Strong thunderstorms developed over the Wind River Mountains and became severe as the moved northward as they tapped into strong mid level winds. Numerous official reporting stations indicated wind gusts past 58 mph in Fremont, Natrona and Johnson Counties.
Every event with a place to put it. Tap one for its entry below.
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.
Strong thunderstorms developed over the Wind River Mountains and became severe as the moved northward as they tapped into strong mid level winds. Numerous official reporting stations indicated wind gusts past 58 mph in Fremont, Natrona and Johnson Counties. The highest wind gust reported was 62 mph at the Buffalo, Wyoming airport.
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 Jun 4, 9:58 PM MST, 4 hours 49 minutes earlier.
Area Forecast Discussion National Weather Service Riverton WY 1058 PM MDT Thu Jun 4 2020 .SHORT TERM...This evening through Friday night Issued at 251 PM MDT Thu Jun 4 2020 Early start to the shower activity in the far west this morning. A weak vort within the westerly aloft seems to be responsible. Convection appears to be weak at the time of this writing. Lifted indices are positive in the west at the moment. Satl loop is indicating trapped waves across the west at the moment indicative of relatively stable air along with windy conditions in some areas(RKS currently gusting to 56 mph coupled with 14 percent RH). Once the clouds associated with these showers clear out, allowing for more heating, we will see a fresh round of some convection today from the next vort lobe later this afternoon and evening. Lifted indices are progged to be around -3 in the far west, -1 over most areas, and -4 over Johnson County. With 30 knot westerly winds at 700mb today, most convective cells will likely occur with gusty winds. Thunderstorms will likely be most numerous in our northern zones today closer to the jet energy. As thunderstorms develop in northern Wyoming today due to the jet energy there, and they move east into juicier air from where dew points are in the upper 30s to low 40s, into where dew points are in the upper 40s, and where lifted indices are already near -4, storms will strengthen in areas like northern Johnson County today. In fact, SPC now has northeast Johnson County in a slight risk area for severe weather for today. The central and southern portions of the CWA east of the Divide as well as Sweetwater County will have a minimum RH that will bottom out to the low to mid teens this afternoon where brisk winds are occurring. An RFD is addressing this. Friday will be a quieter day as a flat ridge builds into the area along with a resultant subsidence inversion. These warmer temperatures aloft will suppress instability. The subsidence inversion will begin to lose its identity later Friday afternoon, so a few isolated thunderstorms could occur late in the day, especially in the northwest where higher capes will be. Many areas on Friday could see the hottest temperatures so far this season with highs in the low to mid 90s in the Wind River and Big Horn Basins and 80s elsewhere. The minimum RH will be in the low teens in the same areas that the RFD is currently addressing now. The winds will be brisk, but not as strong as today. An RFD will likely again be needed in the same areas for Friday. A closed low well off the Baja Ca coast will make landfall onto the southern California Coast Friday and then become an open trough Friday night. This trough will rapidly track northeast to Wyoming Friday night. The GFS appears to be the fastest with this feature and the Euro the slowest. Clouds and showers will increase sometime during the night from the southwest from this feature Friday night. This trough will deliver some active weather over the weekend which my esteemed colleague will address in the long term. .LONG TERM...Saturday through Thursday Issued at 251 PM MDT Thu Jun 4 2020 The open trough over the southwest US will get ejected over Wyoming during the day Saturday. This system will bring widespread rain showers and thunderstorms through the day. Activity will start west of the Divide, then spreading across the east in the afternoon. Precipitable water values are in the 0.6 to 1 inch range so precipitation will have the potential to be heavy at times. Models are still a bit conflicted on the strength of storms. GFS has only a few small areas of CAPE above 200 J/kg available, while NAM is bringing in a large swath of 600 to 1000 J/kg across the western mountains. I have split the difference, including heavy rain and small hail into the grids for now. On Sunday morning, models show a stout trough over the western