A cold front moving across Wyoming mixed strong mid-level winds to the surface and brought high wind to much of western and central Wyoming. The highest wind was at Clark where a maximum gust of 95 mph was reported.
Every event with a place to put it; 9 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 cold front moving across Wyoming mixed strong mid-level winds to the surface and brought high wind to much of western and central Wyoming. The highest wind was at Clark where a maximum gust of 95 mph was reported. An 80 mph wind gust was reported at the Wind River RAWS site along the east slope of the Wind River Mountains. The strong wind led to the closure of South Pass over the southern end of the Wind River Mountains for a time due to blowing snow. Wind gusts exceeding 58 mph were also reported in Johnson, Natrona, Big Horn and Sweetwater counties.
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 4, 10:29 AM MST, 1 hour 1 minute earlier.
Area Forecast Discussion National Weather Service Riverton WY 1029 AM MST Sat Dec 4 2021 .SHORT TERM...Today through Monday night Issued at 356 AM MST Sat Dec 4 2021 Quite a lot to talk about over the next few days. First with some colder air moving in from the north, some low clouds and patchy fog have formed across the north. These should last through the night and into the first part of the morning before lifting. And this brings us to the next concern, high wind. The pattern looks favorable for high wind for many locations. A cold front will be droppings southward out of Montana, tightening the pressure gradient.The first places to see it will be the favored pre frontal locations, like the lee of the Absarokas and the southwestern Wind Corridor. The one area that looks concerning is the Lander Foothills. The 700 millibar flow looks more west than southwest, which is usually not favored for high wind. However, there will be plenty of mid level wind, 50 to as much as 75 knots, depending on which model you believe. Also, there will be plenty of downward forcing courtesy of the front right quadrant of an 140 knot jet streak.So, we will leave the warnings as is for now. We also thought about adding Sweetwater County. The 700 millibar winds are plenty strong, but guidance is borderline. There is a special weather statement up for that area, and again we will stick with that for now. The aforementioned front will then drop southward into Wyoming later tonight and drop through the state on Sunday. The main threat of high wind will then shift to areas favored by the cold advection / northwest flow regime, mainly the Wind River Basin, Big Horn Basin and especially Johnson County. The NAM guidance is especially bullish for northern Johnson County, having 43 knots sustained at the Buffalo airport. This does tend to be overcooked though. The GFS guidance looks more reasonable at 35 knots, but high wind nevertheless. This will likely peak in the morning hours following the frontal passage, then decreasing later in the afternoon as the pressure gradient decreases and the front moves southward. Now on the other threat snow. There will be plenty of upper level forcing with the jet energy. However, the front does not have a lot of moisture to work with. So in most areas, amounts should be on the light side. However, with the front, this will likely be a banded snow. In other words, the kind of snow where accumulations will vary over the short distance and are impossible to pinpoint a few hours out, let alone more than 24 hours out. It would not surprise me if a few spots in the lower elevations picked up 2 or 3 inches of snow on Sunday. Snow would mainly fall over the northern third of the area, roughly north of a line from Casper to Thermopolis to Jackson. Areas in the south will see dry conditions continue. Like the wind, snow showers should become less numerous late and basically end shortly after sunset. As for temperatures, it will be slap to the face for many people. It looks to only go back to seasonal normals for most, but after the record warmth it will feel cold. Temperatures may end up falling during the day on Sunday. There is a large spread in guidance for Sunday night, as much as 15 degrees. The NAM again seems to cold, especially in areas that would see little or no snow on Sunday. We split the middle for now. Concerns then shift to western Wyoming as a Pacific system begins to approach the area. The models continue to slow on its progression though. Most now hold any precipitation off until around sunrise Monday across the west. The heaviest precipitation looks to be Monday night through, when the trough axis reaches the west. Some highlights may be needed for this, although at this point it looks more like advisories. There is much more uncertainty East of the Divide. The GFS continues to split the system and only has light precipitation. The European is more bullish but even it has some splitting. For now, we kept QPF on the light side. We also have the same problem with temperatures, with some areas having a 20 degree spread in guidance. Again, a lot will depend on potential snow cover and the NAM looks too cold again. For now, we blended the guidance. .LONG TERM...Tuesday through Friday Issued at 356 AM MST Sat Dec 4 2021 Northwest flow aloft on Tuesday with a weak weather system in the flow. This would produce some light snow in the mountains. Scattered light snow may occur Tuesday in the central and south per some of the models. Will keep low chance going for now and see how things look in time. Wednesday looks dry east of the divide and breezy to windy. In the west, a moist west northwest flow will occur. A good chance of snow in the western mountains