other top ranked spots (highlighted in yellow).

Figure 78 - Non-Event and Event MD8A Ozone: NWF 2016-2023

Figure 78. Average Non-Event and Event MD8A ozone (ppb) for the period 2016-2023 at UDAQ monitors
within the SLV, including Hawthorne (HW), Copperview (CV), Bountiful (BV), Herriman (H3), and Rose Park
(RP). MD8A ozone is on average 5-8 ppb higher during wildfire events than non-wildfire events.

Figure 79 - Non-Event and Event Average Hourly Diurnal Ozone at CV Monitor: : July 12, 2021

Figure 79. Non-Event, Event, and July 12 Event average diurnal hourly ozone at the CV monitor. The ozone
formation rate on Event days and the flagged July 12 Event is considerably steeper than non-events.
Figure 80 - Flagged Event Hourly Ozone vs. Average Hourly Diurnal Ozone at CV Monitor (2016-2021): :
July 12, 2021

Figure 80. Yearly (2018-2021) and July 12 Event average diurnal hourly ozone at the CV monitor. The
ozone formation rate on the flagged July 12 Event is considerably steeper than the average diurnal ozone
trends.

Wildfire Smoke and Ozone Formation: NOx and VOCs
It is apparent that the significant enrichment of ozone at CV during the July 12 wildfire smoke
event was closely tied to the presence of wildfire smoke. When compared to historical ozone monitor
concentrations, there is a very clear distinction that the observed ozone at CV on July 12 was
uncharacteristic and likely influenced by smoke emissions. In order to distinguish the contributions of
smoke emissions to elevated ozone on July 12, we detail the typical concentrations of key air quality
parameters important to ozone formation on wildfire smoke event days, non-event, and on the flagged
date of July 12. This information will provide evidence of emission changes due to smoke and potential
impact on ozone photochemistry.
On a typical non-event ozone exceedance day, ozone formation within the SLV is dominated by
photochemical reactions of the precursor emissions of NOx and VOCs. The injection of additional NOx and
VOC emissions from wildfire smoke plume alters the typical emission profile within the SLV and can
provide additional fuel for ozone formation. Therefore, UDAQ utilizes hourly GC analyzed VOC
concentrations to investigate trends in VOC emissions on non-event and wildfire smoke event days to
account for the impacts of VOC emissions from smoke. The GC data is from the Hawthorne monitor
located in the northeastern part of the SLV and approximately twelve miles to the north of the CV monitor
(Figure 37). VOC observations from the Hawthorne GC include 57 identified VOC species as well as Total
Non-Methane Organic Carbon (TNMOC).
A few VOC species, including benzene, toluene, and xylene, have been noted by studies to be
contained within wildfire smoke (Wang et al., 2024; Ketcherside et al., 2024; Simms et al., 2021).
Monitored trends in these species are useful for identifying the presence of wildfire smoke as well as the
relative magnitude of added VOC emissions into the air shed from smoke plumes. In Figure 81, the
observed hourly concentrations of benzene, toluene, and xylene are shown for a period centering on the
flagged event date of July 12. The trend in the three VOC species closely correlates with the wildfire smoke
period July 9-14, marking the arrival and clear-out of smoke. All three species increase sharply on July 9,
when the first wave of wildfire smoke arrived in the SLV, and peak near or on July 12 before decreasing
sharply after July 13 as the smoke emissions cleared out (Figure 81). Figure 82 presents the observed
TNMOC through the same period and shows maxima in the TNMOC correspond to the smoke period of
July 9-13.
To determine how the ozone precursor concentrations on July 12 compare with other days, we
contrast the typical monitored VOC concentrations on non-event, flagged smoke event dates, the event
date of July 12, and a day of similar meteorology (July 22, 2021) when no ozone exceedance occurred
(Figure 83). The VOC emissions on the similar meteorology day of July 22 is highlighted in Figure 83 and
Figure 84, with VOC emissions notably lower (but still slightly elevated) than wildfire impacted flagged
dates. Figure 84 shows wildfire event days have much greater TNMOC and total VOC concentrations on
average than non-event days, particularly on days of ozone exceedances with wildfire smoke.
Additionally, the observed average TNMOC and total VOCs on the July 12 event are markedly higher than
on non-event days and the comparable meteorology day of July 22, 2022 (Figure 84).
Diurnal average trends provide insight as to how the temporal variability of total VOCs and
TNMOC on event days compare with non-events (Figure 85). A notable enhancement of VOCs and NOx is
observed on the flagged wildfire event July 12 when compared to non-events and the comparable
meteorology day (Figure 85). This enhancement is most pronounced in the morning, early afternoon, and
evening hours. In particular, during the flagged event period of July 12 TNMOC, total VOCs, and NOx were
significantly larger in the early to mid-morning hours and remained consistently elevated above typical
non-event concentrations through the course of the afternoon/evening. The steep decrease in TNMOC,
total VOCs, and NOx in the late morning and early afternoon coincides with peak ozone production hours

(0700-1300 MST) (Figure 85a). During this period, ozone production ramps up as incident solar radiation
and temperature increases. The precursor emissions of NOx and VOCs are consumed rapidly and depleted
through ozone photochemistry. This rapid titration of the precursor emissions, coinciding with rapid
growth in ozone concentrations, exhibits the significant impact the addition of wildfire smoke emissions
had on ozone concentrations on July 12 (Figure 85). As seen in Figure 80 and Figure 85a, ozone production
rates (dO3/dt) are notably steeper on the flagged event date of July 12 compared with non-events and
the day of similar meteorology, indicating ozone enrichment due to the addition of smoke NOx and VOC
emissions.
The VOC concentrations on the July 12 flagged event were significantly larger than what is
typically observed in the SLV on non-event days (Figure 83). Xylene and toluene emissions within wildfire
smoke plumes have been noted to be relatively reactive species for ozone formation, making the addition
of these emissions impactful for ozone development (Wang et al., 2024; Ketcherside et al., 2024; Simms
et al., 2021). The SLV air shed is characterized by a transitional to VOC-limited regime, which makes ozone
photochemistry sensitive to increases or decreases in VOCs and NOx emissions (e.g. Gonzalez et al., 2024;
Jaffe et al., 2024). However, ozone formation has also been identified to be particularly sensitive to
increases in VOC emissions from wildfire smoke (Jaffe et al., 2024). Here, we show that wildfire smoke
injected supplementary VOC emissions into the urban SLV plume, creating an environment for ozone
enrichment. Similarly, trends in NOx during the wildfire period exhibit elevated concentrations compared
to non-event days (Figure 83c). The combinations of fresh of NOx and VOC emissions from the wildfire
smoke plume into the urban SLV air shed caused the extreme ozone exceedance on July 12.

Figure 81 - HW Average Daily VOCs: Jul-Aug

Figure 81. Daily average VOC concentrations of benzene, toluene, and xylene at the HW monitor for the
period July-August, 2021. The flagged wildfire smoke events (i.e. July 12, July 24, August 7 & 8, and August
16 are noted (vertical solid red lines) as well as periods of wildfire smoke (shaded red regions).
Additionally, the comparable meteorological day of July 22, 2021 is marked (vertical solid blue line).

Figure 82 - HW Average Daily TNMOC: Jul-Aug 2021

Figure 82. Daily average TNMOC concentrations at the HW monitor for the period July-August, 2021. The
flagged wildfire smoke events (i.e. July 12, July 24, August 7 & 8, and August 16 are noted (red stars) as
well as periods of wildfire smoke (shaded red regions). Additionally, the comparable meteorological day
of July 22, 2021 is marked (blue star).
Figure 83 – Event vs. Non-Event: Average Daily VOCs at HW: July 12, 2021

Figure 83. Average daily VOCs and TNMOC at the HW monitor for Non-Event (Exceedance No WF), Event
(Exceedance WF), Comparable Meteorology (Comparable MET – July 22), and the flagged July 12 Event
(WF Event: July 12) during the summer of 2021.

Figure 84 – Event vs. Non-Event: Average Hourly Diurnal Total VOCs, TNMOC, and NOx: July 12, 2021

Figure 84. Average diurnal hourly a.) VOCs, b.) TNMOC, and c.) NOx concentrations at the HW monitor
for Non-Event, Event, All wildfire days, July 12 Event, and Comparable Meteorology day (July 22) in the
summer of 2021.

Figure 85 – Event vs. Comparable MET: Hourly VOCs, NOx, and Ozone at HW and CV: July 12, 2021

Figure 85. Hourly VOCs, ozone, and NOx concentrations at the CV monitor for the a.) July 12 Event and
b.) Comparable Meteorology day (July 22).

Conceptual Model and Clear Causal Relationship: Smoke Event July
24, 2021
Wildfire Conditions: July 24, 2021
Across the west, drought conditions in the week leading up to July 24 (Figure 86) were extreme.
In Figure 87, large scale ridging is shown to have dominated across the Western CONUS the month
preceding the July 24 flagged event, facilitating abnormally dry and hot conditions across the Western
U.S. (Figure 88 and Figure 89) leading up to the flagged EE date on July 24. In Figure 86, the U.S. Drought
Monitor is given for the Western U.S. for the second week of July 2021, with a large portion of the West
under Extreme to Exceptional Drought (D3-D4) conditions. Given the extreme drought, wildfire fuels were

primed for ignition as shown by the high values of the Wildland Fire Potential Index (WFPI)95 in the West
derived on July 24, 2021 in Figure 90. In late July 2021, these conditions led to high fire danger and various
wildfires burned across the Western U.S., with a number of large to medium sized fires noted to the west
and north of Utah in California, Oregon, Washington, and Idaho on July 24 (Figure 91). The major fires of
concern burning on July 24 are shown in Figure 91 and noted in Table 24. The National Interagency
Coordination Center Incident Management Situation Report on July 24, 2021 is provided in Appendix A.
Figure 86 - Western U.S. Drought Monitor: July 2021

Figure 86. Drought monitor for the Western U.S. derived for the seven-day period ending on July 27,
202196. Much of the West was under extreme to exceptional drought (D3-D4) at the time of the July 24
flagged EE event.

95 WFPI can be found at: https://firedanger.cr.usgs.gov/apps/staticmaps
96 U.S. Drought Monitor can be found at: https://droughtmonitor.unl.edu/

Figure 87 - NCEP Reanalysis Average 500 mb GPH: July 24, 2021

Figure 87. NCEP Reanalysis Average 500 mb Geopotential Heights97 for the period June 24 - July 24, 2021.
The presence of higher average 500 mb geopotential heights across the West indicate persistent ridging
in the month preceding July 24.

97 NCEP Reanalysis Data can be found at: https://psl.noaa.gov/data/gridded/data.ncep.reanalysis.html

Figure 88 - PRISM July 2021 Precipitation Anomalies

Figure 88. PRISM precipitation anomalies98 for July 1-30, 2021. Well below normal precipitation was
observed across the Western U.S. in the month prior to the July 24 event.
Figure 89 - PRISM July 2021 Temperature Anomalies

Figure 89. PRISM daily mean temperature anomalies99 for July 1-30, 2021. Well above normal
temperatures were observed across the Western U.S. in the month prior to the July 24 event.

98 PRISM data can be found at: https://prism.oregonstate.edu/graphics/
99 PRISM data can be found at: https://prism.oregonstate.edu/graphics/

Figure 90 – WFPI: July 24, 2021

Figure 90. Wildland Fire Potential Index (WFPI)100 for July 24, 2021. Many areas in the Western U.S.
exceeded WFPI values of > 100, indicating a high potential for wildfires on the flagged event date.

100 WFPI can be found at: https://firedanger.cr.usgs.gov/apps/staticmaps

Figure 91 - WFIGS Wildfire Perimeters: July 24, 2021

Figure 91. WFIGS Wildfire perimeters101 (> 10,000 acres) on July 24, 2021.
Table 24 – Potential Wildfire Smoke Sources: July 24, 2021
Event Date Wildfire Smoke Sources (potential) Fire Size
(Event - acres)
7/24/2021
Dixie fire, CA 167430
Sugar fire/Beckwourth Complex, CA 105670
Tamarack fire, CA/NV 59112
Bootleg fire, OR 400389
Table 24. List of potential wildfire smoke sources contributing to smoke emissions at CV (devised from
forward and backward HYSPLIT trajectories) and the approximate size of the fires in acres102 on July 24,
2021.
Meteorological Conditions
During the flagged event period of July 24, the large-scale synoptic pattern continued to feature
a broad area of high pressure across the Western U.S. (Figure 92). Figure 93 and Figure 94 shows the mid

101 WFIGS Wildfire Perimeters can be found at: https://data-
nifc.opendata.arcgis.com/search?tags=historic_wildlandfire_opendata%2CCategory
102 Dataset of U.S. IMSR found at: https://research.fs.usda.gov/treesearch/67197

to upper level winds and geopotential heights on July 24, with the overall synoptic pattern characterized
by a large dome of high pressure centered over the Western U.S. The ridge axis extended roughly north-
south across the Great Basin region, orienting the anticyclonic southwesterly to westerly mid to upper
level winds across northern Utah (Figure 93 and Figure 94). A cyclonic circulation associated with a mid-
level low was present over the Desert Southwest. This oriented some easterly winds over the central to
southern areas of Utah and westerly winds across northern Utah. At the surface, a stationary boundary
was draped across central Utah, with a mesoscale convective system (MCV) located to the south across
the Desert Southwest (Figure 93 and Figure 95). Given the upper-level pattern, the surface weather
conditions on July 24, 2021 were characterized by maximum temperatures observed in the upper 90s,
low wind speeds (< 5 knots), and clear skies (Figure 97).
Soundings launched at KSLC on July 24 show a deep and well mixed planetary boundary layer
(PBL) up to about 650 mb (~2.3km AGL) and an elevated mixed layer up to about 550 mb (~3.9 km AGL)
(Figure 96b). In Figure 96a, the vertical wind profile at 12z exhibits southerly down-valley winds below
800 mb. As seen in the 00Z sounding, lower level winds below 700 mb in Figure 96b suggest lake-land
breeze influence, with northerly to westerly winds above 700-500 mb. The evolution and associated
impacts of the upper-level ridge and synoptic pattern is described in full detail in the National Weather
Surface (NWS) area forecast discussions (AFDs)103 for KSLC (Appendix A). In general, the NWS AFDs
illuminate how the meteorological pattern influenced the transport of smoke into Utah. For example,
highlighted AFD text discussing the intrusion wildfire smoke into Utah on July 23 is given below:

“Area Forecast Discussion
National Weather Service Salt Lake City UT
506 AM MDT Fri Jul 23 2021

.SHORT TERM (THROUGH 12Z MONDAY)...High pressure that had been positioned over
the Four Corners area has trended flatter in response to a trough moving
across western Canada and is retrograding towards southwest Utah. Meanwhile,
an upper low over far southwest New Mexico this morning will continue to track
west towards Arizona. Westerly flow at 500mb and northwesterly at 700mb is
spreading drier air as well as smoke into northwest Utah this morning. This
drier air and smoke will spread farther into northern Utah during the
afternoon.104”

103 Archived NWS AFDs can be found at: https://mesonet.agron.iastate.edu/wx/afos/list.phtml
104 Archived NWS AFDs can be found at: https://mesonet.agron.iastate.edu/wx/afos/list.phtml

Figure 92 - NCEP Reanalysis Average 500 mb GPH: July 24, 2021

Figure 92. NCEP Reanalysis Average 500 mb Geopotential Heights105 for the period July 23 - July 24, 2021.
The higher 500 mb geopotential heights centered across the Great Basin Region indicates a relatively
strong upper-level ridge.

105 NCEP Reanalysis Data can be found at: https://psl.noaa.gov/data/gridded/data.ncep.reanalysis.html

Figure 93 - NOAA SPC 500 mb and 700 mb Upper Air Charts: July 24, 2021

Figure 93. NOAA-Storm Prediction Center106 upper air charts for a.) 500 mb geopotential heights, winds,
and temperature, b.) 500 mb chart zoomed in over the West, c.) 700 mb geopotential heights, winds,
temperature, and relative humidity, and d.) 700 mb chart zoomed in over the West. An upper-level ridge,
is centered across the Great Basin Region, with anticyclonic flow over the area. A boundary lined across
central Utah, with a mesoscale convective system (MCS) to south of Utah across the northern Sonoran
Desert.

106 NOAA-SPC Mesoscale Analysis Upper Air Charts can be found at: https://www.spc.noaa.gov/

Figure 94 - GFS Analyzed 500 mb GPH and Winds: July 24, 2021

Figure 94. GOES East True Color satellite imagery with overlaid analyzed GFS 500 mb geopotential heights
(m) and winds (kts) and the location of the CV monitor (yellow star) on July 24, 2021 at 2100Z zoomed
over a.) the CONUS and b.) Utah. A dome of high pressure resides across the Great Basin with westerly
upper-level winds across northern Utah.

Figure 95 - WPC Surface Analysis: July 24, 2021

Figure 95. NOAA-Weather Prediction Center (WPC)107 surface analysis and IR satellite imagery on July 24,
2021 at 1800Z zoomed over a.) North America and b.) the Western U.S. - defined red bounding box in a.).
The analyzed fronts show a stationary front draped across central Utah. A low-pressure area is evident
over the Desert Southwest, associated with an MCS across the northern Sonoran Desert.

107 NOAA-WPC Surface Analysis Charts can be found at: https://www.wpc.ncep.noaa.gov/archives/web_pages/sfc/sfc_archive_maps.php

Figure 96 - KSLC Radiosonde Soundings: July 24, 2021

Figure 96. Radiosonde soundings from KSLC on July 24, 2021 at a.) 12Z and b.) 00Z. A deep well mixed PBL
is evident in the 00Z sounding, with winds out of the southwest to west near and above 700 mb in both
the morning and afternoon soundings. Winds at lower levels were a mix of diurnal and mesoscale driven
winds.

Figure 97 - CV Meteogram: July 24, 2021

Figure 97. Meteogram of observed sensible weather conditions at the CV monitor through the period July
23-26, centered on the flagged event date of July 24 (delineated by the red dashed lines). Hot
temperatures, low wind speeds, and low moisture as well as decreased solar radiation due to afternoon
clouds are noted on July 24.

Wildfire Smoke: Remote Sensing and Ground-Based Analysis
It is apparent that the meteorological environment on July 24, 2021 was conducive for the
transport of air parcels from points west of Utah into the state. Visible satellite imagery reveals a large,
consolidated mass of smoke mixed with clouds transported to the CV UDAQ monitor on July 24 (Figure
98 - Figure 101). Figure 98 and Figure 99 show smoke plumes emanating from numerous large fires across
the West circulated and transported within the mean wind field. In Figure 100, visible satellite imagery
merged with the analyzed 500 mb upper-level wind field exhibits the pattern of smoke transport from
areas west around the upper-level ridge into northern Utah. Figure 101 gives an example of what
relatively smoke free conditions look like over Utah on July 21 compared to the smoke conditions on the
event date of July 24. Revealed in the satellite imagery, the synoptic meteorological pattern allowed the
west to east transport and aggregation of smoke plumes from numerous fires in the West around the
upper-level ridge into Utah. Vertical temperature and wind profiles from soundings launched on July 24
reveal a deep PBL mixed layer in the SLV, suggesting that the capture and transport of smoke emissions
from aloft to the surface was possible (Figure 96).
We investigate satellite aerosol optical depth (AOD) and satellite HMS smoke field to distinguish
wildfire smoke density over Utah on July 24. In Figure 102, AOD values ~ 1 are present over the SLV,

indicating dense wildfire smoke in the atmospheric column. Synthesizing the remote sensing imagery and
analysis into one product, the HMS analyzed smoke fields show that medium to heavy dense smoke
plumes converged over the Northern Wasatch Front and the CV monitor from these fires on July 24 (Figure
103). The summarization of smoke field characteristics observed by satellite imagery is given by the NOAA
NEDIS smoke narrative108 published on July 24, 2021 at 0125Z. The smoke discussion notes thick and dense
smoke across Utah from the wildfire activity in the Western U.S.:

“Friday, July 23, 2021
DESCRIPTIVE TEXT NARRATIVE FOR SMOKE/DUST OBSERVED IN SATELLITE IMAGERY THROUGH 0125Z July 24, 2021
SMOKE: Canada/U.S...The huge expanse of smoke of varying density attributed to
significant wildfire activity in central, south central, and southwestern Canada along with the northwestern and western U.S. was again visible covering nearly all of Canada and much of the U.S. with the exception of the Southeast, a
portion of the Southwest, and the western portions of California, Oregon, and Washington. Thicker smoke from fires in east central and northeastern California and south central Oregon spread to the northeast and merged with thick smoke
produced by wildfires in central and eastern Washington, northern Idaho, western Montana, and southern British Columbia.109”
A more detailed characterization of the magnitude and transport pattern of smoke from wildfires
across the West is given by the High-Rapid Refresh (HRRR) smoke model analysis in Figure 104. In Figure
104a, the July 24 12Z initialized HRRR total column smoke density exhibits the extensive and dense shield
of smoke across the Western U.S. and Utah (> 150 μg/m²). Additionally, the total column smoke density
reveals well defined heavy plumes originating from a number of fires across the Western U.S. (as seen in
Figure 98 - Figure 100) being transported west to east around the upper-level ridge centered over the
Great Basin region. A closer inspection of HRRR smoke is given in Figure 104b, showing dense surface level
smoke (> 30 μg/m³) at the CV monitor on July 24. In Figure 105, the BlueSky Smoke model110 outlines the
smoke plumes originating from the fires across the West, ultimately forming a conglomerate mass of
smoke over the entire region.
The presence of wildfire smoke as noted by satellite imagery and HRRR smoke across the Wasatch
Front is corroborated by surface observations of the aerosol optical depth (AOD) from the Aerosol Robotic
Network (AERONET) (Figure 106 and Figure 107). A larger or thicker AOD signifies more
attenuation/scattering of incident solar radiation through the column of the atmosphere and can be
correlated with the presence of wildfire smoke. We utilize AERONET Level 2 AOD111 (Pre- and post-field
calibration applied, automatically cloud cleared and manually inspected112) observations from the
NEON_ONAQ site. Figure 66 and Figure 67 shows AOD ranging from < 0.2 before July 21 to 0.8-1.5 July 24
a dense smoke plume arrived across northern Utah. The increase in AOD from July 21 to July 24 is due to
the increased transport of wildfire smoke across the area. For reference, clear days with no smoke have
AOD’s that are < 0.1. The observed AOD on the days following July 24 shows a sharp decrease to values <

108 NOAA NEDIS Smoke Narrative can be found at: https://www.ssd.noaa.gov/PS/FIRE/smoke.html 109 NOAA NEDIS Smoke Narrative can be found at: https://www.ssd.noaa.gov/PS/FIRE/smoke.html 110 BlueSky Modeling Framework can be found at: https://tools.airfire.org/websky/v2/#status
111 AERONET AOD data can be found at: https://aeronet.gsfc.nasa.gov/cgi-bin/data_display_aod_v3
112 AERONET System description can be found at: https://aeronet.gsfc.nasa.gov/new_web/system_descriptions.html

0.3, indicating the dissipation and clearing of the smoke plume from the area. Observations from ground-
based cameras around the SLV further verify the presence of near surface smoke across the valley on July
24, 2021 (Figure 68). In Figure 68a and Figure 68d, the camera images from July 21 represents a relatively
clear day preceding the flagged smoke event.

Figure 98 - FIRMS Map: July 24, 2021

Figure 98. FIRMS Map113 with VIIRS S-NPP True Color Satellite imagery for July 24, 2021 overlaid with
satellite analyzed fire hotspots (red dots) and fire perimeter burned area (shaded light blue areas). A
large swath of medium to heavy smoke is evident across the Western U.S. and Utah.

113 FIRMS Fire Map can be found at: https://firms.modaps.eosdis.nasa.gov/usfs/map/#d:24hrs;@-100.0,40.0,4.0z

Figure 99 - GOES West True Color: Western CONUS July 24, 2021

Figure 99. GOES West True Color Satellite imagery114 on July 24, 2021 at 2200Z. A large swath of medium
to heavy dense smoke is located across the Western U.S and Utah.

114 NOAA-Aerosol Watch Satellite imagery can be found at: https://www.star.nesdis.noaa.gov/smcd/spb/aq/AerosolWatch/

Figure 100 - GOES East True Color and GFS 500 mb Heights and Winds: July 24, 2021

Figure 100. GOES East True Color satellite imagery with overlaid analyzed GFS 500 mb geopotential
heights (m) and winds (kts) and satellite analyzed wildfire hotspots (red circles) on July 24, 2021 at 2100Z.
The satellite imagery reveals a large swath of wildfire smoke across the Western U.S. being transported
from fires located across the West by anticyclonic flow around the upper-level ridge centered over the
Great Basin.

Figure 101 - GOES East True Color: Utah July 24, 2021

Figure 101. GOES East True Color satellite imagery on the event date a.) July 24, 2021 at 1500Z. GOES East
True Color imagery on b.) a relatively smoke free impacted date July 21, 2021 at 2100Z. On July 24, a
plume of wildfire smoke across Utah being transported by anticyclonic flow around the upper-level ridge.
In b.), key geographical landmarks are more visible due to the smoke free skies.

Figure 102 – GOES West AOD Composite 18-21Z: July 24, 2021

Figure 102. GOES West satellite derived Aerosol Optical Depth (AOD) composite115 on July 24, 2021 for a.)
the Western U.S., and b.) zoomed in over northern Utah. AOD values of ~1 were observed over the SLV,
indicating the presence of dense wildfire smoke attenuating incoming solar radiation.

115 Aerosol Watch AOD product can be found at: https://www.star.nesdis.noaa.gov/smcd/spb/aq/AerosolWatch/index.php

Figure 103 - HMS Smoke Fields and WFIGS Wildfire Perimeters: July 24, 2021

Figure 103. HMS smoke fields 116 with WFIGS Wildfire perimeters117 across the Western U.S. on July 24,
2021. Smoke plumes are shown to be transported west to east from fires in CA, OR, and WA, creating
medium to heavy smoke plumes over Utah. Heavy smoke is analyzed above the CV monitor.

116 HMS Smoke Field data can be found at: https://www.ospo.noaa.gov/products/land/hms.html#0
117 WFIGS Wildfire Perimeters can be found at: https://data-
nifc.opendata.arcgis.com/search?tags=historic_wildlandfire_opendata%2CCategory

Figure 104 - HRRR Smoke VIS and NSFC Smoke: July 24, 2021

Figure 104. HRRR-NCEP smoke fields on July 24 at 15Z of a.) total column smoke (vertically integrated)
over the CONUS and b.) near-surface level smoke focused over Utah. Dense smoke was transported
west to east from fires in CA, OR, WA, and ID into Utah. Both vertically integrated and surface level
smoke reveal heavy-dense smoke over the CV monitor (yellow star).

Figure 105 - BlueSky Dispersion Analysis: July 24, 2021

Figure 105. BlueSky Daily Smoke Dispersion model run 118 (GFS 0.5 deg and 0.15 deg dispersion) from July
24, 2021 at 21Z. Satellite analyzed fire hotspots are overlaid (red flames) along with the location of the
CV monitor (yellow star pin). A large swath of wildfire smoke is indicated across the Western U.S. and over
the CV monitor, with dense plumes evident from a few different fires west and north of Utah.

118 BlueSky Modeling Framework can be found at: https://tools.airfire.org/websky/v2/#status

Figure 106 – AERONET Level 2 AOD: July 2021

Figure 106. AERONET derived Level 2 AOD119 from the NEON_ONAQ site (40 miles SW of the CV monitor)
for the month of July 2021. Periods preceding, during, and after the flagged smoke event are noted, with
corresponding AOD. Increased AOD values, signaling the presence of wildfire smoke, are apparent on July
23-26 compared to preceding and proceeding dates.

119 AERONET AOD data can be found at: https://aeronet.gsfc.nasa.gov/cgi-bin/data_display_aod_v3

Figure 107 - AERONET Level 2 AOD: July 24, 2021

Figure 107. a.) AERONET derived Level 2 AOD120 from the NEON_ONAQ site (40 miles SW of the CV
monitor) on the flagged event date of July 24 and b.) Terra MODIS True Color satellite imagery on July 24
overlaid with the NEON_ONAQ site location (orange circle) and CV monitor location (yellow star). AOD
values 0.6-0.8 on July 24 signal the presence of wildfire smoke. The wildfire smoke was slightly obscured
by a patchy cloud field as revealed in the satellite imagery.
HYSPLIT: Wildfire Smoke Transport to CV Monitor
HYSPLIT multiple particle forward and backward trajectory analysis was performed following
similar methodology as described in Section 4.1.4.
The first two HYSPLIT model configurations chosen were the backward ensemble and frequency
trajectory options, with parcels starting at model derived 1500m AGL (Figure 108). In Figure 108a, 72-

120 AERONET AOD data can be found at: https://aeronet.gsfc.nasa.gov/cgi-bin/data_display_aod_v3

hour ensemble backward trajectories beginning at the CV monitor on the evening of July 24 are shown.
The HMS smoke fields and VIIRS analyzed wildfire hotspots are also include in Figure 108a to help
distinguish the potential source regions of wildfire smoke that impacted the CV monitor. Figure 108a
reveals multiple trajectories ending at CV on July 24 originated or passed over a number of fires in CA and
OR. In Figure 108b, the 72-hour backward trajectory frequencies are provided, with areas of highest
trajectory frequencies corresponding to locations of active wildfires in northern and central CA. The
frequency plot suggests that the smoke plume over the CV monitor on July 24 was an aggregate smoke
mass composed of smoke sourced from multiple wildfire sources across California. In general, frequency
and ensemble trajectories show air parcels mainly originating from fires highlighted in Table 24.
Investigation of smoke transport from a few select fires to the SLV employs multi-particle forward
ensemble and frequency HYSPLIT trajectories (Figure 109). The integration periods for the forward
trajectories were 72 hours, given the influential fires and their respective distances to the CV monitor,
with trajectories ranging from 1000 m to 1500 m AGL for all simulations to replicate smoke lofted in the
atmosphere due to plume rise.
In Figure 109, both the 72-hour forward ensemble and frequency trajectories starting at the
Tamarack, CA fire reveal a well-defined southwest to northeast transport pattern from the fire to the SLV
over the few days preceding July 24, 2021. Similarly, trajectories launched from the Dixie fire show an
east-west transport pattern (Figure 110). The forward ensemble and frequency trajectory paths from the
wildfires mentioned align well with transport patterns outlined by backward trajectories from the CV
monitor. Additionally, the spatial variability, magnitude, and suggested plume transport from the satellite
imagery and HRRR/BlueSky modeled smoke dispersion output described in the previous section verifies
well with the HYSPLIT forward and backward trajectory analysis highlighted in this section. The
corroboration of these analyses adds confidence that wildfire smoke was transported from regional
wildfire sources (Table 24) during the period including July 24 to the CV monitor.

Figure 108 - HYSPLIT 72-hr Ensemble and Frequency Backward Traj: July 24, 2021 23Z

Figure 108. HYSPLIT 72-hr Backward a.) Ensemble and b.) Frequency Trajectories starting at the CV
monitor at 1500m AGL on July 24, 2021 at 23Z.

Figure 109 – Tamarack Fire; HYSPLIT 72-hr Forward Ensemble and Frequency Traj: July 22-24, 2021 12Z

Figure 109. HYSPLIT 72-hr Forward a.) Ensemble and b.) Frequency Trajectories starting at the
Tamarack, CA fire at 1000m AGL on July 22, 2021 at 12Z.

Figure 110 - Dixie Fire; HYSPLIT 72-hr Forward Ensemble and Frequency Traj: July 22-24, 2021 12Z

Figure 110. HYSPLIT 72-hr Forward a.) Ensemble and b.) Frequency Trajectories starting at the Dixie, CA
fire at 1500m AGL on July 22, 2021 at 00Z.

Wildfire Smoke Emissions and Ozone Exceedance: Clear Causal Relationship
In this section, we conduct PM2.5, brown carbon, precursor, and ozone analysis as described in
Section 4.1.5.
Surface Smoke Observations and Historical Monitor Comparison
UDAQ CV monitor hourly and daily (24-hr average) PM2.5 observations indicate the progression of
surface particulate concentrations from relatively smoke free conditions on July 19-22, to periods of
wildfire smoke July 23-26 (Figure 111 and Figure 112). As seen in Figure 111, the largely smoke free days

preceding the July 23-26 smoke event (e.g. July 19-22) saw daytime PM2.5 hourly concentrations ranging
5-10 µg/m3. In comparison, during the smoke impacted period the maximum hourly PM2.5 concentrations
observed during the July 24 flagged event ranged from about 30-65 µg/m3, indicating that significant
enhancement of PM2.5 by wildfire smoke emissions occurred on July 24. Trends in the observed
monitored daily PM2.5 concentrations reveal a similar story of PM2.5 enhancement by wildfire smoke,
with a daily PM2.5 value of 26.2 µg/m3 on July 24 (Figure 112). For contrast, the relatively smoke free
dates of July 19-22 observed daily PM2.5 concentrations of < 10 µg/m3. When compared to PM2.5
concentrations at CV over the 5-year period of 2019-2021, the July 24 daily PM2.5 concentration (26.2
µg/m3) exceeds the 5-year month’s specific 24-hr PM2.5 98th percentile121 value of 17.8 µg/m3 by nearly
10 µg/m3 (Figure 112). Figure 111 and Figure 112 displays the marked departure of the monitored daily
PM2.5 on the flagged event date from the 5-year (2019-2023) month’s daily averages (excluding the fire
year 2021), with 24-hr average PM2.5 observations on the July 24 event ~3-3.5 times larger than the
typical values for this period.
In Figure 113, delta-c concentrations are shown for a period surrounding the July 24 flagged
smoke event. Elevated concentrations of delta-c are observed during the smoke period of July 23-26,
peaking on July 24-25 (> 1500-2000 ng/m3), and tapering to lower concentrations on the clear smoke-free
days of July 22 and 27 (< 100 ng/m3) (Figure 113). Because delta-c is an unambiguous indicator of biomass
burning, the enhanced delta-c observations on the flagged event date undisputedly indicate the residence
of surface-level wildfire smoke in the SLV on July 24. Table 25 provides the average delta-c concentrations
for the 5-year (2019-2023) month’s daily averages compared to concentrations observed during the
flagged event, with the observed delta-c on July 24 ~7 times larger than average.

Figure 111 - CV Hourly PM2.5: July 24, 2021

Figure 111. Monitored hourly PM2.5 concentrations at CV for the period July 18-30, 2021, centered on
July 24 (vertical dashed-red lines). Increased hourly PM2.5 concentrations (20-60 µg/m3) associated with
the arrival of smoke is evident on July 24.

121 EPA PM2.5 Tiering Tool: https://www.epa.gov/air-quality-analysis/pm25-tiering-tool-exceptional-events-analysis

Figure 112 - CV Monitored 24-hr PM2.5 and MD8A Ozone: July 24, 2021
Figure 112. Daily (24-hr avg) PM2.5 (right axis) and MD8A ozone (left axis) observed at the CV monitor for
the period July 19-30, 2021, centered on the July 24 flagged event. Trends in daily PM2.5 and MD8A ozone
correspond well with each other, revealing the close connection between the presence of wildfire smoke
emissions and enhanced ozone formation.

Figure 113 - Hourly Brown Carbon (BrC) Concentrations: July 24, 2021

Figure 113. Monitored hourly BrC concentrations at CV for the period July 21-28, 2021, centered on July
24 (vertical dashed-red lines) from the Bountiful (BV), Inland Port (IP), and Lake Park (LP) UDAQ
monitoring sites. Increased hourly BrC concentrations (>1500-2000 ng/m3) associated with smoke is
evident on July 12.

Table 25 - Average Brown Carbon (BrC) Concentrations July 2019-2023: July 24, 2021
Station 2019 2020 2021 2022 2023 Average July 24
Event Avg.
Bountiful 134 163 280 112 77 153 830
Inland Port -- -- 303 66 71 147 1002
Lake Park -- -- 262 131 92 162 1139
Table 25. 5-year month’s specific (July 2019-2023) average BrC concentrations from the Bountiful (BV),
Inland Port (IP), and Lake Park (LP) UDAQ monitoring sites, with the daily BrC concentration for the flagged
event day of July 24 also given.

Event and non-event Ozone
The presence of surface-level wildfire smoke at the CV monitor has been established in the prior
sections. Here, we show how the addition of wildfire smoke emissions into the SLV airshed caused the
ozone exceedance at the CV monitor. Daily PM2.5 and MD8A ozone concentrations also exhibit a close
positive relationship, where the local MD8A ozone maximum corresponds with the local maxima of PM2.5
(Figure 112). It has been established by prior studies that PM2.5 can be used to indicate the potential
magnitude of ozone enhancement by wildfire smoke. In the case of the July 24 event, both hourly and
daily observed PM2.5 concentrations were within the moderate range and correspond with PM2.5
concentrations that correlate with ozone enhancement from wildfire smoke emissions (Figure 111 and
Figure 112).
The observed ozone concentrations on the July 24, 2021 flagged wildfire smoke event were
significantly elevated and notably anomalous. In Figure 114, the MD8A ozone at CV is given for the 5-year
period 2019-2023 in order to highlight monitored flagged wildfire smoke MD8A ozone relative to non-
events. Compared to the 5-year period MD8A ozone concentrations at CV, the MD8A values on July 24 of
83 ppb is not only higher than the 98th and 99th MD8A percentile but is also the ninth ranked observed
MD8A in the 5-year period (Figure 114) and in the complete historical POR CV has been operational (2018-
2024) (Table 26).
To further quantify the distinct difference in observed ozone on wildfire smoke events compared
to non-events, mean MD8A and average diurnal hourly ozone are given for non-event and wildfire smoke
event days in Figure 115 and Figure 116, respectively. On average, measured MD8A ozone at CV is 6-8
ppb higher on wildfire smoke event days than on non-event days (Figure 115). Diurnal average hourly
ozone also reveals that the rate of ozone formation (dO3/dt) is much greater on wildfire smoke event days
than on non-event days (Figure 116). When the hourly ozone trend from the flagged event of July 24 is
compared with diurnal average hourly ozone concentrations of non-event, other wildfire events, and
across the 5-year period 2019-2023, it is evident that the ozone formation rate on July 24 was significantly
greater than what would be normally observed on non-event days and has similar trend characteristics as
on flagged wildfire event days (Figure 116 and Figure 117).

Figure 114 - MD8A Ozone 2019-2023 at CV Monitor

Figure 114. MD8A ozone (ppb) at the CV monitor for the 5-year period 2019-2023. Wildfire smoke flagged
EE’s (red circles) (July 12 and 24, 2021; August 7-8 and 16, 2021) and dates with flags for wildfire smoke
(orange circles) are highlighted. The July 24 flagged EE is outlined, showcasing the extremely high MD8A
ozone observed on that date compared to the 5-year period.

Table 26 - Top 10 CV POR Ranked MD8A (2018-2024)
Rank CV MD8A Date
1 96 2021-07-12
2 89 2021-08-08
3 87 2021-08-07

4 86 2021-08-16
5 85 2021-08-04
6 85 2021-09-08
7 85 2020-08-21
8 84 2021-07-11
9 83 2021-07-24
10 82 2020-07-11
Table 26. The top 10 ranked MD8A ozone at the CV monitor for the operational POR (2018-2023). The
wildfire smoke flagged EE of July 24 is ninth highest MD8A ever recorded (highlighted red) at CV. Other
flagged EE’s and wildfire impacted events compose almost all other top ranked spots (highlighted in
yellow).

Figure 115 - Non-Event and Event MD8A Ozone: NWF 2016-2023

Figure 115. Average Non-Event and Event MD8A ozone (ppb) for the period 2016-2023 at UDAQ monitors
within the SLV, including Hawthorne (HW), Copperview (CV), Bountiful (BV), Herriman (H3), and Rose Park
(RP). MD8A ozone is on average 5-8 ppb higher during wildfire events than non-wildfire events.

Figure 116 - Non-Event and Event Average Hourly Diurnal MD8A Ozone at CV Monitor

Figure 116. Non-Event, Event, and July 24 Event average diurnal hourly ozone at the CV monitor. The
ozone formation rate on Event days and the flagged July 24 Event is considerably steeper than non-events.

Figure 117 - Flagged Event Hourly Ozone vs. Average Hourly Diurnal MD8A Ozone at CV Monitor: 2016-
2021

Figure 117. Yearly (2018-2021) and July 24 Event average diurnal hourly ozone at the CV monitor. The
ozone formation rate on the flagged July 24 Event is considerably steeper than the average diurnal ozone
trends.

Wildfire Smoke and Ozone Formation: NOx and VOCs
In order to distinguish the contributions of smoke emissions to elevated ozone on July 24, we
detail the typical concentrations of key air quality parameters important to ozone formation on wildfire
smoke event days, non-event, and on the flagged date of July 24. NOx and VOC chemistry regimes related
to wildfire plumes are described in Section 4.1.5.3.
In Figure 118, the observed hourly concentrations of benzene, toluene, and xylene are shown for
a period centering on the flagged event date of July 24. The trend in the three VOC species closely
correlates with the wildfire smoke period of July 23-26, marking the arrival and clear out of smoke. All
three species increase sharply on July 23 when the first wave of wildfire smoke arrived in the SLV, and
peak near or on July 24-25 before decreasing sharply after July 26 as the smoke emissions cleared out
(Figure 118). Figure 119 presents the observed TNMOC through the same period and shows maxima in
the TNMOC correspond to the smoke period of July 23-26.
To determine how the ozone precursor concentrations on July 24 compare with other days, we
contrast the typical monitored VOC concentrations on non-event, flagged smoke event dates, the event
period of July 24, and a day of similar meteorology (July 22, 2021) (Figure 120). The VOC emissions on the
similar meteorology day of July 22 are highlighted in Figure 120, with VOC emissions notably lower,
compared to wildfire impacted flagged dates. Figure 120 shows wildfire event days have much greater
TNMOC and total VOC concentrations on average than non-event days, particularly on days of ozone
exceedances with wildfire smoke. Additionally, the observed average TNMOC and total VOCs on the July
24 event are on average higher than on non-event days and the comparable meteorology day of July 22,
2022.
Diurnal average trends provide insight as to how the temporal variability of total VOCs and
TNMOC on event days compare with non-events (Figure 121). A clear enhancement of VOCs and NOx is
observed on the flagged wildfire event of July 24 when compared to non-events and the comparable
meteorology day (Figure 121). The enhancement in VOCs (~30-100 ppb) is most pronounced in the
morning, early afternoon, and evening hours. In particular, during the July 24 flagged event TNMOC, and
total VOCs were significantly larger in the early to mid-morning hours and remained consistently elevated
above typical non-event concentrations through the course of the afternoon/evening. The decrease in
TNMOC, total VOCs, and NOx in the late morning and early afternoon coincides with peak ozone
production hours (0700-1300 MST) (Figure 122). The precursor emissions of NOx and VOCs are consumed
and depleted through ozone photochemistry. This titration of the precursor emissions, coinciding with
rapid growth in ozone concentrations, exhibits the significant impact the addition of wildfire smoke
emissions had on ozone concentrations on July 24 (Figure 122). As seen in Figure 116 and Figure 122,
ozone production rates (dO3/dt) are notably steeper during the flagged event period July 24 compared
with non-events and the day of similar meteorology, indicating ozone enhancement due to the altered
configuration of NOx and VOC emissions by smoke.
The VOC concentrations on the July 24 flagged event were larger than what is typically observed
in the SLV on non-event days (Figure 116). Xylene and toluene emissions within wildfire smoke plumes
have been noted to be relatively reactive species for ozone formation, making the addition of these
emissions impactful for ozone development (Wang et al., 2024; Ketcherside et al., 2024; Simms et al.,
2021). The SLV air shed is characterized by a transitional to VOC-limited regime, which makes ozone

photochemistry sensitive to increases or decreases in VOCs and NOx emissions (e.g. Gonzalez et al., 2024;
Jaffe et al., 2024). However, ozone formation has also been identified to be particularly sensitive to
increases in VOC emissions from wildfire smoke (Jaffe et al., 2024). Here, we show that wildfire smoke
injected supplementary VOC emissions into the urban SLV plume, creating an environment for ozone
enrichment. The altered ratio of VOC to NOx emissions due to the infiltration of the wildfire smoke plume
into the urban SLV air shed caused the extreme ozone exceedance on July 24.

Figure 118 - HW Average Daily VOCs: Jul-Aug

Figure 118. Daily average VOC concentrations of benzene, toluene, and xylene at the HW monitor for the
period July-August, 2021. The flagged wildfire smoke events (i.e. July 12, July 24, August 7 & 8, and August
16 are noted (vertical solid red lines) as well as periods of wildfire smoke (shaded red regions).
Additionally, the comparable meteorological day of July 22, 2021 is marked (vertical solid blue line).

Figure 119 - HW Average Daily TNMOC: Jul-Aug 2021

Figure 119. Daily average TNMOC concentrations at the HW monitor for the period July-August, 2021.
The flagged wildfire smoke events (i.e. July 12, July 24, August 7 & 8, and August 16 are noted (red stars)
as well as periods of wildfire smoke (shaded red regions). Additionally, the comparable meteorological
day of July 22, 2021 is marked (blue star).

Figure 120 - Event vs. Non-Event: Average Daily VOCs at HW: July 24, 2021

Figure 120. Average daily VOCs and TNMOC at the HW monitor for Non-Event (Exceedance No WF), Event
(Exceedance WF), Comparable Meteorology (Comparable MET – July 22), and the flagged July 24 Event
(WF Event: July 24) during the summer of 2021.

Figure 121 - Event vs. Non-Event: Average Hourly Diurnal Total VOCs, TNMOC, and NOx: July 24, 2021

Figure 121. Average diurnal hourly a.) VOCs, b.) TNMOC, and c.) NOx concentrations at the HW monitor
for Non-Event, Event, All wildfire days, July 24 Event, and Comparable Meteorology day (July 22) in the
summer of 2021.

Figure 122 - Event vs. Comparable MET: Hourly VOCs, NOx, and Ozone at HW and CV: July 24, 2021

Figure 122. Hourly VOCs, ozone, and NOx concentrations at the CV monitor for the a.) July 24 Event and
b.) Comparable Meteorology day (July 22).

Conceptual Model and Clear Causal Relationship: Smoke August 7-8,
2021
Wildfire Conditions: August 7-8, 2021
Extreme western U.S. drought conditions persisted in the week leading up to August 7 and 8
(Figure 123). In Figure 124, large scale ridging is shown to have dominated across the Western CONUS the
month preceding the August 7-8 flagged event, facilitating abnormally dry and hot conditions across the
Western U.S. (Figure 125 and Figure 126) leading up to the flagged EE of August 7-8. In Figure 123, the
U.S. Drought Monitor is given for the Western U.S. for the second first week of August, 2021, with a large
portion of the West under Extreme to Exceptional Drought (D3-D4) conditions. Given the extreme
drought, wildfire fuels were primed for ignition as shown by the high values of the Wildland Fire Potential

Index (WFPI)122 in the West derived August 7 and 8, 2021 in Figure 127. In early August, 2021, these
conditions led to high fire danger and various wildfires burned across the Western U.S., with a number of
large to medium sized fires noted to the west and north of Utah in California, Oregon, Washington, and
Idaho on August 7-8 (Figure 128). The major fires of concern burning on August 7-8 are shown in Figure
128 and noted in Table 27. The National Interagency Coordination Center Incident Management Situation
Report on August 7-8, 2021 is provided in Appendix A.

Figure 123 - Western U.S. Drought Monitor: August 2021

Figure 123. Drought monitor for the Western U.S. derived for the seven-day period ending on August 3rd,
2021123. Much of the West was under extreme to exceptional drought (D3-D4) at the time of the August
7 and 8 flagged EE events.

122 WFPI can be found at: https://firedanger.cr.usgs.gov/apps/staticmaps
123 U.S. Drought Monitor can be found at: https://droughtmonitor.unl.edu/

Figure 124 - NCEP Reanalysis Average 500 mb GPH: July 1 – August 8, 2021

Figure 124. NCEP Reanalysis Average 500 mb Geopotential Heights124 for the period July 1 - August 8,
2021. The presence of higher average 500 mb geopotential heights across the West indicate persistent
ridging in the month preceding August 8.
Figure 125 - PRISM July 2021 Precipitation Anomalies

124 NCEP Reanalysis Data can be found at: https://psl.noaa.gov/data/gridded/data.ncep.reanalysis.html

Figure 125. PRISM precipitation anomalies125 for July 1-30, 2021. Well below normal precipitation was
observed across the Western U.S. in the month prior to the August 7-8 event.

Figure 126 - PRISM July 2021 Temperature Anomalies

Figure 126. PRISM daily mean temperature anomalies126 for July 1-30, 2021. Well above normal
temperatures were observed across the Western U.S. in the month prior to the July 12 event.

125 PRISM data can be found at: https://prism.oregonstate.edu/graphics/
126 PRISM data can be found at: https://prism.oregonstate.edu/graphics/

Figure 127 - WFPI Forecast: August 7-8, 2021

Figure 127. Wildland Fire Potential Index (WFPI)127 for a.) August 7 and b.) August 8. Many areas in the
Western U.S. exceeded WFPI values of > 100, indicating a high potential for wildfires on the flagged event
date.

127 WFPI can be found at: https://firedanger.cr.usgs.gov/apps/staticmaps

Figure 128 - WFIGS Wildfire Perimeters: August 7-8, 2021

Figure 128. WFIGS Wildfire perimeters128 (> 10,000 acres) on August 7-8, 2021. Medium to large fires are
evident across the CA Sierras, central OR, NW ID, and SE WA.

Table 27 - Potential Wildfire Smoke Sources: August 7-8, 2021
Event Date Smoke Sources (potential) Fire Size
(Event - acres)
8/7-8/8/2021
Dixie fire, CA 434813
Haypress (River Complex) fire, CA 23121
Monument fire, CA 44317

128 WFIGS Wildfire Perimeters can be found at: https://data-
nifc.opendata.arcgis.com/search?tags=historic_wildlandfire_opendata%2CCategory

Mcfarland fire, CA 30093
Antelope fire, CA 41410
Tamarack fire, CA/NV 68696
Bootleg fire, OR 413765
Lick Creek fire, OR 80421
Snake River Complex, ID 109444
Black Butte Complex, OR 8612
Elbow Creek fire, OR 22960
Table 27. List of potential wildfire smoke sources contributing to smoke emissions at CV (devised from
forward and backward HYSPLIT trajectories) and the approximate size of the fires in acres129 on August 7-
8, 2021.

Meteorological Conditions
The flagged event of August 7-8 was characterized by a moderately active pattern. The large-scale
ridging that had dominated much of summer momentarily broke down when a compact and fast moving
upper-level short-wave trough punched south from the PNW into the northern Great Basin area (Figure
130 – Figure 135). On August 6, the upper-level low progressed into northern Utah (Figure 131 - Figure
134), bringing some elevated southern to northwesterly surface winds along with an attendant dry cold
front (Figure 129 and Figure 136a). The system lacked moisture but it had enveloped a mass wildfire
smoke within its cyclonic rotation from numerous fires in WA, ID, and CA (Figure 135a and Figure 135b).
As the upper-level trough progressed into Utah on the afternoon of August 6, upper and mid-level winds
shifted westerly to northerly, advecting a wall of accumulated smoke into the SLV (Figure 135a). The dry
cold frontal boundary slid south across northern Utah on afternoon of August 6 (Figure 136 - WPC Surface
Analysis: August 6-8, 2021 and Figure 137 - NOAA SPC Surface Pressure and Chart: August 6, 2021),
bringing cooler temperatures through the course of the afternoon and evening and a period elevated
northwesterly winds (Figure 129). Upper-level conditions quickly rebounded on August 7, and some
moderate ridging attempted to build back over Utah, with weak surface winds and clear skies observed
(Figure 131c and Figure 129). However, a residual cool air mass and marginally cooler conditions aloft
continued to suppress surface temperatures, and the observed highs across the SLV on August 7 were
nearly 10 degrees below average (Figure 129). The upper-level environment quickly shifted again as the
pattern remained fairly progressive and by August 8 an upper-level trough began to dig south from the
PNW and into the northern Rockies. The trough axis was oriented north-south over eastern WA, OR, and
CA (Figure 132b). This allowed mid and upper-level winds to shift more westerly to southwesterly over
Utah through the course of August 8 (Figure 132d and Figure 134d). At the surface, a frontal and a dry
boundary were draped across southern Idaho and northern Utah on the afternoon of August 8,
respectively (Figure 136c and Figure 138 - NOAA SPC Surface Pressure Chart: August 8, 2021). These boundaries
marched south across the SLV late on August 8, bringing the passage of another weak cold front and
additional smoke.
Soundings launched at KSLC show a relatively compressed PBL mixed layer on August 7 up to
about 720 mb (1.6 km AGL) and a very deep and mixed layer up to about 550 mb (~4.1km AGL) on the

129 Dataset of U.S. IMSR found at: https://research.fs.usda.gov/treesearch/67197

afternoon of August 8 (Figure 139). In Figure 56, the vertical wind profile exhibits lower to upper level
westerly to northwesterly winds on August 7 and westerly to southwesterly winds on August 8. The
evolution and associated impacts of the synoptic pattern is described in full detail in the National Weather
Surface (NWS) area forecast discussions (AFDs)130 for KSLC between August 6-8 (Appendix A). In general,
the NWS AFDs illuminate how the meteorological pattern influenced the transport of smoke into Utah.
For example, highlighted AFD text discussing the intrusion wildfire smoke into Utah on August 6-8 is given
below:

“Area Forecast Discussion
National Weather Service Salt Lake City UT
408 PM MDT Fri Aug 6 2021
.SYNOPSIS...Dry conditions are expected to prevail across the region as high pressure
begins to temporarily rebuild. An area of dense smoke will remain in place through at
least Saturday (August 7) with improvement expected over northern Utah, and generally
stable conditions across southern Utah. Another cold front will sweep through the
region Sunday with potential to bring more smoke into the area.”
. . .
Area Forecast Discussion
National Weather Service Salt Lake City UT
435 AM MDT Sun Aug 8 2021
.SYNOPSIS...Dry conditions are expected to prevail across the region today with areas
of smoke. Another cold front will sweep through the region late today, brining breezy
conditions along with the potential to bring more smoke into northern Utah. 131”

130 Archived NWS AFDs can be found at: https://mesonet.agron.iastate.edu/wx/afos/list.phtml
131 Archived NWS AFDs can be found at: https://mesonet.agron.iastate.edu/wx/afos/list.phtml

Figure 129 - CV Meteogram: August 7-8, 2021

Figure 129. Meteogram of observed sensible weather conditions at the CV monitor through the period
August 6-9, centered on the flagged event of August 7-8 (delineated by the red dashed lines.

Figure 130 - NCEP Reanalysis Average 500 mb GPH: August 7-8, 2021

Figure 130. NCEP Reanalysis Average 500 mb Geopotential Heights132 for the period August 7-8, 2021.

132 NCEP Reanalysis Data can be found at: https://psl.noaa.gov/data/gridded/data.ncep.reanalysis.html

Figure 131 - NOAA SPC 500 mb Upper Air Charts: August 7-8, 2021

Figure 131. NOAA-Storm Prediction Center133 upper air charts for 500 mb geopotential heights, winds,
temperature, and relative humidity on a.) August 6 at 1200Z, b.) August 6 2100Z, c.) August 7 2100Z, and
d.) August 8 2100Z.

133 NOAA-SPC Mesoscale Analysis Upper Air Charts can be found at: https://www.spc.noaa.gov/

Figure 132 - NOAA SPC 500 mb Upper Air Charts: Zoomed August 7-8, 2021

Figure 132. NOAA-Storm Prediction Center134 500 mb upper air charts zoomed over the Western U.S. for
a.) August 6 at 1200Z, b.) August 6 2100Z, c.) August 7 2100Z, and d.) August 8 2100Z.

134 NOAA-SPC Mesoscale Analysis Upper Air Charts can be found at: https://www.spc.noaa.gov/

Figure 133 - NOAA SPC 700 mb Upper Air Charts: August 7-8, 2021

Figure 133. NOAA-Storm Prediction Center135 upper air charts for 700 mb geopotential heights, winds,
temperature, and relative humidity on a.) August 6 at 1200Z, b.) August 6 2100Z, c.) August 7 2100Z, and
d.) August 8 2100Z.

135 NOAA-SPC Mesoscale Analysis Upper Air Charts can be found at: https://www.spc.noaa.gov/

Figure 134 - NOAA SPC 700 mb Upper Air Charts: Zoomed August 7-8, 2021

Figure 134. NOAA-Storm Prediction Center136 700 mb upper air charts zoomed over the Western U.S. for
a.) August 6 at 1200Z, b.) August 6 2100Z, c.) August 7 2100Z, and d.) August 8 2100Z.

136 NOAA-SPC Mesoscale Analysis Upper Air Charts can be found at: https://www.spc.noaa.gov/

Figure 135 - GFS Analyzed 500 mb GPH and Winds: August 7-8, 2021

Figure 135. GOES East True Color satellite imagery with overlaid analyzed GFS 500 mb geopotential
heights (m) and winds (kts) and the location of the CV monitor (yellow star) on a.) August 6 at 2100Z, b.)
August 7 at 00Z, c.) August 7 at 1500Z, and d.) August 8 at 1500Z zoomed over the Western U.S.

Figure 136 - WPC Surface Analysis: August 6-8, 2021

Figure 136. NOAA-Weather Prediction Center (WPC)137 surface analysis and IR satellite imagery for
zoomed over North America (left) the Western U.S. (right) - defined red bounding box for a.). August 6,
b.) August 7, and c.) August 8, 2021.

137 NOAA-WPC Surface Analysis Charts can be found at: https://www.wpc.ncep.noaa.gov/archives/web_pages/sfc/sfc_archive_maps.php

Figure 137 - NOAA SPC Surface Pressure and Chart: August 6, 2021

Figure 137. NOAA-Storm Prediction Center138 surface pressure chart and winds (kts) on August 6, 2021 at
1900Z for a.) the CONUS and b.) zoomed in across the Western U.S. A frontal boundary is revealed by the
surface pressure gradient and discontinuity in the wind direction present across northern Utah.

138 NOAA-SPC Mesoscale Analysis Upper Air Charts can be found at: https://www.spc.noaa.gov/

Figure 138 - NOAA SPC Surface Pressure Chart: August 8, 2021

Figure 138. NOAA-Storm Prediction Center139 surface pressure chart and winds (kts) on August 8, 2021 at
2100Z for a.) the CONUS and b.) zoomed in across the Western U.S.

139 NOAA-SPC Mesoscale Analysis Upper Air Charts can be found at: https://www.spc.noaa.gov/

Figure 139 - KSLC Radiosonde Soundings: August 7-8, 2021

Figure 139. Radiosonde soundings from KSLC on August 8, 2021 at a.) 12Z and b.) 00Z. A deep well mixed
PBL is evident in the 00Z sounding, with winds out of the west near and above 700 mb in both the morning
and afternoon soundings. Winds at lower levels were a mix of diurnal and mesoscale driven winds.

Wildfire Smoke: Remote Sensing and Ground-Based Analysis
The meteorological conditions on August 7 and August 8, 2021 facilitated the transport of wildfire
smoke from across the West into northern Utah. Visible satellite imagery reveals a large consolidated
mass of smoke was transported to the CV UDAQ monitor starting on August 6, with additional waves of
smoke arriving over the SLV on August 7 and August 8 (Figure 140 - Figure 148). Figure 140 - Figure 142
reveal the smoke extent and density across the Western U.S Low-level smoke that settled within the SLV
due to the nocturnal valley inversion is indicated in Figure 142, where smoke is shown to reside below the
mountain level along the northern Wasatch Front. In Figure 143 - Figure 145, visible satellite imagery

merged with the analyzed 500 mb upper-level wind field exhibits the pattern of transport of smoke from
areas north and west into northern Utah. The satellite imagery displays how the passage of multiple
upper-level troughs and cool fronts allowed the aggregate smoke plumes from numerous fires in
California north to Washington to be transported into northern Utah August 7-8. Vertical temperature
and wind profiles from soundings launched on August 7 and August 8 reveal a compressed and deep PBL
mixed layer in the SLV, respectively (Figure 139). This suggests wildfire emissions on August 7 had the
potential to accumulate in the lower levels, while the recapture and transport of smoke emissions from
aloft to the surface was possible on August 8.
Satellite AOD and HMS smoke field is shown to distinguish wildfire smoke density over Utah on
August 7-8 (Figure 149 - Figure 152). The analyzed AOD on August 7-8 distinguishes a dense smoke plume
over the SLV, with AOD values equal to 1 present over the SLV (Figure 149 and Figure 150). Synthesizing
the remote sensing imagery and analysis into one product, the HMS analyzed smoke fields show heavy
dense smoke plumes converged over the Northern Wasatch Front and the CV monitor from these fires on
both August 7 and August 8 (Figure 151 and Figure 152). The summarization of smoke field characteristics
observed by satellite imagery is given by the NOAA NEDIS smoke narrative140 published on August 7, 2021
at 2345Z. The smoke discussion notes thick and dense smoke across Utah from the wildfire activity in the
Western U.S.:

“DESCRIPTIVE TEXT NARRATIVE FOR SMOKE/DUST OBSERVED IN SATELLITE IMAGERY THROUGH 2345Z August 7, 2021
SMOKE:
Canada/U.S…
Smoke originating primarily from wildfires in the northwestern U.S., southern British Columbia and northern Manitoba continues to cover central and eastern Canada, and the majority of the Conterminous U.S. with the exception of the Atlantic coast region and parts of the southwestern U.S near the Mexican border. An area of heavy density smoke extends from California to central Canada, including Nevada, Utah, the northern Rockies and northern Great Plains, Saskatchewan, Manitoba, and southern Nunavut, while advancing eastward into Ontario.141”

A more detailed characterization of the magnitude and transport pattern of smoke from wildfires
across the West is given by the High-Rapid Refresh (HRRR) smoke model analysis in Figure 153 and Figure
154. In Figure 153a and Figure 154a, the August 7 18Z and August 8 18Z initialized HRRR total column
smoke density exhibits the extensive and dense shield of smoke across the Western U.S. and Utah (> 150
μg/m²). Additionally, the total column smoke density reveals well defined heavy plumes originating from
fire complexes scattered across the PNW and northern Sierras (Figure 153a and Figure 154) being
transported to Utah. A closer inspection of HRRR smoke is given in Figure 153b and Figure 154b, showing
dense surface level smoke (> 30 μg/m³) at the CV monitor August 7-8. In Figure 155, the BlueSky Smoke
model142 outlines the smoke plumes originating from the fires across the West on August 7-8, ultimately
forming a conglomerate mass of smoke over the entire region.
The presence of wildfire smoke as noted by satellite imagery and HRRR smoke across the Wasatch
Front is corroborated by surface observations of the aerosol optical depth (AOD) from the Aerosol Robotic
Network (AERONET) (Figure 156 - Figure 159). A larger or thicker AOD signifies more
attenuation/scattering of incident solar radiation through the column of the atmosphere and can be
correlated with the presence of wildfire smoke. We utilize AERONET Level 2 AOD143 (Pre- and post-field

140 NOAA NEDIS Smoke Narrative can be found at: https://www.ssd.noaa.gov/PS/FIRE/smoke.html
141 NOAA NEDIS Smoke Narrative can be found at: https://www.ssd.noaa.gov/PS/FIRE/smoke.html
142 BlueSky Modeling Framework can be found at: https://tools.airfire.org/websky/v2/#status 143 AERONET AOD data can be found at: https://aeronet.gsfc.nasa.gov/cgi-bin/data_display_aod_v3

calibration applied, automatically cloud cleared and manually inspected144) observations from the
NEON_ONAQ site, which is located approximately 40 miles due SW (40.17759 N, 112.45244 W) of the CV
monitor. Figure 156 - Figure 159 shows AOD ranging from < 0.2 before August 6 to 1-2 August 7-8 when
the smoke plume arrived across northern Utah. AOD values remained high through August 11 as smoke
continued to poor into the state. For reference on clear days with no smoke, AOD’s are < 0.1. The observed
AOD on the days following August 11 shows a sharp decrease to values < 0.2, indicating the dissipation
and clearing of the smoke plume from the area. Observations from ground-based cameras around the
SLV further verify the presence of near surface smoke across the valley August 6-8 (Figure 160). In Figure
160a and Figure 160f, the camera images from August 5 and August 11 represent relatively clear days
preceding and proceeding the flagged smoke event, respectively. Images in Figure 160b - Figure 160e
from the afternoons of August 6-8 show conditions during the flagged smoke event, with extremely
reduced visibility due to wildfire smoke emissions within the SLV.

