Flash Flood in Wyoming, August 12, 2024

Area Forecast Discussion
National Weather Service Riverton WY
108 PM MDT Mon Aug 12 2024

.KEY MESSAGES...

- Marginal Risk (Level 1 of 5) for severe thunderstorms Monday
  across the western Wyoming border, and Tuesday across the
  whole state. Primary hazards will be severe wind gusts and
  hail.

- Widespread showers and thunderstorms Monday through Wednesday.

- Warmer and mostly dry conditions expected Thursday through the
  day Saturday.

&&

.DISCUSSION...
Issued at 105 PM MDT Mon Aug 12 2024

The first push of moisture is through western and central Wyoming
with many areas receiving at least a sprinkle. The next push of
moisture will begin arriving this afternoon, producing more
widespread showers and thunderstorms. The best chances for rain are
going to be across the southern half of the start where the main
push of moisture is moving in from the southwest, but higher
elevations in western Wyoming also have a 40 to 60 percent chance of
precipitation. In addition, there is a Marginal Risk (Level 1 of 5)
of severe thunderstorms along the western border of Wyoming for the
thunderstorms this afternoon. With skies clearing earlier this
morning, there is more time for heating to occur, resulting in
steeper low-level lapse rates that could lead to severe wind gusts.

Tuesday and Wednesday there are more widespread rain shower and
thunderstorm chances as a stronger mid-level disturbance ejects
through Wyoming from the PACNW. There is also a Marginal Risk (Level
1 of 5) across the state of Wyoming Tuesday due to chances for
severe wind and hail. While the majority of the surface moisture
will have moved off to the east, enough moisture remains with decent
mid and upper-level flow that could lead to the development of
stronger thunderstorms. The majority of thunderstorms will be garden
variety or strong, but an isolated severe thunderstorm cannot be
ruled out that may produce severe wind gusts.

Thursday brings drier and warmer conditions as a ridging pattern
takes back over through the weekend. Weak disturbances embedded in
the flow could kick off a few thunderstorms daily, but the
confidence is low in any widespread impacts. Thunderstorm chances
increase slightly Saturday night into Sunday as the ridge shifts
eastward, placing central and western Wyoming on the western side,
allowing some moisture to creep back in. Temperatures during this
time are expected to be in the 70s to 80s west of the divide and 80s
to low 90s east of the divide. Elevated fire weather concerns are
expected especially Friday and Saturday as minimum relative humidity
values approach critical across central and southern Wyoming with
southwest wind gusts 20 to 25 mph.

&&

.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 1109 AM MDT Mon Aug 12 2024

West of the Divide...KBPI/KJAC/KPNA/KRKS Terminals.

Shower and thunderstorm chances are between 40% and 70% this
afternoon. Chances occur between 18Z/Mon and 06Z/Tue, but will be
decreasing after 00Z/Tue. The exception will be at KRKS, which keeps
at least small rain chances through the night. TAFs were written to
have TEMPO groups for the timeframe of the best shower/storm chances
through this evening. Gusty outflow wind is the main hazard, with
visibility drops likely if a storm passes over a terminal. High-
resolution models show some rain chances early Tuesday morning, so
have included chances at KJAC and KRKS. Smoke will be decreasing
through the TAF period. More shower and thunderstorm chances occur
near the end and after the TAF period, for Tuesday afternoon.

East of the Divide...KCOD/KCPR/KLND/KRIW/KWRL Terminals.

Shower and thunderstorm chances are between 30% and 50% this
afternoon and evening, with only about a 20% chance at KCPR and
KWRL. Have used TEMPO groups in the TAFs to highlight the timeframe
of the best shower/storm chances. Chances begin to decrease after
00Z/Tue, and should be done by 06Z/Tue. Gusty outflow wind is the
main hazard, with visibility drops possible if a storm passes over a
terminal.

Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for
the latest information on smoke, icing, and turbulence forecasts.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...

&&

DISCUSSION...Gross
AVIATION...Wittmann

Hazardous Weather Outlook
National Weather Service Riverton WY
318 AM MDT Mon Aug 12 2024

WYZ001>020-022>030-131300-
Yellowstone National Park-Absaroka Mountains-Cody Foothills-
North Bighorn Basin-Southwest Bighorn Basin-Southeast Bighorn Basin-
Owl Creek and Bridger Mountains-Bighorn Mountains West-
Bighorn Mountains Southeast-Northeast Johnson County-
Southeast Johnson County-Teton and Gros Ventre Mountains-
Jackson Hole-Wind River Mountains West-Wind River Mountains East-
Upper Wind River Basin-Wind River Basin-Lander Foothills-
Green Mountains and Rattlesnake Range-
Natrona County Lower Elevations-Casper Mountain-Star Valley-
Salt River and Wyoming Ranges-Upper Green River Basin Foothills-
Upper Green River Basin-South Lincoln County-
Rock Springs and Green River-Flaming Gorge-East Sweetwater County-
318 AM MDT Mon Aug 12 2024

This Hazardous Weather Outlook is for Western and Central Wyoming.

.DAY ONE...Today and Tonight.

Showers and thunderstorms returning, most numerous in western and
southern Wyoming.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday...

Tuesday through Thursday...Continued chances of showers and
thunderstorms, becoming less numerous Thursday.

.SPOTTER INFORMATION STATEMENT...

Weather spotters are encouraged to report significant weather
conditions according to Standard Operating Procedures.