High based showers developed in an area of very dry surface air and large dew point depressions. This led to some very strong wind gusts when showers collapsed.
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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.
High based showers developed in an area of very dry surface air and large dew point depressions. This led to some very strong wind gusts when showers collapsed.
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 6, 12:07 PM MST, 2 hours 7 minutes earlier. Its key messages:
Area Forecast Discussion National Weather Service Riverton WY 107 PM MDT Sat Jun 6 2026 .KEY MESSAGES... - Widespread critical fire weather conditions continue through the weekend given low humidity, gusty wind, and hot temperatures. - Chances (10-15%) for very isolated showers and thunderstorms today and tonight mainly across northern and western Wyoming. - Thunderstorm chances become more widespread Sunday (15-40%), with a couple of stronger storms possible across the eastern Bighorn Basin and Johnson County. && .UPDATE... Issued at 105 PM MDT Sat Jun 6 2026 Today's forecast of hot and dry conditions is on track, though scattered high clouds have delayed heating slightly. Still, peak temperatures should reach near 100 degrees in portions of the Bighorn Basin, as well as northeastern Johnson County. There are currently some weak, isolated showers across northwestern Wyoming, and there are still indications that there may be additional development later today as cyclonic flow increases. Critical fire weather conditions are the more widespread impact given the elevated southwest wind. Similar concerns will be noted for Sunday, with the additional threat of more widespread and robust convection as the trough begins swinging in. && .DISCUSSION... Issued at 206 AM MDT Sat Jun 6 2026 The long-awaited buckling of the midlevel flow has begun to strengthen across the western US, and will bring the warmest day of 2026 to most of the state. H7 temperatures are already running 12-14C, and will be peaking this afternoon between 16 and 18C, which translates to the sfc as highs in the upper 80s to the upper 90s. Isolated readings at 100 degrees may be noted along the lowest elevations of the Bighorn Basin for a few hours this afternoon. Temperatures aloft will be cooler for NW WY, which is closer to the incoming trough, which will keep temps more modest in the 70s this afternoon. The southwest flow around the approaching trough will be very dry, and with dry air already at the sfc, will mix well down to the sfc this afternoon. Wind gusts will reach 35 to 50 mph through the afternoon, picking up around noon and continuing into the early evening. Humidity levels will also crash down this afternoon, staying below 10 percent through the afternoon. This leads to critical fire weather concerns all day. Tonight, the advancing trough moves off the PacNW coast into the Northern Rockies, pushing the heat ridge eastward and opening up most of the state for increased moisture. There is a hint in some of the convective models that today's heating may be enough to tap the leading edge of the trough to spark a few showers even into central WY this afternoon, but this will be battling against the subsidence with the ridge, so this area may be limited to some increased CU. The better chances for showers first builds into the NW Parks this evening and overnight as the first lobe of the trough passes through. The next band then sets up somewhere in central WY during Sunday afternoon, influenced by an instability axis aloft. As the trough moves east, an enhanced area of shear builds into northern WY, which will also be influenced by terrain shear off the Bighorn Range. Strongly sheared environment and instability could lead to thunderstorms quickly strengthening across Johnson County during the afternoon, with a quickly increasing threat for hail and very strong winds. SPC has this areas in a slight risk on Sunday, and will need to monitor for final timing. Into early next week, the main trough shifts east, putting the axis along the Rockies for the first half of the week. Right now, this puts the northern half of the state in a more showery pattern through most of the upcoming week. && .AVIATION /18Z TAFS THROUGH 18Z SUNDAY/... Issued at 1114 AM MDT Sat Jun 6 2026 Mostly VFR flight conditions are forecast at all terminals through at least 18Z Sunday. Winds will quickly increase from the southwest by 20Z with frequent 25kt to 35kt gusts. The strongest gusts are forecast at KRKS, KPNA, and KWRL and these three terminals could see occasional gusts around 40kts. Gusty winds at all terminals will begin to diminish between 00Z and 03Z Sunday and be 11 kts or less overnight. Wind quickly increase again from the southwest after 14Z Sunday at all terminals. There is 10% chance of a shower at KRKS and KCPR from roughly 23Z today to 03Z Sunday. Low light rain chances exist across western Wyoming between 04Z and 09Z Sunday and brings a 30 percent chance of light rain to KJAC. Isolated to scattered shower and thunderstorm chances are forecast on Sunday, with a 30 percent chance at KJAC as early as 15Z Sunday. A heavier shower could result in brief periods of MVFR visibilities at KJAC. There is potential that KRKS and KWRL sees an isolated thunderstorm after 18Z Sunday. Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for the latest information on icing and turbulence forecasts. && .FIRE WEATHER... Issued at 105 PM MDT Sat Jun 6 2026 Critical/near-critical fire weather conditions will be widespread across the area through at least early next week. An incoming system will also increase the lightning and outflow wind threat starting Sunday as isolated thunderstorms move northeast across the area. The near-surface conditions will remain dry, so much of this may be virga. In addition to the background gusty southwest wind, this activity could produce strong and erratic wind gusts of 50 to 60 mph. && .RIW WATCHES/WARNINGS/ADVISORIES... Red Flag Warning until 8 PM MDT this evening for WYZ280. && UPDATE...Myers DISCUSSION...Straub AVIATION...Gerhardt FIRE WEATHER...Myers
The Salt Lake City radar (KMTX), 153 km away, was scanning. The volume nearest the first event began at 21:10 UTC.
4 thunderstorm wind. Local standard time, as filed.
Wind gusts of 65 mph occurred along Highway 30 near Fossil Butte National Monument.
A 63 mph wind gust occurred along Highway 20 26 near Hiland.
A 59 mph wind gust occurred southeast of Wapiti.
A 59 mph wind gust occurred along Interstate 90 to the north of Buffalo.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Wyoming in 2026Every state in 2026This day in weather historyWarnings in Wyoming, June 2026
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: 1350459, 1350461, 1350460, 1350462.