A Pacific Cold Front and associated trough moved across the Cowboy State and brought heavy snow and high wind to portions of the area. The snow and wind disrupted holiday travel across the affected areas.
Every event with a place to put it; 6 filed by county or forecast zone are drawn at its center, in a lighter ring. Tap one for its entry below.
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 Pacific Cold Front and associated trough moved across the Cowboy State and brought heavy snow and high wind to portions of the area. The snow and wind disrupted holiday travel across the affected areas. The heaviest snow fell in Yellowstone National Park where the higher elevations received up to two feet of new snow. Over a foot of snow also fell in portions of the Teton and Wyoming mountain ranges. The highest amount in the lower elevations was 11 inches near Wilson in the Jackson Valley. High winds also occurred east of the Continental Divide. Ahead of the front, the wind prone areas south of Casper saw wind gusts as high as 68 mph. Behind the front, a wind gust to 59 mph was registered at the airport near Buffalo.
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 23, 2:39 AM MST, 1 hour 21 minutes earlier.
Area Forecast Discussion National Weather Service Riverton WY 239 AM MST Thu Dec 23 2021 .SHORT TERM...(Today through Friday) Issued at 238 AM MST Thu Dec 23 2021 As of 0130 MST, the radar is remaining mostly quiet with the exception of a few areas of orographic snow showers. Radar is indicating a few snow showers coming out of Idaho into the Star Valley and light reflectivity starting to fill in over the Tetons. As the day progresses radar will fill in as the Pacific Northwest trough and California cut-off upper level low pressure begin to interact over the western Wyoming mountains. Models continue to keep significant QPF amounts over the area and present snow amounts have been relatively consistent over the past several model runs. This leads to relatively high confidence in keeping most previously issued winter highlights in effect; however, there are a couple changes to note: 1) A Winter Weather Advisory was issued for the Upper Green River Basin for for light to moderate snow and strong winds this afternoon into Friday. 2) Most of Sweetwater County saw a slight increase in snow amounts and strong wind impacts are likely to be felt here as well, especially this evening into the early overnight hours, so Winter Weather Advisories were upgraded to Winter Storm Warnings. 3) Debated issuing a Winter Weather Advisory for the Green Mountains and Rattlesnake Range, but the travel corridors (including portions of US Hwy 287 and WY Hwy 220) look to only receive and inch or two of snow, despite the strong winds. Opting instead for a strongly worded Special Weather Statement, in addition to the High Wind Warning also in effect. As this complicated system continues to spread eastward, the associated PoP will spread over the Divide. With the west- southwest flow, temperatures east of the Divide will be above freezing and will see areas of rain before CAA changes rain to snow. This will minimize snowfall totals to trace amounts for most, but also can't rule out a little accumulation on the grass or other vegetation. The second aspect of this messy system is the potent upper-level forcing associated with the trough bringing increased surface winds across the forecast area. The High Wind Watches were upgraded to High Wind Warnings as confidence is high on those zones seeing major travel impacts in the lower elevations. Did lean on a mix of the higher model guidance for the sustained winds because of the potency of the jet. Also, tried to make sure the downsloping signature was represented in the forecast. As the main forcing for the high winds shifts eastward, winds will begin to decrease, which coincides with the time when PoP is spreading eastward. Other concerns associated with the wind are the possibility for blowing snow to severely limit visibility over southern Lincoln and Sweetwater counties. This will be monitored, but it's worth noting the potential for near-blizzard conditions. This storm does consume the entire short-term forecast period so I'll end with have a Merry White Christmas (for the western zones) and exercise caution when traveling as road conditions will rapidly deteriorate when the snow shield fills in across the forecast area. .LONG TERM...