A thunderstorm developed in the lee of the Wind River Mountains and become severe as it moved northeastward across Fremont County. The storm produced quarter size hail along Gas Hills Road to the east of Riverton and a 63 mph wind gust north of Shoshoni.
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The episode as NWS RIW wrote it up.
A thunderstorm developed in the lee of the Wind River Mountains and become severe as it moved northeastward across Fremont County. The storm produced quarter size hail along Gas Hills Road to the east of Riverton and a 63 mph wind gust north of Shoshoni.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS Riverton, WY wrote its last area forecast discussion before the first event at Aug 26, 11:52 AM MST, 28 minutes earlier. Its key messages:
Area Forecast Discussion National Weather Service Riverton WY 1252 PM MDT Mon Aug 26 2024 .KEY MESSAGES... - Very active morning thunderstorms are giving way to isolated showers and thunderstorms this afternoon as a storm system moves through Wyoming. Some strong severe storms are expected in eastern and northeast WY. - Weak high pressure Tuesday will bring lighter yet gusty winds and warmer temperatures. - An approaching storm system over Montana on Wednesday will bring stronger winds and dry warm weather for elevated fire weather conditions. Some isolated storms are expected across far northern WY as a cold front sweeps through the area during the afternoon. - Cooler and dry on Thursday will still bring gusty northwest winds; then dry and warm conditions for Friday through Sunday. && .DISCUSSION... Issued at 1250 PM MDT Mon Aug 26 2024 As expected since late last week, a deep and cold upper level system is moving through the state today. This morning saw snow in the highest elevations of western WY as well as some severe morning convection with rainbows and plenty of lightning and wind. Satellite imagery shows the low center moving into north- central WY early this afternoon, with severe storms expected across eastern WY this afternoon. Isolated showers and thunderstorms will continue over northwest WY this afternoon, then move to north-central WY late this afternoon before bringing clearing yet cold skies to the forecast area tonight. The higher elevations and some western valley locations will see temperatures near freezing once again. Tuesday should see weak high pressure over the area, with relatively light winds and much drier conditions. Gusty southwest winds will develop during the afternoon from southwest/southern into central WY for elevated fire weather conditions as RH values drop to around 15-20 percent. Some areas across central WY will remain breezy Tuesday night as the pressure gradient tightens due to a strong storm system moving from BC into western MT Wednesday morning. Models are in pretty good agreement that the strong system will move across MT during the day, dragging a dry cold front across the forecast area through the day. Strong gusty winds will develop mid-morning from southern into central WY. As the mid-level cold front moves from west to east across WY during the day, the winds will shift to more westerly and become stronger with 25-35 mph winds and 35-50 mph wind gusts. Given the dry conditions even behind the front, critical fire weather conditions should develop at least across the southern two-thirds of the forecast area for much of the day. Northern WY will see partly cloudy skies with isolated showers and thunderstorms across far northern WY. As the primary front moves eastward, a surface front will then move from MT into northern WY and shift the winds to the north and increase low-level moisture in the Bighorn Basin and Johnson County. Temperatures shoudl be quite cool Thursday morning with the higher elevations and much of the western valleys dropping below freezing. Thursday will then see dry northwest flow over the area in the post-storm environment. Though temperatures will be on the cool side, the air mass will be quite dry with gusty west winds. Upper-level high pressure is then expected to build over the northern Great Basin into ID/OR/WA. Moisture will be quite limited as the surface pressure gradient weakens. Winds will become light from the west on Friday, then likely from the east on Saturday as the gradient reverses. With 700mb temps returning to around +14 C, surface temps will return to the mid 80s for the weekend with dry conditions. The next precipitation event may not occur until Tuesday after Labor Day. && .AVIATION /18Z TAFS THROUGH 18Z TUESDAY/... Issued at 1146 AM MDT Mon Aug 26 2024 Scattered thunderstorms east of the Continental Divide will be the primary aviation threat this afternoon. Storms have exited the Wind River Basin, and recently moved east of KCPR. Locations in the Bighorn Basin and Johnson County (including