A Pacific Cold Front crossed the state and mixed strong low level winds to the surface. Wind gusts over 58 mph were recorded at Lander, Riverton and Greybull, Wyoming.
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Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.
The episode as NWS RIW wrote it up.
A Pacific Cold Front crossed the state and mixed strong low level winds to the surface. Wind gusts over 58 mph were recorded at Lander, Riverton and Greybull, Wyoming. At the Red Canyon, winds gusted to 75 mph several times. At the Buffalo, Wyoming airport, a wind gust of 66 mph was reported and several tree limbs were downed.
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 May 20, 10:45 AM MST, 1 hour 38 minutes earlier.
Area Forecast Discussion National Weather Service Riverton WY 1145 AM MDT Wed May 20 2020 .SHORT TERM...Today through Friday night We did have a couple of showers and storms pop up this evening, although most are winding down at this time. There could be a sprinkle in spots, but most areas should be dry to start the day. This will be the day that changes the pattern as a Pacific cold front swings across the area. The result will be cooler temperatures Temperatures will still be near to somewhat above normal, but no 90s like yesterday in some areas. Not many areas will reach the 80s as well. The warmest temperatures will likely be across the east where the front will be the slowest to arrive. We will still have windy conditions as well, mainly in the afternoon when lower level winds can mix to the surface. Winds should stay somewhat below yesterdays level. Nevertheless, it will be windy in many areas in the afternoon so people will have to watch things that can blow around, like trash cans, toupees and small furry animals. And although humidity will remain rather low, fire danger should be a little less due to the cooler temperatures so no fire weather statements today. We may issue a special weather statement to cover for this though. This will be a game time decision though. As for the chance of showers and thunderstorms, effected areas will be fairly similar to yesterday. Mainly, across the western areas as the front moves through. Also, in eastern areas largely along and east of Interstate 25 where some moisture will try to return. However, almost all of the severe weather should remain east of the area where there will better instability and moisture present. The main threat from any storm would be strong wind gusts given the expected fast movement of the storms and strong mid level winds. Some small hail may be possible in the west though as cooler air moves in and drops freezing levels. And, speaking of freezing levels... Much cooler air will be moving in the west late today and tonight. Some models are showing 700 millibar levels falling as low as minus 5 late tonight. This would but snow levels around 6000 to 6500 feet. As a result, some snow is possible in the mountains where a couple of slushy inches could accumulate. It would not surprise me to see some snowflakes fly even in a place like Jackson. The bulk of the best moisture should be out of the area by then and given the warm ground temperatures no transportation issues are expected at this time. Thursday at this point looks be a lull in the activity. Another weak wave will rotate around the main upper level low over the Pacific northwest. This one though looks to effect mainly areas further west and north so only light precipitation is expected at this time. This will be mainly confined to the western mountains with the rest of the area mainly dry with near normal temperatures. We will still have the tight pressure gradient though so it will still be a breezy to windy day across much of the area. The main low then approaches the area for Friday. There is more model difference here in regards to the timing and placement of the heaviest precipitation though, as is expected with upper level lows. For now, we made only minor changes to the forecast. .LONG TERM...Saturday through Wednesday. At 12Z Saturday, models are in decent agreement with a compact upper low/shortwave trough over western Wyoming with the 700mb low over north-central Wyoming. This system will slowly push east northeast into the northern High Plains by 00Z Sunday. The bulk of precipitation looks to occur over north-central Wyoming Saturday with some over the west, and central portions of the forecast area. The exact track of this mid-level low will make a big difference in where the heaviest precipitation will occur. Snow levels look to dip down to between 6000 and 7000 feet. The main impacts will be northern mountain passes could be slick and snow covered at times especially in heavier snow bursts as well as people in the backcountry experiencing a cold, heavy, wet snow. Once this system pulls away from the area late Saturday afternoon/evening, 00Z deterministic runs of the GFS and ECMWF are fairly dry Sunday and Monday in a west/northwest flow. However will keep slight PoPs across the area due to some ensemble data showing a chance of some convection. Models are progging a trough pulling across Canada/N. Rockies Tuesday and Wednesday that could bring a cold front and some inclement weather. However there are many different solutions on how this trough will evolve. && .AVIATION...(For the 18Z TAFS through 18Z Thursday) Issued at 1145 AM MDT Wed May 20 2020 Strong low pressure system over western Idaho continues to bring breezy to wind south-southwest flow at the TAF sites today, with most sites seeing gusts over 30 kts. Convection has already started across western Wyoming, where KJAC should see most of the action today, and likely be MVFR at times this afternoon and overnight. KBPI and KPNA will also see showers this afternoon into the evening hours. Wind should be erratic and quick gusty at times. Expecting a bit of a wind shift as flow turns from south-southwest to more westerly; the wind shift will move eastward during the late afternoon hours. Wind should decrease by 21/04Z with rain and snow showers increasing over the western mountains and KJAC overnight. Mountain snow showers will continue into Thursday morning, with west wind increasing around 21/15Z in a cooler post-frontal environment. Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for the latest information on icing and turbulence forecasts. && .FIRE WEATHER... We will have another breezy to windy day today with low humidity in many areas. However, fire conditions should improve somewhat since cooler temperatures are expected. However, with wind gusts past 40 mph and humidity falling into the teens, fire behavior will still be elevated this afternoon. Isolated to scattered thunderstorms will be possible in the west and in eastern Johnson and Natrona Counties. Mixing and smoke dispersal will be generally good to excellent. && .RIW WATCHES/WARNINGS/ADVISORIES...NONE. && SHORT TERM...Hattings LONG TERM...Murrell AVIATION...McDonald FIRE WEATHER...Hattings
Hazardous Weather Outlook National Weather Service Riverton WY 243 AM MDT Wed May 20 2020 WYZ001>020-022>030-211300- Yellowstone National Park-Absaroka Mountains-Cody Foothills- North Big Horn Basin-Southwest Big Horn Basin- Southeast Big Horn 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- 243 AM MDT Wed May 20 2020 This Hazardous Weather Outlook is for Western and Central Wyoming. .DAY ONE...Today and Tonight. Elevated fire conditions possible East of Divide this afternoon. Thunderstorms possible in western Wyoming and east of Interstate 25 this afternoon and evening. High elevation snow possible in the western mountains tonight. .DAYS TWO THROUGH SEVEN...Thursday through Tuesday. Thursday...Isolated thunderstorms in western Wyoming. Some snow possible at night in the western Mountains. Friday and Saturday...Some accumulating mountain snow likely over the west and north. Isolated thunderstorms are also possible. .SPOTTER INFORMATION STATEMENT... Weather spotters are encouraged to report significant weather conditions, according to standard operating procedures.
The national radar mosaic for the moment the first event began.
5 high wind. Local standard time, as filed.
A wind gust of 59 mph was reported at the Lander, Wyoming airport.
A 59 mph wind gust was reported at the Riverton, Wyoming airport.
A 62 mph wind gust was reported at the Greybull, Wyoming airport.
A wind gust of 66 mph was reported at the Buffalo, Wyoming airport. A trained spotter reported several downed tree limbs in Buffalo, Wyoming.
Winds gusted to 75 mph at the WYDOT wind sensor at Red Canyon.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Wyoming in 2020Every state in 2020This day in weather historyWarnings in Wyoming, May 2020
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: 886393, 886392, 886390, 892201, 886391.