(Friday night through Wednesday) Issued at 238 AM MST Thu Dec 23 2021 The active weather pattern will continue next week as a robust longwave trough parks itself over Canada and continues to send multiple shortwaves troughs and their associated jet streaks over the region. After Thursday & Friday's significant snow and wind, snow and wind intensity will likely wane somewhat on Saturday. Given the strong west-southwesterly flow with relatively deep moisture, snow is unlikely to shut off for the western Wyoming ranges and valleys, but snowfall rates will not be as impressive as those seen earlier. The next shortwave currently looks to move through Sunday afternoon into Sunday night, and this could be the next period of winter weather highlights, given the increasing snowfall rates and tight pressure gradient that will likely lead to widespread travel impacts for those returning home after Christmas holiday celebrations. Monday will be a repeat of Saturday, with models showing less intense winter weather, but continued scattered impacts from mountain snow and breezy winds. Monday night into Tuesday morning is a third period of enhanced winter weather as another shortwave moves eastward across the state. Behind this wave, much cooler air is advected into basins east of the Divide as the parent longwave trough finally begins to migrate eastward. Tuesday through late next week looks like it could bring highs in the teens and lows in the negative single digits for many. Western mountains maintain widespread snow showers through this timeframe, while basins east of the Divide look to remain mostly dry but cold. && .AVIATION...(For the 06Z TAFS through 06Z Friday) Issued at 950 PM MST Wed Dec 22 2021 East of the Divide...KCOD/KCPR/KLND/KRIW/KWRL Terminals VFR conditions will occur through the period. Gusty wind will be common at most terminal sites Thursday into Thursday evening. Isolated rain showers are possible after 00Z. West of the Divide...KBPI/KJAC/KPNA/KRKS Terminals VFR conditions will occur overnight at most locations. KJAC will see MVFR conditions around 11Z, then mainly IFR conditions through 06Z Friday. KBPI and KPNA will see MVFR conditions around 18Z and will continue through 06Z Friday. KRKS will see a gusty wind Thursday with VFR conditions through 23Z, then MVFR to IFR conditions through 06Z Friday. Mountains will be frequently obscured through the period. 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 238 AM MST Thu Dec 23 2021 Snow will gradually increase in coverage today for areas west of the Divide. Smoke dispersal and venting will be poor and remain poor for the next several days. High winds will exist across areas east of the Divide through later this evening. As the forcing shifts eastward, precip will cross over the Divide through the day Thursday and linger into Friday. Initially it will be all rain before transitioning to snow as colder air is filtered in behind the front. There's a brief lull in activity for the area Saturday before another system is expected to impact the area again on Sunday. && .RIW WATCHES/WARNINGS/ADVISORIES... Winter Storm Warning from 5 PM this afternoon to 6 PM MST Friday for WYZ028>030. High Wind Warning from 11 AM this morning to 8 PM MST this evening for WYZ010-015-019-020. Winter Weather Advisory from 11 AM this morning to 6 PM MST Friday for WYZ026. Winter Storm Warning from 6 AM this morning to 11 PM MST Friday for WYZ014-023>025. Winter Storm Warning until 11 PM MST Friday for WYZ001-002-012- 013. Winter Storm Warning from 11 AM this morning to 11 PM MST Friday for WYZ027. && SHORT TERM...Vorst LONG TERM...VandenBoogart AVIATION...Straub FIRE WEATHER...Vorst
Hazardous Weather Outlook National Weather Service Riverton WY 251 PM MST Wed Dec 22 2021 WYZ001>020-022>030-232200- 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- 251 PM MST Wed Dec 22 2021 ...Winter Storm Warnings for Western portions Wednesday night through Friday evening... ...Winter Weather Advisories for Southern portions for Thursday evening to Friday evening... ...High Wind Watch in effect for portions of Fremont, Natrona, and Johnson counties through late Thursday evening... This Hazardous Weather Outlook is for Western and Central Wyoming. .DAY ONE...This Afternoon and Tonight. Winds will continue to impact Natrona and Johnson Counties, as well as the Cody Foothills through this evening. Snow will move into the west through this evening and overnight. .DAYS TWO THROUGH SEVEN...Thursday through Tuesday. Thursday into Friday...Accumulating snow will continue for areas west of the Divide and along the I-80 corridor through late Friday. High winds will develop in areas east of the Divide Thursday. Christmas through Tuesday...Snow will lessen on Saturday west of the Divide, and then increase again Saturday night through Monday. .SPOTTER INFORMATION STATEMENT... Weather spotters are encouraged to report significant weather conditions according to standard operating procedures.
The national radar mosaic for the moment the first event began.
4 winter storm, 2 high wind. Local standard time, as filed.
Heavy snow fell in portions of the Teton Range. The highest total was 16 inches at the Grand Targhee SNOTEL.
A trained spotter reported 11 inches of snow to the southwest of Wilson.
Heavy snow fell in the higher elevations of Yellowstone National Park. The highest amount was 25 inches at the Two Ocean Plateau SNOTEL in the southeast corner of the park.
Snow totals topping one foot were observed in portions of the Salt and Wyoming ranges. The highest amount was 16 inches at the Blind Bull Summit SNOTEL.
Wind gusted as high as 59 mph at the Johnson County Airport near Buffalo.
High winds occurred in the wind-prone areas south and east of Casper. Some of the highest gusts included 68 mph along Wyoming Boulevard and 63 mph on the east side of Casper near Hat Six Road.
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: 997050, 997051, 997049, 997052, 997054, 997053.