Figure 140 - FIRMS Map: August 6, 2021

Figure 140. FIRMS Map145 with VIIRS S-NPP True Color Satellite imagery for August 6, 2021 overlaid with
satellite analyzed fire hotspots (red dots) and fire perimeter burned area (shaded light blue areas). A
focused area of heavy smoke is evident across the northern Rockies, with heavy smoke infiltrating Utah.

144 AERONET System description can be found at: https://aeronet.gsfc.nasa.gov/new_web/system_descriptions.html
145 FIRMS Fire Map can be found at: https://firms.modaps.eosdis.nasa.gov/usfs/map/#d:24hrs;@-100.0,40.0,4.0z

Figure 141 - FIRMS Map: August 7, 2021

Figure 141. FIRMS Map146 with VIIRS S-NPP True Color Satellite imagery for August 7, 2021 overlaid with
satellite analyzed fire hotspots (red dots) and fire perimeter burned area (shaded light blue areas). A large
band of medium to heavy smoke is evident across the Western U.S., extending into northern Utah.

146 FIRMS Fire Map can be found at: https://firms.modaps.eosdis.nasa.gov/usfs/map/#d:24hrs;@-100.0,40.0,4.0z

Figure 142 - FIRMS Map: August 8, 2021

Figure 142. FIRMS Map147 with VIIRS S-NPP True Color Satellite imagery for August 8, 2021 overlaid with
satellite analyzed fire hotspots (red dots) and fire perimeter burned area (shaded light blue areas).

147 FIRMS Fire Map can be found at: https://firms.modaps.eosdis.nasa.gov/usfs/map/#d:24hrs;@-100.0,40.0,4.0z

Figure 143 - GOES-East TrueColor Imagery with 500 mb GPH and Winds: August 6, 2021

Figure 143. GOES East True Color satellite imagery with overlaid analyzed GFS 500 mb geopotential
heights (m) and winds (kts) and satellite analyzed wildfire hotspots (red circles) on August 6, 2021 at
2100Z. The satellite imagery reveals a bullseye of heavy smoke being transported from fires located across
the West by the upper-level low into northern Utah.

Figure 144 - GOES-East TrueColor Imagery with 500 mb GPH and Winds: August 7, 2021

Figure 144. GOES East True Color satellite imagery with overlaid analyzed GFS 500 mb geopotential
heights (m) and winds (kts) and satellite analyzed wildfire hotspots (red circles) on August 7, 2021 at
2100Z. The satellite imagery reveals a large swath of smoke being transported into Utah from numerous
fires across the West.

Figure 145 - GOES-East TrueColor Imagery with 500 mb GPH and Winds: August 8, 2021

Figure 145. GOES East True Color satellite imagery with overlaid analyzed GFS 500 mb geopotential
heights (m) and winds (kts) and satellite analyzed wildfire hotspots (red circles) on August 8, 2021 at
2100Z. The satellite imagery reveals a large swath of smoke being transported into Utah from numerous
fires across the West.

Figure 146 – Smoke vs. Smoke Free Conditions: GOES East True Color - Utah August 7-8, 2021

Figure 146. GOES East True Color satellite imagery on a.) August 7 at 1500Z, b.) August 8 at 1500Z, and
c.) August 5, 2021 at 1800. In c.), key geographical landmarks are more visible due to the smoke free
skies.

Figure 147 - GOES-West TrueColor Imagery with Surface PM2.5: August 7, 2021

Figure 147. GOES West True Color Satellite imagery148 on August 7, 2021 at 1400Z for a.) the Western U.S.
and b.) zoomed over Utah (red bounding box in a.)).

148 NOAA-Aerosol Watch Satellite imagery can be found at: https://www.star.nesdis.noaa.gov/smcd/spb/aq/AerosolWatch/

Figure 148 - GOES-West TrueColor Imagery with Surface PM2.5: August 8, 2021

Figure 148. GOES West True Color Satellite imagery149 on August 8, 2021 at 1400Z for a.) the Western U.S.
and b.) zoomed over Utah (red bounding box in a.)).

149 NOAA-Aerosol Watch Satellite imagery can be found at: https://www.star.nesdis.noaa.gov/smcd/spb/aq/AerosolWatch/

Figure 149 - GOES-West AOD Composite 15-18Z: August 7, 2021

Error! Reference source not found.. GOES West satellite derived Aerosol Optical Depth (AOD)150 August
7, 2021 for a.) the Western U.S., and b.) zoomed in over northern Utah. AOD values of 1 were observed
over the SLV, indicating the presence of dense wildfire smoke attenuating incoming solar radiation.

150 Aerosol Watch AOD product can be found at: https://www.star.nesdis.noaa.gov/smcd/spb/aq/AerosolWatch/index.php

Figure 150 - GOES-West AOD Composite 15-18Z: August 8, 2021

Figure 150. GOES West satellite derived Aerosol Optical Depth (AOD)151 August 8, 2021 for a.) the Western
U.S., and b.) zoomed in over northern Utah. AOD values of 1 were observed over the SLV, indicating the
presence of dense wildfire smoke attenuating incoming solar radiation.

151 Aerosol Watch AOD product can be found at: https://www.star.nesdis.noaa.gov/smcd/spb/aq/AerosolWatch/index.php

Figure 151 - HMS Smoke Fields and WFIGS Wildfire Perimeters: August 7, 2021

Figure 151. HMS smoke fields152 with WFIGS Wildfire perimeters153 across the Western U.S. on August 7,
2021.

152 HMS Smoke Field data can be found at: https://www.ospo.noaa.gov/products/land/hms.html#0
153 WFIGS Wildfire Perimeters can be found at: https://data-
nifc.opendata.arcgis.com/search?tags=historic_wildlandfire_opendata%2CCategory

Figure 152 - HMS Smoke Fields and WFIGS Wildfire Perimeters: August 8, 2021

Figure 152. HMS smoke fields154 with WFIGS Wildfire perimeters155 across the Western U.S. on August 8,
2021.

154 HMS Smoke Field data can be found at: https://www.ospo.noaa.gov/products/land/hms.html#0
155 WFIGS Wildfire Perimeters can be found at: https://data-
nifc.opendata.arcgis.com/search?tags=historic_wildlandfire_opendata%2CCategory

Figure 153 - HRRR Smoke VIS and NSFC Smoke: August 7, 2021

Figure 153. HRRR-NCEP smoke fields on August 7, 2021 at 18Z of a.) total column smoke (vertically
integrated) over the CONUS and b.) near-surface level smoke focused over Utah. Both vertically integrated
and surface level smoke reveal heavy-dense smoke over the CV monitor (yellow star).

Figure 154 - HRRR Smoke VIS and NSFC Smoke: August 8, 2021

Figure 154. HRRR-NCEP smoke fields on August 8, 2021 at 18Z of a.) total column smoke (vertically
integrated) over the CONUS and b.) near-surface level smoke focused over Utah. Both vertically integrated
and surface level smoke reveal heavy-dense smoke over the CV monitor (yellow star).

Figure 155 - BlueSky Dispersion Analysis: August 7-8, 2021

Figure 155. BlueSky Daily Smoke Dispersion model run156 (GFS 0.5 deg and 0.15 deg dispersion) from a.)
August 7 and b.) August 8, 2021 at 21Z. Satellite analyzed fire hotspots are overlaid (red flames) along
with the location of the CV monitor (yellow star pin). A large swath of wildfire smoke is indicated across
the Western U.S. and over the CV monitor.

156 BlueSky Modeling Framework can be found at: https://tools.airfire.org/websky/v2/#status

Figure 156 - AERONET Level 2 AOD: August, 2021

Figure 156. AERONET derived Level 2 AOD157 from the NEON_ONAQ site (40 miles SW of the CV monitor)
for the month of August 2021. Periods preceding, during, and after the flagged smoke event are noted,
with corresponding AOD. Increased AOD values, signaling the presence of wildfire smoke, are apparent
on July 9-12 compared to preceding and proceeding dates.

157 AERONET AOD data can be found at: https://aeronet.gsfc.nasa.gov/cgi-bin/data_display_aod_v3

Figure 157 - AERONET Level 2 AOD: August 6, 2021

Figure 157. a.) AERONET derived Level 2 AOD158 from the NEON_ONAQ site (40 miles SW of the CV
monitor) on the flagged event date of July 12 and b.) Terra MODIS True Color satellite imagery on August
6 overlaid with the NEON_ONAQ site location (orange circle) and CV monitor location (yellow star). AOD
values > 5 on August 6 signal the presence of wildfire smoke.

158 AERONET AOD data can be found at: https://aeronet.gsfc.nasa.gov/cgi-bin/data_display_aod_v3

Figure 158 - AERONET Level 2 AOD: August 7, 2021

Figure 158. a.) AERONET derived Level 2 AOD159 from the NEON_ONAQ site (40 miles SW of the CV
monitor) on the flagged event date of July 12 and b.) Terra MODIS True Color satellite imagery on August
7 overlaid with the NEON_ONAQ site location (orange circle) and CV monitor location (yellow star). AOD
values 0.7-1.1 on August 7 signal the presence of wildfire smoke.

159 AERONET AOD data can be found at: https://aeronet.gsfc.nasa.gov/cgi-bin/data_display_aod_v3

Figure 159 - AERONET Level 2 AOD: August 8, 2021

Figure 159. a.) AERONET derived Level 2 AOD160 from the NEON_ONAQ site (40 miles SW of the CV
monitor) on the flagged event date of August 8 and b.) Terra MODIS True Color satellite imagery on August
8 overlaid with the NEON_ONAQ site location (orange circle) and CV monitor location (yellow star). AOD
values ~2.0 on August 8 signal the presence of wildfire smoke.

160 AERONET AOD data can be found at: https://aeronet.gsfc.nasa.gov/cgi-bin/data_display_aod_v3

Figure 160 - MESOWEST WBB Camera Images: August 6-8, 2021

Figure 160. MESOWEST WBBS camera images from a.) August 5 at 1800 MST, b.) August 6 at 0930 MST,
c.) August 6 at 1500 MST, d.) August 7 at 1500 MST, e.) August 8 at 1500 MST, and f.) August 11 at 1520.
The camera is located on the University of Utah campus at the north end of the SLV and faces to the west.
Images a.) and f.) represent conditions on “relatively” smoke free days, with images in b.)- e.) representing
the smoke impacted conditions August 6-8, 2021.
HYSPLIT: Wildfire Smoke Transport to CV Monitor
The August 7-8 flagged event was part of extended period of wildfire smoke that inundated the
SLV from about August 6-20, 2021. In the previous section, the synoptic pattern suggests the transport of
smoke plumes from wildfires across the PNW and northern Sierra to the CV monitor was possible (Table
27). To obtain a more detailed representation of the possible transport paths and all potential smoke

sources that contributed to the observed wildfire smoke emissions on August 7-8 at the CV monitor,
HYSPLIT multiple particle forward and backward trajectory analysis was performed using methods
described in Section 4.1.4.
The first two HYSPLIT model configurations chosen were the backward ensemble and frequency
trajectory options, with parcels starting at model derived mid-boundary layer height (Figure 161a - Figure
162a). Trajectory starting/ending heights, where applicable, were chosen at the mid-boundary layer to
provide information on air parcels residing within the PBL mixed-layer and ultimately impacting the
surface.
In Figure 161a - Figure 162a, 60-hour ensemble backward trajectories beginning at the CV monitor
on the afternoon of August 7 and morning and afternoon of August 8 are shown. The HMS smoke fields
and VIIRS analyzed wildfire hotspots are also include in Figure 161a - Figure 162a to help distinguish the
potential source regions of wildfire smoke that impacted the CV monitor. By selecting the ensemble
configuration, a robust characterization of potential source areas of air parcels arriving at various levels
above the CV monitor on August 7-8 is given. Figure 161a - Figure 162a reveal multiple trajectories ending
at CV on August 7 and August 8 originated or passed over a number of fires in CA, OR, WA, and ID. These
trajectory paths are consistent with the upper-level synoptic environment identified in the previous
section, and showcase how multiple wildfires contributed to the smoke emissions observed August 7-8 in
the SLV. In Figure 161b - Figure 162b, the 60-hour backward trajectory frequencies are provided, with
areas of highest trajectory frequencies corresponding to locations of active wildfires in northern CA, OR,
WA, and ID. The frequency plot suggests that the smoke plume over the CV monitor on August 7-8 was
an aggregate smoke mass composed of smoke sourced from multiple wildfire sources across the Western
U.S. In general, frequency and ensemble trajectories show air parcels mainly originating from fires
highlighted in Table 27.
Investigation of smoke transport from a few select fires to the SLV employs multi-particle forward
ensemble and frequency HYSPLIT trajectories (Figure 163 - Figure 165). The integration periods for the
forward trajectories was varied between 48-72 hours depending on the fire and distance to the CV
monitor, with trajectories starting at mid-PBL height for all simulations to replicate smoke lofted into the
PBL. In Figure 163a and Figure 165a, both the 48-hour forward ensemble and frequency trajectories
starting at the Dixie, CA fire reveal a well-defined west to east transport pattern from the fire to the SLV
over the period of August 5 to the morning of August 7. Similarly, trajectories launched from the Bootleg
Fire on the morning of August 5 show a distinctive NW to SE transport path to the SLV by the afternoon
of August 8 (Figure 165b). These trajectory patterns correspond well with the upper-level flow field and
passage of short-wave troughs across the Western U.S. during the event period as described in the
previous section.
The forward ensemble and frequency trajectory paths from the wildfires mentioned align well
with transport patterns outlined by backward trajectories from the CV monitor. Additionally, the spatial
variability, magnitude, and suggested plume transport from the satellite imagery and HRRR/BlueSky
modeled smoke dispersion output described in the previous section verifies well with the HYSPLIT forward
and backward trajectory analysis highlighted in this section. The corroboration of these analysis adds
confidence that wildfire smoke was transported from regional wildfire sources (Table 27) during the
period August 5-8 to the CV monitor.

Figure 161 - HYSPLIT 60-hr Ensemble Backward and Frequency Traj: August 7, 2021 21Z

Figure 161. HYSPLIT 60-hr Backward a.) Ensemble and b.) Frequency Trajectories starting at the CV
monitor at mid-PBL height on August 7, 2021 at 18Z. The CV monitor is noted (yellow star).

Figure 162 - HYSPLIT 60-hr Ensemble Backward and Frequency Traj: August 8, 21Z

Figure 162. HYSPLIT 60-hr Backward a.) Ensemble and b.) Frequency Trajectories starting at the CV
monitor at mid-PBL height on August 8, 2021 at 18Z. The CV monitor is noted (yellow star).

Figure 163 – Dixie and Bootleg Fires; HYSPLIT 48-hr Ensemble Forward Traj: August 7, 15Z and 18Z

Figure 163. HYSPLIT 48-hr Froward Ensemble Trajectories starting at the a.) Bootleg, OR and b.) Dixie, CA
fire at mid-PBL height on August 5, 2021 at 15Z and 18Z, respectively. The CV monitor is noted (yellow
star).

Figure 164 – Antelope and Bootleg Fires; HYSPLIT 72-hr and 48-hr Ensemble Forward Traj: August 8, 15Z

Figure 164. HYSPLIT 48-hr Froward Ensemble Trajectories starting at the a.) Antelope, CA and b.)
Bootleg, OR fire at mid-PBL height on August 6, 2021 at 15Z, respectively. The CV monitor is noted
(yellow star).

Figure 165 – Dixie and Bootleg Fires; HYSPLIT 48-hr and 60-hr Ensemble Forward Traj: August 7, 15Z and
August 8, 18Z

Figure 165. HYSPLIT 48-hr Froward Frequency Trajectories starting at the a.) Bootleg, OR and 60-hr
Forward Frequency Trajectories starting at the b.) Dixie, CA fire at mid-PBL height on August 4 and 5,
2021 at 21Z and 12Z, respectively. The CV monitor is noted (yellow star)
Wildfire Smoke Emissions and Ozone Exceedance: Clear Causal Relationship
In this section, we conduct PM2.5, brown carbon, and ozone analysis as described in Section 4.1.5.
Surface Smoke Observations and Historical Monitor Comparison
UDAQ CV monitor hourly and daily (24-hr average) PM2.5 observations indicate the progression
of surface particulate concentrations from relatively smoke free conditions on August 1-2, to periods of

wildfire smoke August 6-8 (Figure 166 and Figure 167). As seen in Figure 166, the largely smoke free days
preceding the August 6-8 smoke event (e.g. August 1-2) saw daytime PM2.5 hourly concentrations ranging
5-10 µg/m3. In comparison, during the smoke impacted period the maximum hourly PM2.5 concentrations
observed during the flagged event of August 7 and August 8 ranged from about 30-65 µg/m3 and 30-55
µg/m3, respectively, indicating that significant enhancement of PM2.5 by wildfire smoke emissions
occurred August 7-8. Trends in the observed monitored daily PM2.5 concentrations reveal a similar story
of PM2.5 enhancement by wildfire smoke, with a daily PM2.5 value of 42.8 µg/m3 on August 7 and 49.5
on August 8 (Figure 167). When compared to PM2.5 concentrations at CV over the 5-year period of 2019-
2021, the August 7 and August 8 daily PM2.5 concentrations (42.8 and 49.5 µg/m3) exceed the 5-year
month’s specific 24-hr PM2.5 98th percentile161 value of 26.2 µg/m3 by nearly 15-25 µg/m3 (Figure 167).
Figure 166 and Figure 167 displays the marked departure of the monitored daily PM2.5 on the flagged
event date from the 5-year (2019-2023) month’s daily averages (excluding the fire year 2021), with 24-hr
average PM2.5 observations on the August 7-8 event ~7-8 times larger than the typical values for this
period.
In Figure 168, delta-c concentrations are shown for a period surrounding the August 7-8 flagged
smoke event. Elevated concentrations of delta-c are observed during the smoke period of August 6-13,
peaking on August 6 as the first wave of wildfire smoke inundated the area (>10,000 ng/m3) then slightly
decreasing on August 7-8 but remaining significantly heightened (2000-4500 ng/m3) (Figure 76). Lower
delta-c concentrations are noted in the days prior to August 6 when periods of very light wildfire smoke
were observed. Because delta-c is an unambiguous indicator of biomass burning, the enhanced delta-c
observations on the flagged event date undisputedly indicate the residence of surface-level wildfire
smoke in the SLV on August 7-8. Table 28 provides the average delta-c concentrations for the 5-year
(2019-2023) month’s daily averages compared to concentrations observed during the flagged event, with
the observed delta-c on August 7-8 ~15-20 times larger than average.
Figure 166 – CV Hourly PM2.5: August 7-8, 2021

161 EPA PM2.5 Tiering Tool: https://www.epa.gov/air-quality-analysis/pm25-tiering-tool-exceptional-events-analysis

Figure 166. Monitored hourly PM2.5 concentrations at CV for the period August 1-13, 2021, centered on
August 7-8 (vertical dashed-red lines). Increased hourly PM2.5 concentrations (~30-65 µg/m3) associated
with the smoke is evident August 7-8.

Figure 167 - CV Monitored 24-hr PM2.5 and MD8A Ozone: August 7-8, 2021

Figure 167. Daily (24-hr avg) PM2.5 (right axis) and MD8A ozone (left axis) observed at the CV monitor for
the period August 1-14, 2021, centered on August 7-8 flagged event. Trends in daily PM2.5 and MD8A
ozone correspond well with each other, revealing the close connection between the presence of wildfire
smoke emissions and enhanced ozone formation.

Figure 168 - Hourly Brown Carbon (BrC) Concentrations: August 7-8 2021

Figure 168. Monitored hourly BrC concentrations at CV for the period August 4-11, 2021, centered on
August 7-8 (vertical red lines) from the Bountiful (BV), Inland Port (IP), and Lake Park (LP) UDAQ
monitoring sites. Increased hourly BrC concentrations (2000-4500 ng/m3) associated with smoke is
evident on August 7-8.

Table 28 - Average Brown Carbon (BrC) Concentrations July 2019-2023: August 7-8 2021
Station 2019 2020 2021 2022 2023 Average August 7
Event Avg.
August 8
Event Avg.
Bountiful 134 163 280 112 77 153 2525 1765
Inland
Port -- -- 303 66 71 147 3090 2115
Lake Park -- -- 262 131 92 162 3468 --
Table 28. 5-year month’s specific (July 2019-2023) average BrC concentrations from the Bountiful (BV),
Inland Port (IP), and Lake Park (LP) UDAQ monitoring sites, with the daily BrC concentration for the flagged
event day of August 7-8 is also given.

Event and non-event Ozone
The presence of surface-level wildfire smoke at the CV monitor has been established in the prior
sections. Here, we show how the addition of wildfire smoke emissions into the SLV airshed caused the
ozone exceedance at the CV monitor. Daily PM2.5 and MD8A ozone concentrations also exhibit a close
positive relationship, where the local MD8A ozone maximum corresponds with the local maxima of PM2.5
(Figure 167). It has been established by prior studies that PM2.5 can be used to indicate the potential
magnitude of ozone enhancement by wildfire smoke (e.g. Buysse et al. 2019; Ninneman and Jaffe, 2021).
In the case of August 7-8, both hourly and daily observed PM2.5 concentrations were within the moderate
range and correspond with PM2.5 concentrations that correlate with ozone enhancement from wildfire
smoke emissions (Figure 166 and Figure 167).
In Figure 169, the MD8A ozone at CV is given for the 5-year period 2019-2023 in order to highlight
monitored flagged wildfire smoke MD8A ozone relative to non-events. Compared to the 5-year period
MD8A ozone concentrations at CV, the MD8A values August 7 and August 8 of 87 and 89 ppb, respectively,
are higher than the 98th and 99th MD8A percentile, but is also second and third ranked observed MD8A in
the 5-year period (Figure 169). Furthermore, the observed MD8A on August 7 and August 8 are also the
second and third ranked observed MD8A in the complete historical POR CV has been operational (2018-
2024) (Table 29). To further quantify the distinct difference in observed ozone on wildfire smoke events
compared to non-events, mean MD8A and average diurnal hourly ozone are given for non-event and
wildfire smoke event days in Figure 170 and Figure 171, respectively. On average, measured MD8A ozone
at CV is 6-8 ppb higher on wildfire smoke event days than on non-event days (Figure 170). Diurnal average
hourly ozone also reveals that the rate of ozone formation (dO3/dt) is much greater on wildfire smoke
event days than on non-event days (Figure 171). When the hourly ozone trend from the flagged event of
August 7-8 is compared with diurnal average hourly ozone concentrations of non-event and wildfire

events and across the 5-year period 2019-2023, it is evident that the ozone formation rate August 7 and
August 8 was significantly greater than what would be normally observed on non-event days and has
similar trend characteristics as on flagged wildfire event days (Figure 172). Interestingly, hourly ozone
concentrations the night of August 7 into the morning of August 8 remained elevated well above normal
average concentrations for non-events. The overnight elevated ozone concentrations could be indicative
of transported ozone from aloft to the surface as smoke emissions settled into the SLV as indicated in
Figure 142.
Figure 169 - MD8A Ozone 2019-2023 at CV Monitor

Figure 169. MD8A ozone (ppb) at the CV monitor for the 5-year period 2019-2023. Wildfire smoke flagged
EE’s (red circles) (July 12 and 25, 2021; August 7-8 and 16, 2021) and dates with flags for wildfire smoke
(orange circles) are highlighted. The August 7-8 flagged EE is outlined, showcasing the extremely high
MD8A ozone observed on that date compared to the 5-year period.

Table 29 - Top 10 CV POR Ranked MD8A (2018-2024)
Rank CV MD8A Date
1 96 2021-07-12
2 89 2021-08-08
3 87 2021-08-07
4 86 2021-08-16
5 85 2021-08-04
6 85 2021-09-08
7 85 2020-08-21
8 84 2021-07-11
9 83 2021-07-24
10 82 2020-07-11
Table 29. The top 10 ranked MD8A ozone at the CV monitor for the operational POR (2018-2023). The
wildfire smoke flagged EE of August 7-8 are the second and third highest MD8A ever recorded (highlighted
red) at CV. Other flagged EE’s and wildfire impacted events compose almost all other top ranked spots
(highlighted in yellow).

Figure 170 - Non-Event and Event MD8A Ozone: NWF 2016-2023

Figure 170. Average Non-Event and Event MD8A ozone (ppb) for the period 2016-2023 at UDAQ monitors
within the SLV, including Hawthorne (HW), Copperview (CV), Bountiful (BV), Herriman (H3), and Rose Park
(RP). MD8A ozone is on average 5-8 ppb higher during wildfire events than non-wildfire events.

Figure 171 - Non-Event and Event Average Hourly Diurnal MD8A Ozone at CV Monitor: August 7-8

Figure 171. Non-Event, Event, and the August 7-8 Event average diurnal hourly ozone at the CV monitor.
The ozone formation rate on Event days and the flagged July 12 Event is considerably steeper than non-
events.
Figure 172 - Flagged Event Hourly Ozone vs. Average Hourly Diurnal MD8A Ozone at CV Monitor 2016-
2021: August 7-8

Figure 172. Yearly (2018-2021) and the August 7-8 Event average diurnal hourly ozone at the CV monitor.
The ozone formation rate on the flagged August 7-8 Event is considerably steeper than the average diurnal
ozone trends.

Wildfire Smoke and Ozone Formation: NOx and VOCs
In order to distinguish the contributions of smoke emissions to elevated ozone on August 7-8, we
detail the typical concentrations of key air quality parameters important to ozone formation on wildfire
smoke event days, non-event, and on the flagged date of August 7-8. NOx and VOC chemistry regimes
related to wildfire plumes are described in Section 4.1.5.3.
In Figure 173, the observed hourly concentrations of benzene, toluene, and xylene are shown for
a period centering on the flagged event date of August 7-8. The trend in the three VOC species closely
correlates with the wildfire smoke period August 6-20, marking the arrival and clear out of smoke. All
three species increase sharply on August 6 when the first wave of wildfire smoke arrived in the SLV, peak
near or on August 7-8, remain elevated through August 19, and decrease sharply after August 20 as the
smoke emissions cleared out (Figure 173). Figure 174 presents the observed TNMOC through the same
period and shows maxima in the TNMOC correspond to the smoke period of August 6-20.
To determine how the ozone precursor concentrations on August 7-8 compare with other days,
we contrast the typical monitored VOC concentrations on non-event, flagged smoke event dates, the
event period of August 7-8, and a day of similar meteorology (July 22, 2021) (Figure 175). The VOC
emissions on the similar meteorology day of July 22 are highlighted in Figure 175, with VOC emissions
notably lower, compared to wildfire impacted flagged dates. Figure 175 shows wildfire event days have
much greater TNMOC and total VOC concentrations on average than non-event days, particularly on days
of ozone exceedances with wildfire smoke. Additionally, the observed average TNMOC and total VOCs on
the August 7-8 event are on average higher than on non-event days and the comparable meteorology day
of July 22, 2022 (Figure 175).
Diurnal average trends provide insight as to how the temporal variability of total VOCs and
TNMOC on event days compare with non-events (Figure 176). A clear enhancement of VOCs and slightly
elevated NOx is observed on the flagged wildfire event of August 7 when compared to non-events and
the comparable meteorology day (Figure 176). On August 8, elevated VOCs are also observed but NOx is
near or below concentrations found on the comparable meteorology day (except in the evening hours).
The enhancement in VOCs (~20-60 ppb) is most pronounced in the morning, early afternoon, and evening.
In particular, during the flagged event period of August 7-8 TNMOC, and total VOCs were significantly
larger in the early to mid-morning hours and remained consistently elevated above typical non-event
concentrations through the course of the afternoon/evening. The decrease in TNMOC, total VOCs, and
NOx in the late morning and early afternoon coincides with peak ozone production hours (0700-1300
MST) (Figure 177). The precursor emissions of NOx and VOCs are consumed and depleted through ozone
photochemistry. This titration of the precursor emissions, coinciding with rapid growth in ozone
concentrations, exhibits the significant impact the addition of wildfire smoke emissions had on ozone
concentrations on August 7-8 (Figure 177). As seen in Figure 171 and Figure 177, ozone production rates
(dO3/dt) are notably steeper during the flagged event period August 7-8 compared with non-events and
the day of similar meteorology, indicating ozone enhancement due to the altered configuration of NOx
and VOC emissions by smoke.
The VOC concentrations on the August 7-8 flagged event were larger than what is typically
observed in the SLV on non-event days (Figure 176). Xylene and toluene emissions within wildfire smoke
plumes have been noted to be relatively reactive species for ozone formation, making the addition of

these emissions impactful for ozone development (Wang et al., 2024; Ketcherside et al., 2024; Simms et
al., 2021). The SLV air shed is characterized by a transitional to VOC-limited regime, which makes ozone
photochemistry sensitive to increases or decreases in VOCs and NOx emissions (e.g. Gonzalez et al., 2024;
Jaffe et al., 2024). However, ozone formation has also been identified to be particularly sensitive to
increases in VOC emissions from wildfire smoke (Jaffe et al., 2024). NOx concentrations during the wildfire
period were higher on August 7 but marginally lower on August 8 compared to non-event days (Figure
176c), which could indicate the complexity of the SLV air shed ozone sensitivity to NOx emissions. Here,
we show that wildfire smoke injected supplementary VOC and NOx (to some extent) emissions into the
urban SLV plume, creating an environment for ozone enrichment. The altered ratio of VOC to NOx
emissions, due to the infiltration of the wildfire smoke plume into the urban SLV air shed, caused the
extreme ozone exceedances on August 7-8.
Figure 173 - HW Average Daily VOCs: Jul-Aug

Figure 173. Daily average VOC concentrations of benzene, toluene, and xylene at the HW monitor for the
period July-August, 2021. The flagged wildfire smoke events (i.e. July 12, July 24, August 7 & 8, and August
16 are noted (vertical solid red lines) as well as periods of wildfire smoke (shaded red regions).
Additionally, the comparable meteorological day of July 22, 2021 is marked (vertical solid blue line).

Figure 174 - HW Average Daily TNMOC: Jul-Aug 2021

Figure 174. Daily average TNMOC concentrations at the HW monitor for the period July-August, 2021.
The flagged wildfire smoke events (i.e. July 12, July 24, August 7 & 8, and August 16 are noted (red stars)
as well as periods of wildfire smoke (shaded red regions). Additionally, the comparable meteorological
day of July 22, 2021 is marked (blue star).

Figure 175 – Event vs. Non-Event: Average Daily VOCs at HW

Figure 175. Average daily VOCs and TNMOC at the HW monitor for Non-Event (Exceedance No WF), Event
(Exceedance WF), Comparable Meteorology (Comparable MET – July 22), and the flagged August 7-8
Event (WF Event: August 7 & 8) during the summer of 2021.

Figure 176 – Event vs. Non-Event: Average Hourly Diurnal Total VOCs, TNMOC, and NOx: August 7-8

Figure 176. Average diurnal hourly a.) VOCs, b.) TNMOC, and c.) NOx concentrations at the HW monitor
for Non-Event, Event, All wildfire days, August 7-8 Event, and Comparable Meteorology day (July 22) in
the summer of 2021.

Figure 177 – Event vs. Comparable MET: Hourly VOCs, NOx, and Ozone at HW and CV: August 7-8

Figure 177. Hourly VOCs, ozone, and NOx concentrations at the CV monitor for the a.) August 7, b.) August
8 Event, and b.) Comparable Meteorology day (July 22).

Conceptual Model and Clear Causal Relationship: Smoke Event
August 16, 2021
Wildfire Conditions: August 16, 2021
In the week leading up to August 16, the Western U.S. continued to experience extreme drought
(Figure 178). In Figure 179, large scale ridging is shown to have dominated across the Western CONUS the
month preceding the July 16 flagged event, facilitating abnormally dry and hot conditions across the
Western U.S. (Figure 180 and Figure 181) leading up to the flagged EE date on August 16. In Figure 178,
the U.S. Drought Monitor is given for the Western U.S. for the second week of August, 2021, with a large
portion of the West under Extreme to Exceptional Drought (D3-D4) conditions. Given the extreme
drought, wildfire fuels were primed for ignition as shown by the high values of the Wildland Fire Potential
Index (WFPI)162 in the West derived on August 16, 2021 in Figure 182. In mid-August, 2021, these
conditions led to high fire danger and various wildfires burned across the Western U.S., with a number of
large to medium sized fires noted to the west and north of Utah in California, Oregon, Washington,
Montana, and Idaho on August 16 (Figure 183). The major fires of concern burning on August 16 are
shown in Figure 183 and noted in Table 30. The National Interagency Coordination Center Incident
Management Situation Report on August 16, 2021 is provided in Appendix A.
Figure 178 - Western U.S. Drought Monitor: August 2021

162 WFPI can be found at: https://firedanger.cr.usgs.gov/apps/staticmaps

Figure 178. Drought monitor for the Western U.S. derived for the seven-day period ending on August
17, 2021163. Much of the West was under extreme to exceptional drought (D3-D4) at the time of the July
24 flagged EE event.

Figure 179 - NCEP Reanalysis Average 500 mb GPH: August 16, 2021

Figure 179. NCEP Reanalysis Average 500 mb Geopotential Heights164 for the period July 1 - August 16,
2021. The presence of higher average 500 mb geopotential heights across the West indicate persistent
ridging in the month preceding August 16.

163 U.S. Drought Monitor can be found at: https://droughtmonitor.unl.edu/
164 NCEP Reanalysis Data can be found at: https://psl.noaa.gov/data/gridded/data.ncep.reanalysis.html

Figure 180 - PRISM July 2021 Precipitation Anomalies

Figure 180. PRISM precipitation anomalies165 for August 1-30, 2021. Well below normal precipitation was
observed across the Western U.S. in the month of the August 16 event.
Figure 181 - PRISM July 2021 Temperature Anomalies

Figure 181. PRISM daily mean temperature anomalies166 for August 1-30, 2021. Well above normal
temperatures were observed across the Western U.S. in the month of the August 16 event.

165 PRISM data can be found at: https://prism.oregonstate.edu/graphics/
166 PRISM data can be found at: https://prism.oregonstate.edu/graphics/

Figure 182 – WFPI: August 16, 2021

Figure 182. Wildland Fire Potential Index (WFPI)167 for August 16, 2021. Many areas in the Western U.S.
exceeded WFPI values of 90-100, indicating a high potential for wildfires on the flagged event date.

167 WFPI can be found at: https://firedanger.cr.usgs.gov/apps/staticmaps

Figure 183 - WFIGS Wildfire Perimeters: August 16, 2021

Figure 183. WFIGS Wildfire perimeters168 (> 10,000 acres) on August 16, 2021.

Table 30 - Potential Wildfire Smoke Sources: August 16, 2021
Event Date Wildfire Smoke Sources (potential) Fire Size
(Event - acres)
8/16/2021 Dixie fire, CA 570211
Haypress (River Complex) fire, CA 41031

168 WFIGS Wildfire Perimeters can be found at: https://data-
nifc.opendata.arcgis.com/search?tags=historic_wildlandfire_opendata%2CCategory

Monument fire, CA 85076
Mcfarland fire, CA 43708
Antelope fire, CA 53864
Tamarack fire, CA/NV 68637
Lick Creek fire, OR 80421
Schneider Springs fire, WA 16516
Snake River Complex, ID 10944
Trail Creek, MT 37,412
Alder Creek, MT 13,011
Dixie, ID 43,344
Summit Trail, OR 29,205
Little Bend Creek (Rough Patch Cpx), OR 12280
Bedrock fire, OR 10850
Jack fire, OR 23647
425-Smith (Devils Knob Cpx), OR 7766
Gales (Middle Fork Complex), OR 9253
Table 30. List of potential wildfire smoke sources contributing to smoke emissions at CV (devised from
forward and backward HYSPLIT trajectories) and the approximate size of the fires in acres169 on August
16, 2021.

Meteorological Conditions
The flagged event of August 16 was characterized broad upper-level ridging across the Western
U.S., with a trough entering the PNW and flattening the ridge (Figure 185). Figure 186 shows the upper
level winds and geopotential heights on August 16, with the overall synoptic pattern characterized by a
dampened region of high pressure centered over the Western U.S. The ridge axis roughly extended
southwest to northeast from central CA to ND (Figure 185b). This setup allowed the placement of westerly
to northerly mid to upper-level winds over northern Utah by the afternoon of August 16, potentially
allowing smoke transport from points west and north into Utah. The relatively benign upper-level pattern
translated to calm and hot conditions at the surface, with maximum temperatures observed in the upper
90s, clam winds (< 5 kts), and clear skies (Figure 187). A weak dry surface boundary was in place across
northern Utah on the afternoon of August 16, marking the axis of a very weak surface low associated with
dynamic lift from the approaching trough across the PNW.
Soundings launched at KSLC show moderately deep mixed layer up to about 660 mb (~2.4 km
AGL) on the afternoon of August 16 (Figure 189). In Figure 189, the vertical wind profile at 12z exhibits
southerly down-valley winds below 850mb. As seen in the 00Z sounding, lower level winds below 700 mb
in Figure 189b suggest lake-land breeze influence, with northerly to westerly winds above 700-500 mb.
The evolution and associated impacts of the upper-level ridge and synoptic pattern is described in full

169 Dataset of U.S. IMSR found at: https://research.fs.usda.gov/treesearch/67197

detail in the National Weather Surface (NWS) area forecast discussions (AFDs)170 for KSLC (Appendix A).
In general, the NWS AFDs illuminate how the meteorological pattern influenced the transport of smoke
into Utah. For example, highlighted AFD text discussing the intrusion wildfire smoke into Utah on August
15-16 is given below:

“Area Forecast Discussion
National Weather Service Salt Lake City UT
402 PM MDT Sun Aug 15 2021
Regional smoke which has spread across northern and central Utah today, and
increased in concentration this afternoon, will largely remain in place through
Monday resulting in continued degraded air quality and visibility.
. . .
Area Forecast Discussion
National Weather Service Salt Lake City UT
445 AM MDT Mon Aug 16 2021
.SYNOPSIS...High pressure will maintain dry and stable conditions today as
regional smoke remains across the area. A more unsettled pattern is expected
to develop Tuesday through Thursday as moisture returns northward.171”

170 Archived NWS AFDs can be found at: https://mesonet.agron.iastate.edu/wx/afos/list.phtml
171 Archived NWS AFDs can be found at: https://mesonet.agron.iastate.edu/wx/afos/list.phtml

Figure 184 - NCEP Reanalysis Average 500 mb GPH: August 16, 2021

Figure 184. NCEP Reanalysis Average 500 mb Geopotential Heights 172 for the period August 15-16, 2021.
The higher 500 mb geopotential heights centered across the Sierras/Great Basin Region indicates a
relatively strong upper-level ridge.

172 NCEP Reanalysis Data can be found at: https://psl.noaa.gov/data/gridded/data.ncep.reanalysis.html

Figure 185 - NOAA SPC 500 mb and 700 mb Upper Air Charts: August 16, 2021

Figure 185. NOAA-Storm Prediction Center173 upper air charts for a.) 500 mb geopotential heights, winds,
and temperature, b.) 500 mb chart zoomed in over the West, c.) 700 mb geopotential heights, winds,
temperature, and relative humidity, and d.) 700 mb chart zoomed in over the West. Flow from 700-500
mb is generally from the southwest to west which suggests winds were conducive for smoke transport
from wildfires in the northern CA Sierras and central OR.

173 NOAA-SPC Mesoscale Analysis Upper Air Charts can be found at: https://www.spc.noaa.gov/

Figure 186 - GFS Analyzed 500 mb GPH and Winds: August 16, 2021

Figure 186. GOES East True Color satellite imagery with overlaid analyzed GFS 500 mb geopotential
heights (m) and winds (kts) and the location of the CV monitor (yellow star) on August 16, 2021 at 1800Z
zoomed over a.) the CONUS and b.) Utah. A dome of high pressure resides across the Sierras/Great Basin
with westerly to northerly upper-level winds across northern Utah.

Figure 187 - CV Meteogram: August 16, 2021

Figure 187. Meteogram of observed sensible weather conditions at the CV monitor through the period
August 14-18, centered on the flagged event date of August 16 (delineated by the red dashed lines). Hot
temperatures, low wind speeds, low moisture, and clear skies are noted on August 16.

Figure 188 - WPC Surface Analysis: August 16, 2021

Figure 188. NOAA-Weather Prediction Center (WPC)174 surface analysis and IR satellite imagery on August
16, 2021 at 1800Z zoomed over a.) North America and b.) the Western U.S. (defined red bounding box in
a.)). The analyzed fronts show a surface low and dry boundary located over northern Utah.

174 NOAA-WPC Surface Analysis Charts can be found at: https://www.wpc.ncep.noaa.gov/archives/web_pages/sfc/sfc_archive_maps.php

Figure 189 - KSLC Radiosonde Soundings: August 16, 2021

Figure 189. Radiosonde soundings from KSLC on August 16, 2021 at a.) 12Z and b.) 00Z. A deep well mixed
PBL is evident in the 00Z sounding, with winds out of the west to north near above 700-600 mb in the
afternoon sounding. Winds at lower levels reflect the northwesterly diurnal lake-land breeze.
Wildfire Smoke: Remote Sensing and Ground-Based Analysis
It is apparent that the meteorological environment on August, 2021 was conducive for the
transport of air parcels from points west and north of Utah into the state. Visible satellite imagery reveals
a large consolidated mass of smoke transported to the CV UDAQ monitor on August 16 (Figure 190 - Figure
193). Figure 190 and Figure 191 show how smoke plumes emanating from numerous large fires across
the West are shown were captured and transported within the mean wind field, creating a large swath of
medium to dense smoke over the Intermountain West. In Figure 192, visible satellite imagery merged

with the analyzed 500 mb upper-level wind field exhibits the pattern of transport of smoke from areas
west and north around the upper-level ridge into northern Utah. An example smoke conditions over Utah
on the August 16 event compared to relatively smoke free conditions on August 11 is given in Figure 193.
Revealed in the satellite imagery, the upper-level synoptic pattern allowed the transport and
consolidation of smoke plumes from multiple fires in the West into Utah. Additionally, vertical
temperature and wind profiles from soundings launched on August 16 reveal a relatively deep PBL mixed
layer in the SLV, suggesting that the capture and transport of smoke emissions from aloft to the surface
was also possible (Figure 189).
We investigate satellite aerosol optical depth (AOD) and satellite HMS smoke field to distinguish
wildfire smoke density over Utah on August 16 (Figure 194). In Figure 194, AOD values 0.9-1 are present
over the SLV, indicating dense wildfire smoke in the atmospheric column. Synthesizing the remote sensing
imagery and analysis into one product, the HMS analyzed smoke fields show that medium to heavy dense
smoke plumes converged over the Northern Wasatch Front and the CV monitor from these fires on August
16 (Figure 195). The summarization of smoke field characteristics observed by satellite imagery is given
by the NOAA NEDIS smoke narrative175 published on August 16, 2021 at 1740Z. The smoke discussion
notes thick and dense smoke across Utah from the wildfire activity in the Western U.S.:
“Monday, August 16, 2021
DESCRIPTIVE TEXT NARRATIVE FOR SMOKE/DUST OBSERVED IN SATELLITE IMAGERY THROUGH 1740z August 16, 2021
SMOKE: Numerous wildfires across the western U.S. and southwestern Canada continue to produce/support a very large plume of smoke across a large part of the U.S. and Canada. A thin density plume covered the Gulf of Alaska, most of southern Canada, and the western 2/3rds of the Continental U.S. Within this thin density plume, moderate density smoke was found over the Great Basin, most of the Rockies, the Northern Plains, and a significant portion of southwestern and south-central Canada. The thickest smoke plumes were detected over interior central and northern California, northwestern Nevada and southeastern Oregon,
the Northern Rockies, most of North and South Dakota, southern Saskatchewan and Manitoba, and parts of western Ontario.176”
A more detailed characterization of the magnitude and transport pattern of smoke from wildfires
across the West is given by the High-Rapid Refresh (HRRR) smoke model analysis in Figure 196. In Figure
196a, the August 16 15Z initialized HRRR total column smoke density exhibits the extensive and dense
shield of smoke across the Western U.S. and Utah (> 150 μg/m²). In addition, the total column smoke
density reveals well defined heavy plumes originating from fire complexes scattered across the PNW and
northern Sierras being transported to Utah (Figure 196a). A closer inspection of HRRR smoke is given in
Figure 196b, showing dense surface level smoke (> 50 μg/m³) at the CV monitor August 16. In Figure 197,
the BlueSky Smoke model177 outlines the smoke plumes originating from the fires across the West on
August 16, ultimately forming a consolidated mass of smoke over the entire region.
Observations from ground-based cameras around the SLV further verify the presence of near
surface smoke across the valley August 16 (Figure 198). In Figure 198a and Figure 198d, the camera images
from August 11 and August 21 represent relatively clear days preceding and proceeding the flagged smoke

175 NOAA NEDIS Smoke Narrative can be found at: https://www.ssd.noaa.gov/PS/FIRE/smoke.html
176 NOAA NEDIS Smoke Narrative can be found at: https://www.ssd.noaa.gov/PS/FIRE/2021_archive_smoke.html
177 BlueSky Modeling Framework can be found at: https://tools.airfire.org/websky/v2/#status

event, respectively. Images in Figure 198b - Figure 198c from the afternoon of August 16 show conditions
during the flagged smoke event, with extremely reduced visibility due to wildfire smoke emissions within
the SLV.

Figure 190 - FIRMS Map: August 16, 2021

Figure 190. FIRMS Map178 with VIIRS S-NPP True Color Satellite imagery for August 16, 2021 overlaid with
satellite analyzed fire hotspots (red dots) and fire perimeter burned area (shaded light blue areas). An
area medium to heavy smoke is evident across the Western U.S., with medium to heavy present across
Utah.

178 FIRMS Fire Map can be found at: https://firms.modaps.eosdis.nasa.gov/usfs/map/#d:24hrs;@-100.0,40.0,4.0z

Figure 191 - GOES West True Color: Western CONUS August 16, 2021

Figure 191. GOES West True Color Satellite imagery179 on August 16, 2021 at 2100Z for a.) the Western
U.S. and b.) zoomed over Utah (red bounding box in a.)). Utah is blanketed in medium to heavy-dense
wildfire smoke transported from fires in CA and OR.

179 NOAA-Aerosol Watch Satellite imagery can be found at: https://www.star.nesdis.noaa.gov/smcd/spb/aq/AerosolWatch/

Figure 192 - GOES East True Color and GFS 500 mb Heights and Winds: August 16, 2021

Figure 192. GOES East True Color satellite imagery with overlaid analyzed GFS 500 mb geopotential
heights (m) and winds (kts) and satellite analyzed wildfire hotspots (red circles) on August 16, 2021 at
2100Z. The satellite imagery reveals a large area of wildfire smoke across the Western U.S., extending into
northern Utah.

Figure 193 - GOES East True Color: Utah August 16, 2021

Figure 193. GOES East True Color satellite imagery the event date a.) August 16, 2021 at 2100Z and on
the b.) relatively smoke free date August 11, 2021 at 1800Z. In b.), key geographical landmarks are more
visible due to the smoke free skies.

Figure 194 - GOES West AOD Composite 18-21Z: August 16, 2021

Figure 194. GOES West satellite derived Aerosol Optical Depth (AOD)180 August 16, 2021 for a.) the
Western U.S., and b.) zoomed in over northern Utah. AOD values of 0.9-1 were observed over the SLV,
indicating the presence of dense wildfire smoke attenuating incoming solar radiation.

180 Aerosol Watch AOD product can be found at: https://www.star.nesdis.noaa.gov/smcd/spb/aq/AerosolWatch/index.php

Figure 195 - HMS Smoke Fields and WFIGS Wildfire Perimeters: August 16, 2021

Figure 195. HMS smoke fields181 with WFIGS Wildfire perimeters182 across the Western U.S. on August 16,
2021. Heavy smoke is analyzed above the CV monitor.

181 HMS Smoke Field data can be found at: https://www.ospo.noaa.gov/products/land/hms.html#0
182 WFIGS Wildfire Perimeters can be found at: https://data-
nifc.opendata.arcgis.com/search?tags=historic_wildlandfire_opendata%2CCategory

Figure 196 - HRRR Smoke VIS and NSFC Smoke: August 16, 2021

Figure 196. HRRR-NCEP smoke fields on August 16, 2021 at 15Z of a.) total column smoke (vertically
integrated) over the CONUS and b.) near-surface level smoke focused over Utah. Both vertically integrated
and surface level smoke reveal heavy-dense smoke over the CV monitor (yellow star).

Figure 197 – BlueSky Dispersion Analysis: August 16, 2021

Figure 197. BlueSky Daily Smoke Dispersion model run183 (GFS 0.5 deg and 0.15 deg dispersion) from
August 16, 2021 at 21Z. Satellite analyzed fire hotspots are overlaid (red flames) along with the location
of the CV monitor (yellow star pin).

183 BlueSky Modeling Framework can be found at: https://tools.airfire.org/websky/v2/#status

Figure 198 - MESOWEST WBB Camera: August 16, 2021

Figure 198. MESOWEST WBB camera images from a.) August 11 at 1741 MST, b.) August 16 at 1207
MST, c.) August 16 at 1741 MST, and d.) August 21 1322 MST. The camera is located on the University of
Utah campus at the north end of the SLV and faces to the west. Images a.) and b.) represent conditions
expected on relatively smoke-free days, with images in b.) and c.) representing the conditions during the
early and late afternoon of the smoke impacted date of August 16, 2021.

HYSPLIT: Wildfire Smoke Transport to CV Monitor
HYSPLIT multiple particle forward and backward trajectory analysis was performed following
similar methodology as described in Section 4.1.4. The first two HYSPLIT model configurations chosen
were the backward ensemble and frequency trajectory options, with parcels starting at model derived
automatic mid-boundary height (Figure 199 - Error! Reference source not found.). The HMS smoke fields
and VIIRS analyzed wildfire hotspots are also include in Figure 199 - Error! Reference source not found.
to help distinguish the potential source regions of wildfire smoke that impacted the CV monitor. In Figure
199a, 72-hour ensemble backward trajectories beginning at the CV monitor on the evening of August 16
are shown. Figure 199a reveals multiple trajectories ending at CV on August 16 originated or passed over
a number of fires in WA, ID, MT, OR, and CA. These trajectory paths showcase how multiple wildfires
contributed to the smoke emissions observed August 16 in the SLV. In Figure 199b, the 72-hour backward
trajectory frequencies are provided, with areas of highest trajectory frequencies corresponding to
locations of active wildfires in central and northern ID, western MT, and southeastern WA. The frequency
plot suggests that the smoke plume over the CV monitor on August 16 was an aggregate smoke mass
composed of smoke sourced from multiple wildfire sources across ID, MT, and WA. In general, frequency
and ensemble trajectories show air parcels mainly originating from fires highlighted in Table 30.

Investigation of smoke transport from a few select fires to the SLV employs multi-particle forward
ensemble and frequency HYSPLIT trajectories (Figure 200 - Figure 202). The integration periods for the
forward trajectories varied from 48 to 72 hours, given the influential fires and their respective distances
to the CV monitor, with trajectories set at the automatic mid-layer boundary height for most simulations.
The ensemble trajectory approach launches particles at varying heights above the fire locations, which
more realistically represents air parcels at different levels within the rising smoke plume. In Figure 200 -
Figure 202, both the 72-hour and 48-hour forward ensemble and frequency trajectories, respectively,
starting at the Lick Creek, WA, Trail Creek, MT, and the Boundary, ID fires reveal a well-defined northwest
to southeast transport pattern from the fires to the SLV from August 14 to the afternoon August 16, 2021.
The forward ensemble and frequency trajectory paths from the wildfires mentioned align well
with transport patterns outlined by backward trajectories from the CV monitor. Additionally, the spatial
variability, magnitude, and suggested plume transport from the satellite imagery and HRRR/BlueSky
modeled smoke dispersion output described in the previous section verifies well with the HYSPLIT forward
and backward trajectory analysis highlighted in this section. The corroboration of these analyses adds
confidence that wildfire smoke was transported from regional wildfire sources (Table 30) during the
period including August 16 to the CV monitor.

Figure 199 - HYSPLIT 72-hr Ensemble Backward & Frequency Trajectories: August 16th, 2021 23Z

Figure 199. HYSPLIT 60-hr Backward a.) Ensemble and b.) Frequency Trajectories starting at the CV
monitor at mid-PBL height on August 16, 2021 at 23Z. The CV monitor is noted (yellow star).

Figure 200 – Lick Creek, ID Fire; HYSPLIT 72-hr Ensemble Forward & 48-hr Frequency Trajectories: August
14-17, 2021

Figure 200. HYSPLIT Forward a.) 72-hr Ensemble and b.) 48-hr Frequency trajectories from the Lick Creek,
ID fire starting mid-PBL height August 14, 2021 at 00Z. The trajectory paths suggest transport to the CV
(yellow star).

Figure 201 - Trail Creek & Alder Creek, MT Fires; HYSPLIT 48-hr Ensemble Forward & Frequency
Trajectories Fires: August 14-17, 2021

Figure 201. HYSPLIT Forward a.) 48-hr Ensemble and b.) 48-hr Frequency trajectories from Trail Creek and
Alder Creek, MT fires starting mid-PBL height August 14, 2021 at 23Z. The trajectory paths suggest
potential transport to the CV (yellow star).

Figure 202 – Boundary, ID Fire; HYSPLIT 48-hr Ensemble Forward & 60-hr Frequency Trajectories Fires:
August 14-18, 2021

Figure 202. HYSPLIT Forward a.) 48-hr Ensemble and b.) 60-hr Frequency trajectories from Trail Creek and
Alder Creek, MT fires starting mid-PBL height August 14, 2021 at 23Z and 00Z, respectively. The trajectory
paths suggest potential transport to the CV (yellow star).
Wildfire Smoke Emissions and Ozone Exceedance: Clear Causal Relationship
In this section, we conduct PM2.5, brown carbon, and ozone analysis as described in Section 4.1.5.
Surface Smoke Observations and Historical Monitor Comparison
UDAQ CV monitor hourly and daily (24-hr average) PM2.5 observations indicate the progression of
surface particulate concentrations during the periods of wildfire smoke August 11-20 (Figure 203). As seen

in Figure 203, August 11 was a very light smoke event, with daytime PM2.5 hourly concentrations ranging
5-10 µg/m3. In comparison, during the heavily smoke impacted period of August 16 the maximum hourly
PM2.5 concentrations ranged from about 30-70 µg/m3, indicating that significant enhancement of PM2.5
by wildfire smoke emissions occurred on August 16. Trends in the observed monitored daily PM2.5
concentrations reveal a similar story of PM2.5 enhancement by wildfire smoke, with a daily PM2.5 value
of 48.4 µg/m3 on August 16 (Figure 204). For contrast, on the light smoke day of August 11 the observed
daily PM2.5 concentrations were < 10 µg/m3. When compared to PM2.5 concentrations at CV over the 5-
year period of 2019-2021, the August 16 daily PM2.5 concentration (48.4 µg/m3) exceeds the 5-year
month’s specific 24-hr PM2.5 98th percentile184 value of 26.2 µg/m3 by more than 20 µg/m3 (Figure 204).
Figure 203 and Figure 204 displays the marked departure of the monitored daily PM2.5 on the flagged
event date from the 5-year (2019-2023) month’s daily averages (excluding the fire year 2021), with 24-hr
average PM2.5 observations on the August event ~8-9 times larger than the typical values for this period.
In Figure 205, delta-c concentrations are shown for a period surrounding the August 16 flagged
smoke event. Elevated concentrations of delta-c are observed during the smoke period of August 14-19,
peaking on August 15-16 (> 2000-4000 ng/m3), and tapering to lower concentrations on relatively smoke-
free day of August 11 (< 150 ng/m3) (Figure 205). Because delta-c is an unambiguous indicator of biomass
burning, the enhanced delta-c observations on the flagged event date undisputedly indicate the residence
of surface-level wildfire smoke in the SLV on August 16. Table 31 provides the average delta-c
concentrations for the 5-year (2019-2023) month’s daily averages compared to concentrations observed
during the flagged event, with the observed delta-c on August 16 ~15-16 times larger than average.
Figure 203 - CV Hourly PM2.5: August 16, 2021

Figure 203. Monitored hourly PM2.5 concentrations at CV for the period August 11-21, 2021, centered
on August 16 (vertical dashed-red lines). Increased hourly PM2.5 concentrations (~30-70 µg/m3)
associated with the smoke is evident on August 16.

184 EPA PM2.5 Tiering Tool: https://www.epa.gov/air-quality-analysis/pm25-tiering-tool-exceptional-events-analysis

Figure 204 - CV Monitored 24-hr PM2.5 and MD8A Ozone: August 16, 2021
Figure 204. Daily (24-hr avg) PM2.5 (right axis) and MD8A ozone (left axis) observed at the CV monitor for
the period August 11-18, 2021, centered on the August 16 flagged event. Trends in daily PM2.5 and MD8A
ozone correspond well with each other, revealing the close connection between the presence of wildfire
smoke emissions and enhanced ozone formation.

Figure 205 - Hourly Brown Carbon (BrC) Concentrations: August 16, 2021

Figure 205. Monitored hourly BrC concentrations at CV for the period August 14-18, 2021, centered on
August 16 (vertical red lines) from the Bountiful (BV), Inland Port (IP), and Lake Park (LP) UDAQ monitoring
sites. Increased hourly BrC concentrations (>2000-4000 ng/m3) associated with smoke is evident on
August 16.

Table 31 - Average Brown Carbon (BrC) Concentrations July 2019-2023: August 16, 2021
Station 2019 2020 2021 2022 2023 Average August16
Event Avg.
Bountiful 134 163 280 112 77 153 2171
Inland Port -- -- 303 66 71 147 2515
Lake Park -- -- 262 131 92 162 2490
Table 31. 5-year month’s specific (July 2019-2023) average BrC concentrations from the Bountiful (BV),
Inland Port (IP), and Lake Park (LP) UDAQ monitoring sites, with the daily BrC concentration for the flagged
event day of August 16 also given.

Event and non-event Ozone
The presence of surface-level wildfire smoke at the CV monitor has been established in the prior
sections. Here, we show how the addition of wildfire smoke emissions into the SLV airshed caused the
ozone exceedance at the CV monitor. Daily PM2.5 and MD8A ozone concentrations also exhibit a close
positive relationship, where the local MD8A ozone maximum corresponds with the local maxima of PM2.5
(Figure 204). It has been established by prior studies that PM2.5 can be used to indicate the potential
magnitude of ozone enhancement by wildfire smoke (e.g. Buysse et al. 2019; Ninneman and Jaffe, 2021).
In the case of August 16, both hourly and daily observed PM2.5 concentrations were within the moderate
range and correspond with PM2.5 concentrations that correlate with ozone enhancement from wildfire
smoke emissions (Figure 203 and Figure 204).
The observed ozone concentrations on the August 16, 2021 flagged wildfire smoke event were
significantly elevated and notably anomalous. In Figure 206, the MD8A ozone at CV is given for the 5-year
period 2019-2023 in order to highlight monitored flagged wildfire smoke MD8A ozone relative to non-
events. Compared to the 5-year period MD8A ozone concentrations at CV, the MD8A values on August
16 of 86 ppb is higher than the 98th and 99th MD8A percentile (Figure 206). Furthermore, the observed
MD8A August 16 is the fourth ranked observed MD8A in the complete historical POR CV has been
operational (2018-2024) (Table 32). To further quantify the distinct difference in observed ozone on
wildfire smoke events compared to non-events, mean MD8A and average diurnal hourly ozone are given
for non-event and wildfire smoke event days in Figure 207 and Figure 208, respectively. On average,
measured MD8A ozone at CV is 6-8 ppb higher on wildfire smoke event days than on non-event days
(Figure 207). Diurnal average hourly ozone also reveals that the rate of ozone formation (dO3/dt) is much
greater on wildfire smoke event days than on non-event days (Figure 208). When the hourly ozone trend
from the flagged event of August 16 is compared with diurnal average hourly ozone concentrations of
non-event and wildfire events and across the 5-year period 2019-2023, it is evident that the ozone
formation rate August 16 was significantly greater than what would be normally observed on non-event
days and has similar trend characteristics as on flagged wildfire event days (Figure 209).