KCOD, KWRL, and KBYG) will continue to have the risk of thunderstorms through the afternoon hours, as atmospheric instability lingers for the northern tier of Wyoming. Lightning and wind gusts 35 to 45 kt will be the primary threat with the stronger storms, but small hail is also possible directly under storm cores. The region dries out quickly after sunset, bringing dry conditions and fairly light winds through the day Tuesday. && .FIRE WEATHER... Issued at 1230 PM MDT Mon Aug 26 2024 A deep storm system is moving through Wyoming today, with isolated showers and thunderstorms across the northern two- thirds of the forecast area. The southern part will be gusty and dry, but moisture values will remain higher. Very isolated showers are possible across north-central WY through midnight. Weak high pressure moves over the area Tuesday for clearer skies and drier conditions. Southwest winds will be gusty across southern and central WY, but not critical as winds only gust 15-25 mph. Another strong storm system will move across Montana on Wednesday, increasing the winds from southwest into central WY during the morning hours. As a relatively dry cold front sweeps across the state during the day, winds will increase from the west and combine with low RH values to produce critical fire weather conditions. A red flag warning will likely be issued for the southern two-thirds of the forecast area. The northern portions should remain moister with north winds pushing into the Bighorn Basin and Johnson County late in the afternoon. Isolated showers and thunderstorms are possible with this system across far northern WY. && .RIW WATCHES/WARNINGS/ADVISORIES...None. && DISCUSSION...McDonald AVIATION...VandenBoogart FIRE WEATHER...McDonald
Hazardous Weather Outlook National Weather Service Riverton WY 217 AM MDT Mon Aug 26 2024 WYZ001>020-022>030-271300- 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- 217 AM MDT Mon Aug 26 2024 This Hazardous Weather Outlook is for Western and Central Wyoming. .DAY ONE...Today and Tonight. Isolated to widely scattered thunderstorms in northern Wyoming. Strong to locally severe thunderstorms possible this afternoon, especially in northern Wyoming. Frost possible in the western valleys Monday night. .DAYS TWO THROUGH SEVEN...Tuesday through Sunday... Tuesday...Elevated fire weather possible in central and southern Wyoming. Wednesday...Elevated to critical fire weather possible across central and southern Wyoming. .SPOTTER INFORMATION STATEMENT... Weather spotters are encouraged to report significant weather conditions according to Standard Operating Procedures.
Special Weather Statement
National Weather Service Riverton WY
750 AM MDT Mon Aug 26 2024
WYZ015-017-018-261430-
Wind River Basin-Wind River Mountains East-Lander Foothills-
750 AM MDT Mon Aug 26 2024
...A STRONG THUNDERSTORM WILL IMPACT SOUTH CENTRAL FREMONT COUNTY
THROUGH 830 AM MDT...
At 749 AM MDT, Doppler radar was tracking a strong thunderstorm over
Red Canyon, which is 10 miles southeast of Lander, moving northeast
at 30 mph.
HAZARD...Wind gusts up to 50 mph and nickel size hail.
SOURCE...Radar indicated.
IMPACT...Gusty winds could blow around unsecured objects. Minor hail
damage to vegetation is possible.
This storm will remain over mainly rural areas of south central
Fremont County, including the following locations... Arapahoe
Elementary School and Lander Hunt Field.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
Frequent cloud to ground lightning is occurring with this storm.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.
This storm may intensify, so be certain to monitor local radio
stations and available television stations for additional information
and possible warnings from the National Weather Service.
&&
LAT...LON 4284 10821 4269 10850 4270 10852 4269 10852
4267 10853 4264 10859 4265 10860 4263 10861
4260 10867 4269 10887 4302 10856
TIME...MOT...LOC 1349Z 218DEG 27KT 4270 10865
MAX HAIL SIZE...0.88 IN
MAX WIND GUST...50 MPH
VandenBoogartSpecial Weather Statement
National Weather Service Riverton WY
935 AM MDT Mon Aug 26 2024
WYZ005>009-017-261615-
Owl Creek and Bridger Mountains-Wind River Basin-Bighorn Mountains
Southeast-Southwest Bighorn Basin-Southeast Bighorn Basin-Bighorn
Mountains West-
935 AM MDT Mon Aug 26 2024
...A STRONG THUNDERSTORM WILL IMPACT SOUTHEASTERN HOT SPRINGS...
NORTHWESTERN NATRONA...NORTHEASTERN FREMONT AND SOUTHEASTERN WASHAKIE
COUNTIES THROUGH 1015 AM MDT...
At 935 AM MDT, Doppler radar was tracking a strong thunderstorm near
Cottonwood Pass, which is 24 miles northeast of Shoshoni, moving
northeast at 40 mph.
HAZARD...Wind gusts of 50 to 55 mph and nickel size hail.
SOURCE...Radar indicated.
IMPACT...Gusty winds could knock down tree limbs and blow around
unsecured objects. Minor hail damage to vegetation is
possible.
