Strong mid-level winds mixed to the surface begin a cold frontal passage, producing strong wind across northern portions of Johnson County. A peak wind gust of 59 mph was recorded at the Buffalo airport.
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The episode as NWS RIW wrote it up.
Strong mid-level winds mixed to the surface begin a cold frontal passage, producing strong wind across northern portions of Johnson County. A peak wind gust of 59 mph was recorded at the Buffalo airport.
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 Sep 28, 6:24 PM MST, 1 hour 2 minutes earlier.
Area Forecast Discussion National Weather Service Riverton WY 724 PM MDT Tue Sep 28 2021 .SHORT TERM...This evening through Wednesday night The cold front moved into far western portions between 12pm and 1pm this afternoon. Winds have begun to increase across a few areas and are expected to continue and impact the rest of the forecast area through the rest of the day. The front is still expected to cross into northern portions late this afternoon, toward the evening and quickly progress southward. North to northwest winds will occur behind the front east of the Divide this evening. Gusts of 45 to 55 mph will be possible, with isolated gusts up to 60 mph over northern portions of Johnson County and the Bighorn Basin. RH values will begin to rise this evening, ending the Red Flag Warning. Isolated virga showers have already developed this afternoon, as moisture from the upper low over CO advects northward over the Cowboy State. These showers will become more scattered this evening, occurring east of the Divide and the eastern half of Sweetwater County. The better chance for precipitation will occur after midnight and through the rest of Wednesday morning. Precipitation amounts of 0.10 to 0.30" are possible from the Bighorns southward into the Wind River Basin and Sweetwater County between midnight and 6pm Wednesday. Any snow will occur in the mountains, although only 1 to 2 inches of snow is expected. Temperatures will be much cooler across the forecast area Wednesday, as a result of the cold front and the ongoing precipitation. Some locations will struggle to reach 50 degrees. Showers will end late Wednesday afternoon, however skies will be slow to clear Wednesday night. .LONG TERM...Thursday through Tuesday The trough over the Rockies begins to fragment on Thursday, and partially clearing skies overnight will allow temperature to be quite cold around sunrise. Current model runs show a bit more cloud persisting into the morning hours, which could help moderate surface temperatures; however, locations in the far northwest portion of the state should have clear skies and be chilly, with low temps in the teens to low 20s for the National Parks and typical cold spots. Daytime temperatures Thursday recover somewhat compared to Wednesday, but remain well below average. Flow aloft becomes unorganized and weak Friday into early next week. Models have a hard time latching onto any of the subtle shortwave features, but the overall air mass will moderate to seasonal averages. High temperatures are forecast to be near normal through early next week, with high 60s and low 70s east of the Divide, and low 60s west of the Divide. A few weather systems graze the eastern half of Wyoming, but none of these appear to be major rain makers, with only light showers reaching the ground. Saturday looks to be the breeziest day of this period, especially for the Powder River Basin, as a shortwave and the attendant weak cold front moves across southern Montana. Expect some high clouds through early next week given the vorticity maxima roaming aloft. A large cutoff low looks to congeal over the Plains during the middle of next week, and given the long wavelength of this feature, it could retrograde slightly, bringing continued high cloud cover to Wyoming. However, no major precipitating weather system appear likely for our region through the middle of next week. && .AVIATION...(For the 00Z TAFS through 00Z Wednesday evening) Issued at 529 PM MDT Tue Sep 28 2021 Many locations are seeing gusts in the 25 to 30 kt range this evening as a cold front pushes through the region. Locations such as KBYG and KCPR could see brief gusts in the 40 to 45 kt range locally with the main frontal passage later this evening. Ceilings continue to thicken and lower overnight, with rain showers expected along and east of a KRKS to KRIW to KWRL line overnight. Wednesday, winds decrease throughout the morning and early afternoon. Rain showers could linger into the afternoon for KRKS, but most other areas will likely see showers dissipate by mid-day. && .FIRE WEATHER... Critical fire weather conditions will continue for areas east of the Divide this afternoon, as a cold front begins to move into far western portions. This front will begin to move through northern portions by this evening, quickly exiting the forecast area by early Wednesday morning. Winds will turn north to northwest east of the Divide behind the front. Wind gusts of 40 to 55 mph will be possible, with isolated gusts up to 60 mph possible over northern portions of zones 275/281. Isolated virga showers will continue this afternoon, becoming scattered over areas east of the Divide and zone 279 this evening. Better chances for wetting rain will occur after midnight and continue through the rest of the day Wednesday. Precipitation amounts of 0.10 to 0.30" possible in these areas. && .RIW WATCHES/WARNINGS/ADVISORIES...NONE. && SHORT TERM...LaVoie LONG TERM...VandenBoogart AVIATION...Hensley FIRE WEATHER...LaVoie
Hazardous Weather Outlook National Weather Service Riverton WY 726 PM MDT Tue Sep 28 2021 WYZ001>020-022>030-300130- 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- 726 PM MDT Tue Sep 28 2021 This Hazardous Weather Outlook is for Western and Central Wyoming. .DAY ONE...Tonight. A cold front will move through areas east of the divide this evening. A north to northwest wind of 25 to 35 mph will occur behind the front with gusts from 40 to 50 mph in northern Wyoming. Parts of central Wyoming will see a north wind of 25 to 35 mph with gusts around 40 mph behind the cold front this evening. Scattered showers are possible overnight across central areas. .DAYS TWO THROUGH SEVEN...Wednesday through Monday. Wednesday...Much cooler high temperatures all areas. Some lingering showers are possible. .SPOTTER INFORMATION STATEMENT... Spotter activation will not be needed tonight.
Special Weather Statement National Weather Service Riverton WY 256 PM MDT Tue Sep 28 2021 WYZ003>011-016-017-020-022-290900- 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- Upper Wind River Basin-Wind River Basin- Natrona County Lower Elevations-Casper Mountain- Including the cities of Clark, Cody, Meeteetse, Basin, Greybull, Lovell, Powell, Shell, Thermopolis, Ten Sleep, Worland, Buffalo, Kaycee, Dubois, Riverton, Shoshoni, and Casper 256 PM MDT Tue Sep 28 2021 ...Strong Winds to Occur behind a Cold Front This Evening... This is a special weather statement from the National Weather Service Office in Riverton. * WHAT...Northwest to north winds, with gusts of 35 to 55 mph. Isolated gusts up to 60 mph possible over northern portions of the Bighorn Basin and Johnson County. * WHERE...Bighorn and Wind River basins, Johnson and Natrona counties. * WHEN...6 PM this evening through 3 AM Wednesday.
The national radar mosaic for the moment the first event began.
1 high wind. Local standard time, as filed.
A maximum wind gust of 63 mph was reported at the Johnson County Airport in Buffalo.
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, September 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: 981187.