Figure 206 - MD8A Ozone 2019-2023 at CV Monitor: August 16, 2021

Figure 206. MD8A ozone (ppb) at the CV monitor for the 5-year period 2019-2023. Wildfire smoke flagged
EE’s (red circles) (July 12 and 25, 2021; August 7-8 and 16, 2021) and dates with flags for wildfire smoke
(orange circles) are highlighted. The August 16 flagged EE is outlined, showcasing the extremely high
MD8A ozone observed on that date compared to the 5-year period.

Table 32 - Top 10 CV POR Ranked MD8A (2018-2024): August 16, 2021
Rank CV MD8A Date
1 96 2021-07-12
2 89 2021-08-08
3 87 2021-08-07

4 86 2021-08-16
5 85 2021-08-04
6 85 2021-09-08
7 85 2020-08-21
8 84 2021-07-11
9 83 2021-07-24
10 82 2020-07-11
Table 32. The top 10 ranked MD8A ozone at the CV monitor for the operational POR (2018-2023). The
wildfire smoke flagged EE of August 16 is the fourth highest MD8A ever recorded (highlighted red) at CV.
Other flagged EE’s and wildfire impacted events compose almost all other top ranked spots (highlighted
in yellow).

Figure 207 - Non-Event and Event MD8A Ozone: NWF 2016-2023

Figure 207. Average Non-Event and Event MD8A ozone (ppb) for the period 2016-2023 at UDAQ monitors
within the SLV, including Hawthorne (HW), Copperview (CV), Bountiful (BV), Herriman (H3), and Rose Park
(RP). MD8A ozone is on average 5-8 ppb higher during wildfire events than non-wildfire events.

Figure 208 - Non-Event and Event Average Hourly Diurnal MD8A Ozone at CV Monitor: August 16, 2021

Figure 208. Non-Event, Event, and August 16 Event average diurnal hourly ozone at the CV monitor. The
ozone formation rate on Event days and the flagged August 16 Event is considerably steeper than non-
events.
Figure 209 - Flagged Event Hourly Ozone vs. Average Hourly Diurnal MD8A Ozone at CV Monitor (2016-
2021): August 16, 2021

Figure 209. Yearly (2018-2021) and August 16 Event average diurnal hourly ozone at the CV monitor. The
ozone formation rate on the flagged August 16 Event is considerably steeper than the average diurnal
ozone trends.

Wildfire Smoke and Ozone Formation: NOx and VOCs
In order to distinguish the contributions of smoke emissions to elevated ozone on August 16, we
detail the typical concentrations of key air quality parameters important to ozone formation on wildfire
smoke event days, non-event, and on the flagged date of August 16. NOx and VOC chemistry regimes
related to wildfire plumes are described in Section 4.1.5.3.
In Figure 210, the observed hourly concentrations of benzene, toluene, and xylene are shown for
a period centering on the flagged event date of August 16. The trend in the three VOC species closely
correlates with the wildfire smoke period of August 16, marking the arrival and clear out of smoke. All
three species increase sharply on August 14, when a fresh plume of dense wildfire smoke arrived in the
SLV, and peaked August 15-19 before decreasing sharply after August 20 when smoke emissions
momentarily dissipated (Figure 210). Figure 211 presents the observed TNMOC through the same period
and shows maxima in the TNMOC correspond to the denser smoke period of August 15-19.
To determine how the ozone precursor concentrations on August 16 compare with other days,
we contrast the typical monitored VOC concentrations on non-event, flagged smoke event dates, the
event period of August 16, and a day of similar meteorology (July 22, 2021) Figure 212). The VOC emissions
on the similar meteorology day of July 22 are highlighted in Figure 212, with VOC emissions notably lower,
compared to wildfire impacted flagged dates. Figure 212 shows wildfire event days have much greater
TNMOC and total VOC concentrations on average than non-event days, particularly on days of ozone
exceedances with wildfire smoke. Additionally, the observed average TNMOC and total VOCs on the
August 16 event are on average higher than on non-event days and the comparable meteorology day of
July 22, 2022.
Diurnal average trends provide insight as to how the temporal variability of total VOCs and
TNMOC on event days compare with non-events (Figure 213). A clear enhancement of VOCs and NOx is
observed on the flagged wildfire event of August 16 when compared to non-events and the comparable
meteorology day (Figure 213). The enhancement in VOCs (>100 ppb) is most pronounced in the morning,
early afternoon, and evening hours. In particular, during the August 16 flagged event TNMOC, and total
VOCs were significantly larger in the early to mid-morning hours and remained consistently elevated
above typical non-event concentrations through the course of the afternoon/evening. The decrease in
TNMOC, total VOCs, and NOx in the late morning and early afternoon coincides with peak ozone
production hours (0700-1300 MST) (Figure 214). The precursor emissions of NOx and VOCs are consumed
and depleted through ozone photochemistry. This titration of the precursor emissions, coinciding with
rapid growth in ozone concentrations, exhibits the significant impact the addition of wildfire smoke
emissions had on ozone concentrations on August 16 (Figure 214). As seen in Figure 208, Figure 209, and
Figure 214, ozone production rates (dO3/dt) are notably steeper during the flagged event period August
16 compared with non-events and the day of similar meteorology, indicating ozone enhancement due to
the altered configuration of NOx and VOC emissions by smoke.
The VOC concentrations on the August 16 flagged event were larger than what is typically
observed in the SLV on non-event days (Figure 208). Xylene and toluene emissions within wildfire smoke
plumes have been noted to be relatively reactive species for ozone formation, making the addition of
these emissions impactful for ozone development (Wang et al., 2024; Ketcherside et al., 2024; Simms et
al., 2021). The SLV air shed is characterized by a transitional to VOC-limited regime, which makes ozone

photochemistry sensitive to increases or decreases in VOCs and NOx emissions (e.g. Gonzalez et al., 2024;
Jaffe et al., 2024). However, ozone formation has also been identified to be particularly sensitive to
increases in VOC emissions from wildfire smoke (Jaffe et al., 2024). Here, we show that wildfire smoke
injected supplementary VOC emissions into the urban SLV plume, creating an environment for ozone
enrichment. The altered ratio of VOC to NOx emissions due to the infiltration of the wildfire smoke plume
into the urban SLV air shed caused the extreme ozone exceedance August 16.

Figure 210 - HW Average Daily VOCs: Jul-Aug

Figure 210. Daily average VOC concentrations of benzene, toluene, and xylene at the HW monitor for the
period July-August, 2021. The flagged wildfire smoke events (i.e. July 12, July 24, August 7 & 8, and August
16 are noted (vertical solid red lines) as well as periods of wildfire smoke (shaded red regions).
Additionally, the comparable meteorological day of July 22, 2021 is marked (vertical solid blue line).

Figure 211 - HW Average Daily TNMOC: Jul-Aug 2021

Figure 211. Daily average TNMOC concentrations at the HW monitor for the period July-August, 2021.
The flagged wildfire smoke events (i.e. July 12, July 24, August 7 & 8, and August 16 are noted (red stars)
as well as periods of wildfire smoke (shaded red regions). Additionally, the comparable meteorological
day of July 22, 2021 is marked (blue star).

Figure 212 - Event vs. Non-Event: Average Daily VOCs at HW: August 16, 2021

Figure 212. Average daily VOCs and TNMOC at the HW monitor for Non-Event (Exceedance No WF), Event
(Exceedance WF), Comparable Meteorology (Comparable MET – July 22), and the flagged August 16 Event
(WF Event: August 16) during the summer of 2021.

Figure 213 - Event vs. Non-Event: Average Hourly Diurnal Total VOCs, TNMOC, and NOx: August 16, 2021

Figure 213. Average diurnal hourly a.) VOCs, b.) TNMOC, and c.) NOx concentrations at the HW monitor
for Non-Event, Event, All wildfire days, August 16 Event, and Comparable Meteorology day (July 22) in the
summer of 2021.

Figure 214 - Event vs. Comparable MET: Hourly VOCs, NOx, and Ozone at HW and CV: August 16, 2021

Figure 214. Hourly VOCs, ozone, and NOx concentrations at the CV monitor for the a.) August 16 Event
and b.) Comparable Meteorology day (July 22).

Summary
The analyses in support of EE flagging and data exclusion from modeling demonstrates that
wildfire smoke emissions from multiple wildfires across the Western U.S. adversely impacted ozone
concentrations at the Copperview monitor on the flagged event dates of July 12, July 24, August 7-8, and
August 16. The effects from the smoke emissions on ozone from these four flagged events were
uncontrollable and are determined to be unrepresentative of typical conditions at the monitor. Therefore,
these events are flagged as Exceptional Events and should be excluded from 2021-2023 Average DV
calculations in the 179B model attainment demonstration.
This report:
1. Contains a conceptual model illustrating how wildfire smoke emissions were transported to the
affected monitor, leading to elevated observed ozone concentrations on the flagged events.

2. Demonstrates that there was a clear causal relationship between the smoke emissions at the
monitor and the observed MD8A ozone exceedances.
3. Contains analyses comparing the ozone concentrations during the flagged-event days to
concentrations at the same monitor on non-event days and days with similar meteorological
conditions.
Key findings and evidence supporting the data exclusion:
1. Preceding and ongoing drought and abnormal hot temperatures proved favorable for wildfire
conditions across the Western U.S., leading to an extreme and unprecedented 2021 wildfire
season.
2. Multiple large persistent wildfires across the Western U.S. contributed to large dense
consolidated smoke plumes that were transported across northern Utah in July and August 2021.
3. Meteorological conditions were conducive for the transport of smoke emissions from fires to the
surface at the CV monitor.
4. Satellite imagery and remote sensing revealed expansive and dense plumes of smoke associated
with increased AOD’s that were transported from major wildfires in the West to the CV monitor
on the flagged event days.
5. Analysis from the NOAA HMS smoke product showed medium to heavy-dense smoke plumes over
the CV monitor during flagged events.
6. Ground based-remote sensing identified smoke overhead due to increased solar extinction over
northern Utah due to the increased aerosols/particulate matter from smoke.
7. Camera imagery captured the dense nature of smoke at the surface on flagged event days.
8. HYSPLIT forward and backward ensemble and frequency trajectories outlined potential fires
contributing to smoke emissions and how the wildfire smoke was transported to the CV monitor.
9. Monitored PM2.5 and BrC concentrations were elevated well above average during the flagged
events, marking the presence of smoke at the surface.
10. MD8A ozone concentrations on the flagged events were above the 5-year (2019-2023) ozone
distribution 99th percentile and were also ranked within the top 10 highest MD8A ozone
concentrations for the CV monitor POR (2018-2024).
11. Hourly ozone concentrations on the flagged events were more than 40-50 ppb greater compared
to non-event exceedance dates.
12. Ozone production rates on flagged events (dO3/dt) were significantly steeper compared to non-
event exceedances and average rates.
13. Enhanced ozone precursor emissions of VOCs and NOx were observed due to smoke transport
into the SLV, aiding in increased ozone production and coinciding with enhanced ozone
concentrations at the CV monitor.
14. Comparable meteorological day analysis showed the EE flagged event days had considerably
greater ozone and precursor concentrations than on a day with typical ozone exceedance
meteorological conditions (non-event exceedance conditions).
Data Exclusion and Adjusted BDV
Although the flagged data from July 12, July 24, August 7 & 8, and August 16 potentially meets
the criteria of the Exceptional Events Rule, no exceptional event documentation has been submitted on
these flagged days by UDAQ for review to the EPA. In the past, these flagged events were not deemed
significant enough to affect the attainment/nonattainment status of the Wasatch Front nonattainment
area. Therefore, no demonstration has been submitted to remove the data and the data has, up until
present, remained in the dataset to calculate official design values. However, UDAQ has determined that

the flagged event-influenced data from these days remain unrepresentative and impact the base and
future year model design values for the 179B model attainment demonstration.
To counteract this potentially biased impact of event-influenced data on design value
formulation, UDAQ has followed a process for excluding event-influenced data when determining base
design values as stated in Section 1.2 Significance and Justification. This process is described
in EPA’s modeling guidance, where determinations and analyses other than exceptional events are
allowed when regarding mechanisms for possible monitoring data exclusion, selection, or adjustment.
Specifically, monitoring data exclusion, selection, or adjustment may qualify for determinations if ambient
data are not representative of base period concentrations and have the potential to impact a
determinative value in a past or projected time period. EPA acknowledges one appropriate situation when
this process can be used includes the removal of air quality monitoring data when developing alternative
base year and future year design values for modeling in attainment demonstrations. Following these
guidelines, UDAQ has flagged the four wildfire impacted events in AQS as “RT” and has readjusted design
values and the baseline design value by excluding these flagged events. UDAQ has completed additional
analyses by removing flagged days from the base year design value calculation to identify the impact on
the baseline design and future design values as part of our modeling attainment demonstration. In the
remainder of this section, we describe the adjustment of the 2023 baseline design value (BDV) by data
exclusion and removal of the flagged wildfire smoke impacted MD8A ozone at the CV monitoring site.
The MD8A ozone concentrations at CV for the flagged event periods are given in Table 33. The
impact of wildfire smoke and constituent emissions during these periods has been deemed consequential,
and without the influx of such emissions the observed MD8A ozone concentrations may not have been as
elevated. Therefore, we exclude these MD8A ozone values from the calculation of the 4th max MD8A
ozone for 2021 at the CV monitoring site. By removing these values from the 2021 4th max determination,
we compute a new 4th high MD8A ozone for CV for the year 2021 (Table 33 and Table 34). The new 4th
max MD8A ozone value is then used to derive average 3-year design value (2021-2023) (Table 34). In Table
34, the impact of the removing the flagged data (July 12, July 24, August 7 & 8, and August 16, 2021) is
illustrated by comparing the 3-year DV constructed with and without flagged data. The exclusion of
wildfire impacted data reduces the DV used for model attainment by 2 ppb at CV monitoring site (Table
34).
Table 33 – Copperview Data Exclusion: New 4th Max MD8A 2021
Old Rank New Rank Date CV MD8A (ppb) Smoke Flag PM2.5 (µg/m3)
1 - 7/12/2021 96 SMOKE 27.3
2 - 8/8/2021 89 SMOKE 42.8
3 - 8/7/2021 87 SMOKE 49.5
4 - 8/16/2021 86 SMOKE 48.4
5 1 9/8/2021 85 SMOKE 23.4
6 2 8/4/2021 85 SMOKE 22.4
7 3 7/11/2021 84 SMOKE 31
8 - 7/24/2021 83 SMOKE 26.2

9 4 7/10/2021 80 SMOKE 19.8
10 5 8/29/2021 79 SMOKE 24.3
Table 33. Same as in Table 14 but restated here. Ranked MD8A ozone concentrations (ppb) at CV for 2021
without EE flagged exclusions (old rank) and with EE flagged exclusions (new rank). Old 4th high MD8A
ozone without EE flagged exclusions outlined in red. Flagged EE wildfire dates are highlighted in red and
the new 4th high MD8A ozone with EE flagged exclusions highlighted in green.

Table 34 – DV Flagged Data Excluded
Copperview
Monitor
Annual 4th Max
MD8A (ppb)
Average 3-year Design Value
(2021-2023)
2021 2022 2023 DV Flagged Data
Included
DV Flagged Data
Excluded
Old 4th Max 86 74 73 77 --
New 4th Max 80 74 73 -- 75
Table 34. CV MD8A ozone 4th max for the years 2021-2023, with the unadjusted (old) and adjusted (new
- data excluded) 4th high MD8A ozone. The final DV by excluding the flagged EE events of July 12, July 24,
August 7 & 8, and August 16 is given.
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Appendix A

# 058
FXUS65 KSLC 242203 AFDSLC
Area Forecast Discussion National Weather Service Salt Lake City UT 403 PM MDT Sat Jul 24 2021 .SYNOPSIS...Drier air will remain over northern Utah and southwest Wyoming over the weekend. Deep moisture will linger across southern Utah, leading to daily showers and thunderstorms with localized heavy rainfall. Deep moisture will return northward early next week.
&&
.SHORT TERM (Through 12Z Tuesday)...High pressure remains centered just west of the forecast area this afternoon, resulting in a light but prevailing northerly flow aloft. This flow is allowing
a drier and more stable airmass to move into northern Utah, with PWs around the 0.3 to 0.5 inch range. The direction of the flow is also smoke in the air from fires in Oregon and California to
increase, resulting in some reduction in visibility. Meanwhile, deep moisture remains in place over southern Utah, particularly over southwest Utah where PW values are near 1.4 inch. With increase instability from daytime heating showers and thunderstorms have once again developed, with many producing heavy rain and some producing gusty winds and small hail. The threat of
convection continues through the early evening before tapering off. Little change in the pattern is anticipated tomorrow as a weak low slowly makes its way west across the Desert Southwest. As a result, northern portions of the forecast area should remain dry and stable with a continued slow warming trend in temperatures. Over southern Utah, the threat of flash flooding will remain elevated, especially over southern Utah, and have thus extended the going Flash Flood Watch through tomorrow evening. By Monday, the Desert Southwest low is expected to move off the southern California coast, causing the high to shift east and putting Utah and southwest Wyoming under a more southerly flow for much of the upcoming week. This will allow monsoonal moisture to start making its way back northward, spreading the threat of showers and thunderstorms back across the area. .LONG TERM (After 12Z Tuesday)...High pressure will remain centered to the east through the extended forecast. Differences in
the exact position will have the biggest influence on precipitation chances, but the much of the week is expected to have afternoon showers and thunderstorms. An increase in monsoonal moisture advection is expected Tuesday with winds becoming more southerly as the low bringing moisture to parts of the southwest this weekend moves up the Pacific coast and the high slides to the east. Precipitable water values will increase most in northern Utah. Values of around 1" will build in through much of the state, while amounts slightly over 1" are expected further south. Flash flooding will be the biggest threat with these showers and thunderstorms. Ensembles show nice agreement in the ridge expanding a bit, resulting in drier flow into Utah Wednesday. Isolated to scattered showers and thunderstorms are still expected, but should have fewer

than other days that week.

Later in the week could have the best chances for showers, thunderstorms, and more flash flooding risk with the positioning of the high and precipitable water exceeding 1" in models into northern Utah. Temperatures through the week will remain consistent, with highs in the low to mid 90s in northern Utah. Further south will generally be slightly cooler with more moisture in place, but lower Washington County should still reach the upper 90s to low 100s.
&&
.AVIATION...KSLC...VFR conditions are expected through the valid TAF period. Northwest winds will decrease into the evening and transition to the southeast around 04Z. Largely clear skies will continue, but smoky conditions will remain in place. Visibility dropping to as low as 6 sm is expected.
Rest of Utah and southwest Wyoming...VFR conditions are expected through the valid TAF period. Isolated showers and thunderstorms will diminish in southern Utah in the evening. Smoke will increase
further south, with the largest visibility reduction expected in southwest Wyoming and northern Utah. Scattered showers and thunderstorms are expected after 19Z for the southern TAF sites.
&& .FIRE WEATHER...Scattered to numerous wet thunderstorms will continue across southern Utah through the evening hours with the focus of the best storms primarily across southwest Utah. Meanwhile, northern Utah will see an increasingly hot, dry, and stable airmass, with just a few cumulus buildups possible over the Uintas. Little change in the pattern is anticipated for tomorrow,
so southern Utah will see another round of showers and thunderstorms as northern potions of the district remain dry, High pressure will amplify on Monday with the resulting southerly flow
spreading moisture northward once again. This moisture is expected to lift across central Utah on Monday and reach northern Utah by Tuesday, bringing with it an increase in thunderstorm activity for much of the upcoming week. && .SLC WATCHES/WARNINGS/ADVISORIES... UT...Flash Flood Watch through Sunday evening for UTZ123>125.
WY...None. &&
$$
SHORT TERM/FIRE WEATHER...Traphagan LONG TERM/AVIATION...Wilson
For more information from NOAA's National Weather Service visit... http://weather.gov/saltlakecity
For frequently asked questions about the Area Forecast Discussion visit... http://weather.gov/saltlakecity/general/afd_faqs.php
# # 321

FXUS65 KSLC 241539
AFDSLC
Area Forecast Discussion National Weather Service Salt Lake City UT 939 AM MDT Sat Jul 24 2021
.SYNOPSIS...Drier air will remain over northern Utah and southwest Wyoming over the weekend. Deep moisture will linger across southern Utah, leading to daily showers and thunderstorms with
localized heavy rainfall. Deep moisture will return northward early next week. && .DISCUSSION...Broad high pressure remains centered just west of the area this morning. Under a weak north to northwest flow aloft, the airmass continues to dry from the north, with PWs in northern Utah and southwest Wyoming currently in the 0.3 to 0.5 inch range. However, deep moisture remains in place over southern Utah, particularly for areas near the Arizona border, where PWs are still in the 1.2 to 1.4 inch range, above the 90th percentile for
this time of year. With instability increasing with daytime heating, should see another round of showers and thunderstorms over southern Utah this afternoon into this evening, with any storms that develop capable of producing heavy rain. CAMs show the greatest threat for precip over southwest Utah, particularly in the vicinity of Zion National Park, where PWs are highest, so would expect the greatest threat for flooding to be in this area. Current Flash Flood Watch and RRA product covers this threat well, especially as cloud cover over the area diminishes. In the drier airmass over northern portions of the forecast area, will see a continued warming trend into Sunday with maxes running in excess of 5F above normal, likely producing some high temperatures at or above 100F for portions of the Wasatch Front. Precip and cloud cover will likely keep temperatures near or below seasonal normals over southern Utah. The weak low over New Mexico is expected to track west through the
early part of next week, moving off the southern California coast by Monday afternoon. The movement of this low will shift the position of the ridge, bringing a more southerly component to the
flow aloft across the area by Monday. A bit of moisture may return northward Sunday but this trend should begin in earnest by Monday, allowing the threat of convection to move back northward. Little
change in the pattern is anticipated through much of the upcoming week, keeping a threat of showers and thunderstorms for much or all of the area over the next several days.
No updates expected to the forecast this morning.
&&
.AVIATION...KSLC...VFR conditions are expected across the valid TAF
period. Smoke will increase this afternoon, but visibility is expected to remain above 6SM. Light winds are expected to become prevailing northwesterly by 18Z, increasing during the afternoon.
Rest of Utah and southwest Wyoming...VFR conditions are expected to prevail across the area today. Afternoon showers and thunderstorms are expected to develop across southern Utah after 18Z with gusty and erratic winds possible in and around thunderstorm areas. There is a 30 percent change of brief MVFR

conditions in heavy rain with any storms. Smoke will begin to
increase across northern Utah and southwest Wyoming but no reduction in visibility below 6SM is anticipated. && .FIRE WEATHER...Scattered to numerous wet thunderstorms will develop across southern Utah during the afternoon and evening hours this weekend, with the focus of the best storms primarily across far southwest Utah. Meanwhile, northern Utah will see an increasingly hot, dry, and stable airmass, with just a few cumulus buildups possible over the Uintas. High pressure will amplify on Monday with the resulting southerly flow spreading
moisture northward once again. This moisture is expected to lift across central Utah on Monday and reach northern Utah by Tuesday, bringing with it an increase in thunderstorm activity. &&
.SLC WATCHES/WARNINGS/ADVISORIES... UT...Flash Flood Watch through this evening for UTZ123>125.
WY...None. && $$
Traphagan
For more information from NOAA's National Weather Service visit... http://weather.gov/saltlakecity For frequently asked questions about the Area Forecast Discussion visit...
http://weather.gov/saltlakecity/general/afd_faqs.php # # 252 FXUS65 KSLC 241128 AFDSLC

Area Forecast Discussion National Weather Service Salt Lake City UT 528 AM MDT Sat Jul 24 2021 .SYNOPSIS...A dry westerly flow will remain over northern Utah through the weekend, while deep moisture will linger across the south leading to daily showers and thunderstorms with localized heavy rainfall. The ridge providing dry weather for northern Utah will move east by early next week which will bring a moist southerly flow back to most of the forecast area.
&& .SHORT TERM (THROUGH 12Z TUESDAY)...An elongated ridge remains in place across the Great Basin this morning while a closed low continues to slowly move west across New Mexico. A very moist airmass remains across far southern Utah with PWATs over 1.2 inches along the Arizona border. Meanwhile, across the north, the airmass is drier with PWATs under 0.7 inches. That being said, the Cache Valley and portions of the Wasatch Front are still currently seeing dewpoints in the upper 40s to 50s. A mean north to northeasterly flow aloft is in place across much of Utah this morning and should largely remain in place through the day. Cloud cover remains fairly

extensive across southeast through east-central Utah ahead of the
low and extending to the northeast along a shear axis. Showers embedded within this area remain ongoing this morning, although they have trended weaker.
Given ample moisture, expect scattered to numerous showers and thunderstorms across southern Utah once again today. Cloud cover could serve as a limiting factor to strong convection, but this will be offset somewhat with the ascent ahead of the low. The mean SBCAPE values from the HREF are in the 750-1250 J/kg range for this afternoon across far southwest Utah. Even if this ends up being a bit too high, instability should remain sufficient for some decent convection across southwest Utah. Main focus will be on the area near Brian Head where some of the stronger cells are expected to initiate. Given the northeasterly flow, storms should track into Zion NP and toward the St. George area. While storm motions may be fast enough that any individual storms may not produce large precipitation amounts in any given area, some training may occur. Due to areas sensitive to flash flooding such as the Brian Head burn scar and Zion being within this most favored area for thunderstorms today, have issued a Flash Flood Watch for far southwest Utah. Have left out the south-central Utah zone for now as stroms should largely move across most drainages rather than down them, although a small area of concern still exists near Hildale. Conditions will not be too dissimilar tomorrow as the moisture continues to linger across the far south. Some increase of moisture is noted across portions of east-central Utah, otherwise showers and thunderstorms are expected again across southern Utah. Southwest Utah is expected to see similar CAPE values as today, and with a northeasterly flow continuing, there continues to be a threat of heavy rain and flash flooding in that area.
Northern Utah will remain warm and dry through the weekend. Temperatures will trend warmer with triple digit heat forecast across many northern valleys by Sunday.

On Monday, the ridge will amplify with its axis shifting east of Utah. Southerly flow will develop across southern Utah and lift into central Utah. This will allow the moisture and associated showers
and thunderstorms to start spreading back northward. .LONG TERM (After 12Z Tuesday)...Staying unsettled throughout the long term period with continued pulses of monsoonal moisture continues to surge into Utah. Overall, not much deviations in the
long term forecast from previous forecast updates. Wednesday continues to be the day where the flow aloft will temporarily shut monsoonal surge as the moist southerly flow that has been in place
across Utah will shift to a "drier" west to northwesterly flow. The net effect from this will be a more diurnally driven convective storm mode. Most of the convection will likely initiate along higher
terrain and orographic convergence zones during the afternoon and evening on Wednesday. By Thursday through the rest of the long term period, the magnitude of the monsoonal push will be dependent on a broad area of high pressure that will be meandering near the Four Corners region. Given
the overall H5 pattern remains consistent amongst the model members in having the PFJ displaced well to north while maintaining this large/broad area of high pressure across the Intermountain West,
confidence is high that Utah will continue to experience a monsoonal pattern. PWAT values and far north this moisture goes will have the greatest forecast variability as any slight deviations in the high

pressure center will have a net effect on those parameters.
Nevertheless, the takeaway here is thunderstorms chances will remain in the forecast with flash flooding still a concern, especially across southern Utah. With abundant cloud cover from thunderstorm
debris and a return to a moist airmass, temperatures will also continue to be right at or just slightly below seasonal normals. && .AVIATION...KSLC...VFR conditions are expected across the valid TAF period. Smoke will increase this afternoon, but visibility is expected to remain above 6SM. Light southerly flow will continue through the morning before shifting to a northerly flow and turn
gusty after 18z, with wind gusts approaching 24 knots. There is a 40% chance for gusts to exceed the 26kt/30mph threshold. Winds are expected to shift back to the south after 04z. Rest of Utah and southwest Wyoming...Afternoon showers and thunderstorms are expected to develop across southern Utah after
18z. Gusty and erratic winds can be expected in and around thunderstorm areas. Brief intermittent MVFR conditions can be expected at terminals directly impacted by a thunderstorm, otherwise
expect VFR conditions outside thunderstorm areas. Smoke will begin to increase across the north but no reduction in visibility below 6SM is expected.
&& .FIRE WEATHER...Scattered to numerous wet thunderstorms can be expected once again across southern Utah today and tomorrow, with the focus of the best storms primarily across far southwest Utah
owing to a northeasterly flow. Meanwhile, northern Utah will see a hot, dry, and stable airmass, with just a few cumulus buildups possible over the Uintas. High pressure will amplify on Monday with
the resulting southerly flow spreading moisture northward once again. This moisture is expected to lift across central Utah on Monday and reach northern Utah by Tuesday, bringing with it an
increase in thunderstorm activity. && $$ .SLC WATCHES/WARNINGS/ADVISORIES... UT...Flash Flood Watch from noon MDT today through this evening for UTZ123>125.
WY...None
&&
$$
Cheng/Woodward
For more information from NOAA's National Weather Service visit... http://weather.gov/saltlakecity
For frequently asked questions about the Area Forecast Discussion visit... http://weather.gov/saltlakecity/general/afd_faqs.php
# # 052

FXUS65 KSLC 232203
AFDSLC
Area Forecast Discussion National Weather Service Salt Lake City UT 403 PM MDT Fri Jul 23 2021

.SYNOPSIS...A dry westerly flow will spread over northern Utah through the weekend, while deep moisture will linger across the south leading to daily showers and thunderstorms with localized
heavy rainfall. The ridge providing dry weather for northern Utah will move east by early next week which will open the door for moist southerly flow to move back across most of the forecast
area. && .SHORT TERM (Through 12Z Monday)...Despite drier air moving in across northern Utah today, there remains enough low level
moisture to generate some decent thunderstorms over the Raft River Range this afternoon producing strong winds and heavy rain. However, models are showing that subsidence near the 500mb level
will become stronger and deeper later this afternoon and evening across northern Utah which should put a cap to thunderstorm development, so expecting any storms to die off fast early this
evening. Drier air will continue to spread in across the remainder of northern Utah and Uinta County Wyoming tonight through Saturday, but the ridge will move east by Sunday pushing the subsidence portion of the ridge to our east and allow convection to once again develop over the Uintas by Sunday afternoon and evening. Moisture will be marginal at this time.
Central Utah will dry a little more Saturday as the westerly to northwesterly flow penetrates this portion of the state, but the
hiatus in thunderstorms will be short lived as convection will be on the increased Sunday over the central mountains. Light northerly flow over most of southern Utah combined with deep moisture will have thunderstorms capable of producing heavy rain to move down drainage exacerbating the potential for flash
flooding. A flash flood watch remains in effect until midnight as storms over the higher terrain will drift southward this evening. St. George will have a good chance of having a cluster of
thunderstorms move south southwest across them this evening as some high resolution models are in agreement on an instability bullseye over Washington County this evening. The northerly flow
will continue through Saturday so the threat of flash flooding will continue, especially in the drainages that drain southward. By Sunday the ridge aloft will have moved east and the flow turns
southeast importing moisture northward. Temperatures will average a few degrees above average in the north
with temperatures averaging a few degrees below normal in the south due to clouds and thunderstorms.
.LONG TERM (After 12Z Monday)...The low moving through New Mexico and Arizona over the weekend responsible for transitioning winds to more a of a northeasterly flow will exit to the west. That will allow for southerly flow to kick back in as the ridge centers to the east. Better moisture advection will build in from that direction, especially in northern Utah. Elsewhere, precipitable water values will stay similar from the remnant moisture associated with the aforementioned low along with more monsoonal

moisture. Values around 1" or higher could build into central
Utah. In northern Utah, values will likely surpass that mark Tuesday as conditions remain largely unchanged. Flash flooding will remain a threat. The storms will be similar to recent ones,
aided by daytime heating and diminishing with loss of solar warming. Variations in the ridge position will influence PoPs each day in the forecast, but there's good confidence in the monsoonal set up remaining in place. The warmest temperatures of the week in southwest Wyoming and northern Utah are expected near the start, when the driest
conditions are in place. Highs around 5F warmer than average are expected Monday, followed by slightly cooler, but still near average temperatures through Friday. Temperatures will mainly be around 5F cooler to near average in central and southern Utah. && .AVIATION... KSLC...VFR conditions are expected through the valid TAF period. Scattered mid and high clouds will decrease into the evening, but smoke will increase from the northwest. Visby is expected to remain above P6SM. Winds will switch to southeast around 04Z. Rest of Utah and southwest Wyoming...VFR conditions are expected through the valid TAF period. Isolated showers and thunderstorms
will diminish in southwest Wyoming and northern Utah around 00Z. The chance for precipitation will last through 06Z in southern Utah, with heavy rain the main threat. A shower or thunderstorm over a TAF
site could drop CIGs into MVFR range for a short amount of time. Smoke will increase in southwest Wyoming and northern Utah into Saturday, but visby is expected to remain above P6SM.
&&

.FIRE WEATHER...The drier westerly flow has started to move in across the north today and will penetrate farther into central Utah this weekend, eliminating most thunderstorm activity in the north and
reducing the threat of thunderstorms in the central area. Min RHs will fall below 15% in the north and some western valleys this weekend, but then trend upward as the flow switches to southerly
by early next week importing more moisture and increasing chances of showers and thunderstorms.
Deep moisture will remain over southern Utah, although it will be suppressed a little farther south Saturday than today, but then start spreading northward some Sunday and more so by Monday
reaching fwx zone 492, and northeast into the Uintas. Widespread showers and thunderstorms are expected over the far southern fwx zones Saturday through Tuesday, while scattered showers and
thunderstorms will be common just north of here on Saturday and into central Utah Sunday and Monday. RH values will remain elevated through the entire forecast period with min RH values in the 30-40% range with max RH values above 80% in many areas. && $$
.SLC WATCHES/WARNINGS/ADVISORIES...
UT...Flash Flood Watch until midnight MDT tonight for UTZ122>125-128.

WY...None
&&
$$ SHORT TERM...Struthwolf LONG TERM...Wilson AVIATION...Wilson
FIRE WEATHER...Struthwolf For more information from NOAA's National Weather Service visit... http://weather.gov/saltlakecity
For frequently asked questions about the Area Forecast Discussion visit...
http://weather.gov/saltlakecity/general/afd_faqs.php # # 362 FXUS65 KSLC 231648 AFDSLC
Area Forecast Discussion National Weather Service Salt Lake City UT
1048 AM MDT Fri Jul 23 2021
.SYNOPSIS...A drier westerly flow will move into northern Utah through the weekend, while deep moisture will linger across the south leading to daily showers and thunderstorms with localized heavy rainfall.
&&
.DISCUSSION...Another day of thunderstorms across central and southern Utah with locally heavy rain possible. The PWs remain near 1.50 inches along the Arizona border and the CAPE is even
higher than yesterday reaching 1400 over the southwest by 21Z. The flow aloft is convergent across SW Utah this afternoon and becoming northeast farther to the east. This all spells another
busy day with thunderstorms have a high potential of producing Flash Flooding over the prone areas of of southern Utah as the storm flow will be down drainage in many areas. Have extended the
FFA across all of Washington and Iron Counties from noon until midnight tonight, although the thunderstorms will likely not get going over central Washington County until late this afternoon or
evening. Across northern Utah there is still very high PWs but there will
be a downward trend today as drier air works its way into the region this afternoon. There will be a time frame from about noon until 4pm that areas from the central Wasatch into the Uintas will
have the best chance to have some build ups and isolated thunderstorms, but nothing like yesterday. At 500mb a subsidence inversion will become more widespread across the northern 1/4 of
the state after about 21Z (3pm) which will stabilize the atmosphere.
&& .AVIATION... KSLC...VFR conditions are expected through the valid TAF period. Southeast winds will transition to the northwest around 18Z. Scattered mid and high clouds will decrease into the evening, but smoke will increase from the northwest. Vsby is expected to

remain above 6 sm. Winds will switch to southeast around 04Z. Rest of Utah and southwest Wyoming...VFR conditions are expected through the valid TAF period. There is a slight chance for an isolated shower or thunderstorm in southwest Wyoming and northern Utah through 00Z. Afternoon showers and thunderstorms will primarily be in the south. The chance for precipitation will last through 06Z in this portion of the state, with heavy rain the main threat. A shower or thunderstorm over a TAF site could drop CIGs into MVFR range for a short amount of time. Smoke will increase in southwest Wyoming and northern Utah late, but vsby is expected to remain above
6 sm.
&&
.FIRE WEATHER...Abundant moisture will remain in place across southern Utah today, which will result in scattered to numerous wet thunderstorms. Some of this moisture will continue across far southern Utah through the weekend. Meanwhile, drier air will spread into northern Utah today and spread into central Utah for the weekend. Scattered showers and thunderstorms can still be expected
today across the northern mountains, then become more isolated and drier over the weekend. The moisture will work north again next week, with scattered showers and thunderstorms possible for much of the area through much of the week.
&&
.SLC WATCHES/WARNINGS/ADVISORIES... UT...Flash Flood Watch through this evening for UTZ122-123.
Flash Flood Watch through this evening for UTZ124-125-128.
WY...None. && $$ PUBLIC...Struthwolf AVIATION...Wilson FIRE WEATHER...
For more information from NOAA's National Weather Service visit... http://weather.gov/saltlakecity
For frequently asked questions about the Area Forecast Discussion visit... http://weather.gov/saltlakecity/general/afd_faqs.php # # 336
FXUS65 KSLC 231106 AFDSLC
Area Forecast Discussion
National Weather Service Salt Lake City UT 506 AM MDT Fri Jul 23 2021 .SYNOPSIS...A drier westerly flow will move into northern Utah through the weekend, while deep moisture will linger across the south leading to daily showers and thunderstorms with localized heavy rainfall.

&&
.SHORT TERM (THROUGH 12Z MONDAY)...High pressure that had been positioned over the Four Corners area has trended flatter in
response to a trough moving across western Canada and is retrograding towards southwest Utah. Meanwhile, an upper low over far southwest New Mexico this morning will continue to track west towards Arizona. Westerly flow at 500mb and northwesterly at 700mb is spreading drier air as well as smoke into northwest Utah this morning. This drier air and smoke will spread farther into northern Utah during the afternoon. Across the south, deep moisture remains in place with PWATs in excess of 1.2 inches along the Arizona border.
While mid and high clouds remain in place early this morning, breaks in the clouds are evident in satellite imagery. If this trend holds, there should be enough clearing by afternoon to allow the surface heating necessary to initiate robust convection across portions of southern and central Utah. The HREF is showing areas of mean MUCAPE in the 750-1250 J/kg range this afternoon in south-central and southwest Utah. Expect a heavy rain potential again with thunderstorms. Given a more northerly 700mb flow by afternoon, expect storms initiating off the southern and central mountains to propagate more towards the south today. This would pose a flash flood threat to prone areas extending from the southern mountains into Kane County and the Zion National Park area. Have issued a
Flash Flood Watch for these areas as a result.
Across the north, the drier airmass will cause showers and
thunderstorms to be more lilted. However, with low-level moisture remaining in place as indicated by current dewpoint readings in the 50s and low 60s, expect isolated to scattered thunderstorms to
initiate over the higher terrain despite the drier air aloft. The deeper moisture will become more confined to southern Utah over
the weekend as drier air continues to work its way into central Utah. A more easterly deep-layer flow will develop over southern Utah as it will be on the northern periphery of aforementioned upper
low. With this flow, the heaviest rain may focus more on southwest Utah.
Temperatures across the south where afternoon showers and thunderstorms develop will remain a bit on the cooler side through much of the weekend. However, with clearing across the north, hot
temperatures should return for the weekend, with triple digit heat possible for the lower valleys of northern Utah.
.LONG TERM (After 12Z Monday)...Monsoon moisture surge continues across Utah through midweek. An inverted trough moving across the Desert southwest will phase into a strong area of low pressure sitting off the southern California coast. In response a moist, southerly flow will continue to pump rich, monsoonal moisture across
Utah Monday and again on Tuesday. PWAT values are expected to climb above 1" across southern Utah with lesser values across central and northern Utah. Clusters of showers and thunderstorms are expected to develop across southern Utah on Monday. Once again, the slow storm motions will heighten the risk of flash flooding. Across central and northern Utah, thunderstorm chances will depend on residual outflow boundaries and cold pools and whether these sectors can destabilize throughout the afternoon. This scenario will play out once again on Tuesday with the threat of flash flooding being the main concern. A shift toward a west to northwest upper level flow beginning on Wednesday will turn off the monsoonal moisture hose. Ample amounts

of moisture will remain and diurnal convection can be expected
across much of the forecast area. Most of the convection will likely initiate along higher terrain and orographic convergence zones during the afternoon and evening on Wednesday. Where low level dry
air is undercutting the mid-level moisture, strong outflow winds can be expected. A more typical summertime, diurnal convective cycle looks to be the dominate weather story heading toward the end of the
week. Ample amounts of storm cloud debris will hamper temperatures from climbing to high in this "drier" regime. Temperatures should be right at seasonal normals come Wednesday onward.
&&
.AVIATION...KSLC...VFR conditions are expected across the valid TAF period. There is a 30% chance for vicinity showers and thunderstorms to bring gusty and erratic winds across the terminal. Confidence is low for thunderstorms to directly impact the terminal, but TEMPO groups could be introduced in later updates if confidence increases. Light southerly flow will continue through the morning before shifting to a light northerly flow after 18z. Rest of Utah and southwest Wyoming...Afternoon showers and thunderstorms are expected to develop across southern Utah after 18z. Gusty and erratic winds can be expected in and around thunderstorm areas. Brief intermittent MVFR conditions can be expected at terminals directly impacted by a thunderstorm. Some of this activity may spread into central Utah by the evening. Smoke will begin to increase across the north but we are expecting no reduction in visibility.
&& .FIRE WEATHER...Abundant moisture will remain in place across southern Utah today, which will result in scattered to numerous wet thunderstorms. Some of this moisture will continue across far southern Utah through the weekend. Meanwhile, drier air will spread into northern Utah today and spread into central Utah for the weekend. Scattered showers and thunderstorms can still be expected today across the northern mountains, then become more isolated and drier over the weekend. The moisture will work north again next week, with scattered showers and thunderstorms possible for much of the area through much of the week.
&&
.SLC WATCHES/WARNINGS/ADVISORIES... UT...Flash Flood Watch from noon MDT today through this evening for UTZ124-125-128.
WY...None.
&&
$$
Cheng/Woodward
For more information from NOAA's National Weather Service visit...
http://weather.gov/saltlakecity For frequently asked questions about the Area Forecast Discussion
visit... http://weather.gov/saltlakecity/general/afd_faqs.php #

#
619 FXUS65 KSLC 082148 AFDSLC

Area Forecast Discussion National Weather Service Salt Lake City UT 348 PM MDT Sun Aug 8 2021 .SYNOPSIS...Dry conditions are expected to prevail across the
region through Monday along with areas of smoke. A cold front will bring briefly cooler conditions Monday before a warming trend commences for the rest of the week.
&& .SHORT TERM (Through 12Z/6AM MDT Wednesday)... A seasonably strong (-2 to -2.5 500mb standardized anomaly) area of low pressure will continue to slide eastward across the Northern Rockies tonight through Monday. This will drag a dry cold front across mainly northern Utah tonight. With the bulk of the jet support and moisture relegated well to our north, no
precipitation will accompany this frontal passage, save for an outside shot at an isolated shower or thunderstorm over the Uintas. Temperatures are forecast to drop 5-10 degrees on Monday
across northern Utah in the wake of the boundary. The HRRR smoke model indicates the potential for some relief from the smoke across northern Utah on Monday in the wake of the front, at least
in terms of the boundary layer smoke. HRRR smoke model hangs on to relatively high concentrations of vertically-integrated smoke, which would suggest a continuation of hazy skies. Temperatures will begin a slow rebound on Tuesday as a ridge of high pressure begins to build across the Great Basin. Subtle mid-level moisture advection across southern Utah may be enough to promote the development of isolated showers and thunderstorms over high terrain areas of southern Utah Tuesday
afternoon and evening. Precipitable water values are expected to return to near average for the time of year. Flow through 500mb is forecast to be weak, thus locally heavy rainfall will be possible should convection tie itself to terrain for an extended time, or where cold pools merge. Southern Utah sounding analysis indicates dry sub-cloud layers, so any shower or thunderstorm will be capable of producing gusty outflow winds. Progged DCAPE values in the 1000-1500J/kg range further support the idea of gusty outflow winds. .LONG TERM (AFTER 12Z/6AM MDT Wednesday)... An expanding area of high pressure will engulf the forecast area
through the second half of the week, with the center of this high anticipated to be positioned over the Utah/Nevada border region. Above average 500mb heights will lead to a gradual warming trend,
with high temperatures becoming 5- 10 degrees above average across Utah and southwest Wyoming as we approach the end of the week/ beginning of the weekend. The current record for number of 100 degree days in a year for Salt Lake City is sitting at 21... by the end of the week there is potential to tie or even break that record as the current NBM forecast suggests 98 to 99 degrees.
Given the positioning of the high, we will be lacking substantial southerly flow which may limit our chances of breaking into the triple digits along the Wasatch Front.. but there is still a lower
end chance that we do. Have maintained NBM guidance for the time being.

Additionally, with the area of high pressure progged to be centered
over western Utah/ eastern Nevada, there will be minimal moisture advection into the area. Rather, the moisture will tend to wrap around the high, with the axis of higher PWAT values extending from
NWern Arizona through southern Nevada/ central California. A gradual increase in moisture may be seen across the far southern portions of Utah late in the week as we remain on the edge of this moisture
axis. However, heading into the weekend the high will gradually saturate as moisture is wrapped around its center. With this scenario we should see increasing chances for precipitation Friday
through Sunday, with the best chances along the high terrain (especially across southern Utah). Confidence in rainfall reaching adjacent valley areas remains low given the lack of flow... so the
current thinking is that showers will be largely confined to terrain. Any showers that do occur will have the potential to produce periods of heavy rainfall and could lead to some flash
flooding concerns over the weekend, with each day becoming more and more of a threat. &&
.AVIATION... KSLC...Increasingly smoky skies will continue to encroach the KSLC terminal through the evening hours. High end MVFR visibilities are expected to continue, with potential to drop to IFR as more smoke mixes down with an approaching cold front. There is a 25% chance that surface VIS falls below 3SM around 05Z with the passage of the boundary. Modest south winds will continue through the remainder of the afternoon and evening hours, becoming northerly around 05-06Z as the boundary pushes through the area.
REST OF UTAH AND SOUTHWEST WYOMING...Increasing smoke across the northern half of the area remains the biggest concern through the current TAF period, with widespread MVFR surface visibilities spread
from about KMLF northward. Brief high end IFR visibility due to increased surface smoke may occur near KENV and areas south from ~02- 09Z. Expect VFR conditions to continue from KMLF southward, with
subtle increases in smoke after ~02Z this evening... though remaining VFR.
&& .FIRE WEATHER...
A dry cold front remains on track to pass across mainly northern Utah tonight. Behind the front, temperatures are expected to cool 5-10 degrees on Monday across northern Utah, with a less noticeable cooling trend expected for southern Utah. Wind- prone areas of northern Utah will experience westerly wind gusts in the 25-35 mph range on Monday along with minimum relative
humidity values around 15 percent. Heading through the week, a ridge of high pressure is expected to gradually build into the Great Basin, leading to a warming trend. This ridge is expected to
largely remain in place through next weekend. Moisture will gradually increase across southern Utah through the week. Isolated shower and thunderstorm activity is currently expected to return Tuesday, with continued isolated shower and thunderstorm chances across mainly southern Utah continuing through the week.
&& .SLC WATCHES/WARNINGS/ADVISORIES... UT...None. WY...Red Flag Warning until 8 PM MDT Monday for WYZ277.

&& $$
ADeSmet/Webber
For more information from NOAA's National Weather Service visit... http://weather.gov/saltlakecity
For frequently asked questions about the Area Forecast Discussion visit... http://weather.gov/saltlakecity/general/afd_faqs.php # # 157 FXUS65 KSLC 081035 AFDSLC
Area Forecast Discussion
National Weather Service Salt Lake City UT 435 AM MDT Sun Aug 8 2021 .SYNOPSIS...Dry conditions are expected to prevail across the region today with areas of smoke. Another cold front will sweep through the region late today, brining breezy conditions along with the potential to bring more smoke into northern Utah.
&& .SHORT TERM (THROUGH 12Z WEDNESDAY)...An upper low is noted on
satellite imagery moving into the PacNW this morning. The ridge that was west of Utah is now shifting to the east. Meanwhile, smoke remains in place across the area with reduced visibilities noted in
obs, mainly across southern and central Utah and adjacent areas in Colorado and Nevada. Beyond the smoke layer, nary a cloud is evident over Utah or within a couple hundred miles given the dry airmass in
place. With the ridge axis east of Utah, southwest flow will increase
across the area today, aiding mixing and leading to warmer temperatures. However, H5 winds are more WSW and owing to cyclonic curvature of the flow south of the low, this puts northern Utah in
direct connection to northern Cali wildfire smoke. Latest HRRR indicates fairly significant concentrations spreading into the area by this afternoon, but slightly less than on Friday. Slightly. However, one benefit of the smoke is that it will likely keep max temperatures a couple degrees cooler than it could be.
The upper low will track across northern Idaho this evening and push a dry cold front into Utah tonight. With the flow turning more northerly behind the front, the smoke is expected to pool more over
central Utah for tomorrow. Afternoon max temperatures across northern Utah tomorrow will fall to slightly below Climo tomorrow behind the cold front, with southern Utah remaining near to sightly
above Climo since the front is progged to weaken before it gets there. On Tuesday, Utah will remain under a largely dry westerly flow aloft. However, a shortwave disturbance will lift north through Arizona. This will bring some moisture to the border, with perhaps a
small chance of high-based showers developing over the higher terrain of southern Utah for the afternoon hours if enough of the moisture makes it into Utah.

.LONG TERM (AFTER 12Z WEDNESDAY)...A ridge of high pressure is forecast mid-week which will lead to a fairly mild weather pattern across the region. Moisture is currently centered south, southwest and southeast of our area through Friday around an area of low pressure centered over Arizona. The thing to watch over the weekend is the movement of aforementioned low. Moisture is set to be pulled northward according to the GFS solution, due to the progression of an incoming trough across the Pacific Northwest and the breakdown of the ridge. At this time, the ECMWF solution is not favoring the
development of that trough. The forecast remains largely unchanged at this time in the extended period, and keeps most of the moisture late week and over the weekend over southern Utah.
&&
.AVIATION...KSLC...VFR conditions are expected this forecast period though skies will continue to remain smoky/hazy Sunday. The question Sunday evening will be if visibilities and ceilings will drop to MVFR status with the next boundary pushing in. At this time, we are forecasting 5SM visibility starting at 4Z. Meanwhile, during the day expect some stronger southerly winds before shifting southwesterly mid afternoon.
Rest of Utah and southwest Wyoming...Southern Utah locations
continue to observe MVFR conditions which will remain in the forecast today. Some stronger winds during the afternoon is forecast to scour out some of the smoke/haze and gradually improve
visibility. Northern Utah/EVW locations are expected to generally see VFR conditions though smoky/hazy conditions persist today. The arrival of a boundary later this afternoon and evening will shift
winds and bring in lowered visibilities and ceilings for ENV, LGU and OGD and particular.
&& .FIRE WEATHER...A warm and dry southwest flow will increase across
the area today as the next trough crosses the Pacific northwest. As this trough slides by to the north tonight, a cold front will sag into Utah. A dry and locally breezy west to northwest flow is
expected tomorrow behind the cold front. Thereafter, a near westerly flow will maintain dry conditions into the early part of next week. Some midlevel moisture may enter Utah from the south during the
middle to latter part of next week which could bring some thunderstorm chances to mainly southern Utah.
&&
.SLC WATCHES/WARNINGS/ADVISORIES... UT...None. WY...Red Flag Warning from noon today to 8PM MDT Monday for WYZ277.
&&
$$
Cheng/NDeSmet
For more information from NOAA's National Weather Service visit... http://weather.gov/saltlakecity
For frequently asked questions about the Area Forecast Discussion visit...

http://weather.gov/saltlakecity/general/afd_faqs.php
# # 740
FXUS65 KSLC 072143 AFDSLC
Area Forecast Discussion
National Weather Service Salt Lake City UT 343 PM MDT Sat Aug 7 2021 .SYNOPSIS...Dry conditions are expected to prevail across the region today with areas of smoke. Another cold front will sweep
through the region late Sunday, brining breezy conditions along with the potential to bring more smoke into the area.
&&
.SHORT TERM (Through 12Z/6AM MDT Tuesday)... Quiet weather conditions are expected through this evening beneath the presence of dry zonal flow. On Sunday, deterministic and ensemble models are in good agreement with their depiction of a
seasonably strong (-2 to -2.5 500mb standardized anomalies) area of low pressure slated to slide eastward across the Northern Rockies. This will drag a cold front eastward across northern Utah
Sunday night. Ahead of the frontal boundary, southwesterly flow is progged to increase into the 20-25kt range by afternoon. This will translate to breezy conditions at the surface, with gusts
forecast in the 25-35 mph rage for typically breezy locations. The southwesterly flow ahead of the front will aid in boosting temperatures back to around seasonal normals for early August,
some 10 degrees warmer than what we're experiencing this afternoon. The wildcard will be the smoke concentration and its ultimate impact on the attenuation of incoming solar radiation.
Given that the HRRR smoke model is insistent on advecting another surge of both near surface and vertically-integrated smoke into the forecast area during the afternoon, have shaved 2-4 degrees
off of the NBM's offering, yielding mid-90s in the Wastach front and low 100s in St. George. On Monday, a return to dry zonal flow is anticipated in the wake of the northern Utah frontal passage. Mid-level winds are forecast out of the west in the 25-30kt range across northern Utah and SW
Wyoming, and this will yield wind gusts in the 30-40 mph range across wind-prone areas of northeast Utah and SW Wyoming Monday afternoon and evening. Otherwise, dry conditions are forecast with
the exception of a sneaky, isolated shower or thunderstorm chance over the Uintas. Temperatures are forecast to dip back down to around 10 degrees below seasonal normals for Monday behind the cold frontal passage. Temperatures may underachieve by a degree or two dependent upon attenuation of incoming shortwave radiation
courtesy of lingering wildfire smoke.
.LONG TERM (AFTER 12Z/6AM MDT Tuesday)... Hot and largely dry conditions are expected to prevail across a
majority of the CWA through the first half of the week ahead as high pressure regains control of the eastern Great Basin. Chances for precipitation will increase late in the week to the early
weekend as layer PWAT values slowly increase as the high pressure expands over the area, with higher confidence in PoPs across the southern Utah mountains and lower confidence across the northern
mountains. On Tuesday, an exiting trough will allow a ridge of high pressure to

expand over the Great Basin as the parent ridge beings moving inland
over the PacNW/ BritCol region. With the anticipated frontal boundary associated with the trough progged to exit the region by late Monday/ early Tuesday, the expanding high pressure will allow
H7 temperatures to begin increasing once again. The net impact that this will have at the surface will be to initiate a warming trend beginning Tuesday, generally continuing through the remainder of the
week as the high pressure strengthens. NBM high temperature forecasts show little spread within the bulk of the forecast distribution, so can say with pretty high confidence that
temperatures will be above average. Across the Wasatch Front, we could be pushing the triple digit mark once again toward the end of the work week. For southern Utah the triple digit mark seems likely,
with lower Washington County expected to push into the mid-100s (about 5F above average). After a prolonged dry period, precipitation looks to make a potential comeback to at least the southern Utah mountains through the second half of the week. With the aforementioned high pressure expanding over the Great Basin, light circulations around the high will favor gradual increases in PWAT values across the forecast area. Though there is no noteworthy moisture advection, this gradual increase in PWAT values will bring increased chances for precipitation Tuesday through Saturday. With that being said, confidence remains low in this forecast as ensemble clusters remain
in favor of largely dry conditions. However, with 20-40% of ensemble members suggesting at least some QPF over the southern half of Utah, showers and thunderstorms late in the week seem well within the
realm of possibilities...at least for the southern half of Utah. Will continue to monitor trends going forward.
&&
.AVIATION... KSLC...Minor improvements in the smoke layer will continue through the evening hours with VIS likely to remain in the VFR category. A temporary return to high end MVFR VIS may be possible through the
night, though confidence remains low. Smoke will increase during the late morning/ afternoon hours tomorrow, though likely to remain VFR to high end MVFR through ~03 Monday. Thereafter, significant
increases in near surface smoke is anticipated to bring VIS back down to low end MVFR to high end IFR. Otherwise, light north winds will prevail through the remainder of the day, with light southerly drainage winds returning after 03-04Z. Rest of Utah and southwest Wyoming...Biggest concern with this evening's TAF package continues to coincide with a widespread smoke layer across the area causing reduced surface VIS. Greatest VIS reductions are expected across southern Utah through ~18Z tomorrow,
with minor, but short lived, improvements elsewhere. A substantial decrease in surface VIS to low end MVFR to high end IFR is anticipated across northwestern Utah by 18-20Z Sunday, progressing southeast through the evening and overnight hours. Aside from smoke, light to moderate terrain driven flow is anticipated through the remainder of the day, with increased southerly winds expected through the morning hours for much of Utah and southwest Wyoming. &&
.FIRE WEATHER... Dry conditions are expected tonight and Sunday. Temperatures will trend warmer on Sunday, returning to seasonal normals due to increasing southwest flow ahead of the next

trough and associated cold front. Southwest wind gusts are
forecast to increase into the 25-35 range across the west deserts and other wind-prone areas across the state Sunday. Minimum relative humidity is expected to drop into the single digits to
low teens area-wide. The absence of critically dry fuels will preclude the need for any fire weather headlines, per coordination with the Great Basin Coordination Center. The above-mentioned
front will swing eastward across northern Utah Sunday night. This frontal passage is expected to be of the dry variety. In the wake of the front, temperatures are expected to fall back to 10 degrees
below seasonal averages on Monday. Gusty west winds are expected to achieve 25-35 mph across favored areas of northern Utah Monday, with minimum relative humidity values generally forecast
in the 15-25 percent range. A sprawling ridge of high pressure is forecast to develop across the Great Basin and Pacific Northwest by midweek and is forecast to remain in place through next
weekend. This should bring a gradual warming trend to the region. A subtle increase in moisture across southern Utah beneath the ridge may support isolated showers and thunderstorms across this
area from midweek through next weekend. && .SLC WATCHES/WARNINGS/ADVISORIES...
UT...None. WY...Red Flag Warning from 12PM MDT Sunday to 8PM MDT Monday for WYZ277.
&&
$$
ADeSmet/Webber
For more information from NOAA's National Weather Service visit... http://weather.gov/saltlakecity
For frequently asked questions about the Area Forecast Discussion visit...
http://weather.gov/saltlakecity/general/afd_faqs.php # #
117 FXUS65 KSLC 071000 AFDSLC
Area Forecast Discussion
National Weather Service Salt Lake City UT 400 AM MDT Sat Aug 7 2021 .SYNOPSIS...Dry conditions are expected to prevail across the
region as high pressure begins to temporarily rebuild. An area of dense smoke will remain in place through today with some improvement expected over northern Utah, and generally stable conditions across southern Utah. Another cold front will sweep through the region late Sunday with potential to bring more smoke into the area.
&&
.SHORT TERM (THROUGH 12Z TUESDAY)...A shortwave trough continues to
exit into Colorado this morning, with Utah under a dry northwest flow aloft. Smoke from western wildfires which spread into Utah in abundance yesterday will pool more across southern Utah today given

the northwest flow, with the smoke over northern Utah thinning out a
bit. Otherwise, temperatures will remain on the cooler side today, with most areas expected to see afternoon maxes near to below climatological normals.
Temperatures will rebound tomorrow as southwest flow increases ahead of the next approaching shortwave trough. However, smoke will once again increase across northern Utah, and latest HRRR suggests that it may be about as thick as it was yesterday. Across southern Utah, there is better news as the smoke will thin out over that area. The trough will move by to the north but push another dry cold front into Utah tomorrow night into Monday. This will result in another
temperature swing, while again pushing the smoke plume farther south. Still no moisture expected across the area given that the flow will turn northwesterly again behind the cold front.
.LONG TERM (AFTER 12Z TUESDAY)...High pressure centered to the southeast is forecast to be in control of our weather pattern mid-
week. The chances for precipitation continue to drop as each forecast run comes in with only slight chances for showers and thunderstorms Tuesday through Friday afternoons across a small
portion of southern Utah at this point. The GFS model does want to increase the moisture across a better portion of Utah over the weekend but lets just continue to watch that trend and see how
models play this trend out over the coming days. Temperatures remain forecast to be slightly cooler across northern Utah Tuesday with the passage of a weak cool front but will warm right back up the
remainder of the week. We will continue to see over 100 degree days across the St. George area for highs each afternoon.
&& .AVIATION...KSLC...Light winds with a smoke/haze layer is forecast to continue this morning. The question today will be when or if the layer will allow for an improvement in visibility or ceiling heights. We will forecast VFR conditions early this afternoon with the caveat of a low confidence based on how the smoke decides to behave. Wind direction is expected to shift back from the northwest and remain light around 19Z. Rest of Utah and southwest Wyoming...The forecast for today will be dependent on smoke continues and to what extent. The forecast is for the haze/smoke layer to be more prevalent across southern Utah sites, which would create MVFR or IFR visibility and ceilings conditions. Some improvement to conditions for these locations are forecast mid to late afternoon though haze/smoke would continue. Meanwhile, across northern Utah and the EVW TAF sites, smoke/haze does linger this morning for all but ENV. Forecasts are rather
difficult to time out improvement in the visibility and ceilings and that said, these forecasts come with a low confidence. We are, however, going to forecast a general improvement out of MVFR/IFR
conditions mid-day. &&
.FIRE WEATHER...A shortwave trough exiting the area today will maintain near-seasonal to slightly below normal temperatures and dry conditions across the the area. Dry conditions will continue tomorrow, but temperatures will trend warmer with increasing southwest flow ahead of the next trough. This trough will bring another cold front which will bring another downward swing in temperatures for Tuesday, along with breezy west to northwest winds, although the airmass will remain dry. The winds and dry airmass

would bring hazardous fire weather conditions tomorrow and Monday if
fuels are dry enough, but at this time, fuels are not expected to be critically dry. There is some potential for midlevel moisture to work its way back into southern Utah for the second half of next
week, but not expecting any significant monsoonal moisture surge through the forecast period.
&& .SLC WATCHES/WARNINGS/ADVISORIES... UT...None. WY...None. && $$
Cheng/NDeSmet
For more information from NOAA's National Weather Service visit... http://weather.gov/saltlakecity
For frequently asked questions about the Area Forecast Discussion visit... http://weather.gov/saltlakecity/general/afd_faqs.php
# # 848
FXUS65 KSLC 070342 AFDSLC
Area Forecast Discussion National Weather Service Salt Lake City UT 942 PM MDT Fri Aug 6 2021
.SYNOPSIS...Dry conditions are expected to prevail across the region as high pressure begins to temporarily rebuild. An area of
dense smoke will remain in place through at least Saturday with improvement expected over northern Utah, and generally stable conditions across southern Utah. Another cold front will sweep
through the region Sunday with potential to bring more smoke into the area.
&& .DISCUSSION...Cold front is near a KDRA-KCDC-KCNY line this evening with the associated weak trough moving across northern Utah. West to northwest flow behind the front has drawn smoke from western wildfires into northern and central portions of the
forecast area, resulting in greatly decreased air quality and areas of MVFR/IFR visibilities. As the front continues south, so will the smoke, with models indicating all of the forecast area
seeing large concentrations of smoke by late tomorrow morning. By the afternoon the trough will exit the area, allowing high pressure to rebuild. Decreasing winds will decrease the amount of
smoke coming into northern Utah, which could allow air quality to become a bit less poor. High temperatures are forecast to remain near or just below seasonal normals.
A second trough is expected to move onshore over the Pacific Northwest late Saturday/early Sunday before moving over the top of the ridge and grazing northern Utah Sunday afternoon into Monday, bringing through another mostly dry front. Resultant increase in westerly winds is expected to increase the flow of smoke into

northern Utah, resulting in more reduction in visibility and air
quality. Behind that exiting system flow is expected to remain generally light under the influence of an offshore ridge. Most guidance keeps conditions dry for the remainder of the forecast
period, but there is an outside shot of the position of the ridge shifting enough to allow some southerly flow to develop, allowing moisture to increase by late in the upcoming week.
No updates expected to the forecast this evening.
&&
.AVIATION...KSLC...Smoke from regional wildfires will result in
some reduction of visibility overnight, though low-end VFR conditions are expected to prevail. Light northerly winds are expected to shift back to the south by 06Z. Rest of Utah and southwest Wyoming...Smoke from regional wildfires will result in some areas of MVFR conditions into the overnight
hours, though low-end VFR conditions are expected to prevail. The smoke will continue to spread into southern Utah tonight through tomorrow morning, resulting in areas of MVFR conditions.
Occasionally gusty west to southwest winds over far southern Utah are expected to weaken by the early morning. &&
.FIRE WEATHER...A cold front is making its way into southern Utah
this evening, bring west to northwest winds behind it and occasionally gusty west to southwest winds out ahead of it. The associated weak trough will move in behind it over night,
resulting in temporary building of high pressure and lighter winds during the day Saturday as conditions remain dry.
By Sunday, another trough looks to begin settling over the northern Rockies region, which should bring an uptick in winds aloft over at least the northern half of Utah. Afternoon mixing
will likely lead to a notable increase in wind speeds at the surface on Sunday afternoon. With little to no change in the airmass, afternoon minimum relative humidity values will remain
largely unchanged as well. && .SLC WATCHES/WARNINGS/ADVISORIES... UT...None.
WY...None. &&
$$
Traphagan
For more information from NOAA's National Weather Service visit... http://weather.gov/saltlakecity
For frequently asked questions about the Area Forecast Discussion visit...
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501 FXUS65 KSLC 062208 AFDSLC