U.S. with the upper low centered over Oregon. The upper low is expected to shift into central Idaho by 00Z Monday. Frontogenesis is expected Sunday over the forecast area as the a strong west to east baroclinic zone will develop across western/central Wyoming Sunday. This strong Pacific cold front is then expected to surge east across the forecast area Sunday night. The main mid-upper trough axis looks to pull across the area on Monday/Monday night. There is a very good chance of significant precipitation over the west as a strong jet streak pulls across the area with decent QG forcing. Snow levels over the far west could be down to around 8000 feet Sunday. Snow levels will drop to valley floors west of the Divide Sunday night, but the most of the precipitation should have shifted away, but would not be surprised to see some snow in the western valleys and basins Sunday night. Precipitation totals ar in the 0.50 to 1.00 inch range Saturday into Sunday night west of the Divide. Could see a few inches of snow in the mountains while any higher amounts in the lower elevation might run risk of some flooding. Will continue to monitor. The bulk of chances of precipitaion with this system will continue until the trough axis pulls across the area Monday/Monday night. The precipitation Monday is expected to be much lighter than what occurs Sunday. A trailing shortwave could give a slight chance of shower activity especially over the northwest and north on Tuesday. Ridging develops Wednesday and Thursday with mainly dry conditions and a warming trend. && .AVIATION...(For the 06Z TAFS through 06Z Saturday) Issued at 1056 PM MDT Thu Jun 4 2020 Light winds and VFR cigs continue through most of the next 24 hours. High cirrus will start to move across the region during the day Friday, while gusty winds return during the afternoon. Most areas will see lighter winds overnight Friday night, except for KRKS, which remains 20G30kts and gusty. Rain showers begin to move into southern and western WY Friday night, bringing cigs down at KRKS/KBPI/KPNA after 06Z Saturday. && .FIRE WEATHER... Issued AT 251 PM MDT Thu Jun 4 2020 A weak weather system will move across the state and bring isolated to widely scattered showers and thunderstorms, most numerous in northern Wyoming for the rest of this afternoon. A gusty wind will develop in the afternoon with some elevated fire behavior expected in portions of central and southern Wyoming with relative humidity falling to around 13 percent. Mixing and smoke dispersal will range from good in portions of the north to excellent in the west and south. Even hotter temperatures and slightly lower RH are expected for Friday, but winds will be a little lighter. Still, elevated fire conditions are also expected again Friday. Saturday will feature unsettled weather with considerable cloudiness, along with showers and thunderstorms, and increased wind. Much cooler and wet conditions along with some mountain snow is expected by early next week. && .RIW WATCHES/WARNINGS/ADVISORIES... NONE. && SHORT TERM...Lipson LONG TERM...Hulme AVIATION...Straub FIRE WEATHER...Lipson
Hazardous Weather Outlook National Weather Service Riverton WY 332 AM MDT Fri Jun 5 2020 WYZ001>020-022>030-061215- 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- 332 AM MDT Fri Jun 5 2020 This Hazardous Weather Outlook is for Western and Central Wyoming. .DAY ONE...Today and Tonight. Elevated fire conditions across much of the lower elevations, except for the far north. .DAYS TWO THROUGH SEVEN...Saturday through Thursday. Saturday...Widespread afternoon and evening thunderstorms. Some of the thunderstorms could be strong to severe. Sunday and Monday...Isolated to scattered showers and thunderstorms. Higher elevation snow possible over far western mountains. .SPOTTER INFORMATION STATEMENT... Weather spotters are encouraged to report significant weather conditions.
The Riverton/Lander radar (KRIW), 183 km away, was scanning. The volume nearest the first event began at 09:47 UTC.
3 thunderstorm wind. Local standard time, as filed.
An outflow boundary moving into the area from the thunderstorms to the south brought high winds to the Buffalo, Wyoming airport. The maximum reported wind was 64 mph.
Severe thunderstorm winds occurred at the Natrona County airport. The maximum wind gusts reported was 60 mph.
Winds gusted to 58 mph and 59 mph wind gusts at the Lander and Riverton ASOS sites, respectively. High gusts occurred in the mountains with several 76 mph wind gusts at Red Canyon near Highway 28.
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, June 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: 897821, 897819, 897818.