Scattered afternoon showers and thunderstorms formed, often producing strong outflow winds due to a dry lower atmosphere.
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The episode as NWS RIW wrote it up.
Scattered afternoon showers and thunderstorms formed, often producing strong outflow winds due to a dry lower atmosphere.
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 25, 10:05 AM MST, 55 minutes earlier. Its key messages:
Area Forecast Discussion National Weather Service Riverton WY 1105 AM MDT Mon May 25 2026 .KEY MESSAGES... - A warm day, with highs in the upper 70s to upper 80s. Showers and thunderstorms are possible (15 to 50 percent), with the best chances along and west of the Divide. Gusty outflow winds 30 to 50 mph are the main hazard with any shower or storm. - Increased moisture brings the chance of showers and thunderstorms Tuesday. Strong winds are the main hazard with these storms. - A fairly stagnant weather pattern keeps above normal temperatures much of the week, with daily chances of afternoon showers and thunderstorms. && .DISCUSSION... Issued at 114 AM MDT Mon May 25 2026 The overall theme of the forecast remains largely the same as this time yesterday. Things are largely quiet at this time around western and central Wyoming. And the main players in the forecast remain the same, an approaching upper level low that will move onshore in the Pacific Northwest today and a ridge that will build across the Plains states for much of the week. And their positions will have the main influence on our weather each day, as we will likely be between the two of them. As for today, the axis of the most showers and storms should shift to western Wyoming. Dew points should run around 5 to 10 degrees above yesterday and CAPE is maximized in this location, with up to 1000 J/Kg. We did increase POPS here somewhat, but the chance of any location seeing a shower or thunderstorm generally ranges from 1 out of 5 in the lower elevations to up to 2 out of 5 in the mountains. Most thunderstorms should be of the run of mill variety, although a stronger storm or two can't be ruled out. There is more of a question East of the Divide, where the lower atmosphere will be drier, and southwest flow should bring some downsloping flow. We did bump POPs up a bit, with the best chance across northern Wyoming, where the atmosphere is a bit more unstable, especially the Cody Foothills. Most of any activity in this area would likely be near the mountains, and the chance is generally lower than 1 out of 3. We can't rule a shower out anywhere, but elsewhere the chance is less than 1 out of 10. Southwest flow will bring a warm day as well, with temperatures running around 10 degrees above normal, and maybe a few 90s in the Bighorn Basin. Like previous days, activity will be largely diurnal and most will end shortly after sunset. Things may get a bit more active tomorrow. The upper level low will be onshore by this time and the first shortwave will be moving across the area from south to north. Low level flow will also be turning more to the south and east, bringing in more low level moisture. Precipitable water rise somewhat as well, to as high as an inch in eastern portions of the area, which is greater than 175 percent of normal and above the 90th percentile with climatology. One limiting factor may be cloud cover though, as this may limit instability. The two most likely zones look to again be the western mountains, where CAPE values climb to higher than 1000 J/Kg and lifted indices fall to minus 3. The other is across Johnson and Natrona Counties, where upslope may bringing convective initiation against the Bighorns. As for stronger storms, the best chance of that would be in western Wyoming where there is more directional shear present. Locally heavy rain is possible with any storm put there will be around 20 knots of storm motion, so this should limit any flooding potential. Storm chances range from around 1 out of 2 in the western mountains to less than 1 out 6 in portions of the Bighorn and Wind River Basins where the least activity will be found. Again, most activity should end after sunset, but a few showers may linger through the night. Uncertainty increases after this, as the guidance continues to struggle with the evolution of the movement of the upper level low. However, there has been a trend in the ridge being a bit stronger and keeping the low further to the west. This would mean a somewhat drier and warmer forecast. The forecast for Wednesday is likely the wettest it could be. The most active days may end up bring Friday or Saturday, but again a lot depends on the track of the low and how the trough axis moves as the low eventually opens up. The trend for now is for continued above normal temperatures and some chances of convection each day, with the best chance in western Wyoming. Determining which day will be the most active and where the heavier rain falls remains uncertain. We may also have to deal with some rising creeks, streams and rivers as the warm spell may be able to melt out some of the higher level snowpack. && .AVIATION /18Z TAFS THROUGH 18Z TUESDAY/... Issued at 1105 AM MDT Mon May 25 2026 All terminals to be VFR through the forecast period, with the exception of brief MVFR in heavier rain showers/storms west of the Continental Divide Monday afternoon. Cumulus already forming over the western Wyoming mountains and Uinta Range late Monday morning. Convection becomes scattered in nature between 19Z-21Z/Monday, mainly along and west of the Continental Divide. Deeper moisture and a bit higher dew points will lead to brief, heavier showers, but gusty outflow wind 30-40kts is the primary hazard. Scattered showers and isolated thunderstorms move northeast at 15 to 20 mph and reach the east slope foothills around KCOD and KLND around 21Z/Monday. Wind, with not much rain, will be the impact at these two terminals. A few showers may track near KRIW, KCPR, and KWRL before convection fades between 03Z-05Z/Tuesday, but confidence is low in timing and impacts. Southerly upper- level flow keeps cloud cover and isolated light showers over southwest and far western Wyoming overnight and Tuesday morning. Southerly surface wind develops at most terminals late in the forecast period. Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for the latest information on icing and turbulence forecasts. && .RIW WATCHES/WARNINGS/ADVISORIES... None. && DISCUSSION...Hattings AVIATION...CNJ
The Riverton/Lander radar (KRIW), 176 km away, was scanning. The volume nearest the first event began at 18:03 UTC.
1 thunderstorm wind. Local standard time, as filed.
A 68 mph wind gust occurred at Snider Basin when a high based shower collapsed.
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, May 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: 1342963.