Area Forecast Discussion National Weather Service Salt Lake City UT 408 PM MDT Fri Aug 6 2021 .SYNOPSIS...Dry conditions are expected to prevail across the region as high pressure begins to temporarily rebuild. An area of dense smoke will remain in place through at least Saturday with improvement expected over northern Utah, and generally stable conditions across southern Utah. Another cold front will sweep
through the region Sunday with potential to bring more smoke into the area.
&& .SHORT TERM (Through 12Z/6AM MDT Monday)...An upper trough skirting across far northern Utah/ southern Idaho will continue to move downstream to the east of the area through the evening and overnight hours. The associated frontal boundary that pushed
through northern Utah earlier this morning will continue south and eastward through the remainder of the evening hours. The net effect of this frontal boundary will bring a shift in wind
direction to the west/ northwest and, more notably, an increase in smoke across the area. Current smoke concentration remains greatest across northern and west-central Utah this evening,
however, as northerly flow continues aloft we should begin to see the upper smoke layer begin dissipating during the early morning hours across northern Utah. With that in mind, nocturnal valley
inversions are likely to keep smoke trapped in these areas through the overnight hours. Across the southern half of Utah, smoke conditions are generally expected to worsen through the evening
and overnight hours as the frontal boundary continues southward.
Lower level moisture continues to linger across the area, but a considerable amount of convective inhibition is clearly evident across the northern half of Utah where the smoke layer has settled. With that in mind, minimal chances for precipitation
exist across the area through the remainder of the evening hours. The axis of the upper trough will swing through the CWA overnight
tonight, allowing for deeper, dry northwesterly return flow to prevail across the area with high pressure temporarily building back into the region. With a majority of the smoke layer
anticipated to begin moving out of the area, should begin seeing temperatures rise again. However, if the smoke layer does not exit the region as forecast, temperatures could remain up to 5 degrees
lower than what is expected... as they did today. Latest run of the HRRR near surface/ vertically integrated smoke shows a temporary clearing of smoke across northern Utah and southwest
Wyoming (or at least a substantial decrease), but as westerly flow increases overnight into Sunday another significant increase in layer and near surface smoke is expected. Just how far this smoke
layer will push into the area remains the biggest question at the moment, and is largely dependent on how far south a frontal boundary pushes into Utah and southwest Wyoming as a trough is
currently progged to brush by the far northern portions of Utah. In large though, should see a warming trend through Sunday as H7 temperatures continue to increase, with dry conditions being
maintained across the area. .LONG TERM (After 12Z/6AM MDT Monday)...A fast-moving trough will
move through to the north of the forecast area on Monday, bringing with it some of the coolest 700 mb temperatures in recent months. Under nearly cloudless skies, strong solar heating will

still allow surface temperatures to climb into the upper 80s for
much of northern Utah despite these cooler mid-level temperatures. By Tuesday, the trough will move well to the east, with high pressure returning to the Great Basin and building throughout the
remainder of the extended forecast period. Ensemble forecasts current park the upper-level ridge axis nearly overhead, where subtle variations in the position of the upper-level ridge will have great influence over the outcomes. The spread suggests the axis may trend to the west, which would keep much of the forecast area in subsidence and a gradually warming dry regime on the east side of the ridge. An alternate scenario exists in 20- 30% of ensemble members which pull moisture into the southwestern
corner of Utah. This would have the potential to kick off thunderstorm activity in the afternoons and evenings Tuesday through Friday. These storms would likely be limited in extent and strength, with gusty winds being a greater threat than heavy rain. && .AVIATION...KSLC...Smoke from regional wildfires will keep visibility in the MVFR range through 02Z, with gradual improvement into low end VFR range expected through 06Z. Winds will remain northwest through 04Z before switching back to the south during the 06-09Z timeframe. Rest of Utah and southwest Wyoming...Smoke from regional wildfires will keep visibilities in the MVFR range across northern and central utah along with southwest Wyoming through the evening. Visibility across southern Utah may fall into the MVFR range after 02Z as smoke spread south. Gusty southwest winds across southern Utah will persist through 02Z before diminishing after sunset. && .FIRE WEATHER...A cold front bringing a substantial drop in temperature across the northern half of Utah and southwest Wyoming will continue to push south and east across the area through the
evening hours. Behind this frontal boundary, a wind shift to the northwest/ west is expected with breezy conditions maintained through the remainder of the evening hours. The axis of the trough
associated with the frontal boundary will swing through the area during the overnight hours into Saturday, allowing high pressure to temporarily build back into the area. With the high pressure
building, expect decreased wind speeds during the afternoon and evening hours. While wind speeds will be generally decreased across the area, afternoon minimum relative humidities will remain
at or below 20%. By Sunday, another trough looks to begin settling over the
northern Rockies region, which should bring an uptick in winds aloft over at least the northern half of Utah. Afternoon mixing will likely lead to a notable increase in wind speeds at the
surface on Sunday afternoon. With little to no change in the airmass, afternoon minimum relative humidity values will remain largely unchanged as well.
&&
.SLC WATCHES/WARNINGS/ADVISORIES... UT...None. WY...Red Flag Warning until 8 PM MDT this evening for WYZ277.
&&

$$
SHORT TERM...Webber LONG TERM...Wessler AVIATION...Seaman FIRE WEATHER...Webber

For more information from NOAA's National Weather Service visit... http://weather.gov/saltlakecity For frequently asked questions about the Area Forecast Discussion visit... http://weather.gov/saltlakecity/general/afd_faqs.php # # 910 FXUS65 KSLC 061020 AFDSLC
Area Forecast Discussion
National Weather Service Salt Lake City UT 420 AM MDT Fri Aug 6 2021 .SYNOPSIS... A cold front will cross the state today...bringing a significant area of smoke into the region along with cooler temperatures. Smoke will remain in place through at least Saturday with slight improvement possible, especially over northern Utah. Another cold front will sweep through the region
Sunday. &&
.SHORT TERM (Through 12Z/6AM MDT Monday)... A cold front will gradually move eastward and southeastward across the region today. The front will exit the Wasatch Front by sunrise this morning and pass through southern Utah late in the day. At the same time, a mid-level trough and associated jet max
will track east across Idaho and extreme northern Utah. The combination of jet dynamics and instability via cooling aloft (500mb temperatures forecast to drop to around -13C over northern
Utah this afternoon) will support continued isolated shower and thunderstorm development across northern Utah and SW Wyoming into this evening. 0-6km lapse rates are forecast to rise into the
8-9C/km range this afternoon across northern Utah and SW Wyoming, supportive of a gusty wind potential. Pea-sized hail may also accompany the stronger storms.
A stripe of anomalously strong 700mb SW winds in the 40-45kt range are expected to in advance of the mid-level trough passage. The core of strongest winds are expected to pass overhead this morning before maximum boundary layer mixing/downward momentum transport can be realized. Thus, strongest surface winds this morning will be relegated to exposed higher terrain areas. However, we can't rule out pockets of locally stronger winds at the surface where winds and topography align. By the time vertical boundary layer mixing is maximized this afternoon, the core of strongest mid-level winds aloft are forecast to propagate eastward to eastern Utah, and forecast to weaken slightly to the 25-35kt range. Thus, a Wind Advisory should not be needed, but this will bear watching, especially across southern Utah. EFI values exceed 0.90 across southern Utah this afternoon, while SoT
values approach 1. These values portray the relative rarity of this spring-like or early fall-like nature of this system.

Copious amounts of smoke (per HRRR smoke) are forecast to filter
into the region this morning in the post-frontal airmass as winds switch to the W-WNW. This will advect smoke into our area from California and southern Oregon. Smoke concentrations are forecast
to be high enough to restrict visibility today. The ribbon of thickest smoke is forecast to drift southward into southern Utah this evening. The combination of cold advection behind the
departing cold front and attenuation of incoming shortwave radiation via smoke will result in temperatures 10-15 degrees cooler across the region today when compared to Thursday. Have
followed the previous shifts's lead by lowering NBM temperatures 2-4 degrees to account for the loss of incoming shortwave radiation and associated surface heating due to the smoke.
A quiet day is expected across the region on Saturday with locally breezy conditions and mild temperatures characterized by values 5-10 degrees below climatological normals for early August. Another trough/area of low pressure is then forecast to slide east across the Northern Rockies on Sunday. In response, winds will back to the southwest across the region, forcing a warmup. Winds will increase as well, especially across northern Utah and SW Wyoming. At this time, widespread SW winds in the 25-35 mph range are expected, especially across normally wind-prone areas of northern Utah and the west Utah deserts. An isolated shower may attempt to form near the Idaho border Sunday afternoon and
evening, but at this time moisture appears to be quite limited with this system, so odds for much in the way of measurable precipitation appear low.
.LONG TERM (AFTER 12Z/6AM MDT Monday)...
Dry conditions remain in the forecast Monday with low pressure tracking through Montana. Moisture for Tuesday has backed off this latest forecast run, with south Utah only seeing chances for rain and thunderstorms through Wednesday. At this point the forecast is looking rather dry for the rest of the week with some models wanting precip over the weekend but given the wishy-washyness of what models have been doing the past few days we're prone to a low confidence in the Thursday onward time frame. Temperatures early in the week across northern Utah are expected to be slightly cooler with the passage of a weak cool front passing Monday.&&
.AVIATION... KSLC...Shifting southeast to southwest winds are forecast early this afternoon with VFR conditions. Winds are forecast to shift out of the northwest around 15Z with gusts around 25 knots through this afternoon behind a frontal passage. IFR visibilities accompanying smoke arriving with the front are forecast late this morning which should improve back to VFR visibilities the remainder of the afternoon and evening.
Rest of Utah and southwest Wyoming...Across northern Utah and EVW TAF sites, IFR visibilities are forecast this morning as the
onslaught of smoke arrives from west to east. This means ENV will be impacted first. Strong west to northwest winds will follow behind the smokes arrival, which will persist through much of the
afternoon and early evening hours before improving. Confidence in smoke reduction is less at HCR at this time, with MVFR visibilities currently forecast. For southern Utah TAF sites, it
is also uncertain if the smoke concentrations will be enough to reduce visibility at the surface. Therefore we are forecasting either VFR or MVFR conditions later this evening and this may not
materialize. Confidence in stronger winds this afternoon is however, higher. &&

.FIRE WEATHER...
A cold front will swing eastward through the state today. South to southwest winds ahead of the front will
transition to westerly and southwesterly behind the front. Wind gusts will reach 35-40 mph in many wind-prone areas today. Minimum relative humidity will drop into the low teens for all of Utah with the exception of far northern Utah near the Idaho border, where minimum relative humidity will be in the 20-30 percent range. Isolated showers and thunderstorms will be possible near the Idaho border as well into this evening. For Saturday, dry conditions are expected along with lighter winds. Locally breezy conditions will be possible in wind-prone areas. On Sunday, a cold front will pass eastward through Idaho. As a result, southwest to west winds will increase state-wide, with afternoon gusts in the 25-35 mph range expected. In addition to the winds, relative humidity values are expected to drop down to around 10 percent across much of the state. Overnight humidity recovery will be limited as well Sunday morning, especially across higher terrain areas of central and southern Utah. For the remainder of the week, near to slightly below normal temperatures are expected. Isolated showers and thunderstorms may
return to southern Utah by midweek although confidence is low in thunderstorm potential at this time. Early indications suggest coverage will remain limited and well below what was experienced to
begin the month.
&& .SLC WATCHES/WARNINGS/ADVISORIES...
UT...None. WY...Red Flag Warning from noon today to 8 PM MDT this evening for WYZ277.
&&

$$
ADeSmet/NDeSmet
For more information from NOAA's National Weather Service visit... http://weather.gov/saltlakecity
For frequently asked questions about the Area Forecast Discussion visit... http://weather.gov/saltlakecity/general/afd_faqs.php #

#
862 FXUS65 KSLC 162231 AFDSLC

Area Forecast Discussion National Weather Service Salt Lake City UT 431 PM MDT Mon Aug 16 2021 .SYNOPSIS...A slow moving upper level system will impact the state
with potential for flash flooding, severe convection and heavy rainfall through at least Wednesday. Expect much cooler temperatures Wednesday through the end of the work week.
&& .SHORT TERM (Through 12Z Thursday)...Fairly significant convective event setting up for Utah Tuesday into Wednesday...probably one of the better set ups we will see this year. An elongated area of high pressure remains across the Great Basin southwestward into central California. A deepening upper level trough is approaching the Pacific Northwest this afternoon. Coincident with this trough, the associated surface boundary is currently located across southeastern Oregon into central Idaho. This trough will continue to shift south and east into the Great Basin/southern Idaho by Thursday morning. The associated cold front will cross northern Utah slowly Tuesday into Wednesday...gradually dissipating across southern Utah Wednesday.
Currently, widespread smoke continues to be the main story for Utah, with reduced surface visibilities with some areas in red/unhealthy air quality categories. Smoke will continue to be an
issue across the state through at least Tuesday. Attention then turns to the aforementioned boundary and the pre-
frontal environment across Utah. With southwesterly flow ahead of the trough, substantial moisture advection will continue tonight into Tuesday. This will bring anomalously high precipitable water
values to much of the state by Tuesday evening, with 1"+ values common.
South of the front, expect instability to increase rapidly with daytime heating. SBCAPE values in excess of 1000 J/kg are expected across much of Utah south of the front. At the same time, the
upper level trough will be crossing western Idaho. This will provide a marked increase in deep layer shear for at least the northern half of Utah, with values as high as 40-50kts in the
pre-frontal environment.Further south, deep layer shear and the resulting storm motions will be less progressive.
Expect two modes of convective initiation Tuesday. First, the normal higher terrain/elevated heat source areas in southern Utah should convect rather quickly across southern Utah, in the 18-20Z period. Given sufficient instability, these storms should be able to move off the terrain into the adjacent valleys. This will bring a threat for flash flooding to much of southeastern and south central Utah including the Little Wildhorse/Goblin Valley, the San Rafael Swell, Capitol Reef, and the Grand Staircase/Escalante National Monument. Second, convection is expected to fire ahead of the front. This area with better shear, somewhat deep moisture and significant

instability will represent a higher threat for severe
weather...particularly large hail and strong winds. Profiles are supportive of sufficiently strong updrafts with long enough residence time for larger hail. Given the anomalously high
moisture levels, expect a threat for heavy rainfall with these storms, especially for the burn scars near recent wildfires. Have issued a flash flood watch for both the normally flash flood prone areas of southeastern and south central Utah as well as the recent burn scars of central and southern Utah (including the Ether Hollow burn scar). The Storm Prediction Center has outlooked most of Utah in a marginal area for severe weather Tuesday...and there is some potential this may be upgraded to a slight risk.
The threat won't end with sunset Tuesday as this fall-like trough drops into the Great Basin late Tuesday into Wednesday. Expect an area of moderate rain to continue across portions of northern and central Utah Tuesday night. Another round of strong convection is possible with a resulting threat of flash flooding, small hail and gusty winds across eastern Utah ahead of the cold front Wednesday afternoon and evening. Widespread rainfall is possible across much of Utah south of a Logan to Wendover line well into Wednesday night and across southern and eastern Utah potentially into Thursday morning. The flash flood watch may need to be extended into Wednesday with later packages. .LONG TERM (After 12Z Thursday)...Ensemble guidance is general agreement of the cold core of the trough moving through northern
Utah Thursday. The 12Z ECMWF has 700 mb temperatures dropping to just above freezing over this portion of the state. The ECMWF, along with a majority of its ensemble members are among the deepest
solutions of the trough. A majority of GEFS members are more progressive. Precipitation chances are expected to decrease throughout the day with the trough moving east, while temperatures
could be the coolest of the week. Highs over 20F cooler than average are expected in northern Utah. The departures from average won't be as large to the south, as highs to around 15F cooler than average
are expected. Flow is expected to become zonal Friday in between the exiting
trough and another that will move in over the weekend. Largely dry conditions will follow. Ensembles have varying solutions with regards to the next trough with timing and strength. The general
theme is that it won't be as amplified as the previous one. Confidence is better in increased southwest synoptic flow Saturday afternoon as the trough is likely to be centered in the northwest.
Precipitation chances are lower confidence, but it could be impactful if the track brings better dynamics more into northern Utah Saturday/Saturday night.
By the end of the weekend, a drier, lighter southwest flow should build in, with temperatures gradually warming closer to average
Monday. && .AVIATION...KSLC...VFR conditions are expected through the evening and overnight hours with regional smoke keeping visibility in the 6-8SM range. There is a 30 percent chance for visibility to fall into the MVFR range after 01Z. Scattered showers and thunderstorms are expected around the terminal after 20Z Tuesday with a 40
percent chance of a storm directly impacting the terminal after 22Z.

REST OF UTAH AND SOUTHWEST WYOMING...VFR conditions are expected
across the area through tonight, with pockets of MVFR visibility possible north of I-80 within pockets of heavier regional smoke. Scattered showers and thunderstorms capable of producing
temporary IFR conditions can be expected mainly south of I-80 Tuesday afternoon. && .FIRE WEATHER...A big change in the weather pattern is expected through much of the rest of the week. A front will cross into northwest Utah Tuesday afternoon into Tuesday evening. Ahead of this front, gusty winds and low humidities are expected across
portions of northern Utah including fire weather zones 478, 479 and 492. Ahead of this front, expect thunderstorms to develop during the afternoon and evening, bringing a widespread threat of lightning, gusty microburst winds and small hail to the same area. Meanwhile, across southern Utah, expect thunderstorms to develop across the higher terrain. With higher moisture and slower storm motions, expect the main threat in this area to be heavy rainfall, lightning and small hail.
By Wednesday, this system will be crossing Utah. Expect widespread rainfall to impact the state, with the chance of gusty,
microburst winds and lightning the highest across eastern Utah.
&&
.SLC WATCHES/WARNINGS/ADVISORIES... UT...Red Flag Warning from noon to 9 PM MDT Tuesday for UTZ478-479-
492. Flash Flood Watch from Tuesday afternoon through Tuesday evening for
UTZ111-113-117-120-121-125>131. WY...Red Flag Warning from noon to 9 PM MDT Tuesday for WYZ277.
&&
$$
Kruse/Wilson/Seaman
For more information from NOAA's National Weather Service visit... http://weather.gov/saltlakecity
For frequently asked questions about the Area Forecast Discussion visit...
http://weather.gov/saltlakecity/general/afd_faqs.php # # 979 FXUS65 KSLC 161045 AFDSLC
Area Forecast Discussion National Weather Service Salt Lake City UT 445 AM MDT Mon Aug 16 2021 .SYNOPSIS...High pressure will maintain dry and stable conditions today as regional smoke remains across the area. A more unsettled pattern is expected to develop Tuesday through Thursday as moisture returns northward.

&& .SHORT TERM (THROUGH 12Z THURSDAY)...High pressure remains centered over central California this morning with the ridge axis extending northeast towards southeast Idaho. With northerly flow aloft over Utah, a dry airmass will remain in place across the area. However, this also means that areas of smoke and associated reductions in visibility will also remain in place. Temperatures are expected to warm slightly today across northern Utah, with slightly above normal
temperatures areawide. However, the temperatures will be moderated to some extent by the smoke. This ridge will shift east of the area tomorrow as a low pressure system moves into the PacNW. Southwest flow will increase across Utah ahead of this low, which will aid in drawing moisture north from Arizona and southern Nevada. The winds will aid mixing leading to continued warm temperatures across northern and much of central Utah, while the moisture will lead to increasing convection through the day, focusing more on the central and south during the afternoon.
By Wednesday morning, focus for convection should shift a bit farther north towards the northern and central Wasatch Front and adjacent mountains ahead of a cold front slowly working its way into
the area. The best convection will then gradually shift to central, eastern, and southern Utah later in the day as the cold front continues to progress southward. Much cooler temperatures can be
expected behind the cold front as H7 temperatures drop from between 16-18C across northern Utah 00z Wednesday to between 5-8C by 00z Thursday.
Some thunderstorms will likely produce heavy rain as the airmass moistens fairly quickly, with the potential for flash flooding in prone areas. Furthermore, large-scale ascent ahead of the low and increasing shear will bring the possibility of hail and strong winds. The presence of dynamic forcing will maintain showers and thunderstorm even during the overnight hours Tuesday night and Wednesday night.
.LONG TERM (AFTER 12Z THURSDAY)...The Cluster tool shows a better consistency between the model solutions through 00Z Friday but then the disparity increases for Friday and Saturday. Even with the
higher consistency by 00Z Friday there is enough differences in the exact location of the trough axis/circulation that it impacts the PoPs and QPF across northern and central Utah. The EC is the deepest
and farthest southwest over SW Idaho, while the GFS shows more of a center nearer the Upper Snake River Plain. The EC supports additional QPF amounts closer to 0.25 to 0.50 of an inch over the
central and southern Wasatch Mountains and NE into the Uintas, while the farther NE solution of the GFS results in a much lower QPF of 0.10 of an inch across this same area. The precip amounts decrease
the farther north and west of here. Since there is discrepancy, have gone with a blend with a slight hedge towards the higher QPFs. Temperatures Thursday and Friday will be well below normal across
the entire CWA. The EC is obviously slower in this trough exiting but the GFS and EC both show a secondary trough moving into the Great Basin by Saturday. Although the air mass will be drier there is fairly good dynamics associated with this feature that more showers expected across at least the northern two-thirds of the CWA Saturday into Saturday night. Temperatures will begin to rise by Sunday according to the NBM, but would not be surprised if they straight line between

Saturday and Sunday and then increased on Monday.
Ahead of this trough on Saturday, the EC and GFS show 700mb winds 20- 30kts while the GFS shows 30-40 kts across the western northern
portions of the CWA. Have boosted winds above the NBM. && .AVIATION...KSLC...High end MVFR visibility in smoke is expected this morning through about 17-18Z before thinning some to go to VFR levels for the remainder of the TAF period. There is a 30% chance that the VFR conditions will set in onto 22-24Z. Winds should shift from southeast to northwest at 17Z, albeit light winds.
REST OF UTAH AND SOUTHWEST WYOMING...MVFR conditions are expected to prevail from about SLC northward to Idaho until about midday before
improving to largely VFR conditions. The southern and eastern two- thirds of the region will have mainly VFR conditions but locally MVFR conditions are possible until 18Z.
&&
.FIRE WEATHER...High pressure in place today will maintain a warm and dry airmass over the area. This high pressure will shift east tonight and southwest flow will increase over the area tomorrow
ahead of an approaching low pressure system. The southwest flow may bring spotty and brief hazardous fire weather conditions to portions of the area before humidities rise as showers and thunderstorms
increase across the area by midafternoon. Thunderstorms are generally expected to be wet, with some capable of producing locally heavy rain. This moisture will remain in place through at least
Thursday, with strong and wet thunderstorms expected in many areas. A drying trend looks to be in store for the end of the week as the low pressure system exits the area.
&&
.SLC WATCHES/WARNINGS/ADVISORIES... UT...None. WY...Fire Weather Watch from Tuesday afternoon through Tuesday
evening for WYZ277. &&
$$
Cheng/Struthwolf
For more information from NOAA's National Weather Service visit... http://weather.gov/saltlakecity
For frequently asked questions about the Area Forecast Discussion visit...
http://weather.gov/saltlakecity/general/afd_faqs.php # #
767 FXUS65 KSLC 152202 AFDSLC
Area Forecast Discussion
National Weather Service Salt Lake City UT 402 PM MDT Sun Aug 15 2021 .SYNOPSIS...High pressure will maintain dry and stable conditions

Monday as regional smoke remains across the area. A more
unsettled pattern is expected to develop early to midweek as moisture returns northward. && .SHORT TERM (Through 12Z Wednesday)...Mid level ridging centered over far northwest Nevada is maintaining a dry northerly flow across the forecast area this afternoon. An embedded shortwave trough within this flow is digging through northern Utah, and is helping to maintain scattered weak convection across southern Utah east of I-15 this afternoon. This activity should move out of the area by this evening.
Regional smoke which has spread across northern and central Utah today, and increased in concentration this afternoon, will largely
remain in place through Monday resulting in continued degraded air quality and visibility.
The upper ridge will become centered over the forecast area Monday, as an upstream trough digs into the Pacific Northwest. This will maintain dry and stable conditions across the area with
temperatures perhaps a degree or two warmer across the north. By Tuesday increasing south to southwesterly flow will allow
moisture to quickly spread northward across the forecast area. This will result in an active convective day across much of the area Tuesday afternoon and evening, ahead of an advancing surface
front which is expected to push through northern Utah late in the day. Deep layer shear and ample moisture/instability will support a threat for strong, organized convection capable of producing
hail and strong winds in addition to heavy rainfall. .LONG TERM (AFTER 12Z WEDNESDAY)...Confidence continues to grow over the development of an area of low pressure across Montana/Idaho on Wednesday of this week which will bring about a
change in our weather pattern. Forecast ensembles are in good agreement in the development of this low. Over time, this low has progressively gotten deeper. Shift of tails guidance is currently
showing values of 2 over portions of north and western Utah for Wednesday for QPF values, indicating a truly extreme event is possible. Should we see higher values than this, or over a more
widespread area, preparations and attention to this event should begin. At this time, forecasts for QPF amounts across the Wasatch front for Wednesday range from 1/4 to 1/2 inch with higher amounts
expected in the Wasatch and Central Mountains. In addition to the rain, we are expecting gusty winds Wednesday. Winds will shift out of the north behind the arrival of a cold front from northwest
Utah to the southeast throughout the day. Temperatures will be much cooler than what we have had, with highs in the upper 70s to low 80s.
As the low evolves Thursday and Friday, forecast models struggle in their solutions in how quickly the low loses strength. Some let
the low become a broader trough where others keep a low pressure center. They also differ in the progression of where the low tracks into a trough/low. The general consensus is toward the
northeast, but there is quite the spread from Canada to Colorado in placement of the system Friday. At least for impacts for Utah, Thursday is the least confident day regarding rain and
thunderstorm chances. Friday does look to clear out precip-wise, allowing the much cooler air to continue to filter in. This will persist over the weekend with a slow increase to temperatures by

Sunday.
&&
.AVIATION... KSLC...MVFR visibility is expected going into Monday from regional wildfire smoke. Northwest winds will transition to the southeast around 03Z. Winds will switch back to the northwest around 17Z with some visibility improvement. VFR conditions are expected after 17Z, although there is a 30% chance that MVFR visibility lasts through much of the afternoon.
REST OF UTAH AND SOUTHWEST WYOMING...MVFR visibility is expected going into Monday for southwest Wyoming and northern Utah.
Wildfire smoke concentrations will increase after 03Z in southern Utah, with MVFR visibility also expected. Visibility is expected to improve Monday afternoon, but some obstructions from wildfire smoke will remain. && .FIRE WEATHER...High pressure centered across Nevada will slowly build eastward through Monday. This will maintain dry conditions with regional smoke remaining in place across northern and central Utah. A low pressure system will move into the Great Basin Tuesday allowing moisture to spread northward. This will result in much cooler temperatures, higher humidity, and a good chance of wetting rains beginning Tuesday afternoon, and continuing through the day Wednesday. A drying trend will follow for the latter portion of the week, while temperatures remain below normal through Friday.
&& .SLC WATCHES/WARNINGS/ADVISORIES...
UT...None. WY...None. &&
$$
Seaman/NDeSmet/Wilson
For more information from NOAA's National Weather Service visit...
http://weather.gov/saltlakecity For frequently asked questions about the Area Forecast Discussion
visit... http://weather.gov/saltlakecity/general/afd_faqs.php #
# 687 FXUS65 KSLC 150956
AFDSLC Area Forecast Discussion
National Weather Service Salt Lake City UT
356 AM MDT Sun Aug 15 2021
.SYNOPSIS...A weak cold front will cross northern and central Utah Sunday, ushering regional smoke into the area. A more unsettled pattern is expected to develop early to midweek next week as
moisture returns northward. &&

.SHORT TERM (Through 12Z Wednesday)... High pressure will retrograde and amplify slightly across the western Great Basin today while a weak shortwave rounding the
crest of the ridge early this morning will dive southeastward across northeastern Utah today. This will advect denser wildfire smoke from upstream fires southward across the state today. The densest smoke is expected across northern Utah from late morning through early this evening, with surface visibility restrictions to around 5 miles. In additional depending on fire activity on the
Parley's Canyon fire today, there may be additional locally dense smoke across Park City to Heber given the northwesterly winds today. Otherwise, smoke is expected to thin slightly as it moves
southward across the state, but is expected to remain noticeable through Monday and likely into Tuesday. Otherwise, temperatures will drop a few degrees from yesterday into today with the subtly
cooler air in the northwesterly flow combined with the aerosol scattering from the smoke. The drier northwesterly flow and increased subsidence over the area with the high just to our west
will help suppress convection today. However, there will likely be enough lingering moisture combined with orographic forcing to result in some isolated showers/thunderstorms mainly over the southern Utah Mountains. Storms will struggle to get off the higher terrain today given the much drier low levels. By Monday, the upstream ridge starts to collapse as a Pacific trough moves into the Pacific Northwest. This will maintain drier, subsident northerly flow across the region and thus will maintain another warm day with minimal precipitation chances. There will still be some isolated thunderstorm potential, but again mainly tied to the higher terrain in southern Utah. Tuesday will turn more active as a trough carves out across the Pacific Northwest, while southerly moisture advection ramps up across the state ahead of this trough. This will initially bring moisture return to southern Utah for Tuesday diurnal thunderstorms, which will pose an elevated Flash Flood risk. There will also be a marginal severe weather risk with any storms Tuesday afternoon and evening given the very steep mid and low level lapse rates and forecast CAPE values 1000-2000 J/kg in southern Utah. The increasing moisture advection and synoptic support ahead of the approaching trough axis will then help spread moisture and precipitation northward across Utah through
Tuesday night.
.LONG TERM (After 12Z Wednesday)... The focus in the extended forecast period remains on a trough and associated cold front crossing the region Wednesday and Thursday. With significant moisture transport into the region by early in
the period, synoptic- scale lift, and moderate instability, significant precipitation amounts with an elevated flash flood threat are anticipated. The general trend of ensembles is more
members offering a deeper and slower solution for Wednesday and Wednesday night, lending to high confidence in the precipitation event. With moderate shear present, a potential for organized
convective activity with severe weather will exist. Multiple forecast scenarios emerge for Thursday, as ensemble solutions diverge. In general, EPS members favor a deeper trough, suggesting cooler temperatures and a greater potential for precipitation than GEFS members, which seem to still favor a more progressive pattern. CMCE members favor a weak trough, with the trough axis displaced much farther west. All considered, chances for precipitation will exist across the forecast area, though with

the highest potential over southern and eastern Utah.
Given that some ensemble members suggest troughing over the Great Basin into the weekend, lingering low chances for precipitation seem
reasonable. This stated, most likely scenario will be for warming and drying conditions from Friday into the weekend. && .AVIATION... KSLC...VFR ceilings will prevail today, but expect a period of MVFR visibilities due to smoke from late morning through the afternoon due to smoke. Given northwest flow aloft, southeast drainage winds will switch to a northwest lake breeze a couple of hours earlier than typical diurnal pattern, likely around 16Z.
REST OF UTAH AND SOUTHWEST WYOMING...Given dryer and somewhat more stable air mass, any shower or thunderstorm coverage will be extremely limited today, with any activity likely focused over the
higher terrain of southern Utah, especially near KBCE. Smoke advecting into northern Utah will likely produce periods of MVFR visibilities, especially for KENV, KLGU, KOGD, KSLC, and KPVU.
Otherwise, aside from with any showers or thunderstorms, VFR conditions will prevail. &&
.FIRE WEATHER...
High pressure retrograding and strengthening across Nevada today will allow a cooler airmass to spread into northern Utah. This airmass will also bring considerable drift smoke from regional
wildfires into northern Utah. Meanwhile a drying trend is expected across southern Utah with only isolated afternoon and evening storms mainly over the terrain. Moisture is expected to spread
back north early next week ahead of an approaching weather system. This system will bring a considerable cooling trend for the middle to latter portion of the week.
&&
.SLC WATCHES/WARNINGS/ADVISORIES... UT...None. WY...None.
&& $$
SHORT TERM...Church LONG TERM...Barjenbruch
AVIATION...Barjenbruch FIRE WEATHER...Church
For more information from NOAA's National Weather Service visit... http://weather.gov/saltlakecity
For frequently asked questions about the Area Forecast Discussion visit... http://weather.gov/saltlakecity/general/afd_faqs.php
#

#
483 FXUS65 KSLC 122216 AFDSLC

Area Forecast Discussion National Weather Service Salt Lake City UT 401 PM MDT Mon Jul 12 2021 .SYNOPSIS...Weakening high pressure will allow moisture to return
to the area, bringing the threat of thunderstorms to much of Utah and southwest Wyoming through midweek. Heavy rain will be possible across southern Utah, especially Tuesday and Wednesday.
&& .SHORT TERM...(Through 12Z/6AM MDT Thursday)...With several topics to discuss, have opted to break up the discussion by topic. * Smoke *
The HRRR smoke guidance shows continued smoky conditions for the northern portions of the forecast area through midweek,
with some improvement over southern and perhaps central Utah
* Flash Flooding *
The onset of a significant, albeit brief pattern change is underway early this morning as the much-
discussed strong high pressure ridge is beginning to weaken. This will open the door to northward- advecting moisture as a reservoir of deep moisture resides just to our south and west
across New Mexico, Arizona and Nevada. Flash flooding threat assessment is the primary forecast concern during the period, particularly Tuesday and Wednesday. Moisture will continue to
advect northward by Tuesday and Wednesday, and a moisture rich airmass is forecast to be in place across much of central and southern Utah during this time. Convective-allowing models are
all indicating robust shower and thunderstorm development by late Tuesday morning and early afternoon across high terrain areas of central and southern Utah and along any remnant boundaries. Much
like today, convective activity will lay down outflow boundaries and cold pools and will generally propagate southward both on Tuesday and Wednesday. HREF high-resolution ensemble indicates the
potential for greater than 0.50" of rain in a 3-hr period under the heaviest cores as well as where clusters of convection collide, with several areas showing appreciable chances of 6-hr
QPF exceeding 5yr and 10yr average recurrance intervals. As is the case with any convective forecasting, there is some disagreement on the exact placement of heavy rainfall. That said,
we do know that should the heavier cores materialize across flood-prone areas, flash- flooding will be a concern. Ultimate convective coverage
realization will be dependent upon the extent of early-day cloud cover and resultant instability realization, placement of lingering outflow boundaries as well as the track of any remnant MCV
circulations/vorticity filaments from upstream convection. Regardless, the key takeaway message is that if you're planning to recreate in flood-prone areas Tuesday and Wednesday, be aware of the
flash flood potential and have a possible alternate plan in place. A Flash Flood Watch has been issued to account for the areas of highest threat Tuesday. Wednesday looks to be a potential repeat of Tuesday, but potentially expanding farther north. Thursday should see a net decrease in convective activity with increased westerly flow, but with lingering chances.

* Heat *
Today marked the hottest day of the short term period across the area, as a combination of the weakening ridge and increasing moisture will begin to cap heating potential for the next few days. Thus, the ongoing Excessive Heat Warning will be allowed to expire. That said, latest guidance indicates that the cooling may only consist of a few degrees for the northern half of the forecast area, so while conditions may not meet heat warning
criteria, heat will continue to be noticeable in the north, with temperatures running around 5 degrees above normal instead of 10+ degrees above normal. .LONG TERM (AFTER 12Z THURSDAY)...As the ridge axis straddles the forecast area, some uncertainty remains in how probable and
widespread thunderstorm chances may be through Thursday. A shift further west would enhance subsidence and drying. Given that scenario, scattered thunderstorms are still expected from south to
north in the forecast area east of I-15 with enough lingering moisture and stability that terrain and strong solar heating should trigger convective development by mid-afternoon, spreading north and
across the Uintas through the early evening. The downward trend in thunderstorm probabilities continues Friday and into the weekend, though cannot rule out the potential for a convectively active
Sunday across the southern Utah mountains.
Through the weekend into early next week, a developing trough off the Washington coast will help to rebuild the ridge over the Great Basin, though how far east the ridge axis will fall is still
uncertain with a reasonable amount of spread currently in the ensemble forecasts. Regardless, the GFS and Euro bring 700mb temps exceeding 18C back in over most of the forecast area by Monday,
driving surface temperatures back into the upper 90s and low 100s. Some ensemble members suggest a surge of moisture moving northward around this ridge into Nevada and into Idaho with just enough
seeping into Utah for isolated convection over the higher terrain late Monday.
&& .AVIATION...KSLC...Northwest winds are expected to shift to the southeast after 03z. Smoke will generally remain in place tonight and tomorrow, with visibilities in the 6-10sm range. A 20% chance exists for brief periods of MVFR, with the greatest chance on Tuesday morning. Rest of Utah and southwest Wyoming...Areas of smoke will remain
across much of the area, but especially northern and central Utah and southwest Wyoming. This will result in terrain obscurations and could lead to localized MVFR conditions. Additionally, showers and
thunderstorms can be expected over southern Utah and the Uintas this afternoon and evening, especially over the higher terrain, with gusty outflow winds as a possibility.
&&
.FIRE WEATHER...Isolated dry thunderstorm potential remains this afternoon and evening portions of central and northern Utah, with wetter storms over southern Utah. Expecting the mode of the storms
to transition to wetter in time as deep layer moisture will continue to rapidly spread NE across the southern half of Utah into Tuesday. Thereafter into Thursday, daily thunderstorm activity (becoming

scattered to numerous across central/south) is expected to promote
spotty wetting rains, and increasing RH. Locally heavy rainfall will also be possible. In addition, breezy winds across northern and northeast Utah on Tuesday afternoon could approach fire weather criteria, though relative humidity looks to be a bit too high. This is a potential that will be monitored moving forward.
Moisture will begin to move off to the east Thursday, but enough
moisture is expected to linger across mainly central and eastern Utah to promote additional shower and thunderstorm activity. Activity will trend drier on Friday, as thunderstorm coverage
diminishes to isolated. By next weekend, another ridge of high pressure is expected to build across the Great Basin, promoting a return of hot and dry conditions with any late-day thunderstorm
activity limited to mainly isolated development over high terrain. Elevated winds are possible, but not expected at this time. .SLC WATCHES/WARNINGS/ADVISORIES... UT...Excessive Heat Warning until 9 PM MDT this evening for UTZ101>107-115-116-118>124-128-130-131. Flash Flood Watch from Tuesday afternoon through Tuesday evening for UTZ123>129. Heat Advisory until 9 PM MDT this evening for UTZ114.
WY...Red Flag Warning from 1 PM to 9 PM MDT Tuesday for WYZ277.
&&
$$ Van Cleave/Wessler For more information from NOAA's National Weather Service visit...
http://weather.gov/saltlakecity For frequently asked questions about the Area Forecast Discussion
visit... http://weather.gov/saltlakecity/general/afd_faqs.php #
# 468 FXUS65 KSLC 122201
AFDSLC
Area Forecast Discussion National Weather Service Salt Lake City UT 401 PM MDT Mon Jul 12 2021
.SYNOPSIS...Weakening high pressure will allow moisture to return to the area, bringing the threat of thunderstorms to much of Utah and southwest Wyoming through midweek. Heavy rain will be possible across southern Utah, especially Tuesday and Wednesday. && .SHORT TERM...(Through 12Z/6AM MDT Thursday)...With several topics to discuss, have opted to break up the discussion by topic.
* Smoke * The HRRR smoke guidance shows continued smoky conditions

for the northern portions of the forecast area through midweek,
with some improvement over southern and perhaps central Utah * Flash Flooding *
The onset of a significant, albeit brief pattern change is underway early this morning as the much-
discussed strong high pressure ridge is beginning to weaken. This will open the door to northward- advecting moisture as a reservoir of deep moisture resides just to our south and west
across New Mexico, Arizona and Nevada. Flash flooding threat assessment is the primary forecast concern during the period, particularly Tuesday and Wednesday. Moisture will continue to advect northward by Tuesday and Wednesday, and a moisture rich airmass is forecast to be in place across much of central and southern Utah during this time. Convective-allowing models are all indicating robust shower and thunderstorm development by late Tuesday morning and early afternoon across high terrain areas of central and southern Utah and along any remnant boundaries. Much like today, convective activity will lay down outflow boundaries and cold pools and will generally propagate southward both on Tuesday and Wednesday. HREF high-resolution ensemble indicates the
potential for greater than 0.50" of rain in a 3-hr period under the heaviest cores as well as where clusters of convection collide, with several areas showing appreciable chances of 6-hr
QPF exceeding 5yr and 10yr average recurrance intervals. As is the case with any convective forecasting, there is some disagreement on the exact placement of heavy rainfall. That said, we do know that should the heavier cores materialize across flood-prone areas, flash- flooding will be a concern. Ultimate convective coverage realization will be dependent upon the extent of early-day cloud cover and resultant instability realization, placement of lingering outflow boundaries as well as the track of any remnant MCV circulations/vorticity filaments from upstream convection. Regardless, the key takeaway message is that if you're planning to recreate in flood-prone areas Tuesday and Wednesday, be aware of the flash flood potential and have a possible alternate plan in place. A Flash Flood Watch has been issued to account for the areas of highest threat Tuesday. Wednesday looks to be a potential repeat of Tuesday, but potentially expanding farther north. Thursday should see a net decrease in convective activity with increased westerly flow, but with lingering chances.

* Heat * Today marked the hottest day of the short term period across the area, as a combination of the weakening ridge and increasing moisture will begin to cap heating potential for the next few days. Thus, the ongoing Excessive Heat Warning will be allowed to expire. That said, latest guidance indicates that the cooling may only consist of a few degrees for the northern half of
the forecast area, so while conditions may not meet heat warning criteria, heat will continue to be noticeable in the north, with temperatures running around 5 degrees above normal instead of 10+ degrees above normal. .LONG TERM (AFTER 12Z THURSDAY)...As the ridge axis straddles the forecast area, some uncertainty remains in how probable and widespread thunderstorm chances may be through Thursday. A shift further west would enhance subsidence and drying. Given that scenario, scattered thunderstorms are still expected from south to north in the forecast area east of I-15 with enough lingering moisture and stability that terrain and strong solar heating should

trigger convective development by mid-afternoon, spreading north and
across the Uintas through the early evening. The downward trend in thunderstorm probabilities continues Friday and into the weekend, though cannot rule out the potential for a convectively active
Sunday across the southern Utah mountains.
Through the weekend into early next week, a developing trough off the Washington coast will help to rebuild the ridge over the Great Basin, though how far east the ridge axis will fall is still
uncertain with a reasonable amount of spread currently in the ensemble forecasts. Regardless, the GFS and Euro bring 700mb temps exceeding 18C back in over most of the forecast area by Monday,
driving surface temperatures back into the upper 90s and low 100s. Some ensemble members suggest a surge of moisture moving northward around this ridge into Nevada and into Idaho with just enough
seeping into Utah for isolated convection over the higher terrain late Monday. && .AVIATION...KSLC...Northwest winds are expected to shift to the southeast after 03z. Smoke will generally remain in place tonight and tomorrow, with visibilities in the 6-10sm range. A 20% chance exists for brief periods of MVFR, with the greatest chance on Tuesday morning.
Rest of Utah and southwest Wyoming...Areas of smoke will remain
across much of the area, but especially northern and central Utah and southwest Wyoming. This will result in terrain obscurations and could lead to localized MVFR conditions. Additionally, showers and
thunderstorms can be expected over southern Utah and the Uintas this afternoon and evening, especially over the higher terrain, with gusty outflow winds as a possibility.
&&

.SLC WATCHES/WARNINGS/ADVISORIES... UT...Excessive Heat Warning until 9 PM MDT this evening for UTZ101>107-115-116-118>124-128-130-131.
Flash Flood Watch from Tuesday afternoon through Tuesday evening for UTZ123>129.
Heat Advisory until 9 PM MDT this evening for UTZ114.
WY...Red Flag Warning from 1 PM to 9 PM MDT Tuesday for WYZ277.
&&
$$
Van Cleave/Wessler For more information from NOAA's National Weather Service visit... http://weather.gov/saltlakecity For frequently asked questions about the Area Forecast Discussion visit... http://weather.gov/saltlakecity/general/afd_faqs.php # # 007 FXUS65 KSLC 122220

AFDSLC
Area Forecast Discussion
National Weather Service Salt Lake City UT 401 PM MDT Mon Jul 12 2021 .SYNOPSIS...Weakening high pressure will allow moisture to return to the area, bringing the threat of thunderstorms to much of Utah and southwest Wyoming through midweek. Heavy rain will be possible across southern Utah, especially Tuesday and Wednesday.
&&
.SHORT TERM...(Through 12Z/6AM MDT Thursday)...With several topics to discuss, have opted to break up the discussion by topic. * Smoke *
The HRRR smoke guidance shows continued smoky conditions for the northern portions of the forecast area through midweek,
with some improvement over southern and perhaps central Utah as early as Tuesday morning. Assuming no other upstream fires take off, we should see gradual reduction in smoke from south to north
through midweek. The upper-level flow direction projections over far northern Utah and southwest Wyoming suggests those areas will be the last to clear out, and may remain smoky through the end of the work week.
* Flash Flooding *
The onset of a significant, albeit brief pattern change is underway early this morning as the much-
discussed strong high pressure ridge is beginning to weaken. This will open the door to northward- advecting moisture as a reservoir of deep moisture resides just to our south and west
across New Mexico, Arizona and Nevada. Flash flooding threat assessment is the primary forecast concern during the period, particularly Tuesday and Wednesday. Moisture will continue to
advect northward by Tuesday and Wednesday, and a moisture rich airmass is forecast to be in place across much of central and southern Utah during this time. Convective-allowing models are
all indicating robust shower and thunderstorm development by late Tuesday morning and early afternoon across high terrain areas of central and southern Utah and along any remnant boundaries. Much
like today, convective activity will lay down outflow boundaries and cold pools and will generally propagate southward both on Tuesday and Wednesday. HREF high-resolution ensemble indicates the
potential for greater than 0.50" of rain in a 3-hr period under the heaviest cores as well as where clusters of convection collide, with several areas showing appreciable chances of 6-hr QPF exceeding 5yr and 10yr average recurrance intervals. As is the case with any convective forecasting, there is some disagreement on the exact placement of heavy rainfall. That said,
we do know that should the heavier cores materialize across flood-prone areas, flash- flooding will be a concern. Ultimate convective coverage
realization will be dependent upon the extent of early-day cloud cover and resultant instability realization, placement of lingering outflow boundaries as well as the track of any remnant MCV
circulations/vorticity filaments from upstream convection. Regardless, the key takeaway message is that if you're planning to recreate in flood-prone areas Tuesday and Wednesday, be aware of the
flash flood potential and have a possible alternate plan in place. A Flash Flood Watch has been issued to account for the areas of highest threat Tuesday. Wednesday looks to be a

potential repeat of Tuesday, but potentially expanding farther
north. Thursday should see a net decrease in convective activity with increased westerly flow, but with lingering chances.

* Heat * Today marked the hottest day of the short term period across the area, as a combination of the weakening ridge and increasing moisture will begin to cap heating potential for the next few days. Thus, the ongoing Excessive Heat Warning will be
allowed to expire. That said, latest guidance indicates that the cooling may only consist of a few degrees for the northern half of the forecast area, so while conditions may not meet heat warning
criteria, heat will continue to be noticeable in the north, with temperatures running around 5 degrees above normal instead of 10+ degrees above normal. .LONG TERM (AFTER 12Z THURSDAY)...As the ridge axis straddles the forecast area, some uncertainty remains in how probable and
widespread thunderstorm chances may be through Thursday. A shift further west would enhance subsidence and drying. Given that scenario, scattered thunderstorms are still expected from south to
north in the forecast area east of I-15 with enough lingering moisture and stability that terrain and strong solar heating should trigger convective development by mid-afternoon, spreading north and
across the Uintas through the early evening. The downward trend in thunderstorm probabilities continues Friday and into the weekend, though cannot rule out the potential for a convectively active
Sunday across the southern Utah mountains. Through the weekend into early next week, a developing trough off the Washington coast will help to rebuild the ridge over the Great Basin, though how far east the ridge axis will fall is still
uncertain with a reasonable amount of spread currently in the ensemble forecasts. Regardless, the GFS and Euro bring 700mb temps exceeding 18C back in over most of the forecast area by Monday,
driving surface temperatures back into the upper 90s and low 100s. Some ensemble members suggest a surge of moisture moving northward around this ridge into Nevada and into Idaho with just enough
seeping into Utah for isolated convection over the higher terrain late Monday.
&& .AVIATION...KSLC...Northwest winds are expected to shift to the southeast after 03z. Smoke will generally remain in place tonight and tomorrow, with visibilities in the 6-10sm range. A 20% chance exists for brief periods of MVFR, with the greatest chance on
Tuesday morning.
Rest of Utah and southwest Wyoming...Areas of smoke will remain across much of the area, but especially northern and central Utah and southwest Wyoming. This will result in terrain obscurations and could lead to localized MVFR conditions. Additionally, showers and
thunderstorms can be expected over southern Utah and the Uintas this afternoon and evening, especially over the higher terrain, with gusty outflow winds as a possibility.
&& .FIRE WEATHER...Isolated dry thunderstorm potential remains this afternoon and evening portions of central and northern Utah, with wetter storms over southern Utah. Expecting the mode of the storms

to transition to wetter in time as deep layer moisture will continue
to rapidly spread NE across the southern half of Utah into Tuesday. Thereafter into Thursday, daily thunderstorm activity (becoming scattered to numerous across central/south) is expected to promote
spotty wetting rains, and increasing RH. Locally heavy rainfall will also be possible. In addition, breezy winds across northern and northeast Utah on Tuesday afternoon could approach fire weather criteria, though relative humidity looks to be a bit too high. This is a potential that will be monitored moving forward. Moisture will begin to move off to the east Thursday, but enough
moisture is expected to linger across mainly central and eastern Utah to promote additional shower and thunderstorm activity. Activity will trend drier on Friday, as thunderstorm coverage diminishes to isolated. By next weekend, another ridge of high pressure is expected to build across the Great Basin, promoting a return of hot and dry conditions with any late-day thunderstorm activity limited to mainly isolated development over high terrain. Elevated winds are possible, but not expected at this time.
.SLC WATCHES/WARNINGS/ADVISORIES... UT...Excessive Heat Warning until 9 PM MDT this evening for UTZ101>107-115-116-118>124-128-130-131.
Flash Flood Watch from Tuesday afternoon through Tuesday evening for UTZ123>129.
Heat Advisory until 9 PM MDT this evening for UTZ114.
WY...Red Flag Warning from 1 PM to 9 PM MDT Tuesday for WYZ277.
&&
$$
Van Cleave/Wessler For more information from NOAA's National Weather Service visit...
http://weather.gov/saltlakecity For frequently asked questions about the Area Forecast Discussion
visit... http://weather.gov/saltlakecity/general/afd_faqs.php #
# 021 FXUS65 KSLC 121730
AFDSLC
Area Forecast Discussion National Weather Service Salt Lake City UT 1130 AM MDT Mon Jul 12 2021
.UPDATE...Main focus today is on assessing flash flood potential for the first part of the week, with a secondary look at dry thunder potential related to fire weather today. Made a few
forecast tweaks this morning based on latest CAMs. In general, any storm activity from around Richfield southward will trend wet quickly, while isolated storms along the central spine mountains
this afternoon to the Uintas will likely be slower to turn wet. That said, we've had a report that a minor cu field over northern Utah this morning managed to send raindrops to the surface at

Kaysville, indicating that the atmosphere is more conducive to
wetter storms even in the northern portion of the CWA. On the flash flood side, 12Z CAMs continue to show some threat of heavier precip in Washington County this evening, then a more widespread
threat for many southern Utah parks and monuments tomorrow. Previous discussion has an excellent description of those threats.
&&
.SYNOPSIS...A strong area of high pressure will maintain very hot
conditions across the region through today. A moisture surge will bring the threat of thunderstorms to much of Utah and southwest Wyoming beginning today and peaking on Tuesday and Wednesday.
Heavy rain will be possible, especially across southern Utah.
&&
.SHORT TERM...(Through 12Z/6AM MDT Thursday)...The onset of a significant, albeit brief pattern change is underway early this morning as the much-discussed strong high pressure ridge is beginning to weaken. This will open the door to northward- advecting moisture as a reservoir of deep moisture resides just
to our south and west across New Mexico, Arizona and Nevada. Flash flooding threat assessment is the primary forecast concern during the period, particularly Tuesday and Wednesday as our
National Parks and recreation areas (such as Zion, Bryce Canyon, Kodachrome, Grand Staircase and Capitol Reef -- not an inclusive list) will be susceptible to heavy rains that could lead to flash flooding of slot canyons, normally dry washes and recent burn scars. Additionally, there is an accompanying threat for urban flash flooding in the St. George area during this time as well should heavier convective activity congeal over the city.
Showers and thunderstorm development is expected over high terrain areas of southern Utah by late this morning and early afternoon, with a bit of a boost thanks to a northwest-southeast oriented moisture gradient. This gradient will also serve to act as a focus for convective initiation along with the typical terrain-induced convergence zones. Shower and thunderstorm activity will be a mix of wet and dry today, with activity
trending drier as one works northward. Showers and thunderstorms will generate gusty outflow winds on the leading edge of outward propagating cold pools, and these will serve as a focus for
additional shower and thunderstorm activity -- especially where outflow boundaries/cold pools collide/intersect. Given modest northwest-north flow above the surface and through the
precipitation-generation/cloud-bearing layer, southward propagating convective activity is forecast. This propagation regime is along-drainage for many slot canyons and dry washes, which increases precipitation residence time and associated flash flood potential across drainages. Although locally heavy rainfall is possible this afternoon and evening with any convective activity, flash flooding will be a lower threat than Tuesday or Wednesday.
Moisture will continue to advect northward by Tuesday and Wednesday, and a moisture rich airmass is forecast to be in place across much of central and southern Utah during this time.
Convective-allowing models are all indicating robust shower and thunderstorm development by late Tuesday morning and early afternoon across high terrain areas of central and southern Utah and along any remnant boundaries. Much like Monday, convective activity will lay down outflow boundaries and cold pools and will generally propagate southward both on Tuesday and Wednesday. HREF

high-resolution ensemble indicates the potential for greater than
0.50" of rain in a 3-hr period under the heaviest cores, as well as where clusters of convection collide. As is the case with any convective forecasting, there is some disagreement on the exact
placement of heavy rainfall, but do know that should the heavier cores materialize across flood-prone areas, flash-flooding will be a concern. Ultimate convective coverage realization will be
dependent upon the extent of early-day cloud cover and resultant instability realization, placement of lingering outflow boundaries as well as the track of any remnant MCV
circulations/vorticity filaments from upstream convection. Wide differences in CAPE continue to exist among CAMs, with SBCAPE peaking around 500-1000 J/kg on the HRRR across southern Utah,
ranging to 1000-1500J/kg (and locally greater) on the 3km NAM. Reality will likely lie somewhere in between these two extremes. The key takeaway message is that if you're planning to recreate in flood-prone areas Tuesday and Wednesday, be aware of the flash flood potential and have a possible alternate plan in place. A Flash Flood Watch may be needed to account for the flooding potential as we get closer to the event.
A notable trend in 00Z guidance is a northward shift in convective
potential for both Tuesday and Wednesday -- and this could result in the development of a few heavier showers across central Utah as well for these two days. In addition, showers and thunderstorms
will be possible across northern Utah and SW Wyoming during this time as well, but moisture and instability will be more limited here -- and as such convection should be less organized/numerous
when compared to southern Utah -- but will still be capable of gusty outflow winds and brief heavy rainfall.
Today will be the hottest day of the short term period across the area, as a combination of the weakening ridge and increasing moisture will limit heating potential for Tuesday and Wednesday,
when temperatures will fall back down near seasonal normals down south and a down to a few degrees above seasonal normals across northern Utah and SW Wyoming. Thus, ongoing heat headlines will
continue unchanged, ending this evening. .LONG TERM...(After 12Z/6AM Thursday)...As a zonal flow over the eastern Pacific moves into the PacNW Wednesday the ridge over the Great Basin will get nudged southward to over southern California by Thursday. This position of the ridge will place Utah on the
downstream side of the ridge axis which is the subsidence side. Consequently, drier and more stable conditions are expected Thursday, although lingering moisture will still fire up some
convection over the higher terrain and adjacent eastern valleys. Convection is expected to a lesser extent Friday.
The zonal flow over the eastern Pacific will buckle and form a trough along the BC coast and off the Washington coast by Friday. This will result in a ridge to rebuild over the Central Rockies to 4
Corners region (depending on the model) during the weekend. This will turn the heat back on with 700mb temps exceeding +18C over most of the forecast area, except perhaps the southwest where some
moisture will start to move back in by Sunday. Nonetheless, temperatures in most valleys will be 95-100 degrees with 100-105 in Washington Co Sunday and basically 5 degrees hotter by Monday. The
brunt of moisture moving northward around this ridge will move into Nevada and into Idaho with just enough moisture seeping into Utah for isolated convection over the higher terrain Monday.
&&

.AVIATION... KSLC...VFR conditions are likely to prevail through the forecast period but there is a 10% chance that the visby lowers to near 5SM or 6SM in FU or HZ, respectively. Light southerly winds will shift to northwest around 17-18Z.