This strong thunderstorm will be near...
Cottonwood Pass around 940 AM MDT.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
Torrential rainfall is also occurring with this storm and may lead to
localized flooding. Do not drive your vehicle through flooded
roadways.
Frequent cloud to ground lightning is occurring with this storm.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.
&&
LAT...LON 4356 10701 4328 10747 4329 10752 4326 10751
4319 10763 4341 10796 4388 10750
TIME...MOT...LOC 1535Z 226DEG 35KT 4342 10767
MAX HAIL SIZE...0.88 IN
MAX WIND GUST...55 MPH
VandenBoogartPreliminary Local Storm Report
National Weather Service Riverton WY
956 AM MDT Mon Aug 26 2024
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0929 AM Tstm Wnd Gst 13 NNE Shoshoni 43.40N 107.96W
08/26/2024 M63 MPH Fremont WY Mesonet
&&
RIWSpecial Weather Statement
National Weather Service Riverton WY
1027 AM MDT Mon Aug 26 2024
WYZ006-008-009-011-261715-
Southeast Johnson County-Bighorn Mountains Southeast-Southeast
Bighorn Basin-Bighorn Mountains West-
1027 AM MDT Mon Aug 26 2024
...A STRONG THUNDERSTORM WILL IMPACT SOUTHWESTERN JOHNSON AND EAST
CENTRAL WASHAKIE COUNTIES THROUGH 1115 AM MDT...
At 1027 AM MDT, Doppler radar was tracking a strong thunderstorm 9
miles southeast of Big Trails, which is 26 miles west of Kaycee,
moving northeast at 40 mph.
HAZARD...Wind gusts up to 50 mph and half inch hail.
SOURCE...Radar indicated.
IMPACT...Gusty winds could knock down tree limbs and blow around
unsecured objects. Minor hail damage to vegetation is
possible.
This storm will remain over mainly rural areas of southwestern
Johnson and east central Washakie Counties, including the following
locations... Lost Cabin Campground and Barnum.
This includes Interstate 25 between mile markers 255 and 278.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
If outdoors, consider seeking shelter inside a building.
&&
LAT...LON 4388 10632 4351 10705 4375 10749 4422 10690
4417 10682 4416 10682 4416 10680
TIME...MOT...LOC 1627Z 226DEG 35KT 4371 10716
MAX HAIL SIZE...0.50 IN
MAX WIND GUST...50 MPH
VandenBoogartSpecial Weather Statement
National Weather Service Riverton WY
1127 AM MDT Mon Aug 26 2024
WYZ020-022-261800-
Casper Mountain-Natrona County Lower Elevations-
1127 AM MDT Mon Aug 26 2024
...STRONG THUNDERSTORMS WILL IMPACT EAST CENTRAL NATRONA COUNTY
THROUGH NOON MDT...
At 1126 AM MDT, Doppler radar was tracking a cluster of strong
thunderstorms near Bar Nunn, which is near Casper, moving northeast
at 35 mph.
HAZARD...Wind gusts up to 50 mph and half inch hail.
SOURCE...Radar indicated.
IMPACT...Gusty winds could knock down tree limbs and blow around
unsecured objects. Minor hail damage to vegetation is
possible.
This strong thunderstorm will be near...
Evansville around 1130 AM MDT.
This includes Interstate 25 between mile markers 176 and 207.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
If outdoors, consider seeking shelter inside a building.
Very heavy rainfall is also occurring with this storm and may lead
to localized flooding. Do not drive your vehicle through flooded
roadways.
Frequent cloud to ground lightning is occurring with this storm.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.
This storm may intensify, so be certain to monitor local radio
stations and available television stations for additional information
and possible warnings from the National Weather Service.
&&
LAT...LON 4277 10608 4270 10633 4309 10650 4320 10607
TIME...MOT...LOC 1726Z 240DEG 32KT 4292 10628
MAX HAIL SIZE...0.50 IN
MAX WIND GUST...50 MPH
McDonaldThe Riverton/Lander radar (KRIW), 25 km away, was scanning. The volume nearest the first event began at 19:18 UTC.
1 hail, 1 thunderstorm wind. Local standard time, as filed.
A retired National Weather Service meteorologist reported quarter size hail along Gas Hills Road to the east of Riverton. Hail covered the road to a depth of 1 to 2 inches in some locations.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Wyoming in 2024Every state in 2024This day in weather historyWarnings in Wyoming, August 2024
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 1209171, 1209172.