A high-based thunderstorm produced very strong wind in and around Big Piney. The strong winds blew down limbs from cottonwood trees and caused damage to two mobile homes in Big Piney.
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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 high-based thunderstorm produced very strong wind in and around Big Piney. The strong winds blew down limbs from cottonwood trees and caused damage to two mobile homes in Big Piney.
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 12, 3:50 PM MST, 0 minutes earlier.
Area Forecast Discussion National Weather Service Riverton WY 450 PM MDT Mon Jul 12 2021 .SHORT TERM...(This evening through Tuesday night) Issued at 216 PM MDT Mon Jul 12 2021 Today will be very much the same as yesterday with smoky skies and hot, dry weather. There is a very slight chance of isolated showers and thunderstorms across the region this afternoon, but nothing strong or severe is expected today. Only threat would be some gusty outflow winds, which could gust to 30 to 40 mph. Best areas for development are along the Bighorns, where a few showers have popped up as of 130 PM. Some models are also showing possible convective development off the southern Absarokas and Wind River Mountains later this afternoon and evening. Marginally elevated fire weather will continue across the south and southwest today with breezy conditions and continuing dry weather. Tomorrow, a shortwave will drop south out of Canada across Montana and into northern WY. This will lead to critical fire weather conditions across the south due to hot, dry, and windy conditions. Winds will increase across the southwest late tomorrow morning and continue gusting through the day. Gusts up to 30 to 40 mph are possible through the afternoon. Red Flag Warnings will be issued for this area for the hot, dry, and windy weather. There is also a chance for dry lightning across this same area, and the chance for gusty outflow winds from convection. The front associated with the shortwave, timed up with CAPE around 1000 to 1500 J/kg and steep lapse rates, will lead to a severe thunderstorm threat across much of central and northern WY tomorrow afternoon. Convection will begin early tomorrow morning along the dynamics, then increase into the afternoon. Most of the severe storms will likely develop along outflow boundaries. The main threat will be wind with very strong outflows, which will be possible with any storm that develops. Small hail and some severe hail is also possible, especially across Johnson county, where there will be a bit more moisture to work with. SPC has issued a Day 2 Slight risk across northern Bighorn basin and Johnson county, and this looks to be the area of biggest concern. Red Flag warnings will be issued for those areas because of the lightning threat with the heat and continued dry weather. Most of the convection should be through the region by late evening, but a lingering shower or thunderstorm across Johnson County will be possible through around midnight as the dynamics finally ease and move east. .LONG TERM...(Wednesday through Monday) Issued at 216 PM MDT Mon Jul 12 2021 The weak ridging remains in place along the Rockies for the latter half of the week, but is not initially strong enough to inhibit daytime thunderstorms. These will form along the higher elevations each afternoon, bringing a risk for occasional lightning and gusty winds. Wednesday will be behind the cold front, so lighter north to northwest winds will continue across the state. Temperatures will be 5 to 10 degrees cooler than Tuesday. Temperatures recover back into the 90s for the remainder of the week with drier westerly flow. Models continue to bring the ridge northward across WY over the weekend into early next week. This looks to be strong enough to inhibit daytime convection on higher elevations, and will continue to bring summertime heat to the state. && .AVIATION...For the 00Z TAFS through 00Z Wednesday Issued AT 430 PM MDT Mon Jul 12 2021 Smoke/haze remains in the area, with the greatest impacts at KJAC and KCOD. Local MVFR conditions and mountain obscuration due to lower visibility in smoke or haze will continue as well. Isolated showers or storms will occur over and near the northern mountains will be decreasing after 03Z. KCOD and KWRL will be the most likely to be impacted by this activity. Wind gusts to 40 knots expected from the storms. Isolated showers and storms will occur in the south and southwest until 03Z. Otherwise, VFR conditions will prevail at the terminal sites. Winds increase, especially across the southwest early tomorrow afternoon. Shower and thunderstorm activity will also increase tomorrow. VCTS is included for the terminals with the greatest chance of storms. Very gusty, erratic winds will be expected with these storms. 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 216 PM MDT Mon Jul 12 2021 Red Flag Warnings have been posted for Tuesday for portions of Wyoming, as dry and breezy conditions combine with the increased threat for dry lightning. Strongest winds will be across southern WY, where winds of 25 to 35 mph are expected. Dry lightning threat will be greatest across northern WY, including the Absarokas and the Big Horn Basin, along with Johnson County. Some of the thunderstorms across northern WY are also expected to be strong to severe, with very gusty winds and occasional hail in the strongest storms. Hot and dry conditions are expected to continue through the rest of the week, but winds will remain well below critical thresholds. Some higher elevation thunderstorms may develop each afternoon through Friday. && .RIW WATCHES/WARNINGS/ADVISORIES... Red Flag Warning from 1 PM to 9 PM MDT Tuesday for WYZ275>279- 286-414. Red Flag Warning from 1 PM to 11 PM MDT Tuesday for WYZ281. && SHORT TERM...Fisher LONG TERM...Straub AVIATION...Fisher FIRE WEATHER...Straub
Hazardous Weather Outlook National Weather Service Riverton WY 350 AM MDT Mon Jul 12 2021 WYZ001>020-022>030-131000- 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- 350 AM MDT Mon Jul 12 2021 ...Fire Weather Watches in effect for Tuesday across northern and southern portions... This Hazardous Weather Outlook is for Western and Central Wyoming. .DAY ONE...Today and Tonight. Isolated to widely scattered showers and thunderstorms across the north this afternoon and evening. .DAYS TWO THROUGH SEVEN...Tuesday through Sunday. Tuesday...Strong to severe thunderstorms possible across northern portions east of the Divide during the afternoon and evening. Critical fire weather conditions possible west of the Divide. Wednesday through Friday...Isolated thunderstorms possible across the area. Saturday and Sunday...Well above normal temperatures likely, with high temperatures over 100 possible in some of the lower elevations. .SPOTTER INFORMATION STATEMENT... Weather spotters are encouraged to report significant weather conditions according to standard operating procedures.
The Riverton/Lander radar (KRIW), 144 km away, was scanning. The volume nearest the first event began at 22:51 UTC.
1 thunderstorm wind. Local standard time, as filed.
The ASOS at the Big Piney-Marbleton Airport registered a 61 mph wind gust.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Wyoming in 2021Every state in 2021This day in weather historyWarnings in Wyoming, July 2021
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: 971100.