Rest of Utah and southwest Wyoming...VFR conditions are expected to prevail, although there could be areas where mountains are partially obscured due to smoke from distant fires. In addition, there will be
some isolated to scattered afternoon/evening thunderstorms over the southern mountains south of I-70, and isolated thunderstorms over the central mountains and Uintas. Any shower or thunderstorm
has the potential to produce gusty and erratic winds.
&&
.FIRE WEATHER...Isolated dry thunderstorm potential exists Monday afternoon across portions of southern Utah. Expecting isolated
high based storm development Monday afternoon to form over the higher terrain of districts 495, 496, western portions of 498, and possibly into 497 later on during the evening hours. Expecting
the mode of the storms to transition to wetter in time as deep layer moisture will continue to rapidly spread NE across the southern half of Utah into Tuesday. Thereafter into Thursday daily
thunderstorm activity (becoming scattered to numerous across central/south) is expected to promote spotty wetting rains, and rising RH. Locally heavy rainfall will also be possible.
In addition, forecast winds have increased across northern and northeast Utah on Tuesday afternoon, which may result in near
critical fire weather conditions due to the combination of gusty winds and low relative humidity. At this time, both parameters are forecast to be borderline, but this is potential will be
monitored for the need of fire weather headlines. Moisture will begin to move off to the east Thursday, but enough
moisture is expected to linger across mainly central and eastern Utah to promote additional shower and thunderstorm activity. Activity will trend drier on Friday, as thunderstorm coverage
diminishes to isolated. By next weekend, another ridge of high pressure is expected to build across the Great Basin, promoting a return of hot and dry conditions with any late-day thunderstorm
activity limited to mainly isolated development over high terrain.
.SLC WATCHES/WARNINGS/ADVISORIES... UT...Excessive Heat Warning until 9 PM MDT this evening for UTZ101>107-115-116-118>124-128-130-131.

Heat Advisory until 9 PM MDT this evening for UTZ114. WY...Fire Weather Watch from 1 PM MDT to 9 PM MDT Tuesday for
WYZ277. && .SLC WATCHES/WARNINGS/ADVISORIES... UT...Excessive Heat Warning until 9 PM MDT this evening for UTZ101>107-115-116-118>124-128-130-131. Heat Advisory until 9 PM MDT this evening for UTZ114.
WY...None. &&

$$ PUBLIC... AVIATION... FIRE WEATHER...
For more information from NOAA's National Weather Service visit... http://weather.gov/saltlakecity For frequently asked questions about the Area Forecast Discussion visit... http://weather.gov/saltlakecity/general/afd_faqs.php # # 071 FXUS65 KSLC 120959 AFDSLC
Area Forecast Discussion
National Weather Service Salt Lake City UT 359 AM MDT Mon Jul 12 2021 .SYNOPSIS...A strong area of high pressure will maintain very hot conditions across the region through today. A moisture surge will
bring the threat of thunderstorms to much of Utah and southwest Wyoming beginning today and peaking on Tuesday and Wednesday. Heavy rain will be possible, especially across southern Utah.
&&
.SHORT TERM...(Through 12Z/6AM MDT Thursday)...The onset of a significant, albeit brief pattern change is underway early this morning as the much-discussed strong high pressure ridge is
beginning to weaken. This will open the door to northward- advecting moisture as a reservoir of deep moisture resides just to our south and west across New Mexico, Arizona and Nevada.
Flash flooding threat assessment is the primary forecast concern during the period, particularly Tuesday and Wednesday as our National Parks and recreation areas (such as Zion, Bryce Canyon,
Kodachrome, Grand Staircase and Capitol Reef -- not an inclusive list) will be susceptible to heavy rains that could lead to flash flooding of slot canyons, normally dry washes and recent burn
scars. Additionally, there is an accompanying threat for urban flash flooding in the St. George area during this time as well should heavier convective activity congeal over the city.
Showers and thunderstorm development is expected over high terrain areas of southern Utah by late this morning and early afternoon, with a bit of a boost thanks to a northwest-southeast oriented moisture gradient. This gradient will also serve to act as a focus for convective initiation along with the typical terrain-induced convergence zones. Shower and thunderstorm activity will be a mix of wet and dry today, with activity trending drier as one works northward. Showers and thunderstorms will generate gusty outflow winds on the leading edge of outward propagating cold pools, and these will serve as a focus for additional shower and thunderstorm activity -- especially where outflow boundaries/cold pools collide/intersect. Given modest northwest-north flow above the surface and through the precipitation-generation/cloud-bearing layer, southward propagating convective activity is forecast. This propagation regime is along-drainage for many slot canyons and dry washes, which increases precipitation residence time and associated flash

flood potential across drainages. Although locally heavy rainfall
is possible this afternoon and evening with any convective activity, flash flooding will be a lower threat than Tuesday or Wednesday.
Moisture will continue to advect northward by Tuesday and Wednesday, and a moisture rich airmass is forecast to be in place across much of central and southern Utah during this time. Convective-allowing models are all indicating robust shower and thunderstorm development by late Tuesday morning and early afternoon across high terrain areas of central and southern Utah and along any remnant boundaries. Much like Monday, convective activity will lay down outflow boundaries and cold pools and will generally propagate southward both on Tuesday and Wednesday. HREF high-resolution ensemble indicates the potential for greater than 0.50" of rain in a 3-hr period under the heaviest cores, as well as where clusters of convection collide. As is the case with any convective forecasting, there is some disagreement on the exact placement of heavy rainfall, but do know that should the heavier cores materialize across flood-prone areas, flash-flooding will be a concern. Ultimate convective coverage realization will be dependent upon the extent of early-day cloud cover and resultant instability realization, placement of lingering outflow boundaries as well as the track of any remnant MCV circulations/vorticity filaments from upstream convection. Wide differences in CAPE continue to exist among CAMs, with SBCAPE peaking around 500-1000 J/kg on the HRRR across southern Utah, ranging to 1000-1500J/kg (and locally greater) on the 3km NAM. Reality will likely lie somewhere in between these two extremes. The key takeaway message is that if you're planning to recreate in flood-prone areas Tuesday and Wednesday, be aware of the flash flood potential and have a possible alternate plan in place. A Flash Flood Watch may be needed to account for the flooding potential as we get closer to the event. A notable trend in 00Z guidance is a northward shift in convective potential for both Tuesday and Wednesday -- and this could result in the development of a few heavier showers across central Utah as well for these two days. In addition, showers and thunderstorms will be possible across northern Utah and SW Wyoming during this time as well, but moisture and instability will be more limited here -- and as such convection should be less organized/numerous when compared to southern Utah -- but will still be capable of gusty outflow winds and brief heavy rainfall. Today will be the hottest day of the short term period across the area, as a combination of the weakening ridge and increasing moisture will limit heating potential for Tuesday and Wednesday, when temperatures will fall back down near seasonal normals down south and a down to a few degrees above seasonal normals across northern Utah and SW Wyoming. Thus, ongoing heat headlines will continue unchanged, ending this evening. .LONG TERM...(After 12Z/6AM Thursday)...As a zonal flow over the eastern Pacific moves into the PacNW Wednesday the ridge over the Great Basin will get nudged southward to over southern California by Thursday. This position of the ridge will place Utah on the downstream side of the ridge axis which is the subsidence side. Consequently, drier and more stable conditions are expected Thursday, although lingering moisture will still fire up some convection over the higher terrain and adjacent eastern valleys. Convection is expected to a lesser extent Friday. The zonal flow over the eastern Pacific will buckle and form a

trough along the BC coast and off the Washington coast by Friday.
This will result in a ridge to rebuild over the Central Rockies to 4 Corners region (depending on the model) during the weekend. This will turn the heat back on with 700mb temps exceeding +18C over most
of the forecast area, except perhaps the southwest where some moisture will start to move back in by Sunday. Nonetheless, temperatures in most valleys will be 95-100 degrees with 100-105 in
Washington Co Sunday and basically 5 degrees hotter by Monday. The brunt of moisture moving northward around this ridge will move into Nevada and into Idaho with just enough moisture seeping into Utah
for isolated convection over the higher terrain Monday. &&
.AVIATION...
KSLC...VFR conditions are likely to prevail through the forecast period but there is a 10% chance that the visby lowers to near 5SM or 6SM in FU or HZ, respectively. Light southerly winds will shift to northwest around 17-18Z. Rest of Utah and southwest Wyoming...VFR conditions are expected to prevail, although there could be areas where mountains are partially obscured due to smoke from distant fires. In addition, there will be some isolated to scattered afternoon/evening thunderstorms over the southern mountains south of I-70, and isolated thunderstorms over the central mountains and Uintas. Any shower or thunderstorm has the potential to produce gusty and erratic winds.
&&
.FIRE WEATHER...Isolated dry thunderstorm potential exists Monday afternoon across portions of southern Utah. Expecting isolated high based storm development Monday afternoon to form over the higher terrain of districts 495, 496, western portions of 498, and
possibly into 497 later on during the evening hours. Expecting the mode of the storms to transition to wetter in time as deep layer moisture will continue to rapidly spread NE across the southern half of Utah into Tuesday. Thereafter into Thursday daily thunderstorm activity (becoming scattered to numerous across central/south) is expected to promote spotty wetting rains, and rising RH. Locally heavy rainfall will also be possible. In addition, forecast winds have increased across northern and northeast Utah on Tuesday afternoon, which may result in near critical fire weather conditions due to the combination of gusty winds and low relative humidity. At this time, both parameters are forecast to be borderline, but this is potential will be monitored for the need of fire weather headlines.
Moisture will begin to move off to the east Thursday, but enough moisture is expected to linger across mainly central and eastern Utah to promote additional shower and thunderstorm activity.
Activity will trend drier on Friday, as thunderstorm coverage diminishes to isolated. By next weekend, another ridge of high pressure is expected to build across the Great Basin, promoting a
return of hot and dry conditions with any late-day thunderstorm activity limited to mainly isolated development over high terrain.
.SLC WATCHES/WARNINGS/ADVISORIES... UT...Excessive Heat Warning until 9 PM MDT this evening for UTZ101>107-115-116-118>124-128-130-131.
Heat Advisory until 9 PM MDT this evening for UTZ114.

WY...Fire Weather Watch from 1 PM MDT to 9 PM MDT Tuesday for
WYZ277.
&& $$
ADeSmet/Struthwolf
For more information from NOAA's National Weather Service visit...
http://weather.gov/saltlakecity For frequently asked questions about the Area Forecast Discussion
visit... http://weather.gov/saltlakecity/general/afd_faqs.php #
# 956 FXUS65 KSLC 112143
AFDSLC

Area Forecast Discussion National Weather Service Salt Lake City UT 343 PM MDT Sun Jul 11 2021
.SYNOPSIS...A strong area of high pressure will maintain very hot conditions across the region through early next week. A moisture surge will bring the threat of thunderstorms to portions of Utah
early to midweek next week. &&
.SHORT TERM (Through 12z Wednesday)...There's been minimal change in the strength or placement of the upper ridge oriented over the lower Colorado Basin today. Have noted a slight uptick in mid level moisture across far southwestern Utah within the return flow environment however, with PWAT encroaching upon .80" this afternoon. This area remains on the extreme periphery of the moisture/instability gradient which continues to be draped south and west of the area, but mountain based thermals have been strong enough with the excessive heat in place to form isolated storms over the higher terrain near the Pine Valley and upstream over the last hour or so. This activity will rapidly wane with loss of solar moving forward through this evening...for the time being. SPC HREF continues to indicate the aforementioned
moisture/instability gradient will shift a little further to the northeast over the next 24 hours promoting scattered afternoon convection across the southwest tomorrow, with isolated terrain
based initiation possible northeast on up the spine of the Wasatch Plateau as modest moisture advection continues to spread NE through the day. Storms are expected to continue to remain high
based and primarily gusty in nature through tomorrow, but that trend is expected to change rapidly by Tuesday.
Regarding the excessive heat in place, one more day before things become "less hot" with some ridge suppression leading into Tuesday. Have noted some areas being challenged to reach forecast highs
across the north today due to the abundance of smoke aloft, but most areas continue to at least flirt with triple digits (if not exceed them like KSLC has once again). Heat headlines remains
status quo, with expiration tomorrow evening. For namely southern Utah Tuesday (and the central UT mtns), a

continuation of moisture advection from the SW and further
destabilization within a weakening ridge shifts sensible weather impacts more towards a locally heavy rain and potential flash flood threat. The extent of the latter will be highly tied to
subtleties of the flow (largely NW aloft), and down basin propagation of individual storm cells and attendant cold pools. It remains favorable for storm growth towards the
instability/moisture axis which will remain tied just south/west of the state, and several models evolve things in such a way through the evening and into the overnight hours. Will be watching how things evolve both within the airmass and model guidance over the next 24 hours, and weigh any need for a Flash Flood Watch for Tuesday on future shifts.
Outside of the south, model consensus continues to show the deeper layer moisture and marginal instability creeping up to the
I-80 corridor and points downstream/east, but more isolated in nature and higher based. Will monitor this closely moving forward as well.
.LONG TERM (AFTER 12Z WEDNESDAY)...Smoke lingers around Wednesday, but the attention will shift to the potential for monsoon thunderstorms capable of producing heavy rainfall across southern Utah. Thunderstorm chances will also increase across central an northern Utah Wednesday. Storm chances will continue throughout the week, but become more isolated and transition back to high based dry thunderstorms by Friday. Heat returns by the weekend. The long term discussion will focus on the monsoon moisture period and the heat. (Monsoon Thunderstorms): Southern Utah- A breakdown of the ridge axis has opened the door for a robust surge of monsoonal moisture to
envelop much of southern Utah. PWAT values on Wednesday along the Utah border counties of Washington and Kane, should be just at or above 1". PWAT values across the southern central mountains are
ranging from 0.75-0.85". Additionally, the freezing level to LCL thickness of 2000-2500m, indicates a deep warm cloud layer that heightens the chance for these storms to be proficient rain
producers. With all the heavy rain ingredients coming together, the next focus will be for getting thunderstorms to develop.
Ensemble members and some of the longer range CAM models are in good agreement of modest destabilization occurring during the early afternoon as a warm and moist airmass will be in place. Taking an
average of all the inputs, surface CAPE values are likely to be in the 1000-1250 J/kg range just prior to storm initiation. The most likely area for initial convection will be along the the higher terrain across the southern mountains. Thunderstorm coverage will quickly increase as new storms form on outflow boundaries and typical terrain convergence zones. Expect these storms to move rather slow which only increases the likelihood of flash flooding concerns. The areas of greatest concern will be in our national parks including; Zion, Bryce Canyon, Kodachrome, Grand Staircase and
Capitol Reef. We are most concerned with a rapidly developing storm in and around the park that will produce heavy rainfall in a short period of time leading to quick flash flooding in the dry washes and
slot canyons. Over time the heavy rain threat will slowly move south as new clusters of storms develop along southward moving outflow boundaries. This will shift the flood threat to areas across
Washington and Kane counties just prior to the evening hours. Heading through the end of the week, thunderstorms chances remain in the forecast but the airmass will begin to slowly dry out putting an end to the flash flood threat, although some stronger cores could produce a quick burst of rainfall on Thursday before the convective

mode transitions back to drier, high based thunderstorms by Friday.
Across central and northern Utah, the surge of monsoonal moisture will have reached these areas by Wednesday. While not as significant
across central Utah and even less across northern Utah compared to the conditions across southern Utah, the addition of a warm and moist airmass will be enough to kick start some afternoon convection, primarily across the higher terrain. While not the slam dunk heavy rain threat, some of the strong storms could produce some moderate rainfall, mainly Wednesday and Thursday. Conditions begin to dry out by Friday, but some high based, isolated thunderstorms may still be possible. (Heat Returns): A building ridge across the Four Corners region begins to expand and this should bring and end to precipitation chances across Utah just in time for the weekend. Unfortunately, with a building ridge and clearing skies, hot temperatures are expected across much of Utah. && .AVIATION...KSLC...Northwest winds are expected to shift to the southeast after 04-06z. Areas of smoke will remain in place tonight and tomorrow , with visibilities generally in the 6-10sm range and a
20 percent MVFR visibilities in periods of thicker smoke. Rest of Utah and southwest Wyoming...Areas of smoke will remain across much of the area, but especially northern and central Utah and southwest Wyoming. This will result in terrain obscurations and could lead to localized MVFR conditions. Additionally, a few high- based showers and thunderstorms can be expected over southern Utah this afternoon and evening, especially over the higher terrain, with gusty outflow winds as a possibility. Another round of such storms is expected tomorrow afternoon. &&
.FIRE WEATHER...Of most note over the next 24 hours is an isolated dry thunderstorm potential Monday afternoon across southwestern portions of the district. Expecting isolated high based storm
development Monday afternoon to form over the higher terrain of districts 495, 496, western portions of 498, and possibly into 497 later on during the evening hours. Expecting the mode
of the storms to quickly phase wetter in time as deep layer moisture will continue to rapidly spread NE across the southern half of the district into Tuesday. Thereafter into Thursday daily thunderstorm activity (becoming scattered to numerous across central/south) is expected to promote spotty wetting rains, and rising RH.
Moisture will begin to move off to the east Thursday, but enough moisture is expected to linger across mainly central and eastern
Utah to promote additional shower and thunderstorm activity. Activity will trend even drier on Friday, as thunderstorm coverage diminishes to isolated. By next weekend, another ridge of
high pressure is expected to build across the Great Basin, promoting a return of hot and dry conditions with any late-day thunderstorm activity limited to mainly isolated development over
high terrain. &&
.SLC WATCHES/WARNINGS/ADVISORIES... UT...Excessive Heat Warning until 9 PM MDT Monday for UTZ101>107-115-

116-118>124-128-130-131.
Heat Advisory until 9 PM MDT Monday for UTZ114.
WY...None. &&
$$ Merrill/Woodward/Van Cleave
For more information from NOAA's National Weather Service visit... http://weather.gov/saltlakecity
For frequently asked questions about the Area Forecast Discussion visit...
http://weather.gov/saltlakecity/general/afd_faqs.php # # 031 FXUS65 KSLC 111006 AFDSLC
Area Forecast Discussion National Weather Service Salt Lake City UT 406 AM MDT Sun Jul 11 2021
.SYNOPSIS...A strong area of high pressure will maintain very hot
conditions across the region through early next week. A moisture surge will bring the threat of thunderstorms to portions of Utah early to midweek next week.
&& .SHORT TERM...(Through 12Z/6AM MDT Wednesday)...Very strong 598dam high pressure ridge remains centered near Las Vegas early this morning. This ridge will be responsible for two more days of
heat across much of Utah and SW Wyoming. Although the height of the heatwave across southern Utah occurred on Saturday, temperatures will only drop 1-3 degrees across these areas today
as the ridge begins to weaken -- with temperatures forecast to reach 113-114 in St. George and Zion and around 108 across western Lake Powell. Across central and northern Utah, the temperature
forecast is less certain. 700mb temps and 500mb heights are both expected to increase today and Monday as the northern periphery of the ridge expands northward, which would normally translate to
associated warming at the surface. However, wildfire smoke will work against this. Wildfire smoke attenuates incoming shortwave radiation, resulting in a cooling effect during the day as less solar radiation is received at the surface, assuming smoke is dense enough. It is expected to be dense enough both today and tomorrow. Smoke does not attenuate outgoing longwave radiation at
night. The cumulative effect of less hot days translates into associated cooler than forecast nights, and this results in a net cooling trend with time. Have nudged highs downward 1-3 degrees
across northern Utah and SW Wyoming both today and Monday as a result of anticipated smoke. However, temperatures will still be excessively hot, with many low elevation areas seeing 100 degree
highs -- but perhaps not quite into certain record territory. These temperature forecasts in the presence of wildfire smoke are especially tricky as models (with the exception of the HRRR) to
not parameterize smoke. As such, there is some potential for highs to clock in a degree or two below our downward manual adjustments. Even with cooling due to smoke, it will still be hot.

Attention then turns to precipitation potential as monsoonal moisture begins to ooze northward into southern Utah over the next couple of days. An impressive MCS currently ongoing over Arizona gives some early hints at the anomalous nature of the moisture currently available to our south. Onset of moisture advection will slowly begin today, but overall moisture quality will still remain paltry -- just enough to support an isolated shower or thunderstorm along the Nevada border, near St. George and over high terrain areas of southern Utah such as Border Mountain. A few
CAMs (convective-allowing high resolution models) target the St. George area for measurable precipitation Sunday evening -- but not all members are on board with the idea. The NBM (and going official forecast) represent the more robust solutions and this will bear watching. Moisture transport will continue on Monday, with isolated to locally scattered showers and thunderstorms expected to develop across southern Utah. The leading edge of the activity will tend to be dry, with activity gradually trending towards a mix of wet and dry with time through the afternoon and evening. NAM MUCAPE values are forecast to rise into the very healthy 1000-1500J/kg range across southern Utah Monday afternoon, while the HRRR advertises much less available instability with forecast values in the 200-300J/kg range. This is a significant difference, indeed. HREF mean MUCAPE among all available CAMs indicate CAPE reality will lie somewhere in the middle of these
two extremes -- and even so the HREF mean will be easily sufficient for convective initiation. Bulk shear values are forecast to be a bit healthier than in past runs, with 15-25kt available. The combination of available shear and instability may aid in the development of a strong storm or two. With light, northerly mid-level flow meeting southerly low-level flow, this will set the stage for primarily southward-propagating storm motion, which is along drainage for many slot canyons. This will increase the local flash flood potential Monday afternoon and evening, and will serve as a preview of what's to come. Moisture will continue to increase through Tuesday, when PWAT values are currently forecast to exceed 1" across southern Utah. Instability and buoyancy values are impressive by Tuesday afternoon across southern and central Utah where surface-based CAPE values are forecast to exceed 1000J/kg. Along-drainage flow is again expected to be an issue Tuesday, and when considering the anomalous amounts of available moisture and instability, flash flooding will be a concern across all of southern Utah Tuesday afternoon and evening, perhaps even lingering into Tuesday night. Models indicate the potential for multiple clusters of showers and thunderstorms. Some clusters could produce 0.50" of rain or more in a 3-hr period across southern Utah. Therefore, the risk for slot canyon and dry-wash flash flooding is a concern. Farther north across northern Utah and SW Wyoming, moisture will be on the increase as well, but given the predominant westerly flow aloft, the core of deepest moisture will remain across southern Utah. Nonetheless, isolated showers and thunderstorms are forecast to work into northern Utah, especially by Tuesday. With the increase in moisture, temperatures will begin to cool by Tuesday, dropping down to near seasonal normals across southern Utah and down to 5-10 degrees above seasonal normals across northern Utah, effectively cooling down out of record or near record territory. .LONG TERM...(After 12Z/6AM MDT Wednesday)...The two main concerns for the extended period will be the continued heat, although tempered some, especially across the south Wednesday and Thursday due to cloud cover and rain, and the other concern the threat of heavy rain and flash flooding potential across the south.

The general weather pattern shows the ridge over the southern Great Basin becoming a little flattened by a shortwave moving across the Northern Rockies on Tuesday. This will result in a more westerly flow across northern utah bu but a short period of time a southwest flow will occur on Tuesday over southern Utah and southern Nevada which will import higher PWs into the southern portion of the forecast area. Additional weak shortwaves moving across the PacNW and Northern Rockies will back the flow a little southwesterly across Nevada and Utah allowing the deep moisture to remain in place
through Wednesday before some drying occurs Friday into the weekend as the ridge strengthens and temperatures rise once again. However, Wednesday is the main concern of the extended period. The EPS and GEFs are in agreement with more than 85% of them showing measurable precip across the southern mountains (Bryce Canyon) in particular. The NBM is moving in this direction with a 60% chance of precip at Bryce during the same period. Some of the EPS and GEFs members are showing in excess of 0.20 of an inch, which in a convective environment is significant. The NBM is showing a 20% chance of greater than 0.20 of an inch, which compares rather well. With so many of the members showing high PoPs have adjusted the grids to include likely PoPs over the southern mountains. Have also shown these higher PoPs to drift southward toward the Arizona border as outflow boundaries are likely to induce convection. The GFS shows surface buoyant energy over 1000(J/kg) across Washington County with PWs over an inch. Throw all these ingredients into a blender and we have the makings of a heavy rainier day with potential flash flooding across the southern tier from Washington Co to western Kane Co and portions of the southern mountains. Scattered showers and thunderstorms will extend northward into the central Wasatch and Uinta mountains Wednesday afternoon and evening but the threat of heavy rain the farther you go will lessen. The additional cloud cover should bring temperatures down some Wednesday and into Thursday as well, before the ridge rebuilds and drying with sunnier skies return for the weekend.
&& .AVIATION...
KSLC...Light southerly winds will prevail until about 18Z when a northwest wind will set in. Smoke from distant fires may cause a reduction in visibility, especially between 17z and 19Z as
we transition from SE winds to NW winds. Otherwise no weather concerns through today. There is a 10% chance that smoke brings upper end MVFR conditions after 10Z tonight.
Rest of Utah and southwest Wyoming...VFR conditions are expected to prevail, although there could be areas where mountains become partially obscured due to smoke from distant fires. Also, there will be some isolated thunderstorms over the southern mountains this afternoon into early this evening, producing gusty and erratic winds.
&&
.FIRE WEATHER...Through Monday record to near record breaking heat and very dry conditions will continue to dominate as strong high pressure remains oriented over the lower Colorado Basin.
With lighter winds today than compared to Saturday, only isolated critical areas of critically low RH will combine with critically gusty winds.
Orientation of the ridge will shift slightly beginning early next week allowing sub-tropical moisture which currently remains

pinned to our south to slowly spread north and east across namely
the southern half of the state through the midweek period at least. The initial push of this moisture on Monday will initially promote high based storm development with isolated dry
thunderstorms or a mix of isolated wet and dry showers and thunderstorms. However, the environment will become increasingly moist allowing wetter thunderstorms beginning Tuesday and
continuing through Wednesday, mainly across southern Utah. Pockets of wetting rains across namely the southern/central mountains are possible during the midweek period. Additionally, the increase in moisture will allow for minimum RH values to remain above 15% across much of southern Utah by Tuesday and especially Wednesday.
Moisture will begin to move off to the east Thursday, but enough moisture is expected to linger across mainly central and eastern
Utah to promote additional shower and thunderstorm activity. Activity will trend even drier on Friday, as thunderstorm coverage diminishes to isolated. By next weekend, another ridge of
high pressure is expected to build across the Great Basin, promoting a return of hot and dry conditions with any late-day thunderstorm activity limited to mainly isolated development over
high terrain. &&

.SLC WATCHES/WARNINGS/ADVISORIES... UT...Excessive Heat Warning until 9 PM MDT Monday for UTZ101>107-115-
116-118>124-128-130-131. Heat Advisory from noon today to 9 PM MDT Monday for UTZ114.
WY...None. &&
$$
ADeSmet/Struthwolf
For more information from NOAA's National Weather Service visit... http://weather.gov/saltlakecity For frequently asked questions about the Area Forecast Discussion visit... http://weather.gov/saltlakecity/general/afd_faqs.php # # 539 FXUS65 KSLC 110354 AFDSLC
Area Forecast Discussion National Weather Service Salt Lake City UT 954 PM MDT Sat Jul 10 2021 .UPDATE...No forecast updates this evening. That said, one item of potential interest this evening is the fact that the St George COOP station (the official observational station for the St George area) reported a high for today of 117. This would tie the all- time record warmest temperature for Utah. Given the significance of this mark, further investigation may be needed in the coming
days. More information is available in a Record Event Report (RER).

&& .SYNOPSIS...A strong area of high pressure will maintain very hot conditions across the region through early next week. A moisture surge will bring the threat of thunderstorms to portions of Utah early to midweek next week. &&
.DISCUSSION...Afternoon satellite and H5 analysis place the core of a 599 Dam high over the lower Colorado River basin, centered aloft between Vegas and the St George area. The bulk of the forecast area remains on the downstream side of the attendant axis, with a dry and stable northerly flow dominating on up through the mid levels. Sensibly its impossible to ignore the heat in place, near record to record breaking values, values to watch moving forward for the remainder of the afternoon (especially in the St George area). It's still not out of the question for Utah to reach (and possibly surpass) the all time record high of 117 F there.
Slight suppression of the ridge over the last 24 hours coupled with smoke aloft has allowed for "less hot" conditions across the northern-tier today, but guidance continues to suggest a net
rebounding of the ridge tomorrow through Monday once again turning up the heat dial to excessive values throughout. Have not made any changes to the excessive heat headlines as such, with a
plethora of warnings out through Monday evening remaining in place.
Looking further to our south deep layer sub-trop moisture remains pinned just south of the AZ border attm, with streamlines advecting this north and west into Nevada along the southwestern
periphery of the high. In time this moisture will begin to spread into the far southwest (late tomorrow through Monday), then across much of the southern third of the area (Tuesday into midweek).
PWAT values approaching 1" can't be ruled out as enhanced pooling across those locales does look likely given another weak short wave passage to our north Tue into Wed, but in large values should
be in excess of .80" and more than sufficient for convection. Breadth and significance of this convection will likely remain a bit suppressed into early next week however as lack of instability
will be a limiting factor, but by Tuesday SBCAPE values do look to top 500 J/KG during the peak heating hours. With this coupled, the potential for heavy rainers becomes more notable, and steering
flow does look favorable to propagate cells from the the southern mountains south-southeast (down drainage) into the more primed moisture/instability axis which will be in place. Will be
continuing to monitor the subtleties of this evolution over the next few days, as the potential for flash flood concerns does look to increase across the south Tuesday...likely lingering into the latter portions of the week. Temperature wise, this net increase of moisture, cloud cover, and
a subtle lowering of heights will suppress temps from recent extremes, but only a skosh as most areas will remain 5+ degrees above climatological norms.
&&
.AVIATION... KSLC...Northwest winds are expected to shift to the

southeast after 04-05z. Areas of smoke will remain in place, with
a 20 percent of reducing visibilities to MVFR tonight.
Rest of Utah and southwest Wyoming...Areas of smoke will remain across much of the area, but especially northern and central Utah and southwest Wyoming. This could result in localized MVFR conditions, especially tonight, which could lead to the higher terrain becoming partially obscured.
&&
.FIRE WEATHER...Through Monday near to record breaking heat and very dry conditions will continue to dominate as strong high
pressure remains oriented over the lower Colorado Basin. Elevated winds coming from the northern half of the compass will continue through this evening promoting critical fire weather conditions
for many of our east-central zones, but these winds will be on the decrease for Sunday with only isolated critical areas remaining possible. Orientation of the ridge will shift slightly beginning early next week allowing sub-tropical moisture which currently remains pinned to our south to slowly spread north and east across namely the southern half of the state through the midweek period at least. The initial push of this moisture on Monday will promote high based storm development with isolated dry thunderstorm potential developing across the southwest, but in time the environment will become increasingly moist allowing wetter thunderstorms beginning Tuesday. Pockets of wetting rains across namely the southern/central mountains are possible during the midweek period, but in large the breadth of moisture will allow for RH values to remain above 15% across the south. Further north the environment is expected to remain on the dry side however.
&&
.SLC WATCHES/WARNINGS/ADVISORIES... UT...Excessive Heat Warning until 9 PM MDT Monday for UTZ101>107-115- 116-118>124-128-130-131.
Heat Advisory from noon Sunday to 9 PM MDT Monday for UTZ114. WY...None. && $$
Van Cleave/Merrill/Cheng
For more information from NOAA's National Weather Service visit... http://weather.gov/saltlakecity
For frequently asked questions about the Area Forecast Discussion visit... http://weather.gov/saltlakecity/general/afd_faqs.php # # 152
FXUS65 KSLC 102133 AFDSLC

Area Forecast Discussion National Weather Service Salt Lake City UT 333 PM MDT Sat Jul 10 2021

.SYNOPSIS...A strong area of high pressure will maintain very hot conditions across the region through early next week. A moisture surge will bring the threat of thunderstorms to portions of Utah early to midweek next week. && .DISCUSSION...Afternoon satellite and H5 analysis place the core of a 599 Dam high over the lower Colorado River basin, centered
aloft between Vegas and the St George area. The bulk of the forecast area remains on the downstream side of the attendant axis, with a dry and stable northerly flow dominating on up through the mid levels. Sensibly its impossible to ignore the heat in place, near record to record breaking values, values to watch moving forward for the remainder of the afternoon (especially in the St George area). It's still not out of the question for Utah to reach (and possibly surpass) the all time record high of 117 F there. Slight suppression of the ridge over the last 24 hours coupled with smoke aloft has allowed for "less hot" conditions across the northern-tier today, but guidance continues to suggest a net rebounding of the ridge tomorrow through Monday once again turning up the heat dial to excessive values throughout. Have not made any changes to the excessive heat headlines as such, with a plethora of warnings out through Monday evening remaining in place. Looking further to our south deep layer sub-trop moisture remains pinned just south of the AZ border attm, with streamlines
advecting this north and west into Nevada along the southwestern periphery of the high. In time this moisture will begin to spread into the far southwest (late tomorrow through Monday), then across
much of the southern third of the area (Tuesday into midweek). PWAT values approaching 1" can't be ruled out as enhanced pooling across those locales does look likely given another weak short
wave passage to our north Tue into Wed, but in large values should be in excess of .80" and more than sufficient for convection. Breadth and significance of this convection will likely remain a
bit suppressed into early next week however as lack of instability will be a limiting factor, but by Tuesday SBCAPE values do look to top 500 J/KG during the peak heating hours. With this coupled,
the potential for heavy rainers becomes more notable, and steering flow does look favorable to propagate cells from the the southern mountains south-southeast (down drainage) into the more primed moisture/instability axis which will be in place. Will be continuing to monitor the subtleties of this evolution over the next few days, as the potential for flash flood concerns does look to increase across the south Tuesday...likely lingering into the latter portions of the week.
Temperature wise, this net increase of moisture, cloud cover, and a subtle lowering of heights will suppress temps from recent extremes, but only a skosh as most areas will remain 5+ degrees above climatological norms. && .AVIATION....AVIATION...KSLC...Northwest winds are expected to shift to the southeast after 04-05z. Areas of smoke will remain in place, with a 20 percent of reducing visibilities to MVFR tonight. Rest of Utah and southwest Wyoming...Areas of smoke will remain

across much of the area, but especially northern and central Utah
and southwest Wyoming. This could result in localized MVFR conditions, especially tonight, which could lead to the higher terrain becoming partially obscured.
&&

.FIRE WEATHER...Through Monday near to record breaking heat and very dry conditions will continue to dominate as strong high pressure remains oriented over the lower Colorado Basin. Elevated
winds coming from the northern half of the compass will continue through this evening promoting critical fire weather conditions for many of our east-central zones, but these winds will be on the
decrease for Sunday with only isolated critical areas remaining possible. Orientation of the ridge will shift slightly beginning early next week allowing sub-tropical moisture which currently remains pinned to our south to slowly spread north and east across namely the southern half of the state through the midweek period at least. The initial push of this moisture on Monday will promote high based storm development with isolated dry thunderstorm
potential developing across the southwest, but in time the environment will become increasingly moist allowing wetter thunderstorms beginning Tuesday. Pockets of wetting rains across
namely the southern/central mountains are possible during the midweek period, but in large the breadth of moisture will allow for RH values to remain above 15% across the south. Further north
the environment is expected to remain on the dry side however. && .SLC WATCHES/WARNINGS/ADVISORIES... UT...Excessive Heat Warning until 9 PM MDT Monday for UTZ101>107-115- 116-118>124-128-130-131.
Red Flag Warning until 9 PM MDT this evening for UTZ483-484-488- 489-
493. Heat Advisory from noon Sunday to 9 PM MDT Monday for UTZ114.
WY...None. &&
$$
Merrill/Cheng
For more information from NOAA's National Weather Service visit...
http://weather.gov/saltlakecity For frequently asked questions about the Area Forecast Discussion
visit... http://weather.gov/saltlakecity/general/afd_faqs.php #
# 402 FXUS65 KSLC 101005
AFDSLC
Area Forecast Discussion National Weather Service Salt Lake City UT
405 AM MDT Sat Jul 10 2021

.SYNOPSIS...A strong area of high pressure will maintain very hot
conditions across the region through early next week. A moisture surge will bring the threat of thunderstorms to portions of Utah early to midweek next week.
&&

.SHORT TERM...(Through 12Z/6AM MDT Tuesday)...Early morning observational analysis continues to reveal the presence of a strong ridge (clocking in at 599dm) of high pressure centered
just east of Las Vegas, with a northward extending ridge axis into Idaho. An area of mid-level moisture is evident across central Nevada, and this should advect eastward through mainly northern Utah today. Expect little more than an increase in mid to high clouds with this activity as modest low-level dry advection continues from north to south. The only exception may be around Boulder Mountain or Zion where a light shower cannot be ruled out this afternoon. The main story will continue to be the heat as heat headlines will continue as inherited into Monday evening. We continue to forecast a high temperature of 115 degrees today in St. George -- which would tie the all-time record high temperature for the city. The all-time state record high temperature is not
safe either, with NBM probability of exceedance currently indicating a 23% chance of this threshold being reached at St. George. EFI and SoT plots bear out the anomalous nature of this
heat as well, with EFI values near 1 and SoT values also near 1 across far southern Utah -- further cementing high forecaster confidence in the potential for record or near record all-time highs. With such extreme heat centered over active recreational areas, it is important that folks join together in practicing proactive heat-safe measures, as such extreme temperatures increase the potential of heat-related illnesses. Folks are strongly encouraged to drink plenty of water, even if they don't feel thirsty, wear light- colored, loose-fitting clothing and
avoiding strenuous activity during the heat of the day.
Extreme heat will continue across southern Utah on Sunday while building back into much of northern Utah and SW Wyoming as the ridge rebounds slightly northward. This will follow a hardly
noticeable cooldown of 1-3 degrees across northern Utah today -- and today only. The hot trend will persist through Monday due to the rebounding ridge, maintaining record or near record heat.
Across southern Utah, moisture will begin to creep northward Sunday, with a stronger northward push of moisture Monday. This will manifest itself in the form of an isolated, high-based shower
or thunderstorm in the St. George vicinity Sunday afternoon/evening. Further increases in moisture across southern Utah on Monday will most noticeably promote the onset of a
cooling trend, with highs backing off to a still scorching 111 at St. George Monday, which is a start. Isolated to widely scattered thunderstorms are expected across south-central and southwest
Utah Monday afternoon and evening as PWATs climb back to around 0.8". Weak W-NW flow will promote slow storm motion and MUCAPE values may sneak into the 500J/Kg range, suggesting the potential
for at least a strong storm or two. Weak bulk shear will be a limiting factor to updraft strength/longevity, so any storms should be primarily the pulse variety. The potential for heavy
rainfall is low at this time for Monday, but any storms will bear watching given the forecast weak mean flow and primary north-south storm motion. Farther north, an isolated cell will be possible
along the central mountains and Uintas. With westerly flow in place across northern Utah, it will be difficult to advect deeper moisture into this area through Monday.

Increased smoke was readily apparent across northern Utah Friday evening, as wildfire smoke from California, Nevada and Oregon was advected into the region. Northerly low-level flow behind a weak boundary aided in advecting near-surface smoke into northern Utah. While smoke will persist across northern Utah today, it will be slightly more apparent across central Utah as it continues to advect southward. HRRR smoke model suggests near-surface smoke will once again thicken tonight and Sunday across much of northern and central Utah.
.LONG TERM...(After 12Z/6AM MDT Tuesday)...Models remain in good
agreement regarding the large-scale pattern through the duration of the long- term forecast period. Cluster analysis of ensemble members indicate only subtle differences in H5 height fields. As
such, there is fairly high confidence in the pattern evolution of the ridge over the area gradually flattening before re-amplifying with the ridge axis just to the east for late week.
This previous discussion for the extended period summarizes the general pattern well, so I began with that as my first paragraph.
However, as one gets into the weeds of the forecast there are potential hazards which will/could impact the southern portion of the CWA. As the ridge flattens between Monday and Tuesday, the general consensus of models is for moisture at mid levels to be brought northward across the southern third of the CWA with PWs above 0.90 of an inch, with a bullseye of 1.25 inches over extreme southwest UT according to the GFS deterministic model. There are about 80% or more of the EPS and GEFS members showing measurable precipitation over southern mountains for the 24 hr period ending midnight Tuesday night, while the NBM has about 60% PoPs for the 12 hr period ending at 6pm Tuesday, which probably equates quite closely to 80% if that time period extended through midnight. The
GFS shows nearly 2 inches of QPF near Brian Head for the 12hr period ending midnight Tuesday night, which needs to be taken with a grain of salt, but the underlying message of high QPF potential needs to
be heeded. This is significant because if the 700 and 500mb north to northeast wind forecast is accurate then thunderstorms that form over the higher terrain will drift southward down drainage for many of the flash flood prone canyons of southern Utah including Zion National Park. While the PWs decline some on Wednesday there could be another day of potential flash flooding across southern Utah. The NBM's general downward trend of showers and thunderstorms to only slight chance over the mountains as we head into the end of the week looks too dry. Confidence is low in this PoP forecast as the cluster
of 500mb heights suggest the ridge axis is to our east by Friday evening meaning a southerly flow could easily be in place at low levels importing moisture that is not displaced very far from the
southern Utah border. Temperatures through this extended period will remain above normal with the hottest days likely towards the end of the week. However, cloud cover will play an important role in how hot each day and night will be. && .AVIATION...KSLC...Winds will battle in direction across the terminal through about 10-11Z before most likely settling into a SE direction until about 17Z when a northwest wind will set in. Smoke from distant fires may cause a brief reduction in visibility at about 13Z, otherwise no weather concerns through today. There is a 10% chance that smoke brings upper end MVFR conditions after 03Z tonight.

Rest of Utah and southwest Wyoming...VFR conditions are expected to prevail, although there could be areas where mountains become partially obscured due to haze and smoke from distant fires.
&& .FIRE WEATHER...A strong upper level ridge will remain in place across the region through the weekend. Moisture is expected to increase early to mid-week next week as a potential monsoon surge develops. Moisture quality is expected to be best on Tuesday and Wednesday, with the greatest thunderstorm coverage expected across
central and southern Utah. Thunderstorms will tend to be drier on Monday on the northern fringes of the moisture push, but will gradually trend wetter for Tuesday and Wednesday -- when some wetting rains will be possible. For now, record to near record temperatures will continue through Monday. Gusty winds and low humidities are expected for another day across eastern Utah Sunday afternoon and evening in the wake of a weak front. With lighter winds forecast Sunday, only isolated pockets of critical winds and low RH are expected, thus Red Flag Warnings are not currently anticipated for this time. Increasing moisture next week will lead to pockets of min RH above 15%, especially across southern Utah. More modest increases in moisture are currently expected
across northern Utah. && .SLC WATCHES/WARNINGS/ADVISORIES... UT...Excessive Heat Warning until 9 PM MDT Monday for UTZ101>107-115- 116-118>124-128-
130-131. Red Flag Warning until 9 PM MDT this evening for UTZ483-484-488- 489-493.
Heat Advisory from noon Sunday to 9 PM MDT Monday for UTZ114. WY...None. && $$ ADeSmet/Struthwolf
For more information from NOAA's National Weather Service visit... http://weather.gov/saltlakecity
For frequently asked questions about the Area Forecast Discussion visit... http://weather.gov/saltlakecity/general/afd_faqs.php #

National Interagency Coordination Center Incident Management Situation Report Monday July 12, 2021– 0730 MDT National Preparedness Level 4
National Fire Activity:
Initial attack activity: Light (137 fires)
New large incidents: 9
Large fires contained: 2
Uncontained large fires: *** 50
Area Command teams committed: 0
NIMOs committed: 0
Type 1 IMTs committed 9 Type 2 IMTs committed: 14
Nationally, there are 20 fires being managed under a strategy other than full suppression. ***Uncontained large fires include only fires being managed under a full suppression strategy. Link to Geographic Area daily reports.
Link to Understanding the IMSR.

Two MAFFS C-130 airtankers and support personnel each from the 152nd Airlift Wing (Nevada Air National
Guard) and one additional from the 146th Airlift Wing (California Air National Guard) have been deployed to
McClellan, CA to support wildland fire operations nationally.
One RC-26 aircraft with Distributed Real-Time Infrared (DRTI) capability and support personnel from the 141st Air Refueling Wing (Washington Air National Guard) has been deployed to Reno, NV in support of wildland fire operations.
On July 10, a call when needed Air Attack platform on contract with the United States Forest Service crashed while assigned to the Cedar Basin fire in Arizona. The pilot and the air attack group supervisor were fatally injured. The firefighting community extends its condolences to the family and friends of the deceased.

Active Incident Resource Summary
GACC Incidents Cumulative Acres Crews Engines Helicopters Total Personnel Change in Personnel
AICC 3 121,619 5 9 3 219 -18
NWCC 16 253,494 100 296 21 3,969 714
ONCC 6 111,765 71 168 22 3,005 -591
OSCC 6 4,726 9 10 2 237 -37
NRCC 36 196,060 67 176 18 2,999 488
GBCC 9 22,987 13 19 6 526 182
SWCC 12 150,647 11 24 9 742 68
RMCC 6 23,793 8 42 9 504 44
EACC 1 65 0 4 4 30 0
SACC 1 380 0 4 0 7 0
Total 96 885,539 284 752 94 12,238 850

Northern Rockies Area (PL 5)
New fires: 15
New large incidents: 4
Uncontained large fires: 25
Type 1 IMTs committed 3 Type 2 IMTs committed 6
Snake River Complex (2 fires), Craig Mountain Supervisory Area Office, DOL. IMT 2 (NR Team 4). Twenty miles south of Lewiston, ID. Short grass and timber. Active fire behavior with uphill runs, flanking and spotting. Structures threatened. Evacuations, area, road and trail closures in effect.
Dixie, Nez Perce-Clearwater NF, USFS. IMT 1 (NR Team 2). IMT is also managing the Jumbo incident. Two miles north of Dixie, ID. Timber. Active fire behavior with group torching, uphill runs and long-range spotting. Structures threatened. Area, road and trail closures in effect.
Jumbo, Nez Perce-Clearwater NF, USFS. Eight miles west of Dixie, ID. Timber. Active fire behavior with group torching, uphill runs and long-range spotting. Structures threatened. Area, road and trail closures in effect.
MY Complex, (3 fires) Southern Land Office, DNR. IMT 2 (NR Team 7). Eleven miles northwest of Bighorn, MT. Timber. Active fire behavior with wind-driven runs, group torching and short-range spotting. Residences threatened.
West Lolo Complex, Lolo NF, USFS. IMT 1 (NR Team 1). Six miles north of St. Regis, MT. Brush, closed timber litter and timber. Active fire behavior with wind-driven runs, group torching and short-range spotting.
Structures threatened. Area, road and trail closures in effect.
Leland Complex (2 fires), Ponderosa Area Office, DOL. Five miles southwest of Deary, ID. Timber. Extreme fire behavior with short crown runs, spotting and group torching. Structures threatened. Area, road and trail closures in effect.

Cougar Rock Complex (4 Fires), Clearwater Potlach Timber Protective Association, DOL. IMT 2 (NR Team 6). Seventeen miles northeast of Elk River, ID. Light slash and timber. Active fire behavior with group torching, short-range spotting and flanking.
Goose, Beaverhead-Deerlodge NF, USFS. IMT 2 (NR Team 5). Thirty-two miles southeast of Ennis, MT. Timber and brush. Active fire behavior with running, group torching and short-range spotting. Area and trail
closures in effect.
Divide Complex (2 fires), Helena-Lewis and Clark NF, USFS. Seventeen miles west of Neihart, MT. Timber and light slash. Extreme fire behavior with crowning, wind-driven runs and long-range spotting. Area, road and trail closures in effect. Alder Creek, Beaverhead-Deerlodge NF, USFS. Twenty miles northwest of Wisdom, MT. IMT 1 (SA Blue Team). Timber and medium slash. Active fire behavior with uphill runs, single tree torching and spotting. Structures threatened. Area, road and trail closures in effect. Trail creek, Beaverhead-Deerlodge NF, USFS. Twenty miles west of Wisdom, MT. Active fire behavior with group torching, spotting and short crown runs. Structures threatened. Area, road and trail closures in effect.
Burnt Peak, Kootenai NF, USFS. Nine miles southwest of Troy, MT. Timber. Active fire behavior with group
torching, isolated torching and short-range spotting. Road and area closures in effect. Trestle Creek Complex, Idaho Panhandle NF, USFS. Seven miles north of Hope, ID. Timber and brush.
Moderate fire behavior with group torching, creeping and spotting.
Too Kush 2, Maggie Creek Area Office, DOL. IMT 2 (EA Gold team) mobilizing. Four miles southeast of Kooskia, ID. Timber, brush and short grass. Extreme fire behavior with uphill runs, crowning and single tree torching. Structures threatened. Character Complex, Idaho Panhandle NF, USFS. IMT 2 (NR Team 3) mobilizing. Three miles north of Kellogg, ID. Timber, brush and short grass. Extreme fire behavior with uphill runs, torching and spotting. Area, road and trail closures in effect.
Brewster, Lolo NF, USFS. Twenty miles west of Drummond, MT. Timber and short grass. Minimal fire behavior
with backing, creeping and smoldering. Residences threatened. Road and trail closures in effect. Robertson Draw, Custer Gallatin NF, USFS. Seven miles south of Red Lodge, MT. Short grass, brush and timber. Minimal fire behavior with smoldering. Area, road and trail closures in effect.
* Tumbledown, Idaho Panhandle NF, USFS. Seventeen miles east of Avery, ID. Timber and light slash. Active
fire behavior with group torching and short crown runs. * Storm Creek, Nez Perce-Clearwater NF, USFS. Thirty-five miles southwest of Missoula, MT. Brush and
timber. Moderate fire behavior with creeping, single tree torching and short-range spotting. Area, road and trail closures in effect.
* Fourmile, Big Horn County. Twenty-seven miles south of Lame Deer, MT. Timber. Active fire behavior with running, group torching and wind-driven runs.

Incident Name Unit Size % Ctn/ Comp Est Personnel Resources Strc Lost $$ CTD Origin Own Acres Chge Total Chge Crw Eng Heli
Snake River
Complex ID-CMS 54,407 14,875 0 Ctn 7/30 170 84 3 6 0 0 1.3M ST
Dixie ID-NCF 15,323 1,450 0 Comp 10/30 522 5 8 16 4 0 3.3M FS

Jumbo ID-NCF 898 71 0 Comp 10/30 16 9 0 0 0 0 NR FS
MY Complex MT-SOS 25,437 1,430 60 Ctn 7/15 298 52 7 25 0 0 1.2M ST
Incident Name Unit Size % Ctn/
Comp Est Personnel Resources Strc
Lost
$$ CTD Origin
Own Acres Chge Total Chge Crw Eng Heli
West Lolo Complex MT-LNF 1,017 262 1 Ctn 10/31 220 0 9 1 2 0 1.9M FS
Leland
Complex ID-PDS 1,161 500 25 Ctn 7/23 137 12 3 13 1 0 930K ST
Cougar Rock
Complex ID-CTS 2,055 428 5 Ctn 9/15 132 70 0 9 0 0 650K ST
Goose MT-BDF 11,25 385 1 Comp 10/13 170 151 3 5 0 0 1.2M FS
Divide Complex MT-HLF 4,039 3,439 0 Ctn 10/15 123 46 3 13 2 0 NR FS
Alder Creek MT-BDF 79 61 0 Ctn 11/1 36 31 0 5 0 0 100K FS
Trail Creek MT-BDF 904 322 0 Ctn 9/30 45 16 2 3 0 0 75K FS
Burnt Peak MT-KNF 335 135 0 Ctn 9/10 64 16 0 3 0 0 500K FS
Trestle Creek Complex ID-IPF 236 61 5 Ctn 8/15 88 33 5 1 0 0 NR FS
Too Kush 2 ID-MCS 1,200 0 25 Ctn 7/14 94 0 2 10 0 0 400K ST
Character Complex ID-IPF 1,263 1,156 0 Ctn 11/1 218 136 5 2 0 0 NR FS
Brewster MT-LNF 140 0 40 Ctn 7/17 68 -10 2 1 0 0 450K FS
Robertson Draw MT-CGF 29,841 0 68 Ctn 7/21 82 -35 3 6 1 30 10.4M FS
* Tumbledown ID-IPF 640 --- 0 Ctn UNK 10 --- 0 0 0 0 20K FS
* Storm Creek ID-NCF 515 --- 0 Ctn UNK 0 --- 0 0 0 0 2K FS
* Fourmile MT-LG22 1,000 --- 0 Ctn 7/15 62 --- 0 12 0 0 35K CNTY
* Norville MT-LG50 381 --- 100 Ctn --- 4 --- 1 0 0 0 40K FS
LG50 – Garfield County
Northwest Area (PL 4)
New fires: 13
New large incidents: 3
Uncontained large fires: 6
Type 1 IMTs committed 4
Type 2 IMTs committed: 4
Bootleg, Fremont-Winema NF, USFS. IMT 2 (NW Team 10), IMT 1 (PNW Team 2) and IMT 1 (ODF Team 1). Twenty-three miles east of Chiloquin, OR. Timber, brush and closed timber litter. Extreme fire behavior with crowning, wind-driven runs and spotting. Structures threatened. Evacuations, area and road closures in effect. Jack, Umpqua NF, USFS. IMT 2 (NW Team 9). Thirty-one miles east of Roseburg, OR. Light slash, closed timber litter and brush. Active fire behavior with isolated torching, backing and spotting. Structures and energy infrastructure threatened. Evacuations, area and road closures in effect.
Dry Gulch, Southeast Region, DNR. Transfer of command from IMT 2 (NW Team 7) to IMT 1 (PNW Team 3)
will occur today. Two miles southwest of Asotin, WA. Tall grass, brush and timber. Active fire behavior with uphill runs, wind-driven runs and group torching. Structures threatened. Evacuations, area, road and trail closures in effect.

Lewis Rock, John Day Unit, ODF. Transfer of command from IMT 1 (ODF Team 3) back to the local unit will occur today. Four miles south of Mitchell, OR. Short grass and timber. Minimal fire behavior with smoldering.

* Cedar Creek, Okanogan-Wenatchee NF, USFS. IMT 2 (NW Team 8) mobilizing. Fifteen miles northwest of Winthrop, WA. Timber. Moderate fire behavior with group torching, uphill runs and backing. Structures threatened.
Green Ridge, Umatilla NF, USFS. IMT 2 (NW Team 7) mobilizing. Thirty miles east of Walla Walla, WA. Active fire behavior with torching. Structures threatened. Area, road and trail closures in effect.
* Burbank, Mid-Columbia National Wildlife Refuge Complex, FWS. Eight miles northeast of Yakima, WA. Tall grass. Extreme fire behavior with running, short-range spotting and wind-driven runs. Area, road and trail closures in effect.
* Varden, Okanogan-Wenatchee NF, USFS. Eighteen miles northwest of Winthrop, WA. Timber. Moderate fire behavior with backing, torching and uphill runs. Structures threatened. Last narrative report unless significant activity occurs.

Incident Name Unit Size % Ctn/ Comp Est Personnel Resources Strc Lost $$ CTD Origin Own Acres Chge Total Chge Crw Eng Heli
Bootleg OR-FWF 150,812 60,903 0 Ctn 11/30 1,027 101 19 109 10 50 4.5M FS
Jack OR-UPF 10,937 1,604 8 Ctn 8/15 809 28 21 43 4 0 4.2M FS
Dry Gulch WA-SES 46,352 8,129 20 Ctn 7/31 536 259 14 52 0 6 2.9M ST
Lewis Rock OR-952S 368 0 95 Ctn 7/18 377 -8 11 7 2 0 5.5M ST
* Cedar Creek WA-OWF 75 --- 0 Comp 10/31 46 --- 1 5 0 0 1M FS
Green Ridge OR-UMF 175 32 0 Ctn 8/9 160 31 8 6 0 0 963K FS
* Burbank WA-MCR 6,000 --- 10 Ctn 7/14 113 --- 3 15 0 0 300K FWS
Silcott WA-WFS 8,633 0 100 Ctn --- 135 0 3 25 0 0 500K ST
Large Fires Being Managed with a Strategy Other Than Full Suppression Without a Type 1 or 2 IMT Assigned
* Varden WA-OWF 700 --- 0 Comp 10/31 96 --- 4 0 4 0 1M FS
WFS – Washington State Fire Marshal’s Office
Northern California Area (PL 4)
New fires: 27
New large incidents: 0
Uncontained large fires: 6 Type 1 IMTs committed 2
Beckwourth Complex (2 fires), Plumas NF, USFS. IMT 1 (CA Team 4). Three miles northeast of Beckwourth, CA. Timber, brush and closed timber litter. No new information. Salt, Shasta-Trinity NF, USFS. Transfer of command from IMT 1 (CA Team 2) back to the local unit will occur today. Three miles south of Lakehead, CA. Chaparral, timber and short grass. Minimal fire behavior with smoldering. Several communities threatened. Area closures in effect.
Lava, Shasta-Trinity NF, USFS. Four miles east of Weed, CA. Timber, brush and short grass. Minimal fire behavior with single tree torching and smoldering. Area and road closures in effect.
Tennant, Klamath NF, USFS. Nine miles northwest of Tennant, CA. Timber and brush. Minimal fire behavior with smoldering. Area and trail closures in effect.
Juniper, Modoc NF, USFS. Twenty-three miles north of Alturas, CA. Grass and timber. Minimal fire behavior

with smoldering. Residences threatened. Area and road closures in effect.

Incident Name Unit Size % Ctn/
Comp Est Personnel Resources Strc
Lost
$$ CTD Origin
Own Acres Chge Total Chge Crw Eng Heli
Beckwourth
Complex CA-PNF 61,252 --- 9 Ctn 7/30 534 --- 48 118 16 0 10M FS
Salt CA-SHF 12,650 0 85 Ctn 7/15 504 -332 9 19 2 43 17.1M FS
Lava CA-SHF 26,162 753 77 Ctn 7/12 280 -2 4 11 3 23 33.5M FS
Tennant CA-KNF 10,580 0 95 Ctn 7/31 164 -201 2 10 1 9 14.7M FS
Juniper CA-MDF 1,011 0 80 Ctn UNK 166 -76 5 7 0 0 1.5M FS

Southwest Area (PL 3)
New fires: 19
New large incidents: 1
Uncontained large fires: 5 Type 2 IMTs committed: 2
Tiger, Prescott NF, USFS. IMT 2 (SW Team 3). Eleven miles east of Crown King, AZ. Short grass and brush. Moderate fire behavior with backing, creeping and smoldering. Structures threatened. Area, road and trail closures in effect.
Middle, Tonto NF, USFS. IMT 2 (SW Team 4). Fifty miles northeast of Scottsdale, AZ. Short grass and brush. Minimal fire behavior with backing, creeping and smoldering. Residences threatened. Area and trail closures in effect. Rafael, Prescott NF, USFS. Three miles northeast of Perkinsville, AZ. Brush and timber. Minimal fire behavior with creeping and smoldering. Structures threatened. Area, road and trail closures in effect. Pinnacle, Coronado NF, USFS. Thirteen miles south of Bylas, AZ. Short grass, brush and timber. Minimal fire behavior. Area, road and trail closures in effect.
* Cedar Basin, Colorado River District, BLM. Fifteen miles northeast of Wikeup, AZ. Short grass and brush. Moderate fire behavior with backing, flanking and uphill runs. Residences threatened.
Bottom, San Carlos Agency, BIA. Seven miles west of Bylas, AZ. Timber and brush. No new information.

Incident Name Unit Size % Ctn/
Comp Est Personnel Resources Strc
Lost
$$ CTD Origin
Own Acres Chge Total Chge Crw Eng Heli
Tiger AZ-PNF 16,221 108 43 Ctn 7/20 319 -37 4 9 3 0 4.1M FS
Middle AZ-TNF 2,784 351 0 Comp 7/25 174 28 1 1 3 0 1M FS
Rafael AZ-PNF 78,065 0 96 Ctn 7/15 12 0 0 1 0 1 11M FS
Pinnacle AZ-CNF 34,437 0 91 Ctn 7/15 1 0 0 0 0 0 10.5M FS
* Cedar Basin AZ-CRD 734 --- 75 Ctn 7/15 78 --- 2 5 0 0 500K BLM
Bottom AZ-SCA 6,004 --- 95 Ctn 7/12 56 --- 1 4 0 0 1.5M BIA
Large Fires Being Managed with a Strategy Other Than Full Suppression Without a Type 1 or 2 IMT Assigned
Firebox AZ-ASF 574 224 0 Comp 8/9 49 0 1 3 1 0 60K FS
Bear AZ-TNF 2,000 --- 0 Comp 7/20 1 --- 0 0 0 0 20K FS
Johnson NM-GNF 88,918 --- 75 Comp 7/23 1 --- 0 0 0 0 7.4M FS
Midway AZ-TNF 1,762 --- 99 Comp UNK 0 --- 0 0 0 0 20K FS
Bear AZ-ASF 23,868 --- 20 Comp 7/31 34 --- 1 3 1 0 180K FS

Moore AZ-ASF 798 --- 81 Comp 7/31 0 --- 0 0 0 0 50K FS
ASF – Apache-Sitgreaves NF, USFS GNF – Gila NF, USFS

Great Basin Area (PL 3)
New fires: 15
New large incidents: 0
Uncontained large fires: 3 Type 2 IMTs committed: 1
Mud Lick, Salmon-Challis NF, USFS. IMT 2 (GB Team 5). Twenty-three miles west of Salmon, ID. Timber and
short grass. Extreme fire behavior with uphill runs, wind-driven runs and flanking. Structures and infrastructure
threatened.
Snap Point, Arizona Strip District, BLM. Sixty miles south of St. George, UT. Short grass and brush. Active fire behavior with isolated torching, smoldering creeping. Structures and communication infrastructure threatened.
Morgan Canyon, Uinta-Wasatch-Cache NF, USFS. Twelve miles west of Stockton, UT. Timber and brush.
Minimal fire behavior with smoldering, creeping and single tree torching. Structures and communication
infrastructure threatened. Area and trail closures in effect.

