A Pacific trough and associated cold front brought high wind to areas along and east of the Continental Divide. The highest wind gust reported was 92 mph along the Chief Joseph Highway in the Absaroka Range.
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The episode as NWS RIW wrote it up.
A Pacific trough and associated cold front brought high wind to areas along and east of the Continental Divide. The highest wind gust reported was 92 mph along the Chief Joseph Highway in the Absaroka Range. As for the lower elevations, the peak wind was an 81 mph gust near I-25 and Hat Six Road to the east of Casper. An 84 mph wind gust was reported along Wyoming Highway 28 at Red Canyon in the Wind River Range. Wind gusts exceeding 60 mph were also reported in the lower elevations of Johnson and Fremont counties. The high winds closed numerous roads to high-profile vehicles.
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 Dec 29, 4:25 PM MST, 2 hours 43 minutes earlier.
Area Forecast Discussion National Weather Service Riverton WY 425 PM MST Wed Dec 29 2021 .SHORT TERM...This Afternoon through Thursday Night Some low clouds will continue to increase in coverage across the north and west as the next system rotates through. There are several systems in play, making this system a bit of a mess. To the north, a very broad longwave trough and Arctic low over Canada is keeping seasonably cold temperatures across much of the region, particularly the northern areas. Temperatures today continue to be slightly below normal, but still seasonal. Across basins east of the Continental Divide, a few locations will see lower 20s, but most will not get out of the upper teens. West of the Divide, low teens or even some single digits, especially in the higher terrain, can be expected today. Lows will again drop to near or below zero in most locations, with similar values to this morning. By Thursday afternoon, temperatures will be near normal as the trough moves farther east impacting the northern Plains and Great Lakes, rather than us here in Wyoming. Basins east of the Divide may even see some locations cross the freezing mark briefly during the afternoon. To the south, a circulation is keeping fairly strong southwest winds across much of the usual areas. Winds won't be too bad today, but will increase towards Thursday morning as a stronger jet streak moves across the region. Models continue to indicate a good downsloping signature along the Absarokas and Wind Rivers, as well as Casper Mountain. This will result in High Winds across the usual areas on the south side of Casper. The High Wind Watch will be upgraded to a Warning for this location. Will also issue a High Wind Warning for Red Canyon (South Pass) where winds will likely meet criteria Thursday morning. With the cold temperatures remaining across the north, not seeing a strong temperature gradient that would indicate a similar situation for Cody/Clark so left this area out of any wind highlights. Winds will diminish Thursday late afternoon into the early evening. To the east, a low is rotating along the Pacific coast. Pacific moisture continues to stream along the trough. This keeps a pretty consistent flow of moisture into the western part of the state. Winter Weather Advisories remain in effect for the western zones, as Advisory amounts will likely occur over the next 48 hours or so. More borderline amounts in the valleys, particularly Star Valley, but not enough to cancel the Advisories, as they will see persistent snow. Snowfall rates decrease towards Thursday night as a trough starts to dig to the west, helping to cut of the California moisture train. This will however, help to turn flow more northwesterly and hence keep snow showers across the western mountains into Friday morning. .LONG TERM...Friday through Wednesday Long wave trough stretching across southern Canada to the northern Rockies deepens Friday as a strong 150+ kt jet digs south on the backside. Trough axis to be on our western doorstep by 00Z/Saturday with the bulk of the energy headed to the Four Corners by 12Z/Saturday. As a result, western mountain snow decreases in coverage and intensity Friday afternoon and evening. The digging trough tugs colder air south across areas east of the Continental Divide Friday afternoon and evening. The colder airmass and weak upslope flow leads to light snow showers during this time frame, particularly where northerly upslope would be favored. Again bumped precipitation chances upward across the east to account for this possibility. Snow amounts would be limited given the cold airmass. Any light snow ends overnight as energy drives south to the base of the trough before emerging in the lee of the Rockies Saturday. Saturday will be dry and cold with northerly flow prevailing through much of the day. A brisk westerly wind of 15 to 25 mph across the central and southwest zones will make it feel even colder than the already chilly high temperatures. Have adjusted daytime temperatures downward, especially in the snow-covered western valleys and basins given the cold mid-level temperatures. The cold day combined with a mostly clear sky Saturday night leads to some very cold overnight lows Sunday morning. This cooling will be most pronounced in the same western valleys and basins where lows have been adjusted downward. Ridging over the western US noses into the state Saturday night with good warm air advection aloft. Expect valley and basin inversions, at least across the west, to steepen Sunday with temperatures below blended forecast guidance. Areas east of the Divide, particularly foothill communities, should see temperatures moderate Sunday given the amount of warming aloft. The ridge flattens and translates the forecast area Sunday night and a trough begins to dig off the Pacific Northwest coast. This leaves warmer southwest flow across the state for Monday. Gusty central Wyoming winds Sunday ramp up a bit more Monday in this favored southwest flow. The forecast looks to be dry Monday before more Pacific moisture reaches the far west late Monday night or Tuesday. Snow chances increase Tuesday and more likely on Wednesday across the west. The southwest flow and improved mixing leads to a gradual warm-up for almost all areas over the first part of next week. Expect wind to become more widespread Tuesday and Wednesday. && .AVIATION...