with some snow in the western valleys Wednesday and Wednesday night. Thursday looks dry for most places with lingering light snow possible in the mountains. High temperatures Tuesday through Thursday will be more like what December temps should be, with mainly 30s to around 40 at the lower elevations with teens and 20s in the mountains. The GFS and ECMWF models are trending toward a developing weather system in the Great Basin late Thursday night through Friday. The track in progressive for now, but an upper low may develop in time. Will be watching this weather pattern in the coming days. At this time, the west and south would be the favorable locations for snow, with the central zones on the northern edge of the snow. This may well change in time, so stay tuned. High temps Friday will only be in the 20s to around 30 Friday with teens to lower 20s in the mountains. && .AVIATION...For the 18Z TAFS through 18Z Sunday West of the Divide...KBPI/KJAC/KPNA/KRKS Terminals Winds will be light at the start of the period, with KRKS increasing to 25 kt by 19Z. KBPI and KJAC will also have gusts near 20 kt this afternoon. High clouds will stream over the area from the northwest, with BKN-OVC conditions occurring at KJAC by 12Z. Winds will continue to increase at KJAC and KRKS this evening, with gusts of 30 to 35 kt. Strong winds will occur at KRKS by 10Z, with gusts near 45 kt by 15Z. Gusts of 25 to 30 kt will occur at the other TAF sites through the rest of the TAF period. East of the Divide....KCOD/KCPR/KLND/KRIW/KWRL Terminals Conditions continue to improve, with low clouds and areas of fog lifting. KWRL remains LIFR, but is expected to quickly improve by 19Z. Otherwise, VFR conditions will occur through much of the TAF period. Wind speeds will be on the increase at many terminal sites this afternoon through 12Z Sunday. Wind gusts over 40 knots will be common. Snow will develop in the northern WY mountains after 03Z, with mountain obscurations and continue through the rest of the TAF period. A cold front will enter northern portions by 12Z, with snow showers expected at KCOD by 14Z and KWRL by 17Z. 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 356 AM MST Sat Dec 4 2021 Strong to high winds will occur across many areas today, especially in the lee of the mountain ranges and from the Green and Rattlesnake Range through Natrona County today and tonight. Relative humidity should remain above critical levels for the most part. Mixing and smoke dispersal will be generally fair to poor in the afternoon but locally good in the lee of the Absarokas. A cold front dropping southward will bring colder weather late tonight and Sunday along && .RIW WATCHES/WARNINGS/ADVISORIES... High Wind Watch from Sunday morning through Sunday afternoon for WYZ028>030. High Wind Warning from 3 PM this afternoon to 2 AM MST Sunday for WYZ019-020. High Wind Warning from 6 AM to 3 PM MST Sunday for WYZ004-006- 010. High Wind Warning from 8 PM this evening to 8 AM MST Sunday for WYZ017. High Wind Warning until 8 AM MST Sunday for WYZ016. High Wind Warning until 6 AM MST Sunday for WYZ015. High Wind Warning until 6 AM MST Sunday for WYZ002-003. && SHORT TERM...Hattings LONG TERM...AR AVIATION...TL FIRE WEATHER...Hattings
Hazardous Weather Outlook National Weather Service Riverton WY 949 AM MST Sat Dec 4 2021 WYZ001>020-022>030-051700- 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- 949 AM MST Sat Dec 4 2021 ...High Wind Warning is in effect for portions of northern and central Wyoming through Sunday morning... ...High Wind Watch is in effect for Sweetwater County from early Sunday morning through Sunday evening... This Hazardous Weather Outlook is for Western and Central Wyoming. .DAY ONE...Today and Tonight. Strong to high winds are likely for portions of northern and central Wyoming especially this afternoon and tonight. Please see High Wind Watches and Warnings for details. Snow showers will spread into northern Wyoming after midnight. .DAYS TWO THROUGH SEVEN...Sunday through Friday. Sunday...Strong to high winds continuing for portions of northern and central Wyoming. Please see High Wind Watches and Warnings for details. Snow showers may bring slick roads to the northern half of the area. Monday and Monday night...A chance of snow in the west. Wednesday...A chance of snow in the west. Thursday night and Friday...A chance in the south and central. .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.
9 high wind. Local standard time, as filed.
Winds were sustained over 50 mph along the Chief Joseph Highway for several hours. The maximum wind gust reported was 76 mph.
High winds occurred around Casper. The maximum wind gust reported was 63 mph along Wyoming Boulevard along the south side of Casper.
Very high winds occurred in the vicinity of Clark. A maximum wind gust of 95 mph was recorded. The highest wind gust in Cody was 64 mph.
The Wind River RAWS site had a maximum wind gust of 80 mph. Wyoming Highway 28 over South Pass was shut down for several hours due to snow and blowing snow.
A maximum wind gust of 62 mph was reported at Hunt Field in Lander.
High winds occurred in Johnson County after the passage of a cold front. The highest wind gust reported was 63 mph at the Johnson County Airport near Buffalo.
A 62 mph wind gust was reported at Southwest Wyoming Regional Airport.
A maximum wind gust of 59 mph was recorded in Kemmerer.
High wind occurred behind a cold frontal passage. Some maximum wind gusts included 62 mph at the Willow Creek RAWS and 58 mph at the South Big Horn County airport in Greybull.
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: 995037, 995044, 995040, 995041, 995043, 995045, 995183, 995184, 995182.