Incident Name Unit Size % Ctn/ Comp Est Personnel Resources Strc Lost $$ CTD Origin Own Acres Chge Total Chge Crw Eng Heli
Mud Lick ID-SCF 3,000 2,000 0 Ctn 8/31 315 175 8 4 4 0 2M FS
Snap Point AZ-ASD 9,643 5,643 5 Ctn 7/21 66 41 2 2 1 0 500K BLM
Morgan Canyon UT-UWF 509 0 60 Ctn 10/31 18 -1 0 1 1 0 1.7M FS
Large Fires Being Managed with a Strategy Other Than Full Suppression Without a Type 1 or 2 IMT Assigned
Fritzer ID-SCF 139 --- 75 Comp UNK --- -14 0 0 0 0 111K FS

Eastern Area (PL 3) New fires: 6
New large incidents: 0
Uncontained large fires: 1
Type 2 IMTs committed: 1
2021 SUF West Zone Complex, Superior NF, USFS. IMT 2 (EA Silver Team). Six miles east of Ely, MN.
Timber and heavy slash. Moderate fire behavior with creeping and isolated torching.

Incident Name Unit Size % Ctn/
Comp Est Personnel Resources Strc
Lost
$$ CTD Origin
Own Acres Chge Total Chge Crw Eng Heli
2021 SUF West
Zone Complex MN-SUF 89 24 20 Ctn 7/23 121 91 0 4 1 0 1M FS

Southern California Area (PL 3)
New fires: 25
New large incidents: 1
Uncontained large fires: 1
Willow, Los Padres NF, USFS. Fifteen miles southeast of Big Sur, CA. Chaparral, brush and tall grass. Minimal fire behavior with smoldering. Area, road and trail closures in effect.
* Henry, Stanislaus NF, USFS. Twenty miles south of South Lake Tahoe, CA. Brush and timber. Active fire

behavior with backing, creeping and isolated torching. Structures threatened. Area and trail closures in effect. Last narrative report unless significant activity occurs.

Incident Name Unit Size % Ctn/
Comp Est Personnel Resources Strc
Lost
$$ CTD Origin
Own Acres Chge Total Chge Crw Eng Heli
Willow CA-LPF 2,877 0 97 Ctn UNK 9 0 0 1 0 0 8.4M FS
Large Fires Being Managed with a Strategy Other Than Full Suppression Without a Type 1 or 2 IMT Assigned
* Henry CA-STF 300 --- 13 Comp 7/27 60 --- 4 0 1 0 680K FS

Rocky Mountain Area (PL 2)
New fires: 16
New large incidents: 0
Uncontained large fires: 3
Morgan Creek, Medicine Bow-Routt NF, Thunder Basin National Grassland, USFS. Fifteen miles north of Steamboat Springs, CO. Timber. Active fire behavior with uphill runs, single tree torching and backing Residences threatened. Area road and trail closures in effect. Reduction in acreage due to more accurate mapping.
Muddy Slide, Medicine Bow-Routt NF, Thunder Basin National Grassland, USFS. Twenty miles south of Steamboat Springs, CO. Timber. Moderate fire behavior with smoldering, creeping and single tree torching. Structures and energy infrastructure threatened. Area, road and trail closures in effect.
Sylvan, White River NF, USFS. Fifteen miles south of Eagle, CO. Timber and brush. Minimal fire behavior with creeping and smoldering. Area, road and trail closures in effect.

Incident Name Unit Size % Ctn/
Comp Est Personnel Resources Strc
Lost
$$ CTD Origin
Own Acres Chge Total Chge Crw Eng Heli
Morgan Creek WY-MRF 1,927 -173 0 Ctn 10/15 140 75 4 4 5 0 608K FS
Muddy Slide WY-MRF 4,093 0 50 Ctn 7/30 259 -22 4 18 4 18 9.3M FS
Sylvan CO-WRF 3,792 0 68 Ctn 8/1 21 -9 0 1 0 0 6.9M FS

Alaska Area (PL 2)
New fires: 1
New large incidents: 0
Uncontained large fires: 0

Incident Name Unit Size % Ctn/
Comp Est Personnel Resources Strc
Lost
$$ CTD Origin
Own Acres Chge Total Chge Crw Eng Heli
Large Fires Being Managed with a Strategy Other Than Full Suppression Without a Type 1 or 2 IMT Assigned
Munson Creek AK-FAS 36,609 0 6 Comp 7/30 180 -18 4 9 4 0 1.4M BIA
Dry Creek AK-TAD 51,931 --- 0 Comp UNK 34 --- 1 0 0 0 1.3M TRI
Cultas Creek AK-UYD 20,394 --- 0 Comp 8/7 5 --- 0 0 0 0 36K NPS
Crescent Creek AK-UYD 1,281 --- 0 Comp 8/7 0 --- 0 0 0 0 5K NPS
Shellman Creek AK-TAD 1,972 --- 0 Comp UNK 0 --- 0 0 0 0 NR BLM
Sischu AK-TAD 2,802 --- 0 Comp 8/7 0 --- 0 0 0 0 3.5K BLM
FAS – Fairbanks Area, Alaska DOF TAD – Tanana Zone, BLM UYD – Upper Yukon Zone

Fires and Acres Yesterday (by Protection):

Area BIA BLM FWS NPS ST/OT USFS TOTAL
FIRES 0 0 0 0 1 0 1 Alaska Area ACRES 0 0 0 0 0 0 0
FIRES 0 0 0 0 8 5 13 Northwest Area ACRES 0 0 0 0 8 0 8
FIRES 0 0 0 0 23 4 27 Northern California Area ACRES 0 0 0 0 38 2,134 2,153
FIRES 0 0 0 2 22 1 25
Southern California Area ACRES 0 10 0 0 38 220 268
FIRES 2 0 0 1 5 7 15 Northern Rockies Area ACRES 0 0 0 0 42,313 6,054 48,367
FIRES 0 3 0 1 6 5 15 Great Basin Area ACRES 0 4,975 0 489 2 2,002 7,468
FIRES 0 0 0 0 1 18 19 Southwest Area ACRES 0 0 0 0 10 325 335
FIRES 3 1 0 0 5 7 16
Rocky Mountain Area ACRES 2 0 0 0 38 1 41
FIRES 1 0 0 0 5 0 6 Eastern Area ACRES 1 0 0 0 5 0 6
FIRES 0 0 0 0 0 0 0 Southern Area ACRES 0 0 0 0 0 0 0
TOTAL FIRES: 6 4 0 4 76 47 137
TOTAL ACRES: 3 4,985 0 489 42,433 10,736 58,646

Fires and Acres Year-to-Date (by Protection):

Area BIA BLM FWS NPS ST/OT USFS TOTAL
FIRES 0 85 0 0 193 10 288 Alaska Area
ACRES 0 123,488 0 0 47,723 5 171,216
FIRES 84 161 20 4 1,261 250 1,780 Northwest Area
ACRES 12,176 1,906 1,178 19 47,934 85,834 149,047
FIRES 42 21 4 21 1,929 297 2,314 Northern California Area
ACRES 33 131 332 1 7,111 109,405 117,016
FIRES 16 88 11 27 2,471 301 2,914 Southern California Area
ACRES 1,292 3,509 199 2,880 16,221 5,924 30,026
FIRES 868 56 10 2 788 394 2,118 Northern Rockies Area
ACRES 72,631 2,623 567 20 94,479 45,363 215,683
FIRES 28 373 49 12 505 217 1,184 Great Basin Area
ACRES 2,988 49,734 8 2,126 48,405 19,336 122,598
FIRES 450 148 8 16 335 693 1,650 Southwest Area
ACRES 23,518 81,854 1,518 3,362 22,453 480,842 613,547
FIRES 382 153 5 11 349 166 1,066 Rocky Mountain Area
ACRES 3,930 22,070 1,256 1,114 77,500 17,390 123,260
FIRES 428 0 22 13 6,593 388 7,444 Eastern Area
ACRES 12,363 0 13,276 560 31,666 15,813 73,678
FIRES 376 0 52 35 12,182 369 13,014 Southern Area
ACRES 28,685 0 11,843 8,182 261,590 27,304 337,606
TOTAL FIRES: 2,674 1,085 181 141 26,606 3,085 33,772
TOTAL ACRES: 157,617 285,316 30,178 18,265 655,084 807,218 1,953,681
Ten Year Average Fires (2011 – 2020 as of today) 29,837
Ten Year Average Acres (2011 – 2020 as of today) 2,940,721
***Changes in some agency YTD acres reflect more accurate mapping or reporting adjustments.
***Additional wildfire information is available through the Geographic Areas at https://gacc.nifc.gov/

Canadian Fires and Hectares

PROVINCES FIRES YESTERDAY HECTARES YESTERDAY FIRES YEAR-TO-DATE
HECTARES YEAR-TO- DATE
BRITISH COLUMBIA 58 8,789 963 143,823
YUKON TERRITORY 0 639 47 32,242
ALBERTA 20 10,667 762 29,701
NORTHWEST TERRITORY 1 1,209 54 15,974
SASKATCHEWAN 16 75,884 290 167,257
MANITOBA 10 1,311 170 328,024
ONTARIO 9 16,664 573 170,824
QUEBEC 2 0 449 13,628
NEWFOUNDLAND 1 0 46 278
NEW BRUNSWICK 0 0 145 309
NOVA SCOTIA 0 0 110 194
PRINCE EDWARD ISLAND 0 0 1 0
NATIONAL PARKS 1 0 39 12,754
TOTALS 118 115,164 3,649 915,007
*1 Hectare = 2.47 Acres
Predictive Services Discussion: Above normal temperatures are forecast for the Intermountain West with very
hot, record breaking temperatures continuing for California, the Great Basin, and eastern Oregon. Minimum RH will
be very low, below 15%, for most of the Intermountain West with poor overnight recovery, but the Southwest will
see more moist conditions. Isolated mixed wet/dry thunderstorms with strong outflow winds are possible for the
Peninsular Range, southern Sierra, southern Great Basin, and southwest Colorado. Scattered mainly wet
thunderstorms are forecast for the Southwest with the driest storms in northwest Arizona. Elevated fire weather
conditions are forecast for the deserts of northeast California into northern Nevada. Breezy and very dry conditions
are also expected along eastern slopes of the Coastal Ranges in central and southern California. The Alaskan
Interior will see warming and drying with isolated thunderstorms possible. Heavy rain and severe weather are likely
across the Ohio and Tennessee River valleys, southern Great Lakes, and the Northeast.
http://www.predictiveservices.nifc.gov/outlooks/outlooks.htm

HEAT STRESS
Firefighter Health & First Aid

During activity, the body releases more than 70 percent of the energy used by muscles as heat. As a
result, heat loss is crucial to prevent an excessive rise in body temperature during firefighting activities. If
heat exchange between the body and the environment is impaired, such as in hot or humid environments,
firefighter performance can be substantially impaired.
A heat-related illness (HRI) is a potentially fatal disorder caused by elevated body temperatures from
internal heat produced by activity or external environmental heat added to the body that cannot be
removed to maintain normal body temperature.
Symptoms of an HRI may be difficult to recognize and may occur in no particular order. They may include:
• Profuse sweating with cool, clammy skin leading to hot dry skin.
• Muscle cramps and weakness.
• Dizziness, headache, and irritability.
• Rapid, weak pulse.
• Vomiting.
• Loss of consciousness.

Considerations for mitigation during firefighting activity:

• Ability to handle heat is different between individuals and varies on a daily basis.
• Performing physical tasks, such as hiking or digging fireline, is our largest producer of body heat.
• Hikings typically raises your body temperature 1 to 2 degrees Fahrenheit.
• At elevated body temperatures, the risk of HRI has a lesser margin of error.
• Maintain low skin temperature when possible, as it allows heat transfer from the body.
• Pack weights exceeding 25 percent of body weight add to the body’s demands during activity.
• Recovery of high body temperature requires:
o Reduction of work output.
o Removal from sources of heat.
o Proper nutrition and hydration strategies.
Note: Recovery is not just a shift-to-shift concept. It is also task-to-task and even a minute-to-minute
process.
References
Incident Response Pocket Guide (IRPG), PMS 461, Heat-Related Injury (pink section).

Have an idea? Have feedback? Share it. EMAIL | Facebook | MAIL: 6 Minutes for Safety Subcommittee • 3833 S. Development Ave • Boise, ID 83705 | FAX: [phone]
If you suspect a heat illness stop work and begin treatments to cool down the body and consider

National Interagency Coordination Center Incident Management Situation Report Saturday, July 24, 2021– 0730 MDT National Preparedness Level 5
National Fire Activity:
Initial attack activity: Light (126 fires)
New large incidents: 6
Large fires contained: 2
Uncontained large fires: *** 67
Area Command teams committed: 0
NIMOs committed: 1
Type 1 IMTs committed 14
Type 2 IMTs committed: 19
Nationally, there are 33 fires being managed under a strategy other than full suppression. ***Uncontained large fires include only fires being managed under a full suppression strategy.
Link to Geographic Area daily reports.
Link to Understanding the IMSR.
Two MAFFS C-130 airtankers and support personnel each from the 152nd Airlift Wing (Nevada Air National
Guard), one MAFFS unit from the 302nd Airlift Wing (Colorado Air Force Reserve), one MAFFS unit from the
153rd Airlift Wing (Wyoming Air National Guard) and one from the 146th Airlift Wing (California Air National
Guard) have been deployed to McClellan, CA to support wildland fire operations nationally.
One RC-26 aircraft with Distributed Real-Time Infrared (DRTI) capability and support personnel from the 141st Air Refueling Wing (Washington Air National Guard) has been deployed to Reno, NV in support of wildland fire
operations.

Active Incident Resource Summary
GACC Incidents Cumulative Acres Crews Engines Helicopters Total Personnel Change in Personnel
AICC 3 58,003 9 7 1 132 -2
NWCC 19 653,606 173 423 53 7,492 105
ONCC 5 314,876 83 385 32 4,701 111
OSCC 6 16,225 29 36 11 874 -26
NRCC 42 299,786 77 314 37 5,061 210
GBCC 13 91,701 57 141 44 2,528 25
SWCC 4 20,884 1 3 0 36 -1
RMCC 6 15,597 13 47 9 794 -7
EACC 2 146 5 6 2 259 -12
SACC 1 762 0 1 2 17 0
Total 101 1,471,587 447 1,363 191 21,894 -17

Northern Rockies Area (PL 5)
New fires: 17
New large incidents: 3
Uncontained large fires: 33
NIMOs committed: 1
Type 1 IMTs committed: 3
Type 2 IMTs committed: 9
* Hay Creek, Flathead NF, USFS. Four miles west of Polebridge, MT. Timber. Moderate fire behavior with wind-driven runs, group torching and short-range spotting. Structures threatened. Area, road and trail closures in effect.
* Harris Mountain, Cascade County. Started on state land six miles southeast of Cascade, MT. Timber and short grass. Extreme fire behavior with short crown runs, wind-driven runs and torching. Structures threatened. Evacuations and road closures in effect.
Alder Creek, Beaverhead-Deerlodge NF, USFS. IMT 1 (SA Blue Team). IMT 1 (SW Team 1) mobilizing. IMT is also managing the Trail Creek and Christensen incidents. Twenty miles northwest of Wisdom, MT. Timber
and medium slash. Active fire behavior with uphill runs, group torching and single tree torching. Numerous structures threatened. Area, road and trail closures in effect. Trail Creek, Beaverhead-Deerlodge NF, USFS. Twenty miles west of Wisdom, MT. Timber and medium slash. Active fire behavior with uphill runs, group torching and single tree torching. Structures threatened. Area and trail closures in effect.
Christensen, Beaverhead-Deerlodge NF, USFS. Ten miles northeast of Wisdom, MT. Timber. Moderate fire
behavior with creeping, backing and flanking.
Character Complex (2 fires), Idaho Panhandle NF, USFS. Transfer of command from IMT 2 (NR Team 3) to
IMT 2 (NR Team 5) will occur on 7/26. Three miles north of Kellogg, ID. Timber and brush. Active fire behavior
with flanking, backing and single tree torching. Numerous structures threatened. Area, road and trail closures in
effect.
Dixie, Nez Perce-Clearwater NF, USFS. Transfer of command from IMT 1 (NR Team 2) back to the local unit
will occur tomorrow. IMT is also managing the Jumbo incident. Two miles north of Dixie, ID. Timber. Active fire
behavior with group torching, uphill runs and short-range spotting. Numerous structures threatened.
Evacuations, area, road and trail closures in effect.
Jumbo, Nez Perce-Clearwater NF, USFS. Eight miles west of Dixie, ID. Timber. Active fire behavior with group
torching, uphill runs and short-range spotting. Area, road and trail closures in effect.
Leland Complex (2 fires), Ponderosa Area Office, IDL. IMT 2 (EA Gold Team). Five miles southwest of Deary,
ID. Timber. Active fire behavior with flanking, backing and torching. Residences threatened. Area, road and trail
closures in effect.
Cougar Rock Complex (5 fires), Clearwater Potlach Timber Protective Association, IDL. Transfer of command
from IMT 2 (NR Team 6) back to the local unit will occur on 7/28. Seventeen miles northeast of Elk River, ID.
Light slash and timber. Active fire behavior with single tree torching, short-range spotting and flanking.
Structures threatened. Road closures in effect.
Stateline Complex (3 fires), Idaho Panhandle NF, USFS. IMT 2 (SW Team 5). Twenty-two miles southwest of
Superior, MT. Closed timber litter, timber and light slash. Moderate fire behavior with flanking, isolated torching

and spotting. Area, road and trail closures in effect.

Burnt Peak, Kootenai NF, USFS. IMT 2 (GB Team 4). IMT is also managing the South Yaak incident. Nine
miles southwest of Troy, MT. Timber and light slash. Active fire behavior with flanking, backing and spotting. Structures threatened. Area and road closures in effect. South Yaak, Kootenai NF, USFS. Four miles northwest of Troy, MT. Timber and light slash. Active fire behavior with uphill runs, backing and spotting. Structures threatened. Road closures in effect.
Divide Complex (2 fires), Helena-Lewis and Clark NF, USFS. Seventeen miles west of Neihart, MT. Timber and light slash. Active fire behavior with flanking, backing and torching. Area and trail closures in effect.
American Fork, Helena-Lewis and Clark NF, USFS. IMT 2 (SA Gold Team). Twenty-four miles southwest of Harlowton, MT. Active fire behavior with flanking, backing and torching. Area, road and trail closures in effect.
Reduction in acreage due to more accurate mapping. Granite Pass Complex (3 fires), Lolo NF, USFS. IMT 2 (CA Team 15). Thirty miles southwest of Missoula, MT.
Timber, brush and medium slash. Active fire behavior with group torching, single tree torching and flanking. Structures threatened. Area, road and trail closures in effect.
Black Mountain, Beaverhead-Deerlodge NF, USFS. Twenty miles east of Salmon, ID. Timber, heavy slash and brush. Moderate fire behavior with creeping, smoldering and single tree torching. Residences threatened. Area, road and trail closures in effect.
Goose, Beaverhead-Deerlodge NF, USFS. Transfer of command from IMT 2 (NR Team 5) back to the local unit will occur on 7/26. Thirty-two miles southeast of Ennis, MT. Timber and brush. Moderate fire behavior with flanking, isolated torching and backing. Structures and sage-grouse habitat threatened. Area, road and trail closures in effect.
Anderson Hill, Southwestern Land Office, DNRC. Started on BLM land 30 miles southeast of Missoula, MT. Timber and medium slash. Moderate fire behavior with creeping, single tree torching and smoldering.
Structures threatened. Area and road closures in effect. Storm Creek, Nez Perce-Clearwater NF, USFS. NIMO (Team 1). IMT is also managing the Bar Creek, Bald Mountain, Monroe Lake and Lonesome incidents. Thirty-five miles southwest of Missoula, MT. Brush and timber. Active fire behavior with uphill runs, wind-driven runs and group torching. Area, road and trail closures in effect.
* Bar Creek, Nez Perce-Clearwater NF, USFS. Twenty miles southwest of Orofino, ID. Timber. Moderate fire behavior with isolated torching and backing. Area, road and trail closures in effect.
Bald Mountain, Nez Perce-Clearwater NF, USFS. Forty-one miles northeast of Kooskia, ID. Timber. No new information. Monroe Lake, Nez Perce-Clearwater NF, USFS. Twenty-nine miles east of Pierce, ID. Brush and timber. No new information. Lonesome, Nez Perce-Clearwater NF, USFS. Thirty-four miles east of Pierce, ID. Timber and brush. No new information.
Devils Creek, Miles City Field Office, BLM. Timber, brush, short grass. Extreme fire behavior with running, torching and spotting. Structures and communication infrastructure threatened.
West Lolo Complex (2 fires), Lolo NF, USFS. Six miles north of St. Regis, MT. Brush, closed timber litter and
timber. Moderate fire behavior with backing, single tree torching and group torching. Numerous residences threatened. Area, road and trail closures in effect. Reduction in acreage due to more accurate mapping.

Snake River Complex, Craig Mountain Supervisory Area, IDL. Transfer of command from IMT 2 (NR Team 4)
back to the local unit will occur today. Twenty miles south of Lewiston, ID. Short grass and timber. Minimal fire behavior with creeping, smoldering and single tree torching. Numerous residences threatened. Area, road and trail closures in effect. Slough Grass, Rosebud County. Started on private land ten miles northwest of Lame Deer, MT. Timber. Minimal fire behavior with smoldering. Structures and communication infrastructure threatened. Reduction in acreage due to more accurate mapping. Robertson Draw, Custer Gallatin NF, USFS. Seven miles south of Red Lodge, MT. Short grass, brush and timber. Minimal fire behavior with smoldering. Structures threatened. Area, road and trail closures in effect.
Crooked Creek, Billings Field Office, BLM. Twenty-five miles east of Bridger, MT. Short grass, brush and timber. No new information.

Incident Name Unit Size % Ctn/ Comp Est Personnel Resources Strc Lost $$ CTD Origin Own Acres Chge Total Chge Crw Eng Heli
* Hay Creek MT-FNF 500 --- 0 Ctn 9/30 70 --- 1 4 1 0 400K FS
* Harris Creek MT-LG22 550 --- 0 Ctn 10/1 0 --- 0 0 0 0 100K ST
Alder Creek MT-BDF 6,523 225 7 Ctn 11/1 312 -10 3 16 5 0 4.3M FS
Trail Creek MT-BDF 24,454 311 0 Comp 11/1 147 0 4 4 0 0 2M FS
Christensen MT-BDF 229 15 0 Ctn 11/1 7 6 0 1 0 0 38K FS
Character
Complex ID-IPF 4,473 69 20 Ctn 11/1 365 -32 5 33 1 0 7.3M FS
Dixie ID-NCF 31,970 846 12 Comp 10/30 441 1 10 22 3 0 12.8M FS
Jumbo ID-NCF 1,834 41 0 Comp 10/30 0 0 0 0 0 0 NR FS
Leland
Complex ID-PDS 3,180 63 47 Ctn 9/15 226 -45 3 6 3 0 4.6M ST
Cougar Rock
Complex ID-CTS 5,500 340 25 Ctn 9/15 371 9 6 5 1 0 5.4M ST
Stateline Complex ID-IPF 2,357 95 0 Ctn 10/31 256 36 4 3 1 0 2.2M FS
Burnt Peak MT-KNF 2,136 64 19 Ctn 9/30 238 0 2 10 2 0 4.9M FS
South Yaak MT-KNF 328 167 34 Ctn 9/1 184 -4 7 6 0 0 935K FS
Divide Complex MT-HLF 3,799 13 15 Ctn 10/29 221 32 3 29 5 0 5.4M FS
American Fork MT-HLF 5,726 -1 0 Ctn 10/15 85 7 0 3 1 0 1.6K FS
Granite Pass
Complex MT-LNF 2,606 231 1 Ctn 9/15 224 -2 4 5 3 0 2.3M FS
Black Mountain MT-BDF 958 12 0 Ctn 10/31 67 2 2 3 0 0 250K FS
Goose MT-BDF 7,262 0 49 Comp 10/13 194 -58 2 10 2 1 5.2M FS
Anderson Hill MT-SWS 750 0 85 Ctn 7/28 152 26 3 21 1 1 1.4M BLM
Storm Creek ID-NCF 5,092 1,342 0 Comp 10/15 0 0 0 0 0 0 7K FS
* Bar Creek ID-NCF 540 --- 0 Comp UNK 0 --- 0 0 0 0 2K FS
Bald Mountain ID-NCF 108 --- 0 Comp UNK 0 --- 0 0 0 0 2K FS
Monroe Lake ID-NCF 146 --- 0 Comp 10/15 0 --- 0 0 0 0 3K FS
Lonesome ID-NCF 142 --- 0 Comp 10/15 0 --- 0 0 0 0 5K FS
Devils Creek MT-MCD 1,300 925 10 Ctn 7/25 74 7 2 6 1 0 100K BLM

West Lolo Complex MT-LNF 2,408 -365 21 Ctn 10/31 292 -97 0 1 4 0 8.7M FS
Incident Name Unit Size % Ctn/ Comp Est Personnel Resources Strc Lost $$ CTD Origin Own Acres Chge Total Chge Crw Eng Heli
Snake River
Complex ID-CMS 107,679 0 74 Ctn 7/30 208 0 4 8 1 3 7.4M ST
Slough Grass MT-LG29 9,170 -83 75 Ctn 7/26 176 3 0 48 0 2 1M PRI
Robertson
Draw MT-CGF 29,885 34 90 Ctn 8/29 69 23 1 4 1 30 11.8M FS
Crooked Creek MT-BID 4,141 --- 85 Ctn 7/30 10 --- 1 0 0 1 5.4M BLM
Large Fires Being Managed with a Strategy Other Than Full Suppression Without a Type 1 or 2 IMT Assigned
Trestle Creek
Complex ID-IPF 436 0 37 Comp 9/15 82 -46 4 0 0 0 2.5M FS
Snow Creek ID-NCF 682 22 0 Comp 10/20 139 0 2 7 0 0 1.2M FS
Larkins
Complex ID-IPF 1,581 --- 0 Comp 11/1 3 --- 0 0 0 0 NR FS
Army Mule ID-NCF 600 --- 0 Comp 10/15 0 --- 0 0 0 0 NR FS
Dry Cabin MT-LNF 2,200 --- 0 Comp 8/15 8 --- 0 0 0 0 40K FS
Lynx ID-NCF 220 --- 0 Comp 10/30 2 --- 0 0 0 0 20K FS

Northwest Area (PL 5)
New fires: 13
New large incidents: 2
Uncontained large fires: 18
Type 1 IMTs committed: 7
Type 2 IMTs committed: 6
* Northrup, Spokane District, BLM. Seven miles southeast of Coulee City, WA. Tall grass, timber and hardwood litter. Active fire behavior with group torching, running and spotting. Structures threatened. Evacuations and road closures in effect.
* Racehorse, Vale District, BLM. Twenty-seven miles southwest of Vale, OR. Grass and brush. Active fire behavior with running, creeping and smoldering.
Cedar Creek, Okanogan-Wenatchee NF, USFS. IMT 2 (NW Team 8). IMT 1 (GB Team 1) mobilizing. IMT is also managing the Delancy incident. Fifteen miles northwest of Winthrop, WA. Timber, medium slash and short grass. Active fire behavior with short crown runs, flanking and short-range spotting. Numerous residences threatened. Evacuations, area, road and trail closures in effect. Delancy, Okanogan-Wenatchee NF, USFS. Fifteen miles northwest of Winthrop, WA. Timber, short grass and medium slash. Moderate fire behavior with uphill runs, flanking and short-range spotting. Area, road and trail closures in effect.
Cub Creek 2, Southeast Region, DNR. IMT 1 (CA Team 1) Five miles north of Winthrop, WA. Timber, brush and closed timber litter. Moderate fire behavior with backing, torching and flanking. Numerous residences threatened. Evacuations, area, road and trail closures in effect. Bootleg, Fremont-Winema NF, USFS. Transfer of command from IMT 1 (NW Team 2) and IMT 1 (ODF Team
1) to IMT 1 (AK Type 1 Team) will occur on 7/27. Twenty-three miles east of Chiloquin, OR. Timber, brush and closed timber litter. Extreme fire behavior with running, flanking and group torching. Numerous structures and

infrastructure threatened. Evacuations, area and road closures in effect. Summit Trail, Colville Agency, BIA. IMT 2 (CA Team 10). Seventeen miles west of Inchelium, WA. Medium slash, timber and brush. Active fire behavior with spotting and torching. Numerous structures threatened. Area, road and trail closures in effect.

Elbow Creek, Umatilla NF, USFS. IMT 1 (ODF Team 3). Twenty-six miles northeast of Elgin, OR. Timber and short
grass. Active fire behavior with group torching, short crown runs and spotting. Numerous structures threatened. Evacuations, area, road and trail closures in effect. Chuweah Creek, Colville Agency, BIA. IMT 2 (NW Team 12). Four miles north of Nespelem, WA. Brush, timber and short grass. Active fire behavior with torching, spotting and flanking. Numerous structures threatened. Area and road closures in effect.
Jack, Umpqua NF, USFS. IMT 2 (NW Team 10). Thirty-one miles east of Roseburg, OR. Timber, closed timber litter and brush. Active fire behavior with uphill runs, flanking and backing. Numerous structures threatened.
Evacuations, area, road and trail closures in effect.
Lick Creek, Umatilla NF, USFS. IMT 1 (NW Team 3). IMT 2 (CA Team 12) mobilizing. IMT is also managing the Green Ridge incident. Fifteen miles southeast of Pomeroy, WA. Timber and closed timber litter. Moderate fire behavior with creeping, isolated torching and smoldering. Numerous structures threatened. Area, road and trail closures in effect. Green Ridge, Umatilla NF, USFS. Thirty miles east of Walla Walla, WA. Brush and timber. Active fire behavior
with flanking, backing and group torching. Structures threatened. Area, road and trail closures in effect. Bruler, Willamette NF, USFS. IMT 2 (NW Team 13). Nine miles south of Detroit, OR. Closed timber litter and
timber. Moderate fire behavior with backing, flanking and torching. Area, road and trail closures in effect.
Goddard Road, Northeast Region, DNR. Started on private land 12 miles southwest of Kettle Falls, WA.
Timber and short grass. Active fire behavior with single tree torching, creeping and smoldering. Numerous structures threatened.
Sherwood, Spokane Agency, BIA. Thirty miles northwest of Spokane, WA. Timber. Active fire behavior with group torching, spotting and running. Structures threatened. Evacuations in effect. Steptoe Canyon, Washington State Fire Marshal’s Office. Five miles southwest of Colton, WA. Short grass and brush. Moderate fire behavior with backing and smoldering. Structures threatened. Road closures in effect.
Red Apple, Southeast Region, DNR. Two miles southeast of Cashmere, WA. Tall grass, brush and timber. Minimal fire behavior with smoldering.
Grandview, Sisters Unit, ODF. Ten miles northeast of Sisters, OR. Timber and brush. Minimal fire behavior with smoldering.

Incident Name Unit Size % Ctn/ Comp Est Personnel Resources Strc Lost $$ CTD Origin Own Acres Chge Total Chge Crw Eng Heli
* Northrup WA-SPD 442 --- 0 Ctn 7/26 29 --- 0 8 2 0 200K BLM
* Racehorse OR-VAD 500 --- 95 Ctn 7/30 55 --- 0 7 1 0 180K BLM
Cedar Creek WA- OWF 20,806 2,172 11 Ctn 10/31 459 42 9 35 7 0 7M FS
Delancy WA- OWF 221 2 0 Ctn 10/31 0 0 0 0 0 0 300K FS
Cub Creek 2 WA-SES 40,877 2,206 10 Ctn 8/31 441 107 13 23 0 3 3.8M ST
Bootleg OR-FWF 400,389 1,053 42 Ctn 10/1 2,224 -165 49 152 20 184 48.7M FS
Summit Trail WA-COA 6,943 1,001 2 Ctn 8/5 391 31 9 11 3 0 3.3M BIA
Elbow Creek OR-UMF 20,810 817 25 Ctn 8/15 686 227 31 25 6 1 4.2M FS
Chuweah Creek WA-COA 36,820 90 50 Ctn 7/27 344 59 8 24 4 14 6.1M BIA

Jack OR-UPF 19,956 298 57 Ctn 8/15 606 -15 12 24 4 0 16.5M FS
Incident Name Unit Size % Ctn/ Comp Est Personnel Resources Strc Lost $$ CTD Origin Own Acres Chge Total Chge Crw Eng Heli
Lick Creek OR-UMF 78,158 4,630 75 Ctn 9/1 278 -141 2 23 0 10 12.8M FS
Green Ridge OR-UMF 4,585 670 15 Ctn 9/6 379 -15 11 4 7 0 6.8M FS
Bruler OR-WIF 195 0 25 Ctn 9/30 254 0 4 10 1 0 3M FS
Goddard Road WA-NES 784 0 54 Ctn 7/30 235 -21 3 21 0 3 2M PRI
Sherwood WA-SPA 500 125 30 Ctn 7/31 71 26 2 9 0 0 1.3M BIA
Steptoe Canyon WA-WFA 2,700 700 20 Ctn 7/25 60 3 1 15 0 0 420K ST
Red Apple WA-SES 12,288 0 95 Ctn 7/25 50 0 1 4 0 1 4.7M ST
Grandview OR-955S 6,032 0 95 Ctn UNK 366 0 12 19 0 0 10M ST

Northern California Area (PL 4) New fires: 26
New large incidents: 1
Uncontained large fires: 4
Type 1 IMTs committed: 2
Dixie, Butte Unit, Cal Fire. Fifteen miles northeast of Paradise, CA. IMT 1 (Cal Fire Team 1) and IMT 1 (CA Team 2). IMT 1 (CA Team 2) is also managing Fly incident. Timber and chaparral. Active fire behavior with short crown runs, group torching and long-range spotting. Several communities threatened. Evacuations, area, road and trail closures in effect.
* Fly, Plumas NF, USFS. Four miles north of Quincy, CA. Timber, brush and short grass. Extreme fire behavior with torching, crowning and running. Numerous structures threatened. Evacuations, area, road and trail
closures in effect.
Beckwourth Complex, Plumas NF, USFS. Three miles northeast of Beckwourth, CA. Timber, brush and closed timber litter. Minimal fire behavior with smoldering and creeping. Area, road and trail closures in effect. Lava, Shasta-Trinity NF, USFS. Four miles east of Weed, CA. Timber and brush. Minimal fire behavior with
creeping and smoldering. Area and road closures in effect.

Incident Name Unit Size % Ctn/
Comp Est Personnel Resources Strc
Lost
$$ CTD Origin
Own Acres Chge Total Chge Crw Eng Heli
Dixie CA-BTU 167,430 54,424 18 Ctn 7/31 4,266 261 75 365 31 8 35.1M ST
* Fly CA-PNF 2,800 --- 5 Ctn 8/5 117 --- 4 6 0 0 1M FS
Beckwourth
Complex CA-PNF 105,670 0 98 Ctn 7/30 186 -269 3 7 1 148 52.9M FS
Lava CA-SHF 26,316 0 77 Ctn 8/1 52 2 0 4 0 23 34.5M FS

Great Basin (PL3) New fires: 19
New large incidents: 0
Uncontained large fires: 6
Type 1 IMTs committed: 2

Tamarack, Humboldt-Toiyabe NF, USFS. IMT 1 (RM Team 1). Sixteen miles south of Gardnerville, NV. Timber
and chaparral. Active fire behavior with crowning, short crown runs and uphill runs. Several communities
threatened. Evacuations, road and trail closures in effect.

Iron, Salmon-Challis NF, USFS. Eighteen miles southwest of Salmon, ID. IMT 1 (GB Team 2). IMT is also
managing the Haynes and Mud Lick incidents. Timber, brush and short grass. Minimal fire behavior with
smoldering. Structures and sage-grouse habitat threatened. Area, road and trail closures in effect.

Haynes, Salmon-Challis NF, USFS. Thirteen miles southeast of Salmon, ID. Timber and short grass. Moderate
fire behavior with creeping and smoldering. Sage-grouse habitat threatened. Road closures in effect.
Mud Lick, Salmon-Challis NF, USFS. Twenty-three miles west of Salmon, ID. Timber and short grass. Active
fire behavior with group torching, uphill runs and creeping. Structures and sage-grouse habitat threatened.
Road and trail closures in effect.
Shale Creek, Bridger-Teton NF, USFS. Thirty miles north of Kemmerer, WY. Timber, light slash and brush.
Moderate fire behavior with backing, creeping and smoldering. Residences threatened. Area, road and trail
closures in effect.
Morgan Canyon, Uinta-Wasatch-Cache NF, USFS. Twelve miles west of Stockton, UT. Timber and brush.
Minimal fire behavior with creeping and smoldering. Structures and communication infrastructure threatened.
Area and trail closures in effect. Precipitation occurred over the fire area yesterday.
Black Pine, Bear River Area, Utah DOF. Fifteen miles west of Snowville, UT. Short grass, bush and timber. No new
information.

Incident Name Unit Size % Ctn/
Comp Est Personnel Resources Strc
Lost
$$ CTD Origin
Own Acres Chge Total Chge Crw Eng Heli
Tamarack NV-HTF 59,112 8,983 4 Ctn 8/31 1,425 72 31 108 11 15 11.1M FS
Iron ID-SCF 132 0 75 Ctn 7/31 112 48 5 0 8 0 164K FS
Haynes ID-SCF 461 0 25 Ctn 7/31 75 -19 3 0 8 0 535K FS
Mud Lick ID-SCF 16,534 62 0 Comp 8/31 573 3 11 18 7 0 8.5M FS
Shale Creek WY-BTF 189 0 45 Ctn 8/5 127 -8 3 0 6 0 1.3M FS
Morgan Canyon UT-UWF 509 0 75 Ctn 8/15 18 0 0 1 1 0 1.8M FS
Black Pine UT-BRS 563 --- 60 Ctn 7/30 38 --- 1 4 1 0 350K ST
Lusk ID-2PN 1,620 0 100 Ctn --- 103 -5 3 10 1 0 600K CNTY
Large Fires Being Managed with a Strategy Other Than Full Suppression Without a Type 1 or 2 IMT Assigned
Tango ID-SCF 102 --- 0 Comp 10/1 22 --- 0 0 0 0 20K FS
Vinegar ID-PAF 323 --- 0 Comp 10/1 5 --- 0 0 0 0 30K FS
Rush Creek ID-PAF 1,616 --- 0 Comp 10/1 18 --- 0 0 1 0 30K FS
2PN – Power County PAF – Payette NF, USFS
Rocky Mountain Area (PL 3)
New fires: 15
New large incidents: 0
Uncontained large fires: 3 Type 2 IMTs committed: 2
Morgan Creek, Medicine Bow-Routt NF, Thunder Basin National Grassland, USFS. Transfer of command from IMT 2 (RM Team Black) back to the local unit will occur on 7/26. IMT is also managing the Muddy Slide incident. Fifteen miles north of Steamboat Springs, CO. Timber and brush. Minimal fire behavior with creeping,

backing and single tree torching. Structures threatened. Area, road and trail closures in effect. Precipitation occurred
over the fire area yesterday.
Muddy Slide, Medicine Bow-Routt NF, Thunder Basin National Grassland, USFS. Twenty miles south of Steamboat Springs, CO. Timber. Minimal fire behavior with smoldering. Area, road and trail closures in effect.
Crater Ridge, Bighorn NF, USFS. IMT 2 (RM Team Blue). Thirty-one miles west of Sheridan, WY. Timber and heavy slash. Minimal fire behavior with creeping and smoldering. Area, road and trail closures in effect.

Incident Name Unit Size % Ctn/
Comp Est Personnel Resources Strc
Lost
$$ CTD Origin
Own Acres Chge Total Chge Crw Eng Heli
Morgan Creek WY-MRF 5,651 34 4 Ctn 9/1 391 -12 8 14 3 0 6.5M FS
Muddy Slide WY-MRF 4,093 0 70 Ctn 8/31 69 -10 0 5 2 18 12.2M FS
Crater Ridge WY-BHF 383 0 0 Ctn 8/15 270 28 5 6 4 0 1.8M FS
Large Fires Being Managed with a Strategy Other Than Full Suppression Without a Type 1 or 2 IMT Assigned
Sylvan CO-WRF 3,792 --- 68 Comp 8/1 13 --- 0 2 0 0 7M FS
WRF – White River NF, USFS
Southern California Area (PL 3) New fires: 22
New large incidents: 0
Uncontained large fires: 1
Type 2 IMTs committed: 1
Peak, Central California District, BLM. IMT 2 (CA Team 11). Thirty-three miles east of Bakersfield, CA. Timber,
brush and short grass. Moderate fire behavior with backing, creeping and smoldering. Residences threatened.

Incident Name Unit Size % Ctn/
Comp Est Personnel Resources Strc
Lost
$$ CTD Origin
Own Acres Chge Total Chge Crw Eng Heli
Peak CA-CND 2,096 8 57 Ctn 7/30 636 47 22 25 8 1 4.3M BLM
Large Fires Being Managed with a Strategy Other Than Full Suppression Without a Type 1 or 2 IMT Assigned
Dexter CA-INF 2,965 -20 97 Comp 7/28 102 -2 2 4 1 0 5.5M FS
Henry CA-STF 1,316 0 60 Comp 8/3 56 -18 3 0 2 0 1.8M FS
County Line CA-YNP 224 --- 85 Comp 8/15 0 --- 0 0 0 0 114K NPS
Lukens CA-YNP 460 --- 50 Comp 8/15 22 --- 0 1 0 0 451K NPS
INF – Inyo NF, USFS STF – Stanislaus NF, USFS YNP – Yosemite NP, NPS
Eastern Area (PL 3)
New fires: 5
New large incidents: 0
Uncontained large fires: 1 Type 2 IMTs committed: 1
2021 SUF West Zone Complex, Superior NF, USFS. Transfer of command from IMT 2 (EA Silver Team) back to the local unit will occur tomorrow. Six miles east of Ely, MN. Timber and medium slash. Minimal fire behavior with smoldering. Area and trail closures in effect.

Incident Name Unit Size % Ctn/
Comp Est Personnel Resources Strc
Lost
$$ CTD Origin
Own Acres Chge Total Chge Crw Eng Heli
2021 SUF West
Zone Complex MN-SUF 88 2 80 Ctn 7/26 213 -12 4 4 2 0 4.6M FS

Southwest Area (PL 2)
New fires: 3
New large incidents: 0
Uncontained large fires: 1
Tiger, Prescott NF, USFS. Eleven miles east of Crown King, AZ. Short grass, brush and timber. No new information. Last report unless new information is received.

Incident Name Unit Size % Ctn/ Comp Est Personnel Resources Strc Lost $$ CTD Origin Own Acres Chge Total Chge Crw Eng Heli
Tiger AZ-PNF 16,278 --- 90 Ctn 7/30 5 --- 0 1 0 0 5.6M FS
Large Fires Being Managed with a Strategy Other Than Full Suppression Without a Type 1 or 2 IMT Assigned
Paradise Park AZ-ASF 262 --- 0 Comp 8/13 1 --- 0 0 0 0 2K FS
Oconnell AZ-KNF 180 --- 50 Comp UNK 23 --- 1 3 0 0 20K FS
ASF – Apache Sitgreaves NF, USFS KNF – Kaibab NF, USFS
Alaska Area (PL 2)

New fires: 2
New large incidents: 0
Uncontained large fires: 0
Munson Creek, Fairbanks Area, Alaska DOF. Fifty-two miles northeast of Fairbanks, AK. Timber. Minimal fire
behavior with creeping and smoldering. Numerous structures threatened. Trail closures in effect. Precipitation
occurred over the fire area yesterday. Last narrative report unless significant activity occurs.

Incident Name Unit Size % Ctn/
Comp Est Personnel Resources Strc
Lost
$$ CTD Origin
Own Acres Chge Total Chge Crw Eng Heli
Large Fires Being Managed with a Strategy Other Than Full Suppression Without a Type 1 or 2 IMT Assigned
Munson Creek AK-FAS 54,000 4,000 5 Comp 7/30 36 -2 1 7 0 0 2.5M ST
Black Hills AK-TAS 4,000 500 6 Comp 7/26 43 -5 2 0 1 0 150K ST
Cultas Creek AK-UYD 37,054 --- 0 Comp 8/7 14 --- 1 0 1 0 50K NPS
Sischu AK-TAD 13,792 --- 0 Comp 8/7 0 --- 0 0 0 0 5K BLM
Crescent Creek AK-UYD 1,329 --- 0 Comp 8/7 0 --- 0 0 0 0 5K NPS
Shellman Creek AK-TAD 1,972 --- 0 Comp UNK 0 --- 0 0 0 0 NR BLM
TAS – Tok Area, Alaska DOF UYD – Upper Yukon Zone, BLM TAD – Tanana Zone, BLM
Southern Area (PL 1)

New fires: 4
New large incidents: 0

Uncontained large fires: 0
Incident Name Unit Size % Ctn/
Comp Est Personnel Resources Strc
Lost
$$ CTD Origin
Own Acres Chge Total Chge Crw Eng Heli
Large Fires Being Managed with a Strategy Other Than Full Suppression Without a Type 1 or 2 IMT Assigned
Shark Slough FL-EVP 762 185 50 Comp 7/25 17 0 0 1 2 0 18K NPS
EVP – Everglades NP, NPS

Fires and Acres Yesterday (by Protection):

Area BIA BLM FWS NPS ST/OT USFS TOTAL
FIRES 0 2 0 0 0 0 2 Alaska Area ACRES 0 4,293 0 0 4,469 0 8,762
FIRES 1 1 0 0 10 1 13 Northwest Area ACRES 0 0 0 0 11 0 11
FIRES 0 0 0 0 21 5 26 Northern California Area ACRES 0 0 0 0 772 2,205 2,977
FIRES 0 0 0 0 19 3 22 Southern California Area ACRES 0 0 0 0 22 3 25
FIRES 2 0 0 0 8 7 17 Northern Rockies Area ACRES 2 1,000 0 0 2,333 5,051 8,387
FIRES 1 8 0 1 3 6 19 Great Basin Area ACRES 0 7 0 1 1,120 10 1,138
FIRES 2 1 0 0 0 0 3 Southwest Area ACRES 0 0 0 0 0 0 0
FIRES 3 2 0 0 6 4 15 Rocky Mountain Area ACRES 0 0 0 0 30 35 65
FIRES 0 0 0 0 4 1 5
Eastern Area ACRES 0 0 0 0 1 20 21
FIRES 0 0 0 0 4 0 4 Southern Area ACRES 0 0 0 0 1 0 1
TOTAL FIRES: 9 14 0 1 75 27 126
TOTAL ACRES: 2 5,300 0 1 8,760 7,324 21,388

Fires and Acres Year-to-Date (by Protection):

Area BIA BLM FWS NPS ST/OT USFS TOTAL
FIRES 0 94 0 0 212 11 317 Alaska Area
ACRES 0 134,814 0 0 63,241 5 198,060
FIRES 149 184 21 3 1,451 290 2,098 Northwest Area
ACRES 47,783 13,162 1,178 19 75,671 468,822 606,636
FIRES 43 24 4 21 2,129 333 2,554 Northern California Area
ACRES 38 268 332 1 20,270 157,994 178,904
FIRES 16 93 11 31 2,715 363 3,229 Southern California Area
ACRES 1,299 3,510 199 3,007 16,555 9,291 33,861
FIRES 1,030 64 21 5 968 545 2,633 Northern Rockies Area
ACRES 73,530 4,030 2,639 51 168,674 122,122 371,046
FIRES 35 518 51 17 581 293 1,495 Great Basin Area
ACRES 3,005 54,084 10 2,191 54,852 37,096 151,239
FIRES 475 172 9 22 333 813 1,824 Southwest Area
ACRES 24,699 83,887 1,528 3,362 33,217 490,648 637,343
FIRES 515 203 6 17 429 199 1,369 Rocky Mountain Area
ACRES 4,200 22,633 1,260 1,116 81,665 23,061 133,935
FIRES 431 0 22 13 6,734 404 7,604 Eastern Area
ACRES 12,367 0 13,276 560 31,901 15,843 73,947
FIRES 376 0 53 36 12,350 371 13,186 Southern Area
ACRES 28,685 0 11,844 8,321 261,801 27,347 338,000
TOTAL FIRES: 3,070 1,352 198 165 27,902 3,622 36,309
TOTAL ACRES: 195,608 316,390 32,267 18,629 807,850 1,352,230 2,722,976
Ten Year Average Fires (2011 – 2020 as of today) 32,924
Ten Year Average Acres (2011 – 2020 as of today) 3,652,071
***Changes in some agency YTD acres reflect more accurate mapping or reporting adjustments. ***Additional wildfire information is available through the Geographic Areas at https://gacc.nifc.gov/

Canadian Fires and Hectares

PROVINCES FIRES YESTERDAY HECTARES YESTERDAY FIRES YEAR-TO-DATE
HECTARES YEAR-TO- DATE
BRITISH COLUMBIA 14 19,903 1,212 361,461
YUKON TERRITORY 8 3,910 97 66,314
ALBERTA 5 0 882 50,187
NORTHWEST TERRITORY 11 2,721 100 45,348
SASKATCHEWAN 2 12,071 450 555,761
MANITOBA 5 13,542 326 596,931
ONTARIO 6 174 886 508,520
QUEBEC 0 1 463 29,297
NEWFOUNDLAND 0 0 57 306
NEW BRUNSWICK 0 0 148 307
NOVA SCOTIA 0 0 110 197
PRINCE EDWARD ISLAND 0 0 1 0
NATIONAL PARKS 1 0 49 12,873
TOTALS 52 52,322 4,782 2,227,503
*1 Hectare = 2.47 Acres
Predictive Services Discussion: Westerly flow aloft will continue for the northern Intermountain West north of
high pressure over the Great Basin as an upper low moves from New Mexico into Arizona. A decaying cold front
will bring breezy winds with low relative humidity to portions of the northern Great Basin, and typical dry and breezy
gap winds will develop on the east side of the Cascades and Sierra Front. Minnesota will also have post- frontal
breezy northwest winds and relative humidity in the teens. Very dry conditions will continue for the northern
Intermountain West, including poor overnight recovery for mid-slopes and ridges. Isolated mixed wet and dry
thunderstorms are possible for southeast California and Wyoming, while monsoonal thunderstorms continue for
much of the Southwest and broader Four Corners region. The potential for flash flooding will remain elevated over
Arizona into western New Mexico. Severe thunderstorms are likely along and ahead of a cold front in the Great
Lakes with severe outflow winds also possible in northern Arizona.

http://www.predictiveservices.nifc.gov/outlooks/outlooks.htm

On a Hillside Where Rolling Material Can Ignite Fuel Below
Operational Engagement Category

When firefighters find themselves in Watch Out Situation #13, on a hillside where rolling material can ignite fuel
below, they must answer the following questions:

Can you locate/construct a line to prevent material from rolling below? What do you call line that catches rolling material?
o Describe how you would construct this type of line and what factors you would have to consider (e.g., slope, fuels, etc.).

Will you get enough warning of rolling material to prevent being hit by it? Who needs to be watching for rolling material? What kinds of warning systems could you establish?

Can you see where any material that rolls below you goes and what it does? What can happen when material rolls out of the fire and below you, out of view? What needs to be done to mitigate this danger?
Is the area free of large amounts of flashy fuels? Is the area free of chimneys, gullies, and steep slopes?
o Review the Common Denominators of Tragedy Fires.
Do you have two escape routes so you can go either way? Talk about where your most likely escape routes and safety zones will be when you are on a hillside where rolling material can ignite fuel below.

To reduce the risks:

• Post lookouts.
• Consider locating line in a defensible position.
• Talk about fires in steep terrain where you had material roll out below you and how you dealt with it.
Resources:
Incident Response Pocket Guide (IRPG), PMS 461
Interagency Standards for Fire and Fire Aviation Operations (Red Book) 10
Standard Firefighting Orders, PMS 110
18 Watch Out Situations, PMS 118 10 and 18 Poster, PMS 110-18

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National Interagency Coordination Center Incident Management Situation Report Saturday, August 7, 2021– 0730 MDT National Preparedness Level 5
National Fire Activity:
Initial attack activity: Light (177 fires)
New large incidents: 6
Large fires contained: 3
Uncontained large fires: *** 94
Area Command teams committed: 0
NIMOs committed: 2
Type 1 IMTs committed 14
Type 2 IMTs committed: 19
Nationally, there are 50 fires being managed under a strategy other than full suppression. ***Uncontained large fires include only fires being managed under a full suppression strategy. Link to Geographic Area daily reports.
Link to Understanding the IMSR.
Two MAFFS C-130 airtankers and support personnel each from the 152nd Airlift Wing (Nevada Air National
Guard), one MAFFS unit from the 302nd Airlift Wing (Colorado Air Force Reserve), one MAFFS unit from the
153rd Airlift Wing (Wyoming Air National Guard) and one from the 146th Airlift Wing (California Air National
Guard) have been deployed to McClellan, CA to support wildland fire operations nationally.
One RC-26 aircraft with Distributed Real-Time Infrared (DRTI) capability and support personnel from the 141st Air Refueling Wing (Washington Air National Guard) have been deployed to Fairchild, WA. One RC-26 aircraft
with Distributed Real-Time Infrared (DRTI) capability and support personnel from the 162nd Operations Group (Arizona Air National Guard) have been deployed to Eugene, OR in support of wildland fire operations. Also supporting these aircraft are eight ground controllers from multiple U.S. Air National Guard squadrons.
One Boeing 737 airtanker from New South Wales, Australia is supporting fire suppression efforts in the western United States.

Active Incident Resource Summary
GACC Incidents Cumulative Acres Crews Engines Helicopters Total Personnel Change in Personnel
AICC 2 7,061 2 0 3 65 0
NWCC 36 774,411 196 440 74 8,260 -247
ONCC 11 733,349 148 636 57 8,340 223
OSCC 2 3,162 2 2 0 72 -80
NRCC 41 552,634 70 407 50 5,511 39
GBCC 13 101,128 23 40 12 1,070 -8
SWCC 0 0 0 0 0 0 0
RMCC 8 20,310 5 49 6 424 89
EACC 1 265 1 1 0 22 0
SACC 1 2 0 1 0 3 0
Total 115 2,192,324 447 1,576 202 23,767 16

Northwest Area (PL 5) New fires: 44
New large incidents: 3
Uncontained large fires: 40
Type 1 IMTs committed: 6 Type 2 IMTs committed: 9

Whitmore, Colville Agency, BIA. IMT 2 (NW Team 12). IMT is also managing the Hamilton incident. Twenty- seven miles northeast of Bridgeport, WA. Timber. Extreme fire behavior with crowning, flanking and spotting. Community of Nespelem and infrastructure threatened. Evacuations, area and road closures in effect.
Hamilton, Colville Agency, BIA. Twenty-six miles northeast of Bridgeport, WA. Timber and brush. No new information. Last report unless new information is received.
Devil’s Knob Complex (5 fires), Umpqua NF, USFS. IMT 2 (NW Team 8). Twenty miles northeast of Azalea, OR. Timber and medium slash. Active fire behavior with uphill runs, torching and uphill runs. Structures threatened. Evacuations, area, road and trail closures in effect. Skyline Ridge Complex (3 fires), South Unit, ODF. IMT 1 (ODF Team 1). Five miles southeast of Days Creek, OR.
Timber and light slash. Active fire behavior with group torching, running and spotting. Residences and infrastructure threatened. Evacuations in effect.
Rough Patch Complex (3 fires), Umpqua NF, USFS. IMT 2 (NW Team 13). IMT is also managing the Jack incident. Eighteen miles southwest of Oakridge, OR. Closed timber litter and timber. No fire behavior received. Area, road and trail closures in effect. Precipitation occurred over the fire area yesterday. Jack, Umpqua NF, USFS. Thirty-one miles east of Roseburg, OR. Timber and closed timber litter. Active fire behavior with backing, single tree torching and flanking. Numerous structures threatened. Area, road and trail closures in effect.

Summit Trail, Colville Agency, BIA. IMT 2 (NW Team 7). IMT is also managing the Chuweah Creek incident. Seventeen miles west of Inchelium, WA. Timber and light slash. Active fire behavior with uphill runs, flanking

and backing. Numerous structures and communication infrastructure threatened. Area and road closures in
effect.
Chuweah Creek, Colville Agency, BIA. Four miles north of Nespelem, WA. Brush, timber and light slash. Minimal fire behavior with creeping and smoldering. Area and road closures in effect.
Lick Creek, Umatilla NF, USFS. Transfer of command from IMT 2 (CA Team 12) to IMT 2 (RM Team Black) will occur tomorrow. IMT is also managing the Green Ridge incident. Fifteen miles southeast of Pomeroy, WA. Timber, closed timber litter and medium slash. Moderate fire behavior with single tree torching, creeping and
smoldering. Numerous structures threatened. Evacuations, area, road and trail closures in effect. Green Ridge, Umatilla NF, USFS. Thirty miles east of Walla Walla, WA. Closed timber litter, timber and
medium slash. Moderate fire behavior with isolated torching, creeping and spotting. Several communities threatened. Evacuations, area, road and trail closures in effect. Cedar Creek, Okanogan-Wenatchee NF, USFS. IMT 1 (GB Team 1). IMT is also managing the Delancy incident. Fifteen miles northwest of Winthrop, WA. Timber, brush and short grass. Active fire behavior with single tree torching, uphill runs and flanking. Several communities threatened. Evacuations, area, road and trail
closures in effect. Delancy, Okanogan-Wenatchee NF, USFS. Fifteen miles northwest of Winthrop, WA. Timber, short grass and closed timber litter. Minimal fire behavior with creeping. Area, road and trail closures in effect. Middle Fork Complex (3 fires), Willamette NF, USFS. Transfer of command from IMT 2 (NW Team 9) to IMT 1 (PNW Team 3) will occur today. IMT is also managing the Bull Complex. Nine miles northeast of Oakridge, OR. Closed timber litter, timber and light slash. Moderate fire behavior with backing, isolated torching and flanking.
Residences threatened. Area, road and trail closures in effect. Bull Complex, Mt. Hood NF, USFS. Twenty-five miles northeast of Mill City, OR. Timber. Moderate fire
behavior with smoldering, creeping and single tree torching. Area, road and trail closures in effect. Cub Creek 2, Southeast Region, DNR. IMT 1 (SW Team 2). Five miles north of Winthrop, WA. Short grass, closed timber litter and timber. Moderate fire behavior with flanking, creeping and running. Numerous residences and communication infrastructure threatened. Area, road and trail closures in effect.
Bootleg, Fremont-Winema NF, USFS. IMT 1 (PNW Team 2). IMT is also managing the Yainax and Walrus incidents. Twenty-three miles east of Chiloquin, OR. Timber and brush. Active fire behavior with torching, short crown runs and short-range spotting. Several communities and infrastructure threatened. Evacuations, area and road closures in effect. * Yainax, Klamath Unit, ODF. Ten miles northeast of Bonanza, OR. Timber and brush. Active fire behavior with short crown runs, torching and short-range spotting. Structures threatened. Evacuations and road closures in effect.
* Walrus, Klamath Unit, ODF. Eleven miles north of Bonanza, OR. Timber and brush. Active fire behavior with short crown runs, torching and short-range spotting. Structures threatened. Evacuations and road closures in effect.
Schneider Springs, Okanogan-Wenatchee NF, USFS. IMT 1 (RM Team 1) mobilizing. Twenty-one miles northwest of Tieton, WA. Short grass, timber and brush. Moderate fire behavior with torching and short crown runs. Area, road and trail closures in effect.
Walker Creek, Northeast Region, DNR. IMT 2 (NR Team 6) mobilizing. Four miles northwest of Wauconda, WA. Timber and short grass. Active fire behavior with torching, short crown runs and spotting. Community of Bonaparte threatened. Evacuations in effect.

Mud Springs, Vale District, BLM. Twenty-eight miles northwest of Harper, OR. Brush, short grass and timber.
Minimal fire behavior with creeping and smoldering.
MM 206, Vale District, BLM. Started on private land 16 miles southwest of Harper, OR. Brush and short grass. Moderate fire behavior with creeping and smoldering. Sage-grouse habitat threatened.
Elbow Creek, Umatilla NF, USFS. Twenty-six miles northeast of Elgin, OR. Timber and short grass. Minimal fire behavior with smoldering. Communication infrastructure threatened. Area, road and trail closures in effect. * Windy Pass, Okanogan-Wenatchee NF, USFS. Eleven miles southwest of Cle Elum, WA. Timber and short grass. Moderate fire behavior with creeping and smoldering. Structures threatened. Area, road and trail closures in effect.
Nine Mine, Northeast Region, Washington DNR. Twelve miles northwest of Barstow, WA. Timber, brush and tall grass. Active fire behavior with single tree torching, short-range spotting and running. Structures threatened.
Bruler, Willamette NF, USFS. Nine miles south of Detroit, OR. Closed timber litter and timber. Moderate fire behavior with backing and creeping. Area, road and trail closures in effect.
Spruce Canyon, Northeast Region, DNR. Fifteen miles east of Colville, WA. Heavy slash and timber. Minimal fire behavior with smoldering. Residences threatened. Cottonwood Creek, John Day Unit, ODF. Five miles southeast of Fossil, OR. Timber and tall grass. Minimal fire behavior with smoldering. Black Butte, Malheur NF, USFS. IMT 2 (NW Team 9) mobilizing. Thirty-six miles southeast of John Day, OR. Brush and tall grass. No new information. Last report unless new information is received.
Deep Creek 0685 RN, Prineville District, BLM. Started on private land 21 miles northeast of Warm Springs, OR.
Short grass and timber. No new information. Last report unless new information is received.

