A combination of an abnormally strong ridge and dry soil produced very hot temperatures in many areas. The hottest temperature during the period was 107 degrees at Greybull on July 19th.
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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 combination of an abnormally strong ridge and dry soil produced very hot temperatures in many areas. The hottest temperature during the period was 107 degrees at Greybull on July 19th. Record high temperatures were also recorded at Worland, Riverton, Lander, Buffalo, Rock Springs, and 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 16, 10:07 PM MST, 1 hour 53 minutes earlier.
Area Forecast Discussion National Weather Service Riverton WY 1107 PM MDT Fri Jul 16 2021 .SHORT TERM...This afternoon through Saturday night An upper level ridge will build over the region today, however temperatures will be around the same as Thursday. Surface dewpoints will still range between the mid 30s to mid 40s across the forecast area. Winds will remain light today, with gusts of 20 to 25 mph this afternoon. Widely scattered thunderstorms will begin developing after midday, with the best chances over the Wind River and Absaroka Mountains, the Wind River Basin and southern portions of the Bighorn Basin. Isolated thunderstorms will be possible across the remaining areas in the forecast area. These storms are not expected to be strong, due to the lack of instability. Gusty winds will be the main threat with these storms, however locally heavy rain could also occur due to the high dewpoints and precipitable water values. This convective activity will quickly subside this evening through sunset. Smoke could start to thin out today. Additional smoke from the western wildfires will be shunted northward, as a result of the building ridge. Similar conditions will occur Saturday, as temperatures remain hot. Highs in the middle to upper 90s will occur east of the Divide, with areas near Greybull approaching the century mark. The best chances for thunderstorms will be over the far west, with isolated storms possible east of the Divide and over Sweetwater County. Instability will again be very limited, while dewpoints remain in the mid 30s to near 40 degrees. && .LONG TERM...(Sunday through Friday) Issued at 1250 PM MDT Fri Jul 16 2021 A strong dome of high pressure will dominate the region through much of the long term period. This will be reflected in the weather as it will be mainly hot and dry. There will be fluctuations in the tilt and strength of the high and ridge through the week, with a few periods of convective activity popping up in times of weaker subsidence. Presently looking at areas with elevated fire weather conditions but due to the lack of strong, gusty winds red flag conditions are not likely in the long term. Sunday and Monday look to remain dry. Afternoon showers thunderstorms are likely to return Tuesday, and will redevelop most afternoons through the end of the period. Temperatures will continue to climb Sunday through Tuesday with 100+ degree highs very possible in portions of the Bighorn and Wind River basins, as well as Johnson county. Keep an eye on the temperature forecasts for your area, and make sure you are prepared for the heat. && .AVIATION...For the 06Z TAFS through 06Z Sunday Issued at 1055 PM MDT Fri Jul 16 2021 Expect VFR conditions throughout the TAF period. Isolated showers will end by 10Z in central WY. Isolated showers and storms will occur Saturday afternoon which may impact some terminals after 20z through about 02Z. Wind gusts over 40 mph will be a threat from storms. Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for the latest information on icing and turbulence forecasts. && .FIRE WEATHER... Scattered showers and thunderstorms will develop early this afternoon, with the best chances occurring in the Absaroka and Wind River Mountains, the Wind River Basin and southern portions of the Bighorn Basin. Isolated thunderstorms will be possible elsewhere across the forecast area. Red Flag Warnings remain in effect for lightning from this convective activity. Lightning and gusty winds will be the main threats from these storms, however locally heavy rain cannot be ruled out. Wind will remain below critical levels this afternoon, outside of the thunderstorm activity. RH recovery will be fair in the central basins to the eastern half of zone 279 and good to excellent in the western valleys and zone 280/281. Expect similar conditions Saturday, with the best thunderstorm chances occurring over the far western zones. && .RIW WATCHES/WARNINGS/ADVISORIES...None. && SHORT TERM...LaVoie LONG TERM...Swanson AVIATION...Clayton/AR FIRE WEATHER...LaVoie
Hazardous Weather Outlook National Weather Service Riverton WY 234 AM MDT Fri Jul 16 2021 WYZ001>020-022>030-171045- 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- 234 AM MDT Fri Jul 16 2021 ...Red Flag Warning in Effect for portions of western and central Wyoming... This Hazardous Weather Outlook is for Western and Central Wyoming. .DAY ONE...Today and Tonight. Critical fire weather for portions of western and central Wyoming. Please see Red Flag Warning for details. Isolated to widely scattered afternoon and evening thunderstorms possible for much of the area. .DAYS TWO THROUGH SEVEN...Saturday through Thursday. Saturday through Tuesday...Hot with well above normal temperatures .SPOTTER INFORMATION STATEMENT... Weather spotters are encouraged to report significant weather conditions according to standard operating procedures.
PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE RIVERTON WY
915 PM MDT FRI JUL 16 2021
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0749 PM TSTM WND GST BIG PINEY 42.54N 110.12W
07/16/2021 M60 MPH SUBLETTE WY ASOS
&&
MCDONALDThe national radar mosaic for the moment the first event began.
7 heat. Local standard time, as filed.
Record high temperatures of 104 and 107 were recorded at South Big Horn County Airport on July 18th and 19th.
A record high temperature of 106 degrees was recorded at Worland Municipal Airport on July 18th.
A record high temperature of 100 degrees was reported at Central Wyoming Regional Airport on July 18th.
Record high temperatures of 98 and 101 were set the the Johnson County Airport on July 17th and 19th, respectively.
A record high temperature of 100 was set at Hunt Field in Lander July 18th.
At the Southwest Wyoming Regional Airport east of Rock Springs, record high temperatures of 94 and 96 were recorded on July 18th and 19th, respectively.
Record high temperatures of 92 and 94 were set at the Big Piney-Marbleton Airport on July 18th and 19th, respectively.
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: 971318, 971319, 971320, 971321, 971322, 971323, 971324.