A gust front from thunderstorms to the north pushed southward across Thermopolis WY. Around a dozen trees were downed in Thermopolis, including two that were uprooted.
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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 gust front from thunderstorms to the north pushed southward across Thermopolis WY. Around a dozen trees were downed in Thermopolis, including two that were uprooted. Some trees and branches fell and damaged power lines. Winds were estimated to be around 50 mph. One tall structure had a metal roof which was peeled back by the strong winds.
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 Jul 17, 2:31 PM MST, 1 hour 19 minutes earlier.
Area Forecast Discussion National Weather Service Riverton WY 331 PM MDT Mon Jul 17 2023 .DISCUSSION...(This evening through Monday) Issued at 325 PM MDT Mon Jul 17 2023 High pressure is trying to hold on today as the ridge axis passes through Wyoming. This will lead to some of the hottest temperatures we've seen thus far this summer as 700mb temperatures peak around 20C this afternoon. Accordingly, some locations east of the Divide will approach 100 degrees. There is some decent high cloud cover, which could keep temperatures a few degrees cooler than earlier forecasts. Other than the heat, there are a couple of forecast concerns. The first is critical/elevated fire weather across much of the area. A strong surface pressure gradient currently extends across the area as a cold front moves east from western Wyoming. This will lead to gusty westerly winds at the surface. Given the low humidity, this will create elevated fire weather conditions for most, with critical conditions across central and southern Wyoming where humidity will drop into the lower teens. Fortunately, fuels still not fully cured will help to mitigate concerns somewhat. The other concern is strong thunderstorm potential. The ridge is not the only player in today's forecast game as a trough across the northwest begins to flatten it. Given decent moisture influx, this will help kick off some showers and thunderstorms today. With the still mostly dry boundary layer, the main concern with this activity will be strong wind gusts. Current observations are showing temperature/dew point spreads ranging from the 40s on the lower end to over 70 degrees (KRKS), so the potential for severe outflow wind is certainly there today. However, northern and eastern portions of the forecast area will actually see dewpoints in the upper 40s and 50s, which will also lead to a low hail threat. Wind will wane with sunset as the front sweeps east. A few showers may linger overnight across the southern half of the area. Otherwise, westerly flow will persist on Tuesday. While humidity levels will be increased slightly and temperatures decreased, elevated fire weather conditions will continue as west wind again picks up during the afternoon. A few showers and thunderstorms are also likely to return as well, mainly across the southern half of the forecast area. Looking ahead, enough moisture and upper-level divergence in the pattern will keep daily convection through the end of the week, with Thursday the best chance of wider impacts. && .AVIATION...(For the 18Z TAFS through 18Z Tuesday) Issued at 1153 AM MDT Mon Jul 17 2023 Shortwave energy moving across the Northern Rockies has spread a baroclinic leaf across Idaho and Montana Monday morning. A cold front associated with this feature makes its way east Monday afternoon with gusty west to northwest surface wind 18-35kts following frontal passage. There is enough mid-level moisture available to initiate high-based convection mainly after 20Z/Monday until around 02Z/Tuesday. The primary hazard is outflow wind gusts in excess of 40kts given large temperature-dew point spreads. Convection and gusty wind decrease between 02Z-04Z/Tuesday. High-resolution models depict weak showers or virga traversing the southern half of the forecast area overnight and Tuesday morning. Again, gusty and erratic outflow wind would be the primary hazard with any lingering convection. && .FIRE WEATHER... Issued at 325 PM MDT Mon Jul 17 2023 Elevated to critical fire weather conditions are ongoing this afternoon. Westerly wind gusts over 30 mph are possible across much of the area. A few storms are also likely with strong to severe wind gusts the main threat. Humidity recovery will generally be decent tonight, with a few showers lingering overnight. While humidity will remain slightly higher on Tuesday as compared to this afternoon, gusty west winds will still help to create elevated fire weather conditions. Another round of showers and thunderstorms is likely as well, mainly across the southern half of the area. These will generally not be very good rain producers, and the main concern will again be gusty outflow winds. && .RIW WATCHES/WARNINGS/ADVISORIES... NONE. && DISCUSSION...Myers AVIATION...CNJ FIRE WEATHER...Myers
Hazardous Weather Outlook National Weather Service Riverton WY 1237 PM MDT Mon Jul 17 2023 WYZ001>020-022>030-181300- 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- 1237 PM MDT Mon Jul 17 2023 This Hazardous Weather Outlook is for Western and Central Wyoming. .DAY ONE...This Afternoon and Tonight. Hot temperatures, low relative humidity, and gusty west wind combine to elevate fire weather conditions this afternoon and early evening. Also, isolated showers and possibly a thunderstorm could create gusty outflow wind in excess of 50 mph from mid- afternoon until shortly after sunset. .DAYS TWO THROUGH SEVEN...Tuesday through Sunday. Tuesday...Elevated fire weather conditions continue in the afternoon. Isolated showers and thunderstorms over far southern Wyoming may generate gusty outflow wind exceeding 40 mph. Wednesday...Far southern Wyoming could again see isolated showers and thunderstorms producing gusty outflow wind exceeding 40 mph. Thursday...A better chance of more widespread afternoon and evening showers and thunderstorms. Saturday and Sunday...Temperatures again rising to above normal, with many areas seeing highs in the 90s.
Special Weather Statement National Weather Service Riverton WY 413 PM MDT Mon Jul 17 2023 WYZ002>011-014>020-022-028>030-180400- 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-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- Rock Springs and Green River-Flaming Gorge-East Sweetwater County- Including the cities of Clark, Cody, Meeteetse, Basin, Greybull, Lovell, Powell, Shell, Thermopolis, Ten Sleep, Worland, Buffalo, Kaycee, Dubois, Riverton, Shoshoni, Lander, Jeffrey City, Casper, Rock Springs, Green River, and Wamsutter 413 PM MDT Mon Jul 17 2023 ...Showers and thunderstorms with strong wind gusts into this evening... This is a special weather statement from the National Weather Service office in Riverton. * WHAT...Scattered showers and thunderstorms. Wind gusts of 40 to 50 mph with occasional gusts to 60 mph are possible with any shower or thunderstorm. * WHERE...Most of central and southern Wyoming. * WHEN...Through 10 pm tonight. * ADDITIONAL DETAILS...Strong wind gusts can occur several miles away from any shower or thunderstorm, even if no rain is occurring.
The national radar mosaic for the moment the first event began.
1 strong wind. Local standard time, as filed.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Wyoming in 2023Every state in 2023This day in weather historyWarnings in Wyoming, July 2023
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: 1124971.