Incident Name Unit Size % Ctn/
Comp Est Personnel Resources Strc
Lost
$$ CTD Origin
Own Acres Chge Total Chge Crw Eng Heli
Whitmore WA-COA 15,000 10,700 0 Ctn 8/31 149 62 2 9 0 0 495K BIA
Hamilton WA-COA 400 --- 0 Ctn 8/11 24 --- 1 2 1 0 120K BIA
Devils Knob
Complex OR-UPF 1,500 1,034 0 Ctn 9/30 345 -12 11 15 0 0 920K FS
Skyline Ridge Complex OR-732S 2,059 543 7 Ctn 8/17 924 100 29 29 10 0 2.2M ST
Rough Patch Complex OR-UPF 805 -405 3 Ctn 10/31 255 27 3 13 6 0 1M FS
Jack OR-UPF 23,644 364 54 Ctn 10/31 358 -51 11 23 5 1 25.8M FS
Summit Trail WA-COA 27,931 5,225 23 Ctn 8/31 679 0 15 33 5 0 17.9M BIA
Chuweah Creek WA-COA 36,752 0 95 Ctn 8/14 96 -3 2 0 0 14 8.8M BIA
Lick Creek OR-UMF 80,421 0 90 Ctn 9/1 58 0 0 8 0 10 16.8M FS
Green Ridge OR-UMF 14,053 555 15 Ctn 9/6 384 48 8 25 5 0 21.5M FS
Cedar Creek WA-OWF 52,859 26 26 Ctn 10/31 759 -25 13 60 9 2 23.1M FS
Delancy WA-OWF 223 0 0 Ctn 10/31 0 0 0 0 0 0 122K FS
Middle Fork
Complex OR-WIF 3,308 502 10 Ctn 8/25 773 72 19 21 5 0 3.4M FS
Bull Complex OR-MHF 380 19 0 Ctn 10/30 94 40 2 5 0 0 151K FS

Cub Creek 2 WA-SES 61,391 365 24 Ctn 10/1 633 -40 12 29 7 3 17.4M ST
Incident Name Unit Size % Ctn/
Comp Est Personnel Resources Strc
Lost
$$ CTD Origin
Own Acres Chge Total Chge Crw Eng Heli
Bootleg OR-FWF 413,765 0 87 Ctn 10/1 1,124 -128 25 57 9 408 89.3M FS
* Yainax OR-981S 88 --- 0 Ctn 8/13 0 --- 0 0 0 0 50K ST
* Walrus OR-981S 85 --- 0 Ctn 8/13 0 --- 0 0 0 0 101K ST
Schneider
Springs WA-OWF 4,200 2,700 0 Ctn 10/1 22 -1 0 3 0 0 15K FS
Walker Creek WA-NES 120 20 5 Ctn 8/20 157 10 2 19 0 0 680K ST
Mud Springs OR-VAD 517 0 85 Ctn 8/9 21 -1 0 5 0 0 50K BLM
MM 206 OR-VAD 694 0 40 Ctn 8/9 89 30 2 10 0 0 300K PRI
Elbow Creek OR-UMF 22,960 0 95 Ctn 8/15 281 16 11 10 2 6 21.5M FS
* Windy Pass WA-OWF 119 --- 15 Ctn 8/19 86 --- 3 2 1 0 105K FS
Nine Mine WA-NES 300 0 5 Ctn 8/15 63 6 3 5 2 0 350K ST
Bruler OR-WIF 195 0 75 Ctn 9/30 107 -18 2 3 1 0 6.2M FS
Spruce Canyon WA-NES 130 0 95 Ctn UNK 26 -4 1 1 0 0 3.6M ST
Cottonwood Creek OR-952S 159 0 95 Ctn UNK 8 -106 0 2 0 0 650K ST
Black Butte OR-MAF 4,000 --- 0 Ctn 10/1 59 --- 2 2 1 0 650K FS
Deep Creek 0685 RN OR-PRD 1,250 --- 95 Ctn 8/5 60 --- 2 4 0 0 395K PRI
Large Fires Being Managed with a Strategy Other Than Full Suppression Without a Type 1 or 2 IMT Assigned
Bear Creek WA-NCP 998 --- 5 Comp 10/1 12 --- 1 0 1 0 30K NPS
NCP – North Cascades NP, NPS
Northern California Area (PL 5)
New fires: 23
New large incidents: 0
Uncontained large fires: 11
NIMOs committed: 1
Type 1 IMTs committed: 3
Type 2 IMTs committed: 4
Dixie, Butte Unit, Cal Fire. Unified command between IMT 1 (Cal Fire Team 1) and IMT 1 (CA Team 4). Fifteen miles northeast of Paradise, CA. Timber and brush. Active fire behavior with crowning, uphill runs and long-range spotting. Several communities and infrastructure threatened. Evacuations, area, road and trail closures in effect.
Monument, Shasta-Trinity NF, USFS. IMT 1 (CA Team 5). One mile southwest of Del Loma, CA. Timber and brush. Active fire behavior with uphill runs, short-range spotting and group torching. Several communities and infrastructure threatened. Evacuations, road and trail closures in effect.
McFarland, Shasta-Trinity NF, USFS. IMT 2 (CA Team 11). Four miles southeast of Wildwood, CA. Timber, chaparral and closed timber litter. Active fire behavior with group torching, uphill runs and spotting. Several
communities and infrastructure threatened. Evacuations, area and road closures in effect. Antelope, Klamath NF, USFS. IMT 2 (SW Team 4). Twenty miles northeast of McCloud, CA. Timber and brush.

Active fire behavior with spotting, wind-driven runs and group torching. Several communities threatened. Evacuations, area and road closures in effect.

River Complex (3 fires), Klamath NF, USFS. IMT 2 (CA Team 14). NIMO (Team 3) mobilizing. Nine miles
southwest of Etna, CA. Timber and brush. Moderate fire behavior with isolated torching, flanking and backing. Several communities threatened. Evacuations and road closures in effect. McCash, Six Rivers NF, USFS. IMT 2 (SW Team 3) mobilizing. Fourteen miles northeast of Somes Bar, CA. Timber, brush and tall grass. Moderate fire behavior with flanking, isolated torching and backing. Communities of Ti-Bar and Patterson, and communication infrastructure threatened. Road closures in effect.
River, Nevada-Yuba-Placer Unit, Cal Fire. Two miles southwest of Colfax, CA. Timber, brush and heavy slash.
Moderate fire behavior with smoldering. Numerous structures threatened. Area, road and trail closures in effect. Lava, Shasta-Trinity NF, USFS. Four miles east of Weed, CA. Timber and brush. Minimal fire behavior with
torching. Area and road closures in effect. Beckwourth Complex, Plumas NF, USFS. Three miles northeast of Beckwourth, CA. Timber, brush and closed
timber litter. Minimal fire behavior. Area, road and trail closures in effect.

Incident Name Unit Size % Ctn/
Comp Est Personnel Resources Strc
Lost
$$ CTD Origin
Own Acres Chge Total Chge Crw Eng Heli
Dixie CA-BTU 434,813 73,001 21 Ctn 8/20 5,118 -104 80 384 27 268 171.3M ST
Monument CA-SHF 36,015 11,296 0 Ctn 9/1 464 145 4 50 5 2 4M FS
McFarland CA-SHF 27,148 2,901 21 Ctn 8/21 743 124 17 51 6 0 6.7M FS
Antelope CA-KNF 38,601 15,996 20 Ctn 9/30 452 61 10 30 5 0 3.3M FS
River Complex CA-KNF 20,810 4,011 3 Ctn 10/1 412 117 6 23 3 0 2.5M FS
McCash CA-SRF 1,194 243 1 Ctn 9/29 175 0 7 3 2 1 750K FS
River CA-NEU 2,600 0 40 Ctn 8/13 744 -114 22 68 0 88 2.4M ST
Lava CA-SHF 26409 0 81 Ctn 8/14 23 -1 0 2 0 23 35.2M FS
Beckwourth
Complex CA-PNF 105,670 0 98 Ctn UNK 49 -7 1 5 0 148 54.2M FS
Evans CA-PNF 89 0 100 Ctn --- 41 2 1 3 0 0 300K FS
PNF – Plumas NF, USFS
Northern Rockies Area (PL 5)
New fires: 28
New large incidents: 0
Uncontained large fires: 36
NIMOs committed: 1
Type 1 IMTs committed: 5 Type 2 IMTs committed: 5
Boulder 2700, Flathead Agency, BIA. IMT 2 (NR Team 4). Three miles northeast of Finley Point, MT. Timber and brush. Active fire behavior with flanking, single tree torching and creeping. Numerous residences and communication infrastructure threatened. Evacuations, area, road and trail closures in effect.
Harris Mountain, Cascade County. IMT 2 (NR Team 7). Seven miles southeast of Cascade, MT. Closed timber litter and timber. Active fire behavior with flanking, group torching and short crown runs. Structures threatened. Evacuations in effect. West Lolo Complex, Lolo NF, USFS. Six miles north of St. Regis, MT. IMT 1 (NR Team 1). IMT is also managing the Granite Pass Complex. Timber, closed timber litter and brush. Moderate fire behavior with

creeping, backing and single tree torching. Numerous residences threatened. Evacuations, area, road and trail
closures in effect.
Granite Pass Complex (4 fires), Lolo NF, USFS. Thirty miles southwest of Missoula, MT. Timber, brush and closed timber litter. Minimal fire behavior with single tree torching, creeping and smoldering. Structures and communication infrastructure threatened. Area, road and trail closures in effect. Alder Creek, Beaverhead-Deerlodge NF, USFS. Transfer of command from IMT 1 (SW Team 1) to IMT 1 (SA Blue Team) will occur today. IMT is also managing the Trail Creek, Christensen and Black Mountain incidents.
Twenty miles northwest of Wisdom, MT. Timber and brush. Minimal fire behavior with creeping and smoldering. Numerous threatened. Area, road and trail closures in effect. Precipitation occurred over the fire area yesterday.
Trail Creek, Beaverhead-Deerlodge NF, USFS. Twenty miles west of Wisdom, MT. Timber and brush. Minimal fire behavior with creeping and smoldering. Community of Gibbonsville and communication infrastructure
threatened. Area, road and trail closures in effect. Precipitation occurred over the fire area yesterday. Christensen, Beaverhead-Deerlodge NF, USFS. Ten miles northeast of Wisdom, MT. Timber and brush.
Minimal fire behavior with creeping and smoldering. Structures threatened. Area, road and trail closures in
effect. Precipitation occurred over the fire area yesterday.
Black Mountain, Beaverhead-Deerlodge NF, USFS. Twenty miles east of Salmon, ID. Timber, heavy slash and brush. Minimal fire behavior with creeping and smoldering. Residences threatened. Area, road and trail closures in effect. Precipitation occurred over the fire area yesterday. Character Complex (2 fires), Idaho Panhandle NF, USFS. IMT 1 (NR Team 2). IMT is also managing the
Stateline Complex incident. Three miles north of Kellogg, ID. Timber and brush. Moderate fire behavior with
backing, creeping and isolated torching. Numerous structures threatened. Area, road and trail closures in effect.
Stateline Complex (6 fires), Idaho Panhandle NF, USFS. Twenty-two miles southwest of Superior, MT. Closed
timber litter, timber and light slash. Moderate fire behavior with isolated torching, backing and creeping. Area,
road and trail closures in effect.
Dixie, Nez Perce-Clearwater NF, USFS. IMT 2 (NR Team 5). IMT is also managing the Jumbo incident. Two miles north of Dixie, ID. Timber. Minimal fire behavior with creeping and smoldering. Several communities
threatened. Evacuations, area, road and trail closures in effect. Precipitation occurred over the fire area yesterday. Jumbo, Nez Perce-Clearwater NF, USFS. Eight miles west of Dixie, ID. Timber and brush. Minimal fire behavior with creeping and smoldering. Area, road and trail closures in effect. Precipitation occurred over the fire area yesterday.
Divide Complex (2 fires), Helena-Lewis and Clark NF, USFS. IMT 1 (SA Red Team). IMT is also managing the American Fork and Woods Creek incidents. Seventeen miles west of Neihart, MT. Short grass and timber. Active fire behavior with backing, creeping and single tree torching. Communities of Neihart and Monarch threatened. Area, road and trail closures in effect.
American Fork, Helena-Lewis and Clark NF, USFS. Twenty-four miles southwest of Harlowton, MT. Short grass and timber. Active fire behavior with flanking, backing and single tree torching. Numerous structures threatened. Area, road and trail closures in effect.
Woods Creek, Helena-Lewis and Clark NF, USFS. Sixteen miles northeast of Townsend, MT. Short grass and
timber. Active fire behavior with running, group torching and flanking. Residences threatened. Evacuations, area, road and trail closures in effect.

Burnt Peak, Kootenai NF, USFS. IMT 2 (GB Team 6). IMT is also managing the South Yaak incident. Nine
miles southwest of Troy, MT. Timber and light slash. Moderate fire behavior with torching, flanking and backing. Structures threatened. Road and trail closures in effect. South Yaak, Kootenai NF, USFS. Four miles northwest of Troy, MT. Timber and light slash. Moderate fire behavior with backing, flanking and group torching. Numerous structures threatened. Evacuations, area, road and trail closures in effect.
Hay Creek, Flathead NF, USFS. IMT 2 (CA Team 13). Four miles west of Polebridge, MT. Timber. Moderate
fire behavior with uphill runs, flanking and backing. Community of Polebridge threatened. Area, road and trail closures in effect. Storm Theatre Complex (12 fires), Nez Perce-Clearwater NF, USFS. NIMO (Team 1). Thirty-five miles southwest of Missoula, MT. Brush, timber and closed timber litter. Minimal fire behavior with backing, flanking and creeping. Area, road and trail closures in effect. Precipitation occurred over the fire area yesterday.
Cougar Rock Complex (4 fires), Clearwater Potlach Timber Protective Association, IDL. Seventeen miles
northeast of Elk River, ID. Light slash and timber. Moderate fire behavior with backing and flanking. Area and
road closures in effect.
Leland Complex (2 fires), Ponderosa Area Office, IDL. Five miles southwest of Deary, ID. Timber, closed
timber litter and brush. Minimal fire behavior with smoldering and creeping. Communication infrastructure threatened. Road and trail closures in effect.
Sharp Tail, Charles M. Russell NWR, FWS. Forty miles northeast of Roy, MT. Timber, short grass and brush. Minimal fire behavior. Area closures in effect. Reduction in acreage due to more accurate mapping.
Taylor, Fergus County. Thirteen miles southwest of Winifred, MT. Short grass, timber and brush. Minimal fire behavior. Area closures in effect. Reduction in acreage due to more accurate mapping.
Whitetail Creek, Northwestern Land Office, DNR. Nine miles northeast of Finley Point, MT. Timber and medium slash. Moderate fire behavior. Area and road closures in effect.
Robertson Draw, Custer Gallatin NF, USFS. Seven miles south of Red Lodge, MT. Short grass, brush and timber. Minimal fire behavior. Structures threatened. Area, road and trail closures in effect. Precipitation occurred over the fire area yesterday. Crooked Creek, Billings Field Office, BLM. Twenty-five miles east of Bridger, MT. Short grass, brush and
timber. Minimal fire behavior. Area, road and trail closures in effect.
Snake River Complex, Craig Mountain Supervisory Area, IDL. Twenty miles south of Lewiston, ID. Short grass and timber. Minimal fire behavior with creeping and smoldering. Numerous residences threatened. Area, road and trail closures in effect. Precipitation occurred over the fire area yesterday. Goat, Beaverhead-Deerlodge NF, USFS. Eleven miles northeast of Philipsburg, MT. Timber and brush. No new information.
Bradshaw, Powder River County. Thirty-nine miles southeast of Ashland, MT. Short grass and timber. No new information. Trestle Creek Complex, Idaho Panhandle NF, USFS. Previously reported incident. Seven miles north of Hope, ID. Timber and brush. Moderate fire behavior with torching, backing and creeping. Residences threatened.
Area, road and trail closures in effect. Last narrative report unless significant activity occurs.

Incident Name Unit Size % Ctn/
Comp Est Personnel Resources Strc
Lost
$$ CTD Origin
Own Acres Chge Total Chge Crw Eng Heli
Boulder 2700 MT-FHA 1,922 78 16 Ctn 8/15 300 27 6 18 2 31 2.4M BIA
Harris Mountain MT-LG02 31,460 0 20 Ctn 10/1 298 25 6 9 10 6 5.8M CNTY
West Lolo Complex MT-LNF 19,100 766 15 Ctn 10/31 347 -1 2 20 4 0 15.2M FS
Granite Pass Complex MT-LNF 5,739 0 4 Ctn 9/15 199 0 3 10 3 0 7.3M FS
Alder Creek MT-BDF 11,467 0 10 Ctn 11/1 380 13 3 23 6 0 11.5M FS
Trail Creek MT-BDF 35,881 0 23 Ctn 11/1 137 0 2 18 0 0 7M FS
Christensen MT-BDF 8,510 0 0 Ctn 11/1 18 0 0 4 0 1 218K FS
Black Mountain MT-BDF 1,041 0 0 Ctn 10/31 52 -23 0 6 1 0 1.7M FS
Character
Complex ID-IPF 7,800 284 30 Ctn 11/1 294 9 4 18 0 0 14.8M FS
Stateline Complex ID-IPF 10,874 0 0 Ctn 10/31 220 -13 1 10 3 0 10M FS
Dixie ID-NCF 43,168 0 59 Comp 10/30 252 3 2 14 2 0 20.5M FS
Jumbo ID-NCF 2,647 0 45 Comp 10/30 2 0 0 0 0 0 110K FS
Divide Complex MT-HLF 9,824 0 26 Comp 10/29 314 -4 2 22 1 0 12.1M FS
American Fork MT-HLF 17,537 0 10 Comp 10/15 132 10 3 16 0 0 4.2M FS
Woods Creek MT-HLF 25,745 5,074 4 Comp 10/31 264 16 4 34 1 1 5M FS
Burnt Peak MT-KNF 3,495 30 46 Ctn 9/30 126 -2 0 3 2 0 11.2M FS
South Yaak MT-KNF 10,153 308 10 Ctn 9/30 220 -1 3 19 2 0 3.3M FS
Hay Creek MT-FNF 2,743 44 22 Ctn 9/30 219 14 1 15 2 0 5.2M FS
Storm Theatre Complex ID-NCF 21,772 360 0 Comp 10/15 113 2 0 10 0 0 3.7M FS
Cougar Rock
Complex ID-CTS 8,079 0 42 Ctn 9/15 432 80 11 19 4 0 12M ST
Leland
Complex ID-PDS 3,514 0 84 Ctn 8/8 140 -16 4 8 0 0 11.4M ST
Sharp Tail MT-CMR 509 -131 40 Ctn 8/9 36 2 0 8 1 0 80K FWS
Taylor MT-LG08 22,916 -5,084 55 Ctn 8/9 183 -54 3 26 1 10 1.2M CNTY
Whitetail Creek MT-NWS 358 10 13 Ctn 10/1 83 2 2 5 0 0 264K ST
Robertson Draw MT-CGF 29,885 0 90 Ctn 10/1 13 0 0 2 0 30 13M FS
Crooked Creek MT-BID 4,141 0 85 Ctn 8/30 10 0 0 0 1 1 5M BLM
Snake River Complex ID-CMS 109,444 0 90 Ctn 8/15 23 0 0 3 0 3 9.2M ST
Goat MT-BDF 212 --- 30 Ctn 10/1 37 --- 0 2 0 0 350K FS
Bradshaw MT-LG09 833 --- 50 Ctn 8/9 51 --- 0 4 1 0 375K CNTY
Large Fires Being Managed with a Strategy Other Than Full Suppression Without a Type 1 or 2 IMT Assigned
Trestle Creek
Complex ID-IPF 3,586 136 0 Comp 10/15 64 6 1 4 0 0 3.2M FS
Crooks MT-FHA 1,000 96 0 Comp 8/30 97 0 2 9 1 0 525K BIA
Goose MT-BDF 7,522 0 80 Comp 10/13 70 -11 1 1 1 1 7.6M FS
Swanson Creek ID-NCF 535 20 0 Comp 10/10 47 0 0 2 0 0 115K FS
Lynx ID-NCF 4,800 --- 0 Comp 10/30 0 --- 0 0 0 0 175K FS

Porphyry ID-NCF 150 --- 0 Comp 10/15 0 --- 0 0 0 0 NR FS
Incident Name Unit Size % Ctn/
Comp Est Personnel Resources Strc
Lost
$$ CTD Origin
Own Acres Chge Total Chge Crw Eng Heli
Greenside Butte ID-NCF 725 --- 0 Comp 10/31 0 --- 0 0 0 0 10K FS
Larkins
Complex ID-IPF 3,357 --- 0 Comp 11/1 15 --- 0 0 0 0 150K FS
Army Mule ID-NCF 1,720 --- 0 Comp 10/15 0 --- 0 0 0 0 2K FS
Dry Cabin MT-LNF 3,060 --- 0 Comp 10/10 15 --- 0 0 0 0 74K FS

Great Basin (PL 3)
New fires: 45
New large incidents: 1
Uncontained large fires: 2
Type 2 IMTs committed: 1
Mud Lick, Salmon-Challis NF, USFS. IMT 2 (GB Team 7). Twenty-three miles west of Salmon, ID. Timber and
short grass. Minimal fire behavior with creeping and smoldering. Area, road and trail closures in effect.
Precipitation occurred over the fire area yesterday.
* Bruneau, Twin Falls District, BLM. Twenty-two miles southwest of Hammett, ID. Short grass and brush.
Minimal fire behavior with creeping and smoldering. Sage-grouse habitat threatened.
Shale Creek, Bridger-Teton NF, USFS. Twenty miles northeast of Cokeville, WY. Timber, light slash and brush.
No new information.

Incident Name Unit Size % Ctn/ Comp Est Personnel Resources Strc Lost $$ CTD Origin Own Acres Chge Total Chge Crw Eng Heli
Mud Lick ID-SCF 20,643 0 48 Comp 9/19 343 -14 4 15 5 0 19.2M FS
* Bruneau ID-TFD 2,196 --- 60 Ctn 8/7 24 --- 0 5 0 0 39K BLM
Shale Creek WY-BTF 189 --- 79 Ctn UNK 18 --- 0 0 1 0 1.8M FS
Sugar Cane ID-PAF 133 0 100 Ctn --- 52 -10 2 0 0 0 45K FS
Large Fires Being Managed with a Strategy Other Than Full Suppression Without a Type 1 or 2 IMT Assigned
Tamarack NV-HTF 68,696 0 78 Comp 8/31 434 12 11 10 5 25 28M FS
Vinegar ID-PAF 2,462 --- 0 Comp 10/1 5 --- 0 0 0 0 207K FS
Rush Creek ID-PAF 3,181 --- 0 Comp 10/1 7 --- 0 0 1 0 207K FS
Club ID-PAF 395 --- 0 Comp 10/1 0 --- 0 0 0 0 207K FS
Tango ID-SCF 103 --- 0 Comp 10/1 0 --- 0 0 0 0 10K FS
Morgan Canyon UT-UWF 509 --- 90 Comp 8/15 1 --- 0 0 0 0 1.8M FS
PAF – Payette NF, USFS HTF – Humboldt-Toiyabe NF, USFS UWF – Uinta-Wasatch-Cache NF, USFS
Rocky Mountain Area (PL 2)
New fires: 8
New large incidents: 1
Uncontained large fires: 4

Crater Ridge, Bighorn NF, USFS. Thirty-one miles west of Sheridan, WY. Timber, heavy slash and short grass. Moderate fire behavior with wind-driven runs, uphill runs and torching. Area, road and trail closures in effect. Precipitation occurred over the fire area yesterday.

Morgan Creek, Medicine Bow-Routt NF, Thunder Basin National Grassland, USFS. Fifteen miles north of
Steamboat Springs, CO. Timber and brush. Minimal fire behavior with smoldering and creeping. Structures threatened. Area, road and trail closures in effect. Precipitation occurred over the fire area yesterday. Calico, Pine Ridge Agency, BIA. Five miles northwest of Pine Ridge, SD. Short grass and timber. Moderate fire behavior. Community of Calico threatened.
* Hackberry CA, Nebraska Forest Service. Eighteen miles southwest of Bridgeport, NE. Timber. Extreme fire behavior. Structures threatened.

Incident Name Unit Size % Ctn/ Comp Est Personnel Resources Strc Lost $$ CTD Origin Own Acres Chge Total Chge Crw Eng Heli
Crater Ridge WY-BHF 905 147 32 Ctn 8/31 145 34 3 7 3 0 6.2M FS
Morgan Creek WY-MRF 7,505 0 24 Ctn 9/1 120 -9 0 5 3 0 10.5M FS
Calico SD-PRA 401 0 75 Ctn 8/10 22 8 0 5 0 0 400K BIA
* Hackberry CA NE-NES 1,500 --- 0 Ctn UNK 69 --- 0 23 0 0 30K ST
Whipple Camp SD-SDS 2,565 0 100 Ctn --- 0 -10 0 0 0 0 70K ST
Large Fires Being Managed with a Strategy Other Than Full Suppression Without a Type 1 or 2 IMT Assigned
Muddy Slide WY-MRF 4,093 --- 70 Comp 8/31 14 --- 0 1 0 18 13M FS
Sylvan CO-WRF 3,792 --- 75 Comp UNK 3 --- 0 1 0 0 7.1M FS
SDS – South Dakota Wildland Fire Suppression WRF – White River NF, USFS
Eastern Area (PL 3)
New fires:

1
New large incidents: 0
Uncontained large fires: 1
Fourtown Lake, Superior NF, USFS. Thirteen miles northeast of Ely, MN. Timber. Minimal fire behavior with
creeping and smoldering. Area and trail closures in effect.

Incident Name Unit Size % Ctn/ Comp Est Personnel Resources Strc Lost $$ CTD Origin Own Acres Chge Total Chge Crw Eng Heli
Fourtown Lake MN-SUF 265 0 90 Ctn 8/7 22 0 1 1 0 0 350K FS

Southern California Area (PL 3)
New fires: 17
New large incidents: 0
Uncontained large fires: 0

Incident Name Unit Size % Ctn/ Comp Est Personnel Resources Strc Lost $$ CTD Origin Own Acres Chge Total Chge Crw Eng Heli
Large Fires Being Managed with a Strategy Other Than Full Suppression Without a Type 1 or 2 IMT Assigned
Tilttill CA-YNP 700 180 15 Comp 8/24 61 7 2 0 0 0 150K NPS
Lukens CA-YNP 510 --- 75 Comp 8/15 0 --- 0 0 0 0 451K NPS
YNP – Yosemite NP, NPS

Southwest Area (PL 2)
New fires: 0
New large incidents: 0
Uncontained large fires: 0

Incident Name Unit Size % Ctn/
Comp Est Personnel Resources Strc
Lost
$$ CTD Origin
Own Acres Chge Total Chge Crw Eng Heli
Large Fires Being Managed with a Strategy Other Than Full Suppression Without a Type 1 or 2 IMT Assigned
Paradise Park AZ-ASF 262 --- 0 Comp 8/13 0 --- 0 0 0 0 2K FS
ASF – Apache-Sitgreaves NF, USFS
Alaska Area (PL 2)
New fires: 3
New large incidents: 0
Uncontained large fires: 0
Discovery Creek, Upper Yukon Zone, BLM. Previously reported incident. Thirty miles northwest of Venetie, AK. Timber and brush. Moderate fire behavior with creeping and smoldering. Precipitation occurred over the fire area yesterday. Last narrative report unless significant activity occurs.

Incident Name Unit Size % Ctn/ Comp Est Personnel Resources Strc Lost $$ CTD Origin Own Acres Chge Total Chge Crw Eng Heli
Large Fires Being Managed with a Strategy Other Than Full Suppression Without a Type 1 or 2 IMT Assigned
Discovery
Creek AK-UYD 4,527 3,655 0 Comp 8/17 33 10 1 0 1 0 315K FWS
Twentyfour Mile AK-UYD 657 0 0 Comp 9/30 0 0 0 0 0 0 2K BLM
Marten Creek AK-UYD 2,534 -466 0 Comp 8/31 32 3 1 0 2 0 733K TRI
South Fork AK-UYD 658 --- 0 Comp UNK 0 --- 0 0 0 0 4K BLM
Sischu AK-TAD 16,383 0 0 Comp 8/7 0 0 0 0 0 0 7K BLM
Cultas Creek AK-UYD 38,202 0 0 Comp 8/7 0 0 0 0 0 0 822K NPS
Munson Creek AK-FAS 54,050 --- 5 Comp UNK 0 --- 0 0 0 0 1M ST
Crescent Creek AK-UYD 1,374 --- 0 Comp 9/10 0 --- 0 0 0 0 5K NPS
Shellman Creek AK-TAD 1,972 --- 0 Comp UNK 0 --- 0 0 0 0 NR BLM
UYD – Upper Yukon Zone, BLM TAD – Tanana Zone, BLM FAS – Fairbanks Area, Alaska DOF
Southern Area (PL 1)
New fires:

8

New large incidents: 1
Uncontained large fires: 0

Incident Name Unit Size % Ctn/ Comp Est Personnel Resources Strc Lost $$ CTD Origin Own Acres Chge Total Chge Crw Eng Heli
* WF Wildcow TX-MCR 1,500 --- 100 Ctn --- 5 --- 0 1 1 0 40K FWS
MCR – McFaddin NWR, FWS

Fires and Acres Yesterday (by Protection):

Area BIA BLM FWS NPS ST/OT USFS TOTAL
FIRES 0 1 0 0 2 0 3 Alaska Area ACRES 0 4,606 0 0 0 0 4,607
FIRES 1 12 0 0 18 13 44 Northwest Area ACRES 0 1 0 0 8 7,307 7,316
FIRES 0 0 0 0 14 9 23 Northern California Area ACRES 0 0 0 0 2 33,843 33,845
FIRES 0 0 0 2 15 0 17 Southern California Area ACRES 0 0 0 3 6 0 9
FIRES 7 0 0 0 11 10 28 Northern Rockies Area ACRES 3 0 0 0 46 3,977 4,026
FIRES 0 11 0 2 11 21 45 Great Basin Area ACRES 0 2,202 0 0 4 14 2,220
FIRES 0 0 0 0 0 0 0 Southwest Area ACRES 0 0 0 0 0 0 0
FIRES 0 0 0 0 6 2 8 Rocky Mountain Area ACRES 0 0 0 0 109 1 110
FIRES 0 0 0 0 1 0 1
Eastern Area ACRES 0 0 0 0 1 0 1
FIRES 0 0 0 0 8 0 8 Southern Area ACRES 0 0 0 0 9 0 9
TOTAL FIRES: 8 24 0 4 86 55 177
TOTAL ACRES: 3 6,810 0 3 186 45,142 52,145

Fires and Acres Year-to-Date (by Protection):

Area BIA BLM FWS NPS ST/OT USFS TOTAL
FIRES 0 113 0 0 227 14 354 Alaska Area
ACRES 0 131,016 0 0 95,969 5 226,990
FIRES 180 253 26 13 1,754 451 2,677 Northwest Area
ACRES 69,785 14,993 13,180 172 144,433 521,645 764,210
FIRES 60 28 4 23 2,322 445 2,882 Northern California Area
ACRES 70 274 332 2 258,985 348,368 608,032
FIRES 16 96 12 59 2,980 411 3,574 Southern California Area
ACRES 1,299 3,526 199 3,235 17,353 9,528 35,141
FIRES 1,131 68 22 5 1,161 646 3,033 Northern Rockies Area
ACRES 75,854 18,464 2,689 51 214,004 229,629 540,692
FIRES 40 637 52 25 682 419 1,855 Great Basin Area
ACRES 3,008 57,393 10 2,191 55,828 45,949 164,380
FIRES 487 185 9 27 335 869 1,912 Southwest Area
ACRES 24,879 83,888 1,528 3,362 33,218 490,702 637,579
FIRES 500 317 6 20 512 263 1,618 Rocky Mountain Area
ACRES 6,377 25,045 1,260 1,116 55,093 25,446 114,337
FIRES 447 0 50 22 6,834 420 7,773 Eastern Area
ACRES 12,376 0 14,336 588 32,545 15,884 75,731
FIRES 377 0 54 39 12,587 373 13,430 Southern Area
ACRES 28,685 0 11,845 8,437 262,825 27,433 339,226
TOTAL FIRES: 3,238 1,697 235 233 29,394 4,311 39,108
TOTAL ACRES: 222,334 334,600 45,379 19,156 1,170,256 1,714,592 3,506,321
Ten Year Average Fires (2011 – 2020 as of today) 36,576
Ten Year Average Acres (2011 – 2020 as of today) 4,234,069
***Changes in some agency YTD acres reflect more accurate mapping or reporting adjustments. ***Additional wildfire information is available through the Geographic Areas at https://gacc.nifc.gov/

Canadian Fires and Hectares

PROVINCES FIRES YESTERDAY HECTARES YESTERDAY FIRES YEAR-TO-DATE
HECTARES YEAR-TO- DATE
BRITISH COLUMBIA 23 13,160 1,430 584,015
YUKON TERRITORY 2 1,062 108 102,400
ALBERTA 18 123 1,024 54,751
NORTHWEST TERRITORY 0 0 131 112,244
SASKATCHEWAN 4 94,359 530 1,003,686
MANITOBA 1 41,975 426 987,630
ONTARIO 7 205 1,065 706,984
QUEBEC 0 0 479 56,712
NEWFOUNDLAND 4 0 62 307
NEW BRUNSWICK 1 0 154 308
NOVA SCOTIA 0 0 110 197
PRINCE EDWARD ISLAND 0 0 1 0
NATIONAL PARKS 1 0 49 15,628
TOTALS 61 150,883 5,578 3,624,860
*1 Hectare = 2.47 Acres
Predictive Services Discussion: An upper low will move through Washington and push a cold front into the
Pacific Northwest. Windy conditions are forecast near and east of the Cascades in Washington and Oregon but
will be moderated by cooler temperatures and higher relative humidity. Dry and windy conditions are likely across
much of the northern and eastern Great Basin into Wyoming with the greatest threat of critical conditions near and
east of the Continental Divide in Montana. Dry and breezy conditions are also likely in the Four Corners area but will
be mitigated by the strong start to the monsoon. Showers will spread west of the Cascades in Washington and
northwest Oregon with scattered showers and isolated thunderstorms in northern Washington east of the
Cascades. Isolated mixed wet and dry thunderstorms are possible over southeast Arizona and southern New
Mexico. Severe thunderstorms are forecast for the northern Plains into the Midwest and western Great Lakes and
may stretch southward across the central Plains.
http://www.predictiveservices.nifc.gov/outlooks/outlooks.htm

Terrain and Fuels Make Escape to Safety Zones Difficult
Operational Engagement Category

When fighting wildland fires, it is often easy to get committed to areas that put you in Watch Out Situation #17.
As firefighters progress along the fireline, it is imperative to constantly keep the following considerations in mind:

Retreat times should be based on the slowest member of the crew.
• Does the crew’s condition allow for fast travel?
• Discuss physical and mental conditions that could interfere with a crew’s ability to travel quickly.

Will you get adequate warning to make it to your safety zone? Who will you rely on to warn you? How will you ensure that everyone gets the word?

Can escape routes be improved to make travel to safety zones faster? Are escape routes marked?

• Review what you have done on past fires to locate, mark, and improve escape routes.
Will posting more lookouts give adequate warning? Talk about situations where there was more than one firefighter assigned to be a lookout.
To reduce the risks, consider other tactics that will allow you to be in a safer location. Review fires
where you have had to change tactics because escape to safety zones was not adequate.

Resources:
Incident Response Pocket Guide (IRPG), PMS 461
Interagency Standards for Fire and Fire Aviation Operations (Red Book)
10 Standard Firefighting Orders, PMS 110
10 and 18 Poster, PMS 110-18
18 Watch Out Situations, PMS 118

Have an idea? Have feedback? Share it.
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National Interagency Coordination Center Incident Management Situation Report Sunday, August 8, 2021– 0730 MDT National Preparedness Level 5
National Fire Activity:
Initial attack activity: Light (130 fires)
New large incidents: 4
Large fires contained: 2
Uncontained large fires: *** 93
Area Command teams committed: 0
NIMOs committed: 2
Type 1 IMTs committed 12 Type 2 IMTs committed: 18
Nationally, there are 52 fires being managed under a strategy other than full suppression.
***Uncontained large fires include only fires being managed under a full suppression strategy. Link to Geographic Area daily reports.
Link to Understanding the IMSR.

Two MAFFS C-130 airtankers and support personnel each from the 152nd Airlift Wing (Nevada Air National
Guard), one MAFFS unit from the 302nd Airlift Wing (Colorado Air Force Reserve), one MAFFS unit from the
153rd Airlift Wing (Wyoming Air National Guard) and one from the 146th Airlift Wing (California Air National
Guard) have been deployed to McClellan, CA to support wildland fire operations nationally.
One RC-26 aircraft with Distributed Real-Time Infrared (DRTI) capability and support personnel from the 141st Air Refueling Wing (Washington Air National Guard) have been deployed to Fairchild, WA. One RC-26 aircraft with Distributed Real-Time Infrared (DRTI) capability and support personnel from the 162nd Operations Group
(Arizona Air National Guard) have been deployed to Eugene, OR in support of wildland fire operations. Also supporting these aircraft are eight ground controllers from multiple U.S. Air National Guard squadrons.
One Boeing 737 airtanker from New South Wales, Australia is supporting fire suppression efforts in the western United States.

Active Incident Resource Summary
GACC Incidents Cumulative Acres Crews Engines Helicopters Total Personnel Change in Personnel
AICC 2 7,061 3 0 1 81 16
NWCC 35 823,824 205 469 70 8,603 343
ONCC 11 762,702 132 636 59 8,245 -95
OSCC 2 3,762 2 2 0 72 0
NRCC 41 549,508 78 369 50 5,565 54
GBCC 12 100,548 22 31 11 1,010 -60
SWCC 1 300 0 3 0 17 17
RMCC 5 15,623 2 41 5 331 -93
EACC 1 265 0 0 0 6 -16
SACC 0 0 0 0 0 0 -3
Total 110 2,263,594 444 1,551 196 23,930 163

Northwest Area (PL 5) New fires: 31
New large incidents: 1
Uncontained large fires: 39
Type 1 IMTs committed: 5 Type 2 IMTs committed: 8

Whitmore, Colville Agency, BIA. IMT 2 (NW Team 12). Includes previously reported Hamilton incident. Twenty-seven miles northeast of Bridgeport, WA. Timber. Extreme fire behavior with crowning, flanking and spotting. Community of Nespelem and infrastructure threatened. Evacuations, area and road closures in effect. Precipitation occurred over the fire area yesterday.
Devil’s Knob Complex (6 fires), Umpqua NF, USFS. IMT 2 (NW Team 8). Twenty miles northeast of Azalea,
OR. Timber and medium slash. Active fire behavior with uphill runs, flanking and short-range spotting. Numerous structures threatened. Evacuations, area, road and trail closures in effect. Skyline Ridge Complex (3 fires), South Unit, ODF. IMT 1 (ODF Team 1). Five miles southeast of Days Creek, OR. Timber and light slash. Active fire behavior with group torching, running and spotting. Residences and infrastructure threatened. Evacuations in effect.
Bootleg, Fremont-Winema NF, USFS. IMT 1 (PNW Team 2). IMT is also managing the Yainax and Walrus incidents. Twenty-three miles east of Chiloquin, OR. Timber and brush. Moderate fire behavior with torching.
Structures threatened. Evacuations, area and road closures in effect.
Yainax, Klamath Unit, ODF. Ten miles northeast of Bonanza, OR. Timber and brush. Moderate fire behavior with group torching, single tree torching and short-range spotting. Structures threatened. Evacuations and road closures in effect. Walrus, Klamath Unit, ODF. Eleven miles north of Bonanza, OR. Timber and brush. Moderate fire behavior with short crown runs and torching. Structures threatened. Evacuations and road closures in effect.

Lick Creek, Umatilla NF, USFS. IMT 2 (RM Team Black). IMT is also managing the Green Ridge incident.
Fifteen miles southeast of Pomeroy, WA. Timber, closed timber litter and medium slash. Moderate fire behavior with single tree torching, creeping and smoldering. Numerous structures threatened. Evacuations, area, road and trail closures in effect. Green Ridge, Umatilla NF, USFS. Thirty miles east of Walla Walla, WA. Closed timber litter, timber and medium slash. Active fire behavior with running, flanking and spotting. Several communities threatened. Evacuations, area, road and trail closures in effect. Rough Patch Complex (3 fires), Umpqua NF, USFS. IMT 2 (NW Team 13). IMT is also managing the Jack incident. Eighteen miles southwest of Oakridge, OR. Closed timber litter and timber. Active fire behavior with single tree torching, flanking and uphill runs. Area, road and trail closures in effect.
Jack, Umpqua NF, USFS. Thirty-one miles east of Roseburg, OR. Timber and closed timber litter. Active fire behavior with backing, single tree torching and flanking. Numerous structures threatened. Area, road and trail closures in effect. Summit Trail, Colville Agency, BIA. IMT 2 (NW Team 7). IMT is also managing the Chuweah Creek incident.
Seventeen miles west of Inchelium, WA. Timber and light slash. Active fire behavior with group torching, flanking and backing. Numerous structures and communication infrastructure threatened. Area and road closures in effect. Chuweah Creek, Colville Agency, BIA. Four miles north of Nespelem, WA. Brush, timber and light slash. Minimal fire behavior with smoldering. Area and road closures in effect.
Cub Creek 2, Southeast Region, DNR. IMT 1 (SW Team 2). Five miles north of Winthrop, WA. Short grass,
closed timber litter and timber. Minimal fire behavior with flanking, creeping and smoldering. Numerous residences and communication infrastructure threatened. Area, road and trail closures in effect. Precipitation occurred over the fire area yesterday.
Middle Fork Complex (3 fires), Willamette NF, USFS. IMT 1 (PNW Team 3). Nine miles northeast of Oakridge, OR. Closed timber litter and timber. Moderate fire behavior with backing, torching and flanking. Residences
threatened. Area, road and trail closures in effect. Cedar Creek, Okanogan-Wenatchee NF, USFS. IMT 1 (GB Team 1). IMT is also managing the Delancy
incident. Fifteen miles northwest of Winthrop, WA. Timber, brush and short grass. Moderate fire behavior with creeping and smoldering. Several communities threatened. Evacuations, area, road and trail closures in effect.
Delancy, Okanogan-Wenatchee NF, USFS. Fifteen miles northwest of Winthrop, WA. Timber, short grass and closed timber litter. Minimal fire behavior with creeping. Area, road and trail closures in effect. Bull Complex, Mt. Hood NF, USFS. Twenty-five miles northeast of Mill City, OR. Timber. Moderate fire behavior with backing, creeping and single tree torching. Area, road and trail closures in effect. Schneider Springs, Okanogan-Wenatchee NF, USFS. IMT 2 (EA Silver Team) mobilizing. IMT is also managing the Windy Pass incident. Twenty-one miles northwest of Tieton, WA. Short grass, timber and brush. Moderate fire behavior with torching, short-range spotting and uphill runs. Area, road and trail closures in effect. Windy Pass, Okanogan-Wenatchee NF, USFS. Eleven miles southwest of Cle Elum, WA. Timber and short grass. Moderate fire behavior with creeping and backing. Structures threatened. Area, road and trail closures in effect. Reduction in acreage due to more accurate mapping. Walker Creek, Northeast Region, DNR. IMT 2 (NR Team 6). Four miles northwest of Wauconda, WA. Timber and short grass. Active fire behavior with torching, short crown runs and spotting. Community of Bonaparte threatened. Evacuations in effect.

* Bulldog Mountain, Colville NF, USFS. Sixteen miles northwest of Kettle Falls, WA. Heavy slash and timber.
Active fire behavior with torching, flanking and short-range spotting. Residences threatened. Area, road and trail closures in effect. Mud Springs, Vale District, BLM. Twenty-eight miles northwest of Harper, OR. Brush, short grass and timber. Minimal fire behavior with smoldering.
Elbow Creek, Umatilla NF, USFS. Twenty-six miles northeast of Elgin, OR. Timber and short grass. Minimal fire behavior with smoldering. Communication infrastructure threatened. Area, road and trail closures in effect.
Nine Mine, Northeast Region, Washington DNR. Twelve miles northwest of Barstow, WA. Timber, brush and tall grass. Moderate fire behavior with single tree torching and backing. Structures threatened.
Bruler, Willamette NF, USFS. Nine miles south of Detroit, OR. Closed timber litter and timber. Moderate fire behavior with backing, smoldering and creeping. Area, road and trail closures in effect.
Cottonwood Creek, John Day Unit, ODF. Five miles southeast of Fossil, OR. Timber and tall grass. Minimal fire behavior with smoldering.
Black Butte, Malheur NF, USFS. IMT 2 (NW Team 9). Thirty-six miles southeast of John Day, OR. Brush and tall grass. Active fire behavior with isolated torching, flanking and wind-driven runs. Residences threatened. Area, road and trail closures in effect.
Spruce Canyon, Northeast Region, DNR. Fifteen miles east of Colville, WA. Heavy slash and timber. No new information.

Incident Name Unit Size % Ctn/
Comp Est Personnel Resources Strc
Lost
$$ CTD Origin
Own Acres Chge Total Chge Crw Eng Heli
Whitmore WA-COA 53,314 38,314 0 Ctn 8/31 218 49 4 14 0 8 600K BIA
Devils Knob
Complex OR-UPF 2,401 901 0 Ctn 9/30 500 1500 14 30 0 1 2M FS
Skyline Ridge Complex OR-732S 2,418 359 9 Ctn 8/24 964 40 33 29 9 0 3.2M ST
Bootleg OR-FWF 413,765 0 96 Ctn 10/1 1,125 1 25 56 7 408 91.2M FS
Yainax OR-981S 89 1 0 Ctn 8/13 0 0 0 0 0 0 174K ST
Walrus OR-981S 85 0 0 Ctn 8/13 0 0 0 0 0 0 111K ST
Lick Creek OR-UMF 80,421 0 90 Ctn 9/1 58 0 0 8 0 10 17M FS
Green Ridge OR-UMF 15,390 1,337 15 Ctn 9/6 373 -11 7 25 5 0 22.5M FS
Rough Patch
Complex OR-UPF 2,194 1,389 3 Ctn 10/31 255 0 3 13 6 0 1.2M FS
Jack OR-UPF 23,788 144 54 Ctn 10/31 359 1 10 17 5 1 26.2M FS
Summit Trail WA-COA 28,250 319 23 Ctn 8/31 563 -116 10 33 5 0 19.2M BIA
Chuweah Creek WA-COA 36,752 0 95 Ctn 8/14 95 -1 2 0 0 14 8.8M BIA
Cub Creek 2 WA-SES 62,368 977 24 Ctn 10/1 589 -44 11 26 7 3 18.6M ST
Middle Fork
Complex OR-WIF 3,703 395 10 Ctn 9/15 591 -182 15 17 6 0 4M FS
Cedar Creek WA-OWF 52,859 0 32 Ctn 10/31 758 -1 13 60 9 2 24.4M FS
Delancy WA-OWF 223 0 0 Ctn 10/31 0 0 0 0 0 0 122K FS
Bull Complex OR-MHF 450 70 0 Ctn 10/30 101 7 2 6 0 0 218K FS
Schneider Springs WA-OWF 5,000 0 0 Ctn 10/1 24 2 0 3 0 0 40K FS

Windy Pass WA-OWF 89 -30 16 Ctn 8/19 103 17 3 5 0 0 137K FS
Incident Name Unit Size % Ctn/
Comp Est Personnel Resources Strc
Lost
$$ CTD Origin
Own Acres Chge Total Chge Crw Eng Heli
Walker Creek WA-NES 238 118 10 Ctn 8/20 165 8 2 21 0 0 1.6M ST
* Bulldog Mountain WA-COF 1,800 0 --- Ctn 8/20 58 --- 1 4 0 0 60K FS
Mud Springs OR-VAD 517 0 95 Ctn 8/9 21 0 0 5 0 0 55K BLM
Elbow Creek OR-UMF 22,960 0 95 Ctn 8/15 301 20 10 15 2 6 20.4M FS
Nine Mine WA-NES 300 0 5 Ctn 8/15 136 73 6 3 2 0 160K ST
Bruler OR-WIF 195 0 75 Ctn 9/30 106 -1 2 3 1 0 6.3M FS
Cottonwood
Creek OR-952S 159 0 95 Ctn UNK 0 -8 0 0 0 0 650K ST
Black Butte OR-MAF 8,612 4,612 0 Ctn 10/1 348 289 10 11 1 0 1.5M FS
Spruce Canyon WA-NES 130 --- 95 Ctn UNK 26 --- 1 1 0 0 3.6M ST
MM 206 OR-VAD 694 0 100 Ctn --- 68 -21 2 7 0 0 400K PRI
Large Fires Being Managed with a Strategy Other Than Full Suppression Without a Type 1 or 2 IMT Assigned
Bear Creek WA-NCP 998 --- 5 Comp 10/1 12 --- 1 0 1 0 30K NPS
NCP – North Cascades NP, NPS
Northern California Area (PL 5)
New fires: 16
New large incidents: 0
Uncontained large fires: 11
NIMOs committed: 1
Type 1 IMTs committed: 3
Type 2 IMTs committed: 4
Dixie, Butte Unit, Cal Fire. Transfer of command from IMT 1 (Cal Fire Team 1) to IMT 1 (Cal Fire Team 3)
occurred yesterday. Unified command between IMT 1 (Cal Fire Team 3) and IMT 1 (CA Team 4). Fifteen miles northeast of Paradise, CA. Timber and brush. Active fire behavior with running, flanking and isolated torching. Several communities and infrastructure threatened. Evacuations, area, road and trail closures in effect.
Monument, Shasta-Trinity NF, USFS. IMT 1 (CA Team 5). One mile southwest of Del Loma, CA. Timber and brush. Active fire behavior with uphill runs, short-range spotting and group torching. Several communities and infrastructure threatened. Evacuations, road and trail closures in effect. McFarland, Shasta-Trinity NF, USFS. IMT 2 (CA Team 11). Four miles southeast of Wildwood, CA. Timber, chaparral and closed timber litter. Active fire behavior with group torching, uphill runs and flanking. Several communities and infrastructure threatened. Evacuations, area and road closures in effect. Antelope, Klamath NF, USFS. IMT 2 (SW Team 4). Twenty miles northeast of McCloud, CA. Timber and brush. Active fire behavior with uphill runs, group torching and spotting. Several communities threatened. Evacuations, area and road closures in effect.
River Complex (3 fires), Klamath NF, USFS. IMT 2 (CA Team 14). NIMO (Team 3) mobilizing. Nine miles southwest of Etna, CA. Timber and brush. Moderate fire behavior with backing, creeping and smoldering. Several communities threatened. Evacuations and road closures in effect. McCash, Six Rivers NF, USFS. IMT 2 (SW Team 3). Fourteen miles northeast of Somes Bar, CA. Timber, brush

and tall grass. Moderate fire behavior with flanking, isolated torching and backing. Communities of Ti-Bar and Patterson, and communication infrastructure threatened. Road closures in effect.

River, Nevada-Yuba-Placer Unit, Cal Fire. Two miles southwest of Colfax, CA. Timber, brush and heavy slash.
Moderate fire behavior with smoldering. Numerous structures threatened. Area, road and trail closures in effect. Lava, Shasta-Trinity NF, USFS. Four miles east of Weed, CA. Timber and brush. Minimal fire behavior with
creeping and smoldering. Area and road closures in effect.
Beckwourth Complex, Plumas NF, USFS. Three miles northeast of Beckwourth, CA. Timber, brush and closed timber litter. Minimal fire behavior. Area, road and trail closures in effect.

Incident Name Unit Size % Ctn/
Comp Est Personnel Resources Strc
Lost
$$ CTD Origin
Own Acres Chge Total Chge Crw Eng Heli
Dixie CA-BTU 447,723 12,910 21 Ctn 8/20 5,137 18 80 398 30 268 178.9M ST
Monument CA-SHF 44,317 8,302 0 Ctn 9/1 628 64 4 57 5 2 5.2M FS
McFarland CA-SHF 30,093 2,945 21 Ctn 8/21 695 -48 18 34 6 0 8M FS
Antelope CA-KNF 41,410 2,809 20 Ctn 9/30 452 121 10 30 5 0 4M FS
River Complex CA-KNF 23,121 2,311 3 Ctn 10/1 437 25 7 23 3 0 3M FS
McCash CA-SRF 1,270 76 1 Ctn 9/29 133 -42 4 3 2 0 750K FS
River CA-NEU 2,600 0 56 Ctn 8/13 523 -221 11 62 0 88 3M ST
Lava CA-SHF 26,409 0 82 Ctn 8/14 10 -13 0 2 0 23 35.2M FS
Beckwourth
Complex CA-PNF 105,670 0 98 Ctn UNK 49 0 1 5 0 148 54.2M FS

Northern Rockies Area (PL 5) New fires: 13
New large incidents: 1
Uncontained large fires: 36
NIMOs committed: 1
Type 1 IMTs committed: 4
Type 2 IMTs committed: 5
West Lolo Complex, Lolo NF, USFS. Six miles north of St. Regis, MT. IMT 1 (NR Team 1). IMT is also managing the Granite Pass Complex. Timber, closed timber litter and brush. Moderate fire behavior with creeping, backing and single tree torching. Numerous residences threatened. Evacuations, area, road and trail closures in effect. Granite Pass Complex (4 fires), Lolo NF, USFS. Thirty miles southwest of Missoula, MT. Timber, brush and closed timber litter. Minimal fire behavior with backing and creeping. Structures and communication infrastructure threatened. Area, road and trail closures in effect. Harris Mountain, Cascade County. IMT 2 (NR Team 7). Seven miles southeast of Cascade, MT. Closed timber litter and timber. Active fire behavior with group torching, uphill runs and flanking. Structures threatened. Evacuations in effect.
Burnt Peak, Kootenai NF, USFS. IMT 2 (GB Team 6). IMT is also managing the South Yaak incident. Nine miles southwest of Troy, MT. Timber and light slash. Moderate fire behavior with torching, flanking and backing. Structures threatened. Road and trail closures in effect.
South Yaak, Kootenai NF, USFS. Four miles northwest of Troy, MT. Timber and light slash. Moderate fire behavior with backing, flanking and group torching. Numerous structures threatened. Evacuations, area, road and trail closures in effect.

Boulder 2700, Flathead Agency, BIA. IMT 2 (NR Team 4). Three miles northeast of Finley Point, MT. Timber
and brush. Active fire behavior with flanking, backing and creeping. Numerous residences and communication infrastructure threatened. Evacuations, area, road and trail closures in effect. Divide Complex (2 fires), Helena-Lewis and Clark NF, USFS. IMT 1 (SA Red Team). IMT is also managing the American Fork and Woods Creek incidents. Seventeen miles west of Neihart, MT. Short grass and timber. Active fire behavior with flanking, backing and single tree torching. Communities of Neihart and Monarch threatened. Evacuations, area, road and trail closures in effect. American Fork, Helena-Lewis and Clark NF, USFS. Twenty-four miles southwest of Harlowton, MT. Short grass and timber. Moderate fire behavior with flanking, backing and single tree torching. Evacuations, area, road and trail closures in effect. Woods Creek, Helena-Lewis and Clark NF, USFS. Sixteen miles northeast of Townsend, MT. Short grass and timber. Active fire behavior with flanking, running and group torching. Residences threatened. Evacuations, area, road and trail closures in effect.
* Needle, Helena-Lewis and Clark NF, USFS. Nineteen miles northeast of Townsend, MT. Short grass and
timber. Active fire behavior with flanking, backing and single tree torching. Area and road closures in effect. Alder Creek, Beaverhead-Deerlodge NF, USFS. IMT 1 (SA Blue Team). IMT is also managing the Trail Creek,
Christensen and Black Mountain incidents. Twenty miles northwest of Wisdom, MT. Timber and brush. Moderate fire behavior with flanking, torching and smoldering. Numerous structures threatened. Area, road and trail closures in effect.
Trail Creek, Beaverhead-Deerlodge NF, USFS. Twenty miles west of Wisdom, MT. Timber and brush. Moderate fire behavior with flanking, torching and smoldering. Community of Gibbonsville and communication
infrastructure threatened. Area, road and trail closures in effect. Christensen, Beaverhead-Deerlodge NF, USFS. Ten miles northeast of Wisdom, MT. Timber and brush.
Moderate fire behavior with flanking, torching and smoldering. Structures threatened. Area, road and trail
closures in effect.
Black Mountain, Beaverhead-Deerlodge NF, USFS. Twenty miles east of Salmon, ID. Timber, heavy slash and brush. Minimal fire behavior with smoldering. Area, road and trail closures in effect. Character Complex (2 fires), Idaho Panhandle NF, USFS. IMT 1 (NR Team 2). IMT is also managing the
Stateline Complex incident. Three miles north of Kellogg, ID. Timber and brush. Active fire behavior with single
tree torching, flanking and creeping. Numerous structures threatened. Area, road and trail closures in effect.
Stateline Complex (6 fires), Idaho Panhandle NF, USFS. Twenty-two miles southwest of Superior, MT. Closed
timber litter, timber and light slash. Active fire behavior with single tree torching, flanking and creeping. Area,
road and trail closures in effect.
Storm Theatre Complex (12 fires), Nez Perce-Clearwater NF, USFS. NIMO (Team 1). Thirty-five miles southwest of Missoula, MT. Brush, timber and closed timber litter. Minimal fire behavior with backing, flanking and creeping. Area, road and trail closures in effect. Precipitation occurred over the fire area yesterday. Reduction in acreage due to more accurate mapping. Dixie, Nez Perce-Clearwater NF, USFS. IMT 2 (NR Team 5). IMT is also managing the Jumbo incident. Two miles north of Dixie, ID. Timber. Minimal fire behavior with creeping and smoldering. Several communities threatened. Evacuations, area, road and trail closures in effect.
Jumbo, Nez Perce-Clearwater NF, USFS. Eight miles west of Dixie, ID. Timber and brush. Minimal fire behavior

with creeping and smoldering. Area, road and trail closures in effect.

Hay Creek, Flathead NF, USFS. IMT 2 (CA Team 13). Four miles west of Polebridge, MT. Timber. Moderate
fire behavior with uphill runs, flanking and backing. Community of Polebridge threatened. Area, road and trail closures in effect. Cougar Rock Complex (4 fires), Clearwater Potlach Timber Protective Association, IDL. Seventeen miles
northeast of Elk River, ID. Light slash and timber. Active fire behavior with group torching and flanking. Area and
road closures in effect.
Leland Complex (2 fires), Ponderosa Area Office, IDL. Five miles southwest of Deary, ID. Timber, closed
timber litter and brush. Minimal fire behavior with smoldering and creeping. Communication infrastructure threatened. Road and trail closures in effect. Sharp Tail, Charles M. Russell NWR, FWS. Forty miles northeast of Roy, MT. Timber, short grass and brush. Minimal fire behavior with smoldering. Area closures in effect. Taylor, Fergus County. Thirteen miles southwest of Winifred, MT. Short grass, timber and brush. Minimal fire behavior. Reduction in acreage due to more accurate mapping.
Whitetail Creek, Northwestern Land Office, DNR. Nine miles northeast of Finley Point, MT. Timber and medium slash. Moderate fire behavior. Area and road closures in effect.
Robertson Draw, Custer Gallatin NF, USFS. Seven miles south of Red Lodge, MT. Short grass, brush and timber. Minimal fire behavior with smoldering. Structures threatened. Area, road and trail closures in effect.
Precipitation occurred over the fire area yesterday.
Crooked Creek, Billings Field Office, BLM. Twenty-five miles east of Bridger, MT. Short grass, brush and
timber. Minimal fire behavior with smoldering. Area, road and trail closures in effect. Snake River Complex, Craig Mountain Supervisory Area, IDL. Twenty miles south of Lewiston, ID. Short grass
and timber. Minimal fire behavior with creeping and smoldering. Numerous residences threatened. Area, road and trail closures in effect. Precipitation occurred over the fire area yesterday.
Goat, Beaverhead-Deerlodge NF, USFS. Eleven miles northeast of Philipsburg, MT. Timber and brush. Minimal fire behavior with creeping and smoldering. Structures threatened. Area closures in effect. Bradshaw, Powder River County. Thirty-nine miles southeast of Ashland, MT. Short grass and timber. Minimal fire behavior with smoldering. Structures threatened.