(For the 00Z TAFS through 00Z Thursday evening) Issued at 424 PM MST Wed Dec 29 2021 West of the Divide...KBPI/KJAC/KPNA/KRKS Terminals KJAC to see MVFR through most the period with the best chance for heavier snow and IFR conditions through 05Z/Thursday. Southerly wind increases this evening with a better potential for blowing snow. Ceilings should rise briefly to low-end VFR after a trough in westerly flow aloft clears the area around 09Z/Thursday. However, could certainly see a situation where MVFR OVC025 ceilings linger at KJAC through the night. Brief MVFR possible at KBPI and KPNA this evening as the same trough progresses east. Similar to KJAC, expect MVFR or low-end VFR ceilings to stick around through late Thursday morning at KBPI and KPNA. KRKS to remain VFR with a gusty westerly wind 13-25kts for most of the period. Conditions again deteriorate after 18Z/Thursday as the next wave of moisture reaches western Wyoming. IFR/MVFR anticipated again at KJAC Thursday afternoon. East of the Divide...KCOD/KCPR/KLND/KRIW/KWRL Terminals Terminals remain VFR through 00Z/Friday. Primary hazard will be gusty southwest wind at KCPR which increases overnight and persists through Thursday afternoon in response to strengthening mid-level wind. These same westerly mid-level wind descends the east slopes of the Absaroka and Wind River mountain ranges between 06Z- 15Z/Thursday. LLWS remains a distinct possibility at KCOD and KLND with 12-25kt winds surfacing at these two terminals. KRIW to also see gusty westerly wind late Thursday afternoon. Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for the latest information on icing and turbulence forecasts. && .FIRE WEATHER... Snow continues over the Yellowstone and Teton dispatch areas through Thursday night. The heaviest snow is anticipated through Wednesday evening and again Thursday afternoon and evening. To the east of the Continental Divide, conditions remain dry with southwest wind increasing Wednesday night and Thursday. Speeds of 30 to 45 mph will be common in central Wyoming and along the east slopes of the Absaroka and Wind River mountains. The High Desert District and portions of Johnson and Fremont counties can expect a southwest breeze Thursday afternoon. After a more seasonal day Thursday, temperatures take a downturn Friday as cold air filters into the state from Montana. The arrival of the colder air leads to scattered light snow for many areas Friday afternoon and evening. Saturday will be drier but quite cold. As for smoke dispersal, the warmer temperatures and gusty southwest wind improve atmospheric mixing substantially Thursday across central Wyoming and in the foothills. The return of the colder air will keep smoke dispersal poor to at best fair Friday and Saturday. && .RIW WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory until 5 AM MST Friday for WYZ001-012-013- 023-024. High Wind Warning from 10 PM this evening to 7 PM MST Thursday for WYZ015-020. && SHORT TERM...Hensley LONG TERM...CNJ AVIATION...Jones FIRE WEATHER...CNJ
Hazardous Weather Outlook National Weather Service Riverton WY 210 PM MST Wed Dec 29 2021 WYZ001>020-022>030-301400- 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- 210 PM MST Wed Dec 29 2021 ...Winter Weather Advisory Continues for Western Wyoming through Thursday Night... ...High Wind Warning for Natrona County and the area around Red Canyon and South Pass from 10 PM Wednesday Until 7 PM Thursday... This Hazardous Weather Outlook is for Western and Central Wyoming. .DAY ONE...Rest of Today and Tonight. Snow continues across far western Wyoming through Wednesday evening before slowing after midnight. Please see Winter Weather Advisory for details. Southwest wind increases late Wednesday evening across Natrona County, especially along the south side of Casper. The wind will also increase along Wyoming Highway 28 around Red Canyon. .DAYS TWO THROUGH SEVEN...Thursday through Tuesday. Thursday...After a brief lull, snow increases again across western Wyoming around midday Thursday into the evening hours. Strong southwest wind persists across Natrona County and along Wyoming Highway 28 near Red Canyon. Friday...Turning colder with a chance of light snow during the afternoon and evening. .SPOTTER INFORMATION STATEMENT... Weather spotters are encouraged to report new snowfall totals.
The national radar mosaic for the moment the first event began.
6 high wind. Local standard time, as filed.
A maximum wind gust of 84 mph was reported at Red Canyon. The wind gusts and blowing snow lead to the closure of South Pass to high-profile vehicles.
There were widespread high wind gusts around Natrona County. Some notable wind gusts included 81 mph near Hat Six Road, 76 mph along Wyoming Boulevard, and 61 mph at the Casper-Natrona County International Airport. Several trees were blown down in the city of Casper.
High winds occurred along the Chief Joseph Highway. The maximum wind gust recorded was 92 mph.
At the Camp Creek RAWS, a maximum wind gust of 82 mph was reported. In the lower elevations, a wind gust of 68 mph was reported along Wyoming Highway 220 near Pathfinder Reservoir.
A 59 mph wind gust was recorded at the Dubois airport.
A maximum gust of 70 mph was reported along Interstate 90 north of 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, December 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: 997104, 997103, 997108, 997105, 997106, 997107.