Incident Name Unit Size % Ctn/ Comp Est Personnel Resources Strc Lost $$ CTD Origin Own Acres Chge Total Chge Crw Eng Heli
West Lolo
Complex MT-LNF 21,414 2,314 15 Ctn 10/31 420 73 5 19 4 0 16M FS
Granite Pass
Complex MT-LNF 5,739 0 13 Ctn 9/15 197 -2 3 11 3 0 7.6M FS
Harris Mountain MT-LG02 31,546 86 40 Ctn 10/1 381 83 11 9 10 6 6.4M CNTY
Burnt Peak MT-KNF 3,495 0 46 Ctn 9/30 124 -2 0 3 2 0 11.4M FS
South Yaak MT-KNF 10,153 0 15 Ctn 9/30 218 -2 3 19 1 0 3.7M FS
Boulder 2700 MT-FHA 1,922 0 16 Ctn 8/15 277 -23 3 19 3 31 3.5M BIA
Divide Complex MT-HLF 9,824 0 45 Comp 10/29 287 -27 0 19 1 0 12.6M FS
American Fork MT-HLF 19,028 1,491 10 Comp 10/15 87 45 2 11 0 0 4.6M FS
Woods Creek MT-HLF 31,069 5,324 2 Comp 10/31 302 36 3 42 1 1 5.5M FS
* Needle MT-HLF 2,852 --- 0 Comp 10/31 84 --- 4 0 0 0 35K FS

Incident Name Unit Size % Ctn/
Comp Est Personnel Resources Strc
Lost
$$ CTD Origin
Own Acres Chge Total Chge Crw Eng Heli
Alder Creek MT-BDF 11,540 73 10 Ctn 11/1 362 -18 3 21 6 0 11.9M FS
Trail Creek MT-BDF 35,897 16 23 Ctn 11/1 137 0 2 18 0 0 7.4M FS
Christensen MT-BDF 8,575 65 0 Ctn 11/1 18 0 0 4 0 1 234K FS
Black Mountain MT-BDF 1,041 0 32 Ctn 10/31 51 -1 0 6 1 0 1.8M FS
Character
Complex ID-IPF 7,800 0 30 Ctn 11/1 294 0 4 17 0 0 15.2M FS
Stateline Complex ID-IPF 10,874 0 0 Ctn 10/31 254 24 1 13 3 0 10.5M FS
Storm Theatre Complex ID-NCF 21,769 -3 0 Comp 10/15 113 0 0 10 0 0 3.8M FS
Dixie ID-NCF 43,204 36 59 Comp 10/30 244 -8 2 13 2 0 21.1M FS
Jumbo ID-NCF 2,680 33 45 Comp 10/30 0 -2 0 0 0 0 110K FS
Hay Creek MT-FNF 2,894 155 23 Ctn 9/30 216 -3 1 15 2 0 5.5M FS
Cougar Rock
Complex ID-CTS 8,079 0 42 Ctn 9/15 432 0 11 19 4 0 14M ST
Leland Complex ID-PDS 3,514 0 88 Ctn 8/8 112 -28 3 6 0 0 11.6M ST
Sharp Tail MT-CMR 509 0 60 Ctn 8/9 36 0 0 8 1 0 100K FWS
Taylor MT-LG08 22,909 -7 90 Ctn 8/9 126 -57 1 16 1 9 1.5M CNTY
Whitetail Creek MT-NWS 360 2 13 Ctn 10/1 103 20 3 4 0 0 323K ST
Robertson Draw MT-CGF 29,885 0 90 Ctn 10/1 13 0 0 2 0 30 15M FS
Crooked Creek MT-BID 4,141 0 85 Ctn 8/30 10 0 0 0 1 1 5.5M BLM
Snake River Complex ID-CMS 109,444 0 90 Ctn 8/15 23 0 0 3 0 3 9.2M ST
Goat MT-BDF 212 0 50 Ctn 10/1 31 -6 1 2 0 0 924K FS
Bradshaw MT-LG09 833 0 75 Ctn 8/9 27 -24 0 6 0 0 400K CNTY
Large Fires Being Managed with a Strategy Other Than Full Suppression Without a Type 1 or 2 IMT Assigned
Trestle Creek Complex ID-IPF 3,586 0 0 Comp 10/15 95 31 2 4 0 0 3.2M FS
Crooks MT-FHA 1,000 0 0 Comp 8/30 115 18 3 9 3 0 650K BIA
Goose MT-BDF 7,522 0 80 Comp 10/13 70 0 2 1 1 1 7.7M FS
Swanson Creek ID-NCF 542 7 0 Comp 10/10 47 0 0 2 0 0 125K FS
Lynx ID-NCF 4,834 34 0 Comp 10/30 2 2 0 0 0 0 176K FS
Porphyry ID-NCF 150 --- 0 Comp 10/15 0 --- 0 0 0 0 NR FS
Greenside
Butte ID-NCF 725 --- 0 Comp 10/31 0 --- 0 0 0 0 10K FS
Larkins
Complex ID-IPF 3,357 --- 0 Comp 11/1 15 --- 0 0 0 0 150K FS
Army Mule ID-NCF 1,720 --- 0 Comp 10/15 0 --- 0 0 0 0 2K FS
Dry Cabin MT-LNF 3,060 --- 0 Comp 10/10 15 --- 0 0 0 0 74K FS

Great Basin (PL 3)
New fires: 10
New large incidents: 0
Uncontained large fires: 1
Type 2 IMTs committed: 1
Mud Lick, Salmon-Challis NF, USFS. IMT 2 (GB Team 7). Twenty-three miles west of Salmon, ID. Timber and
short grass. Minimal fire behavior with creeping and smoldering. Area, road and trail closures in effect.
Shale Creek, Bridger-Teton NF, USFS. Twenty miles northeast of Cokeville, WY. Timber, light slash and brush.
No new information.

Incident Name Unit Size % Ctn/ Comp Est Personnel Resources Strc Lost $$ CTD Origin Own Acres Chge Total Chge Crw Eng Heli
Mud Lick ID-SCF 20,643 0 48 Comp 9/19 343 0 4 15 5 0 19.3M FS
Shale Creek WY-BTF 189 --- 79 Ctn UNK 18 --- 0 0 1 0 1.8M FS
Bruneau ID-TFD 2,196 0 100 Ctn --- 20 --- 0 4 0 0 39K BLM
Large Fires Being Managed with a Strategy Other Than Full Suppression Without a Type 1 or 2 IMT Assigned
Tamarack NV-HTF 68,696 0 80 Comp 8/31 407 -27 10 9 4 25 28.5M FS
Vinegar ID-PAF 2,462 --- 0 Comp 10/1 5 --- 0 0 0 0 207K FS
Rush Creek ID-PAF 3,181 --- 0 Comp 10/1 7 --- 0 0 1 0 207K FS
Club ID-PAF 395 --- 0 Comp 10/1 0 --- 0 0 0 0 207K FS
Tango ID-SCF 103 --- 0 Comp 10/1 0 --- 0 0 0 0 10K FS
Morgan Canyon UT-UWF 509 --- 90 Comp 8/15 1 --- 0 0 0 0 1.8M FS
TFD – Twins Falls District, BLM HTF – Humboldt-Toiyabe NF, USFS PAF – Payette NF, USFS
UWF – Uinta-Wasatch-Cache NF, USFS

Rocky Mountain Area (PL 2)
New fires: 26
New large incidents: 0
Uncontained large fires: 4
Crater Ridge, Bighorn NF, USFS. Thirty-one miles west of Sheridan, WY. Timber, heavy slash and short grass. Moderate fire behavior with creeping, smoldering and isolated torching. Area, road and trail closures in effect.
Hackberry CA, Nebraska Forest Service. Eighteen miles southwest of Bridgeport, NE. Timber. Extreme fire behavior. Structures threatened.
Morgan Creek, Medicine Bow-Routt NF, Thunder Basin National Grassland, USFS. Fifteen miles north of Steamboat Springs, CO. Timber and brush. Minimal fire behavior with smoldering and creeping. Structures threatened. Area, road and trail closures in effect.
Calico, Pine Ridge Agency, BIA. Five miles northwest of Pine Ridge, SD. Short grass and timber. Moderate fire behavior. Community of Calico threatened.

Incident Name Unit Size % Ctn/
Comp Est Personnel Resources Strc
Lost
$$ CTD Origin
Own Acres Chge Total Chge Crw Eng Heli
Crater Ridge WY-BHF 1,258 353 20 Ctn 8/31 112 -31 2 7 2 0 6.4M FS

Incident Name Unit Size % Ctn/
Comp Est Personnel Resources Strc
Lost
$$ CTD Origin
Own Acres Chge Total Chge Crw Eng Heli
Hackberry CA NE-NES 3,500 2,000 5 Ctn 8/12 69 0 0 23 0 0 5K ST
Morgan Creek WY-MRF 7,505 0 24 Ctn 9/1 120 0 0 4 3 0 10.7M FS
Calico SD-PRA 401 0 75 Ctn 8/10 22 0 0 5 0 0 400K BIA
Large Fires Being Managed with a Strategy Other Than Full Suppression Without a Type 1 or 2 IMT Assigned
Muddy Slide WY-MRF 4,093 --- 70 Comp 8/31 14 --- 0 1 0 18 13M FS
Sylvan CO-WRF 3,792 --- 75 Comp UNK 3 --- 0 1 0 0 7.1M FS
WRF – White River NF, USFS
Eastern Area (PL 3)
New fires: 2
New large incidents: 0
Uncontained large fires: 1
Fourtown Lake, Superior NF, USFS. Thirteen miles northeast of Ely, MN. Timber. Minimal fire behavior with
creeping and smoldering. Area and trail closures in effect.

Incident Name Unit Size % Ctn/ Comp Est Personnel Resources Strc Lost $$ CTD Origin Own Acres Chge Total Chge Crw Eng Heli
Fourtown Lake MN-SUF 265 0 90 Ctn UNK 6 -16 0 0 0 0 355K FS

Southern California Area (PL 3)
New fires: 26
New large incidents: 0
Uncontained large fires: 0

Incident Name Unit Size % Ctn/ Comp Est Personnel Resources Strc Lost $$ CTD Origin Own Acres Chge Total Chge Crw Eng Heli
Large Fires Being Managed with a Strategy Other Than Full Suppression Without a Type 1 or 2 IMT Assigned
Tilttill CA-YNP 1,300 600 15 Comp 8/24 61 7 2 0 0 0 250K NPS
Lukens CA-YNP 510 --- 75 Comp 8/15 0 --- 0 0 0 0 451K NPS
YNP – Yosemite NP, NPS
Southwest Area (PL 2)
New fires: 4
New large incidents: 1
Uncontained large fires: 1
* Amargo, Jicarilla Agency, BIA. One mile west of Dulce, NM. Timber, chaparral and brush. Active fire behavior
with short crown runs, wind-driven runs and torching. Structures threatened. Road and area closures in effect.

Incident Name Unit Size % Ctn/
Comp Est Personnel Resources Strc
Lost
$$ CTD Origin
Own Acres Chge Total Chge Crw Eng Heli
* Amargo NM-JIA 300 --- 0 Ctn 8/14 17 --- 0 3 0 0 5K BIA

Incident Name Unit Size % Ctn/
Comp Est Personnel Resources Strc
Lost
$$ CTD Origin
Own Acres Chge Total Chge Crw Eng Heli
Large Fires Being Managed with a Strategy Other Than Full Suppression Without a Type 1 or 2 IMT Assigned
Paradise Park AZ-ASF 262 --- 0 Comp 8/13 0 --- 0 0 0 0 2K FS
ASF – Apache-Sitgreaves NF, USFS
Alaska Area (PL 2)
New fires: 0
New large incidents: 1
Uncontained large fires: 0
* Nation River, Upper Yukon Zone, BLM. Started on Native Corporation land 39 miles northeast of Eagle, AK.
Timber and short grass. Moderate fire behavior with smoldering, creeping and backing. Last narrative report
unless significant activity occurs.

Incident Name Unit Size % Ctn/ Comp Est Personnel Resources Strc Lost $$ CTD Origin Own Acres Chge Total Chge Crw Eng Heli
Large Fires Being Managed with a Strategy Other Than Full Suppression Without a Type 1 or 2 IMT Assigned
* Nation River AK-UYD 1,300 --- 0 Comp 9/1 0 --- 0 0 0 0 NR TRI
Discovery Creek AK-UYD 4,527 0 0 Comp 8/17 30 -3 1 0 1 0 331K FWS
Marten Creek AK-UYD 2,534 0 0 Comp 8/31 51 19 2 0 0 0 792K TRI
Twentyfour Mile AK-UYD 657 --- 0 Comp 9/30 0 --- 0 0 0 0 2K BLM
South Fork AK-UYD 658 --- 0 Comp UNK 0 --- 0 0 0 0 4K BLM
Sischu AK-TAD 16,383 --- 0 Comp UNK 0 --- 0 0 0 0 7K BLM
Cultas Creek AK-UYD 38,202 --- 0 Comp UNK 0 --- 0 0 0 0 822K NPS
Munson Creek AK-FAS 54,050 --- 5 Comp UNK 0 --- 0 0 0 0 1M ST
Crescent Creek AK-UYD 1,374 --- 0 Comp 9/10 0 --- 0 0 0 0 5K NPS
Shellman Creek AK-TAD 1,972 --- 0 Comp UNK 0 --- 0 0 0 0 NR BLM
TAD – Tanana Zone, BLM FAS – Fairbanks Area, Alaska DOF

Fires and Acres Yesterday (by Protection):

Area BIA BLM FWS NPS ST/OT USFS TOTAL
FIRES 0 0 0 0 0 0 0 Alaska Area ACRES 0 3,426 0 0 1,767 0 5,193
FIRES 0 8 0 0 11 12 31 Northwest Area ACRES 0 1 0 0 176 961 1,138
FIRES 0 0 0 0 14 2 16 Northern California Area ACRES 0 0 0 0 2 20,769 20,771
FIRES 1 0 0 0 21 4 26 Southern California Area ACRES 74 0 0 0 3 13 90
FIRES 1 1 0 0 6 5 13 Northern Rockies Area ACRES 80 1 0 0 431 3,457 3,969
FIRES 0 1 0 0 4 5 10 Great Basin Area ACRES 0 0 0 0 1 5 6
FIRES 0 2 0 0 0 2 4 Southwest Area ACRES 299 1 0 0 0 2 302
FIRES 0 4 0 0 11 11 26 Rocky Mountain Area ACRES 0 5 0 0 3,729 4 3,738
FIRES 2 0 0 0 0 0 2
Eastern Area ACRES 4 0 0 0 0 0 4
FIRES 0 0 0 0 2 0 2 Southern Area ACRES 0 0 0 0 0 0 0
TOTAL FIRES: 4 16 0 0 69 41 130
TOTAL ACRES: 457 3,434 0 0 6,109 25,211 35,212

Fires and Acres Year-to-Date (by Protection):

Area BIA BLM FWS NPS ST/OT USFS TOTAL
FIRES 0 113 0 0 227 14 354 Alaska Area
ACRES 0 134,119 0 0 96,888 5 231,013
FIRES 184 261 26 13 1,765 472 2,721 Northwest Area
ACRES 69,787 14,994 13,180 172 144,610 522,671 765,415
FIRES 60 28 4 23 2,336 447 2,898 Northern California Area
ACRES 70 274 332 2 258,987 369,137 628,803
FIRES 17 96 12 59 3,002 415 3,601 Southern California Area
ACRES 1,373 3,526 199 3,235 17,355 9,541 35,230
FIRES 1,140 69 22 5 1,167 654 3,057 Northern Rockies Area
ACRES 76,004 18,465 2,689 51 214,435 233,287 544,932
FIRES 40 638 52 25 687 424 1,866 Great Basin Area
ACRES 3,008 57,393 10 2,191 55,831 45,954 164,388
FIRES 487 187 9 27 336 871 1,917 Southwest Area
ACRES 25,178 83,889 1,528 3,362 33,218 490,706 637,883
FIRES 500 321 6 20 524 274 1,645 Rocky Mountain Area
ACRES 6,377 25,050 1,260 1,116 58,821 25,450 118,074
FIRES 449 0 50 22 6,834 420 7,775 Eastern Area
ACRES 12,380 0 14,336 588 32,545 15,884 75,735
FIRES 377 0 55 39 12,589 373 13,433 Southern Area
ACRES 28,685 0 11,845 8,437 262,825 27,433 339,226
TOTAL FIRES: 3,254 1,713 236 233 29,467 4,364 39,267
TOTAL ACRES: 222,863 337,713 45,379 19,156 1,175,519 1,740,071 3,540,703
Ten Year Average Fires (2011 – 2020 as of today) 36,657
Ten Year Average Acres (2011 – 2020 as of today) 4,321,832
***Changes in some agency YTD acres reflect more accurate mapping or reporting adjustments. ***Additional wildfire information is available through the Geographic Areas at https://gacc.nifc.gov/

Canadian Fires and Hectares

PROVINCES FIRES YESTERDAY HECTARES YESTERDAY FIRES YEAR-TO-DATE
HECTARES YEAR-TO- DATE
BRITISH COLUMBIA 17 24,239 1,447 608,254
YUKON TERRITORY 3 679 111 103,079
ALBERTA 6 4 1,030 54,755
NORTHWEST TERRITORY 3 1,137 134 113,381
SASKATCHEWAN 2 24,446 532 1,028,133
MANITOBA 2 4,584 428 992,214
ONTARIO 4 438 1,069 707,422
QUEBEC 2 0 481 56,712
NEWFOUNDLAND 1 3 63 309
NEW BRUNSWICK 0 0 154 308
NOVA SCOTIA 0 0 110 197
PRINCE EDWARD ISLAND 0 0 1 0
NATIONAL PARKS 1 20,635 49 36,263
TOTALS 41 76,165 5,619 3,701,026
*1 Hectare = 2.47 Acres
Predictive Services Discussion: An upper low will move into the Northern Rockies today with a strong cold front
moving through Wyoming and the northern Great Basin. Windy and dry conditions are forecast ahead of the front
across southeast Oregon, the Great Basin, and Rockies. The strongest winds with elevated to locally critical
conditions are forecast for the northern Great Basin, Wyoming and south-central to southeast Montana. Behind
the front, much cooler temperatures and higher relative humidity are forecast along with showers and embedded
thunderstorms for northern Idaho into western Montana. California is forecast to be dry and warm with locally
strong winds over the southeastern deserts, east side of the Coast Ranges, and Sierra Nevada. Monsoon moisture
will be limited to southeast Arizona and southwest New Mexico with isolated wet thunderstorms forecast. Heavy
rains are forecast along a decaying cold front in the western Great Lakes while a cool, moist southwest flow pattern
continues for Alaska.
http://www.predictiveservices.nifc.gov/outlooks/outlooks.htm

Propane Tank Safety
Miscellaneous Fireline Hazards

Liquefied Propane Gas (LPG) tanks are commonly found in the wildland urban interface and present hazards to firefighters in that environment. LPG tanks may be found around motor homes, travel trailers, grills, camp stoves, lanterns, etc. Directly attacking LPG tank fires is a structural fire task involving hazardous materials and should only be attempted by trained personnel using full structural personal protective equipment and equipped with a volume of water adequate to safely attack the fire.
Boiling Liquid Expanding Vapor Explosions (BLEVE)
• The most recognized hazard with LPG tanks is BLEVE or sudden complete failure of the tank. Some training courses have directed responders to approach the tank from the sides, believing that the force of the explosion will occur on the ends of the tank. However, this is not a guarantee that you will be safe from projectiles or missiles from the explosion as they may travel in all directions up to 2,500 feet away. Leave the area immediately if you smell propane, hear a rising sound from venting safety devices, or see discoloration or deformation of the tank. Move at least 2,500 feet away, and do not go downwind or downslope of the leaking propane. BLEVEs are a major hazard to emergency responders!
Fuel Reduction Around Tanks
• Wildland firefighters may take action to prevent direct flame impingement on LPG tanks by removing wildland fuels in the area. However, be aware that lines from the tank to structures may be above or below ground and may be cut by tools or equipment. Propane gas is heavier than air. It may move along the ground at some
distance and may ignite when in reaches open flame or another ignition source. Use extreme caution when doing fuels reduction around tanks, and flag any lines you encounter.
Other Wildland Fire Considerations

• Do not position engines or other apparatus near LPG tanks or downwind/downslope from tanks.
• Do not deploy fire shelters near LPG tanks or downwind or downslope from tanks.
Cooling Tanks

• In light fuels such as grasses, where any heat exposure to the tank will be very limited, the rapid application of cooling water on the outside of the tank above the liquid level can reduce the likelihood of container failure by lowering the external temperature of the shell of the exposed tank. Water should not be directed at the valve safety devices, due to the potential of icing the valve closed.
• In heavy fuels where long duration heat exposure to the LPG tank is likely, evacuate all personnel and equipment to 2,500 feet away and not downwind or downslope. The National Fire Protection Association (NFPA) says that direct flame impingement protection requires water flow of at least 500 gallons per minute from an unmanned monitor nozzle. This is a situation for properly trained, equipped, and supported structural firefighters.
Resources: Propane Safety, NIOSH, National Propane Gas Association, NFPA

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National Interagency Coordination Center Incident Management Situation Report Monday, August 16, 2021– 0730 MDT National Preparedness Level 5
National Fire Activity:
Initial attack activity: Light (87 fires)
New large incidents: 3
Large fires contained: 1
Uncontained large fires: *** 87
Area Command teams committed: 0
NIMOs committed: 2
Type 1 IMTs committed 12
Type 2 IMTs committed: 19
Nationally, there are 50 fires being managed under a strategy other than full suppression. ***Uncontained large fires include only fires being managed under a full suppression strategy. Link to Geographic Area daily reports.
Link to Understanding the IMSR.
Two MAFFS C-130 airtankers and support personnel each from the 152nd Airlift Wing (Nevada Air National
Guard), two MAFFS unit from the 302nd Airlift Wing (Colorado Air Force Reserve), one MAFFS unit from the
153rd Airlift Wing (Wyoming Air National Guard) and one from the 146th Airlift Wing (California Air National
Guard) have been deployed to McClellan, CA to support wildland fire operations nationally.
One RC-26 aircraft with Distributed Real-Time Infrared (DRTI) capability and support personnel from the 141st Air Refueling Wing (Washington Air National Guard) have been deployed to Fairchild, WA. One RC-26 aircraft
with Distributed Real-Time Infrared (DRTI) capability and support personnel from the 162nd Operations Group (Arizona Air National Guard) have been deployed to Eugene, OR in support of wildland fire operations. Also supporting these aircraft are eight ground controllers from multiple U.S. Air National Guard squadrons.
One Boeing 737 airtanker from New South Wales, Australia is supporting fire suppression efforts in the western United States.

Active Incident Resource Summary
GACC Incidents Cumulative Acres Crews Engines Helicopters Total Personnel Change in Personnel
AICC 2 10,358 2 0 0 49 -20
NWCC 34 944,300 186 496 82 8,947 -24
ONCC 12 971,879 154 803 51 10,518 103
OSCC 1 1,927 0 0 2 27 0
NRCC 38 695,087 71 296 40 4,585 -181
GBCC 11 94,607 29 33 20 1,229 161
SWCC 1 1,296 0 3 0 22 -25
RMCC 5 19,930 4 20 5 243 -16
EACC 3 844 0 11 2 68 5
SACC 0 0 0 0 0 0 0
Total 107 2,740,231 446 1,662 202 25,688 3

Northwest Area (PL 5) New fires: 3
New large incidents: 1
Uncontained large fires: 36
Type 1 IMTs committed: 5 Type 2 IMTs committed: 7

Walker Creek, Northeast Region, DNR. IMT 2 (NR Team 6). IMT is also managing the Chickadee Creek incident. Four miles northwest of Wauconda, WA. Timber and short grass. Active fire behavior with wind-driven runs, long-range spotting and group torching. Several communities and numerous structures threatened.
Evacuations, area, road and trail closures in effect.
Chickadee Creek, Northeast Region, DNR. Sixteen miles northwest of Tonasket, WA. Timber and short grass.
Active fire behavior with flanking, single tree torching and short-range spotting. Fox Complex (2 fires), Fremont-Winema NF, USFS. IMT 1 (ODF Team 3). Fourteen miles west of Lakeview,
OR. Timber, short grass and brush. Active fire behavior with torching, spotting and flanking. Numerous residences and infrastructure threatened. Evacuations and road closures in effect.
Schneider Springs, Okanogan-Wenatchee NF, USFS. IMT 2 (EA Silver Team). IMT is also managing the Windy Pass incident. Twenty-one miles northwest of Tieton, WA. Short grass, timber and brush. Active fire behavior with uphill runs, running and torching. Evacuations, area, road and trail closures in effect. Windy Pass, Okanogan-Wenatchee NF, USFS. Eleven miles southwest of Cle Elum, WA. Timber and short grass. Minimal fire behavior with creeping and smoldering. Structures threatened. Area, road and trail closures in effect.
Middle Fork Complex (3 fires), Willamette NF, USFS. IMT 1 (PNW Team 3). IMT is also managing the Knoll incident. Nine miles northeast of Oakridge, OR. Closed timber litter and timber. Moderate fire behavior with flanking, backing and torching. Evacuations, area, road and trail closures in effect.

Knoll, Willamette NF, USFS. Seven miles northeast of McKenzie Bridge, OR. Timber, closed timber litter and
light slash. Minimal fire behavior with flanking, backing and torching. Structures and infrastructure threatened. Evacuations, area, road and trail closures in effect. Skyline Ridge Complex (3 fires), South Unit, ODF. IMT 1 (ODF Team 1). Five miles southeast of Days Creek, OR. Timber and light slash. Moderate fire behavior with flanking, backing and torching. Numerous residences and infrastructure threatened. Evacuations in effect.
Cub Creek 2, Southeast Region, DNR. IMT 1 (CA Team 2). IMT is also managing the Muckamuck, Cedar
Creek and Delancy incidents. Five miles north of Winthrop, WA. Short grass, closed timber litter and timber. Moderate fire behavior with short crown runs, short-range spotting and group torching. Infrastructure threatened. Area, road and trail closures in effect.
Muckamuck, Colville NF, USFS. Four miles northwest of Conconully, WA. Timber and closed timber litter. Extreme fire behavior with group torching, short crown runs and short-range spotting. Several communities
threatened. Area, road and trail closures in effect. Cedar Creek, Okanogan-Wenatchee NF, USFS. Fifteen miles northwest of Winthrop, WA. Timber, brush and
short grass. Active fire behavior with short crown runs, short-range spotting and group torching. Several communities threatened. Area, road and trail closures in effect. Delancy, Okanogan-Wenatchee NF, USFS. Fifteen miles northwest of Winthrop, WA. Timber, short grass and closed timber litter. Minimal fire behavior. Area, road and trail closures in effect.
Devil’s Knob Complex (5 fires), Umpqua NF, USFS. Transfer of command from IMT 2 (NW Team 8) to IMT 1 (GB Team 2) will occur on 8/18. Twenty miles northeast of Azalea, OR. Timber and medium slash. Active fire behavior with running, torching and spotting. Numerous structures threatened. Area, road and trail closures in effect.
Summit Trail, Colville Agency, BIA. IMT 2 (NW Team 10). IMT is also managing the Upper Lime Creek incident. Seventeen miles west of Inchelium, WA. Timber and light slash. Active fire behavior with short crown runs and torching. Numerous structures and communication infrastructure threatened. Area and road closures in effect.
Upper Lime Creek, Colville Agency, BIA. Six miles northwest of Keller, WA. Timber and light slash. Moderate
fire behavior with backing, creeping and smoldering. Community of Keller threatened. Evacuations, area and road closures in effect.
Rough Patch Complex (4 fires), Umpqua NF, USFS. IMT 1 (GB Team 2). IMT is also managing the Jack incident. Eighteen miles southwest of Oakridge, OR. Closed timber litter and timber. Active fire behavior with uphill runs, torching and creeping. Area, road and trail closures in effect.
Jack, Umpqua NF, USFS. Thirty-one miles east of Roseburg, OR. Timber and closed timber litter. Active fire behavior with single tree torching, flanking and backing. Numerous structures threatened. Area, road and trail closures in effect. Black Butte, Malheur NF, USFS. IMT 2 (NW Team 6). Thirty-six miles southeast of John Day, OR. Timber and light slash. Active fire behavior with group torching and short-range spotting. Structures threatened. Area, road and trail closures in effect.
Green Ridge, Umatilla NF, USFS. Thirty miles east of Walla Walla, WA. IMT 2 (RM Team Black). IMT is also managing the Lick Creek incident. Closed timber litter, timber and medium slash. Moderate fire behavior with
uphill runs, single tree torching and short-range spotting. Several communities threatened. Evacuations, area, road and trail closures in effect.

Lick Creek, Umatilla NF, USFS. Fifteen miles southeast of Pomeroy, WA. Short grass, hardwood litter and
timber. Minimal fire behavior with creeping and smoldering. Structures threatened. Area, road and trail closures in effect. Whitmore, Colville Agency, BIA. IMT 2 (NW Team 12). Twenty-seven miles northeast of Bridgeport, WA. Timber. Minimal fire behavior with smoldering, creeping and isolated torching. Community of Nespelem and infrastructure threatened. Area and road closures in effect.
Bull Complex, Mt. Hood NF, USFS. Twenty-five miles northeast of Mill City, OR. Timber. Active fire behavior
with flanking, uphill runs and spotting. Area, road and trail closures in effect. Bulldog Mountain, Colville NF, USFS. Sixteen miles northwest of Kettle Falls, WA. Heavy slash and timber. Active
fire behavior with torching, flanking and backing. Residences threatened. Area, road and trail closures in effect. * Twentyfive Mile, Okanogan-Wenatchee NF, USFS. Twelve mile northwest of Chelan, WA. Timber, grass and
brush. Extreme fire behavior with long-range spotting, running and flanking. Structures threatened. Evacuations, area, road and trail closures in effect.
Chuweah Creek, Colville Agency, BIA. Four miles north of Nespelem, WA. Brush, timber and light slash. No new information.

Incident Name Unit Size % Ctn/ Comp Est Personnel Resources Strc Lost $$ CTD Origin Own Acres Chge Total Chge Crw Eng Heli
Walker Creek WA-NES 17,691 3,751 0 Ctn 9/10 485 42 10 35 0 6 6.4M ST
Chickadee
Creek WA-NES 798 142 55 Ctn 9/15 143 27 3 9 0 0 1M FS
Fox Complex OR-FWF 6,230 1,908 18 Ctn 8/28 543 128 8 52 12 4 1.2M FS
Schneider
Springs WA-OWF 16,516 1,474 0 Ctn 10/1 440 69 11 21 3 0 5M FS
Windy Pass WA-OWF 82 0 70 Ctn UNK 98 0 3 1 1 0 1.5M FS
Middle Fork
Complex OR-WIF 9,253 313 7 Ctn 10/15 663 -5 13 27 5 0 12.5M FS
Knoll OR-WIF 544 0 50 Ctn 8/25 46 -7 1 5 0 0 280K FS
Skyline Ridge
Complex OR-732S 5,760 489 49 Ctn 8/30 1,190 -35 38 41 10 0 13.9M ST
Cub Creek 2 WA-SES 67,458 0 55 Ctn 10/1 404 10 8 23 7 3 22M ST
Muckamuck WA-COF 1,924 0 5 Ctn 10/15 89 3 2 12 0 0 3.6M FS
Cedar Creek WA-OWF 53,475 0 50 Ctn 10/31 422 0 7 28 7 2 29.5M FS
Delancy WA-OWF 223 0 90 Ctn UNK 0 0 0 0 0 0 122K FS
Devils Knob
Complex OR-UPF 7,766 740 15 Ctn 9/30 700 33 16 47 3 1 11M FS
Summit Trail WA-COA 29,205 408 35 Ctn 10/31 337 -59 3 12 4 0 25.2M BIA
Upper Lime Creek WA-COA 376 0 65 Ctn 9/8 74 -1 2 3 0 0 607K BIA
Rough Patch
Complex OR-UPF 12,280 2,375 3 Ctn 10/31 441 0 9 19 4 0 4.3M FS
Jack OR-UPF 23,647 33 54 Ctn 10/31 131 0 1 12 0 1 32.3M FS
Black Butte OR-MAF 18,325 754 30 Ctn 8/25 533 -79 13 16 4 0 7.6M FS
Green Ridge OR-UMF 34,644 2,346 19 Ctn 10/15 494 -11 7 26 14 0 31.2M FS
Lick Creek OR-UMF 80,421 0 97 Ctn 9/1 28 0 0 4 0 10 16M FS
Whitmore WA-COA 58,276 11 50 Ctn 8/31 317 -55 5 24 1 6 7.8M BIA

Incident Name Unit Size % Ctn/
Comp Est Personnel Resources Strc
Lost
$$
CTD
Origin
Own Acres Chge Total Chge Crw Eng Heli
Bull Complex OR-MHF 3,427 1,562 0 Ctn 10/30 270 34 6 6 1 0 NR FS
Bulldog Mountain WA-COF 2,900 0 5 Ctn 8/20 174 8 3 10 1 0 1.9M FS
* Twentyfive
Mile WA-OWF 2,000 --- 0 Ctn 10/30 0 --- 0 0 0 0 100K FS
Chuweah Creek WA-COA 36,752 --- 98 Ctn UNK 16 --- 1 1 0 14 7.3M BIA
Large Fires Being Managed with a Strategy Other Than Full Suppression Without a Type 1 or 2 IMT Assigned
Nason WA-OWF 103 --- 0 Comp 11/1 12 --- 1 0 0 0 20K FS
Pincer Creek WA-MSF 153 --- 0 Comp 10/1 4 --- 0 1 0 0 50K FS
Bear Creek WA-NCP 857 --- 5 Comp 10/1 12 --- 1 0 1 0 80K NPS
MSF – Mt. Baker-Snoqualmie NF, USFS NCP – North Cascades NP, NPS
Northern California Area (PL 5)

New fires: 14
New large incidents: 1
Uncontained large fires: 10
NIMOs committed: 1
Type 1 IMTs committed: 5 Type 2 IMTs committed: 5
Dixie, Butte Unit, Cal Fire. Unified command between IMT 1 (Cal Fire Team 3) and IMT 1 (CA Team 4). Transfer of command from IMT 1 (CA Team 4) to IMT 1 (CA Team 1) will occur tomorrow. Fifteen miles northeast of Paradise, CA. Timber and brush. Active fire behavior with uphill runs, group torching and short- range spotting. Several communities and infrastructure threatened. Evacuations, area, road and trail closures in effect.
Monument, Shasta-Trinity NF, USFS. Transfer of command from IMT 1 (CA Team 5) to IMT 1 (AK Team 1) will occur on 8/18. One mile southwest of Del Loma, CA. Timber and brush. Active fire behavior with uphill runs, short-range spotting and group torching. Several communities and infrastructure threatened. Evacuations, area, road and trail closures in effect.
McFarland, Shasta-Trinity NF, USFS. IMT 2 (CA Team 10). Four miles southeast of Wildwood, CA. Timber, chaparral and closed timber litter. Active fire behavior with short-range spotting, wind-driven runs and group torching. Several communities and infrastructure threatened. Area, road and trail closures in effect. Antelope, Klamath NF, USFS. IMT 2 (SW Team 4). Twenty miles northeast of McCloud, CA. Timber and brush.
Moderate fire behavior with flanking, torching and spotting. Several communities and numerous structures threatened. Evacuations, area, road and trail closures in effect.
River Complex (3 fires), Klamath NF, USFS. NIMO (Team 3). Transfer of command from IMT 2 (CA Team 14) to IMT 2 (CA Team 15) will occur tomorrow. Nine miles southwest of Etna, CA. Timber and brush. Moderate fire behavior with short-range spotting, backing and creeping. Several communities, numerous structures and infrastructure threatened. Evacuations and road closures in effect. McCash, Six Rivers NF, USFS. IMT 2 (SW Team 3). Fourteen miles northeast of Somes Bar, CA. Timber, brush and tall grass. Active fire behavior with uphill runs, isolated torching and flanking. Several communities and communication infrastructure threatened. Area, road and trail closures in effect.
Lava, Shasta-Trinity NF, USFS. Four miles east of Weed, CA. Timber and brush. Minimal fire behavior with

creeping and smoldering. Area and road closures in effect.

* Caldor, Eldorado NF, USFS. Sixteen miles northeast of Plymouth, CA. Timber and brush. Active fire behavior
with running, torching and short crown runs. Numerous residences threatened. Evacuations in effect.

Incident Name Unit Size % Ctn/
Comp Est Personnel Resources Strc
Lost
$$
CTD
Origin
Own Acres Chge Total Chge Crw Eng Heli
Dixie CA-BTU 570,211 17,622 31 Ctn 8/30 6,546 -4 75 561 20 1,173 266M ST
Monument CA-SHF 85,076 5,076 10 Ctn 9/1 863 16 10 76 6 32 16.5M FS
McFarland CA-SHF 43,708 784 68 Ctn 8/21 662 18 17 35 7 1 18.6M FS
Antelope CA-KNF 53,864 2,382 27 Ctn 9/30 831 51 17 40 2 17 14.7M FS
River Complex CA-KNF 41,031 1,681 10 Ctn 10/1 692 39 13 37 5 0 11.3M FS
McCash CA-SRF 2,387 100 1 Ctn 9/29 366 7 8 8 2 0 3.6M FS
Lava CA-SHF 26,409 0 85 Ctn 9/1 6 0 0 1 0 23 35.3M FS
* Caldor CA-ENF 400 --- 0 Ctn 8/31 285 --- 10 16 0 0 150K FS

Northern Rockies Area (PL 5)
New fires: 7
New large incidents: 0
Uncontained large fires: 32
NIMOs committed: 1
Type 1 IMTs committed: 2
Type 2 IMTs committed: 4
Bedrock, Ponderosa Area Office, IDL. IMT 2 (RM Team Blue). Started on tribal land 25 miles northeast of
Lewiston, ID. Timber and brush. Active fire behavior with running, flanking and backing. Community of Lenore, infrastructure and numerous structures threatened. Evacuations, area and road closures in effect. Richard Spring, Rosebud County. IMT 2 (NR Team 3). Started on private land ten miles southwest of Colstrip, MT. Short grass, brush and timber. Active fire behavior with flanking, backing and isolated torching. Numerous structures, communities and infrastructure threatened. Evacuations, area and road closures in effect.
Lame Deer, Northern Cheyenne Agency, BIA. Five miles northwest of Lame Deer, MT. Timber and short grass. Active fire behavior with flanking, backing and isolated torching. Community of Lame Deer and numerous residences threatened. Evacuations, area and road closures in effect. Character Complex (2 fires), Idaho Panhandle NF, USFS. Three miles north of Kellogg, ID. Timber and brush.
Active fire behavior with group torching, flanking and backing. Numerous structures threatened. Area, road and
trail closures in effect. Reduction in acreage due to more accurate mapping.
West Lolo Complex, Lolo NF, USFS. IMT 2 (SA Gold Team). Six miles north of St. Regis, MT. Timber, closed timber litter and brush. Active fire behavior with torching, backing and flanking. Numerous residences and
infrastructure threatened. Evacuations, area, road and trail closures in effect.
Woods Creek, Helena-Lewis and Clark NF, USFS. IMT 1 (RM Team 1). IMT is also managing the Divide Complex and American Fork incident. Sixteen miles northeast of Townsend, MT. Short grass and timber. Active fire behavior with flanking, backing group torching. Residences threatened. Area, road and trail closures in effect. Divide Complex (2 fires), Helena-Lewis and Clark NF, USFS. Seventeen miles west of Neihart, MT. Short grass
and timber. Minimal fire behavior with backing, creeping and smoldering. Several communities threatened.

Area, road and trail closures in effect.

American Fork, Helena-Lewis and Clark NF, USFS. Twenty-four miles southwest of Harlowton, MT. Short
grass, timber and brush. Active fire behavior with short crown runs, flanking and group torching. Area, road and trail closures in effect. Stateline Complex (7 fires), Idaho Panhandle NF, USFS. Twenty-two miles southwest of Superior, MT. Closed
timber litter, timber and light slash. Moderate fire behavior with single tree torching and backing. Area, road and
trail closures in effect.
Cougar Rock Complex (4 fires), Clearwater Potlach Timber Protective Association, IDL. Seventeen miles
northeast of Elk River, ID. Light slash and timber. Active fire behavior with creeping, smoldering and single tree
torching. Area and road closures in effect.
Burnt Peak, Kootenai NF, USFS. IMT 2 (GB Team 5). IMT is also managing the South Yaak incident. Nine miles southwest of Troy, MT. Timber and light slash. Active fire behavior with backing, single tree torching and group torching. Structures threatened. Area, road and trail closures in effect.
South Yaak, Kootenai NF, USFS. Four miles northwest of Troy, MT. Timber and light slash. Active fire behavior with backing, flanking and group torching. Numerous structures threatened. Evacuations, area, road and trail closures in effect.
Harris Mountain, Cascade County. Seven miles southeast of Cascade, MT. Closed timber litter and timber. Moderate fire behavior with backing, creeping and isolated torching. Structures threatened.
Storm Theatre Complex (12 fires), Nez Perce-Clearwater NF, USFS. NIMO (Team 1). Thirty-five miles southwest of Missoula, MT. Brush, timber and closed timber litter. Minimal fire behavior with flanking, backing
and creeping. Area, road and trail closures in effect. Alder Creek, Beaverhead-Deerlodge NF, USFS. IMT 1 (SA Blue Team). IMT is also managing the Trail Creek, Christensen and Black Mountain incidents. Twenty miles northwest of Wisdom, MT. Timber and brush. Active fire behavior with short crown runs, group torching and short-range spotting. Numerous structures threatened. Area, road and trail closures in effect. Trail Creek, Beaverhead-Deerlodge NF, USFS. Twenty miles west of Wisdom, MT. Timber and brush. Active fire behavior with short crown runs, group torching and short-range spotting. Community of Gibbonsville, numerous structures and communication infrastructures threatened. Area, road and trail closures in effect. Christensen, Beaverhead-Deerlodge NF, USFS. Ten miles northeast of Wisdom, MT. Timber and brush.
Active fire behavior with short crown runs, group torching and short-range spotting. Structures threatened.
Area, road and trail closures in effect.
Black Mountain, Beaverhead-Deerlodge NF, USFS. Twenty miles east of Salmon, ID. Timber, heavy slash and brush. Minimal fire behavior with smoldering. Area, road and trail closures in effect.
Granite Pass Complex (4 fires), Lolo NF, USFS. Thirty miles southwest of Missoula, MT. Timber, brush and closed timber litter. Minimal fire behavior with creeping and smoldering. Structures and communication infrastructure threatened. Area, road and trail closures in effect. Boulder 2700, Flathead Agency, BIA. Three miles northeast of Finley Point, MT. Timber and brush. Moderate fire behavior with backing, creeping and smoldering. Numerous residences and infrastructure threatened. Evacuations, area and trail closures in effect. Whitetail Creek, Northwestern Land Office, DNR. Nine miles northeast of Finley Point, MT. Timber and medium slash. Minimal fire behavior with smoldering. Area and road closures in effect.

Snake River Complex, Craig Mountain Supervisory Area, IDL. Twenty miles south of Lewiston, ID. Short grass
and timber. Minimal fire behavior with creeping and smoldering. Numerous residences threatened. Area, road and trail closures in effect. Cottonwood, Crow Agency, BIA. Eighteen miles southeast of Billings, MT. Short grass and brush. Minimal fire behavior with smoldering.

Incident Name Unit Size % Ctn/ Comp Est Personnel Resources Strc Lost $$ CTD Origin Own Acres Chge Total Chge Crw Eng Heli
Bedrock ID-PDS 10,850 1,845 20 Ctn 8/21 260 143 6 14 2 21 750K TRI
Richard Spring MT-LG29 170,848 10 65 Ctn 8/21 262 -39 4 14 2 12 4.9M PRI
Lame Deer MT- NCA 5,427 0 60 Ctn 8/21 46 16 2 9 0 0 450K BIA
Character
Complex ID-IPF 7,649 -1,306 47 Ctn 11/1 222 -50 4 12 1 0 16.8M FS
West Lolo
Complex MT-LNF 25,930 1,273 15 Ctn 10/31 383 -21 6 17 5 0 21.2M FS
Woods Creek MT-HLF 55,576 503 47 Comp 10/31 540 -62 7 48 4 1 NR FS
Divide Complex MT-HLF 9,834 0 52 Comp 10/29 145 -10 2 9 3 0 16.8M FS
American Fork MT-HLF 20,187 438 57 Comp 10/15 90 11 3 3 0 0 5.4M FS
Stateline Complex ID-IPF 11,422 0 15 Ctn 10/31 204 0 2 11 2 0 14M FS
Cougar Rock
Complex ID-CTS 8,410 0 53 Ctn 9/15 213 -6 6 4 0 0 17.8M ST
Burnt Peak MT-KNF 3,777 0 35 Ctn 9/30 152 6 1 4 2 0 20.3M FS
South Yaak MT-KNF 10,713 0 54 Ctn 9/30 244 3 4 10 0 0 5.2M FS
Harris Mountain MT-LG02 31,595 1 53 Ctn 10/1 73 -75 2 3 1 7 9.3M CNTY
Storm Theatre
Complex ID-NCF 22,319 91 3 Comp 10/15 52 -6 0 4 0 0 4.4M FS
Alder Creek MT-BDF 13,011 217 10 Ctn 11/1 279 0 0 15 4 0 15.8M FS
Trail Creek MT-BDF 37,412 624 26 Ctn 11/1 2273 45 6 27 0 0 11M FS
Christensen MT-BDF 10,196 420 10 Ctn 11/1 45 0 1 3 0 1 789K FS
Black Mountain MT-BDF 1,041 0 75 Ctn 10/31 20 6 0 1 1 0 2.4M FS
Granite Pass
Complex MT-LNF 5,902 0 15 Ctn 9/15 123 -5 1 8 0 0 9.7M FS
Boulder 2700 MT-FHA 2,072 0 46 Ctn 10/1 142 -28 3 9 0 31 5.9M BIA
Whitetail Creek MT-NWS 340 0 65 Ctn 9/15 56 -5 2 4 0 0 1.1M ST
Snake River
Complex ID-CMS 109,444 0 90 Ctn UNK 5 0 0 1 0 3 9.5M ST
Cottonwood MT-CRA 3,900 0 90 Ctn 8/24 43 0 1 2 0 0 80K BIA
Large Fires Being Managed with a Strategy Other Than Full Suppression Without a Type 1 or 2 IMT Assigned
Dixie ID-NCF 43,344 51 63 Comp 10/30 80 -37 1 7 0 0 24M FS
Jumbo ID-NCF 2,710 8 46 Comp 10/30 0 0 0 0 0 0 110K FS
Hay Creek MT-FNF 2,894 0 30 Comp 9/30 90 0 1 3 1 0 9M FS
Crooks MT-FHA 1,130 0 0 Comp 8/30 126 15 2 9 4 0 1M BIA
Trestle Creek
Complex ID-IPF 4,554 0 5 Comp 10/15 135 -12 2 11 0 0 5.1M FS
Swanson Creek ID-NCF 611 0 0 Comp 10/10 37 0 0 2 0 0 200K FS
Lynx ID-NCF 5,170 306 0 Comp 10/30 11 0 0 0 0 0 190K FS

Trout Creek MT-LG32 8,315 --- 80 Comp UNK 62 --- 1 11 0 0 550K CNTY
Incident Name Unit Size % Ctn/
Comp Est Personnel Resources Strc
Lost
$$ CTD Origin
Own Acres Chge Total Chge Crw Eng Heli
Goose MT-BDF 7,522 --- 90 Comp 10/13 28 --- 0 2 0 1 8.4M FS
Robertson Draw MT-CGF 29,885 --- 90 Comp 10/1 13 --- 0 2 0 30 13.2M FS
Crooked Creek MT-BID 4,141 --- 85 Comp 8/30 11 --- 0 0 1 1 5.3M BLM
Army Mule ID-NCF 3,626 --- 0 Comp 10/15 0 --- 0 0 0 0 2K FS
Greenside Butte ID-NCF 725 --- 0 Comp 10/31 0 ---- 0 0 0 0 10.5K FS
Larkins
Complex ID-IPF 3,358 --- 0 Comp 11/1 13 --- 0 0 0 0 22K FS
Dry Cabin MT-LNF 3,060 --- 0 Comp 10/10 8 --- 0 0 0 0 201K FS
Porphyry ID-NCF 170 --- 0 Comp 10/15 0 --- 0 0 0 0 NR FS
FNF – Flathead NF, USFS LG32 – Stillwater County CGF – Custer Gallatin NF, USFS BID – Billings Field Office, BLM
Great Basin (PL 3)
New fires: 13
New large incidents: 0
Uncontained large fires: 4
Type 2 IMTs committed: 2
Parleys Canyon, Northwest Area, Utah Division of Forestry Fire and State Lands. IMT 2 (GB Team 4). Eight
miles east of Salt Lake City, UT. Timber and brush. Moderate fire behavior with single tree torching, backing
and creeping. Several communities and numerous residencies threatened. Evacuations, area, road and trail
closures in effect. Reduction in acreage due to more accurate mapping.
Mud Lick, Salmon-Challis NF, USFS. Transfer of command from IMT 2 (GB Team 7) back to local unit will
occur tomorrow. Twenty-three miles west of Salmon, ID. Timber and short grass. Minimal fire behavior with
creeping and smoldering. Road closures in effect.

French, Payette NF, USFS. Fifteen miles east of Riggins, ID. Timber. Active fire behavior with flanking, backing
and isolated torching Structures threatened. Road closures in effect.
East Desolation, Uintah and Ouray Agency, BIA. Twenty-three miles east of East Carbon, UT. Timber, brush
and short grass. Moderate fire behavior with single tree torching, smoldering and creeping.
Scarface, Salmon-Challis NF, USFS. Thirty-five miles west of Challis, ID. Tall grass, brush and light slash. No
new information.

Incident Name Unit Size % Ctn/ Comp Est Personnel Resources Strc Lost $$ CTD Origin Own Acres Chge Total Chge Crw Eng Heli
Parleys Canyon UT-NWS 619 -1,381 10 Ctn 9/01 191 128 5 14 4 0 750K ST
Mud Lick ID-SCF 20,677 0 68 Comp 9/19 186 11 1 3 2 0 22.3M FS
French ID-PAF 1,160 860 30 Ctn 9/01 131 8 2 5 2 0 425K FS
East Desolation UT-UOA 350 0 50 Ctn 8/25 3 -4 0 0 1 0 165K BIA
Scarface ID-SCF 315 --- 60 Ctn 8/21 2 --- 0 0 1 0 320K FS

Large Fires Being Managed with a Strategy Other Than Full Suppression Without a Type 1 or 2 IMT Assigned
Tamarack NV-HTF 68,637 0 82 Comp 8/31 361 14 9 4 3 25 32K FS
Vinegar ID-PAF 2,500 ---- 30 Comp 10/15 5 --- 0 0 0 0 242K FS
Incident Name Unit Size % Ctn/
Comp Est Personnel Resources Strc
Lost
$$ CTD Origin
Own Acres Chge Total Chge Crw Eng Heli
Rush Creek ID-PAF 3,213 --- 31 Comp 10/15 7 --- 0 0 1 0 242K FS
Club ID-PAF 395 --- 0 Comp 10/15 0 --- 0 0 0 0 242K FS
Morgan Canyon UT-UWF 509 --- 90 Comp UNK 1 --- 0 0 0 0 1.8M FS
HTF – Humboldt-Toiyabe NF, USFS UWF – Uinta-Wasatch-Cache NF, USFS
Eastern Area (PL 3)

New fires: 16
New large incidents: 1
Uncontained large fires: 1
Type 2 IMTs committed: 1
* Greenwood, Superior NF, USFS. IMT 2 (EA Gold Team) mobilizing. Ten miles south-west of Isabella, MN. Timber. Extreme fire behavior with long-range spotting and group torching.

Incident Name Unit Size % Ctn/
Comp Est Personnel Resources Strc
Lost
$$ CTD Origin
Own Acres Chge Total Chge Crw Eng Heli
* Greenwood MN-SUF 750 --- 0 Ctn 9/1 33 --- 2 8 0 0 300K FS

Rocky Mountain Area (PL 2)
New fires: 9
New large incidents: 0
Uncontained large fires: 2
Crater Ridge, Bighorn NF, USFS. Thirty-one miles west of Sheridan, WY. Timber, heavy slash and short grass. Moderate fire behavior with flanking, group torching and short crown runs. Area, road and trail closures in effect.
Cross, Nebraska Forest Service. Thirteen miles southwest of Terrytown, NE. Timber and short grass. Minimal fire behavior with smoldering. Structures and energy infrastructure threatened.

Incident Name Unit Size % Ctn/
Comp Est Personnel Resources Strc
Lost
$$ CTD Origin
Own Acres Chge Total Chge Crw Eng Heli
Crater Ridge WY-BHF 2,785 308 30 Ctn 10/9 180 -8 4 12 3 0 8.4M FS
Cross NE-NES 2,460 0 90 Ctn 8/16 3 -4 0 1 0 0 200K ST
Hackberry CA NE-NES 6,177 0 100 Ctn --- 0 -3 0 0 0 0 620K ST
Large Fires Being Managed with a Strategy Other Than Full Suppression Without a Type 1 or 2 IMT Assigned
Morgan Creek WY-MRF 7,505 --- 24 Comp 9/1 48 --- 2 5 0 0 11.4M FS
Muddy Slide WY-MRF 4,093 --- 80 Comp 8/31 4 --- 0 1 0 18 13M FS
Sylvan CO-WRF 3,792 --- 75 Comp UNK 3 --- 0 1 0 0 7.2M FS
MRF – Medicine Bow-Routt NF, USFS WRF – White River NF, USFS

Southern California Area (PL 3)
New fires: 20
New large incidents: 0
Uncontained large fires: 0

Incident Name Unit Size % Ctn/
Comp Est Personnel Resources Strc
Lost
$$ CTD Origin
Own Acres Chge Total Chge Crw Eng Heli
Large Fires Being Managed with a Strategy Other Than Full Suppression Without a Type 1 or 2 IMT Assigned
Tiltill CA-YNP 1,927 0 76 Comp 8/24 27 0 0 0 2 0 650K NPS
Lukens CA-YNP 530 --- 85 Comp UNK 8 --- 0 0 0 0 455K NPS
YNP – Yosemite NP
Southwest Area (PL 2)
New fires: 1
New large incidents: 0
Uncontained large fires: 1
Amargo, Jicarilla Agency, BIA. Twenty-one miles south of Pagosa Springs, CO. Timber, chaparral and brush. Minimal fire behavior with smoldering.

Incident Name Unit Size % Ctn/
Comp Est Personnel Resources Strc
Lost
$$ CTD Origin
Own Acres Chge Total Chge Crw Eng Heli
Amargo NM-JIA 1,296 0 85 Ctn 8/31 22 -25 0 3 0 0 750K BIA
Alaska Area (PL 1)
New fires: 2
New large incidents: 0
Uncontained large fires: 0

Incident Name Unit Size % Ctn/ Comp Est Personnel Resources Strc Lost $$ CTD Origin Own Acres Chge Total Chge Crw Eng Heli
Large Fires Being Managed with a Strategy Other Than Full Suppression Without a Type 1 or 2 IMT Assigned
Marten Creek AK-UYD 2,662 0 90 Comp 8/31 43 -1 2 0 0 0 1.3M TRI
Discovery Creek AK-UYD 7,696 0 0 Comp 8/17 6 -19 1 0 0 0 650K FWS
Twentyfour Mile AK-UYD 1,562 --- 0 Comp 9/30 0 --- 0 0 0 0 3K BLM
Nation River AK-UYD 771 --- 0 Comp 9/1 0 --- 0 0 0 0 NR TRI
UYD – Upper Yukon Zone, BLM

Fires and Acres Yesterday (by Protection):

Area BIA BLM FWS NPS ST/OT USFS TOTAL
FIRES 0 0 0 0 2 0 2 Alaska Area ACRES 0 0 0 0 2 0 2
FIRES 0 0 0 0 3 0 3 Northwest Area ACRES 0 35 0 0 2 0 37
FIRES 0 0 0 0 10 4 14 Northern California Area ACRES 0 0 0 0 87 11,698 11,785
FIRES 0 0 0 0 18 2 20 Southern California Area ACRES 0 0 0 0 13 5 18
FIRES 1 0 0 0 4 2 7 Northern Rockies Area ACRES 0 0 0 0 1,973 622 2,595
FIRES 2 4 0 0 5 2 13 Great Basin Area ACRES 0 1 0 0 1 2,022 2,024
FIRES 0 0 0 1 0 0 1 Southwest Area ACRES 0 0 0 0 0 0 0
FIRES 0 1 0 0 4 4 9 Rocky Mountain Area ACRES 0 0 0 0 166 100 266
FIRES 0 0 0 0 13 3 16
Eastern Area ACRES 0 0 0 0 44 0 44
FIRES 0 0 0 0 2 0 2 Southern Area ACRES 0 0 0 0 0 0 0
TOTAL FIRES: 3 5 0 1 61 17 87
TOTAL ACRES: 0 36 0 0 2,289 14,447 16,773

Fires and Acres Year-to-Date (by Protection):

Area BIA BLM FWS NPS ST/OT USFS TOTAL
FIRES 0 114 0 0 229 14 357 Alaska Area
ACRES 0 156,402 0 0 96,889 5 253,296
FIRES 189 263 27 14 1,860 540 2,893 Northwest Area
ACRES 69,805 16,103 13,202 877 144,232 565,513 809,732
FIRES 61 30 4 23 2,459 471 3,048 Northern California Area
ACRES 284 278 332 2 259,594 460,913 721,404
FIRES 18 99 12 71 3,119 444 3,763 Southern California Area
ACRES 1,373 3,526 199 5,645 17,473 9,653 37,870
FIRES 1,186 78 23 5 1,253 682 3,227 Northern Rockies Area
ACRES 82,766 15,243 2,752 51 422,096 242,371 765,279
FIRES 46 654 52 28 728 458 1,966 Great Basin Area
ACRES 3,358 77,727 10 2,191 69,322 85,669 238,279
FIRES 490 187 9 31 343 891 1,951 Southwest Area
ACRES 26,176 83,889 1,528 3,362 33,286 490,737 638,980
FIRES 523 328 6 21 565 292 1,735 Rocky Mountain Area
ACRES 7,282 25,055 1,260 1,116 101,900 26,035 162,648
FIRES 541 0 51 29 6,897 434 7,952 Eastern Area
ACRES 12,441 0 14,381 652 32,886 15,887 76,247
FIRES 379 0 56 40 12,733 375 13,583 Southern Area
ACRES 28,688 0 11,845 8,438 263,858 27,433 340,264
TOTAL FIRES: 3,433 1,753 240 262 30,186 4,601 40,475
TOTAL ACRES: 232,175 378,226 45,509 22,335 1,441,538 1,924,218 4,044,003
Ten Year Average Fires (2011 – 2020 as of today) 38,659
Ten Year Average Acres (2011 – 2020 as of today) 4,766,603
***Changes in some agency YTD acres reflect more accurate mapping or reporting adjustments. ***Additional wildfire information is available through the Geographic Areas at https://gacc.nifc.gov/

Canadian Fires and Hectares

PROVINCES FIRES YESTERDAY HECTARES YESTERDAY FIRES YEAR-TO-DATE
HECTARES YEAR-TO- DATE
BRITISH COLUMBIA 7 26,727 1,525 698,202
YUKON TERRITORY 0 0 112 103,134
ALBERTA 11 384 1,082 55,318
NORTHWEST TERRITORY 0 0 137 118,466
SASKATCHEWAN 3 491 551 992,919
MANITOBA 0 88 433 1,196,713
ONTARIO 8 9,198 1,099 716,241
QUEBEC 1 28 499 56,859
NEWFOUNDLAND 1 0 67 321
NEW BRUNSWICK 1 9 159 372
NOVA SCOTIA 0 0 110 197
PRINCE EDWARD ISLAND 0 0 1 0
NATIONAL PARKS 0 0 49 36,268
TOTALS 32 36,925 5,836 3,975,011
*1 Hectare = 2.47 Acres
Predictive Services Discussion: A deep trough will move into the Northwest, with troughing extending into
northern California helping to break down the upper-level ridge. A cold front will move into the northern
Intermountain West, but temperatures are likely to remain above average, especially east of the Cascades.
Elevated to critical conditions are likely across much of the northern Intermountain West and the northern Plains
ahead of the approaching cold front. Isolated drier thunderstorms are possible within a corridor stretching from
northwest Nevada and southeast Oregon through central Montana with the highest chances in southwest and
central Montana. Smoke will begin to get scoured out from northwest to southeast as well across the northwest
US. Isolated mixed wet and dry thunderstorms are also possible over the southern Sierra and Peninsular Ranges
with monsoon thunderstorms continuing in the Southwest and southern Colorado. Isolated to scattered showers
are likely in portions of western Washington and western Oregon with showers possibly moving into northern
Montana overnight. Tropical Storm Fred is likely to make landfall tonight in the western Florida Panhandle with
strong winds and heavy rainfall.

http://www.predictiveservices.nifc.gov/outlooks/outlooks.htm

Transfer Of Command
Operational Engagement Category

Risks to fireline personnel increase significantly during transfer of command periods regardless of the size or
complexity of the incident. There is a high potential for fatalities, serious injuries, or incidents during transfer of
command. Be proactive in mitigating the risks by proper implementation of LCES –Lookouts, Communications,
Escape Routes, and Safety Zones.
Factors for increased risks to fireline personnel during transition periods include:

No or poor briefing of incoming personnel.
Lack of fire weather and behavior information, both forecast and observed.
Communications: face-to-face briefings may not be possible and radio frequencies may be overextended and/or changing due to the increased demands on the system.
Initial attack resources may not have checked in and the Incident Commander (IC) may not be aware of the number, type, and location of all resources.
Location of safety zones and escape routes may not be known and communicated to all resources. Not all resources know who is in command.
Mitigation actions to take:

Lookouts: post and maintain your own lookouts.
Communications: Maintain existing communications with your own and adjacent resources, as well as your original supervisor, while you are developing communications with incoming adjacent resources and
your new supervisor.
Escape routes and safety zones: Identify escape routes and ensure incoming resources are aware of their locations; be aware that your original escape routes and safety zones may no longer be accessible
due to changing fire behavior or your increased distance from them.
Plan for transitions to occur at the morning briefing.
Utilize the Incident Response Pocket Guide (IRPG), PMS 461, Briefing Checklist (inside back cover).
Resources:
10 Standard Firefighting Orders, PMS
110 10 and 18 Poster, PMS 110-18
18 Watchout Situations, PMS 118
Incident Response Pocket Guide (IRPG), PMS 461
Interagency Standards for Fire and Fire Aviation Operations (Red Book)
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