A combination of a Pacific Cold Front and an ample supply of moisture brought heavy snow to western Wyoming. In the mountains, the highest snowfall total was 28 inches at the Jackson Hole Ski Resort.
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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 a Pacific Cold Front and an ample supply of moisture brought heavy snow to western Wyoming. In the mountains, the highest snowfall total was 28 inches at the Jackson Hole Ski Resort. Around 20 inches of snow was the maximum amount in the Salt and Wyoming Range. In the western Valleys, over a foot of snow fell in portions of the Star Valley with up to 10 inches in the northern Jackson Valley.
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 Feb 4, 2:59 PM MST, 1 hour 1 minute earlier.
Area Forecast Discussion National Weather Service Riverton WY 259 PM MST Thu Feb 4 2021 .SHORT TERM...(This evening through Friday night) Issued at 130 PM MST Thu Feb 4 2021 Cool northwest slightly unstable flow continues over western and central Wyoming today. Isolated snow showers continue around the Bighorns and the northwest mountains as a result. In addition, moderate mid-level flow with decent height and pressure gradients are keeping breezy to windy conditions over much of the area, with some areas seeing gusts over 30 mph. High clouds are starting to stream over northwest WY as high and mid level moisture starts coming back into the area. This next shortwave trough in the northwest flow is associated with a 120+ knot jet, and models are showing precipitation starting in the northwest mountains as early as 6 PM to 8 PM with the dynamics. Moisture and precipitation will increase during the night, so have moved the northwest Winter Weather Advisories up 3 hours to 8 PM based on recent forecast guidance. In addition, have included the west Bighorn Mountain zone with expected snow of 6 to 10 inches through Friday evening. The northwest mid-level flow will be favorable for some location of far western Wyoming, so wouldn't be surprised if areas pick up 1 to 3 inches more than expected. Overall, expecting 6 to 12 inches in the mountains with 3 to 6 in the valleys. A couple of areas to watch out for a couple of inches of snow include southern Lincoln County from Cokeville to Kemmerer where 20-30 mph west winds could create hazardous blowing snow. Bondurant to Daniel is likely to see 2 to 3 inches also, but only an inch or so around Pinedale. In addition, the Frannie to Lovell to Shell to Ten Sleep stretch may also see 1 to 3 inches if unstable conditions develop Friday morning. Some models are also showing precipitation developing across southwest into southern WY for some light to moderate snow showers with gusty west wind during the day. The vorticity pocket is expected to move southeast through the area late Friday afternoon, diminishing snowfall across western WY. However, gusty west-northwest wind and near to below freezing temps will continue into the evening and overnight hours. And of course, not expecting precipitation in the holes in the Wind River Basin and central Big Horn Basin over to Natrona County, though some elongated snow bands have a slight chance of developing Friday afternoon and evening. Complicating the forecast Friday night into Saturday is a boundary draped NW to SE from central Montana to western Nebraska. This feature should keep snow going in the Bighorn Mountains through late Friday, as well as light snow and gusty northwest wind in northern Johnson County. Models are showing Arctic air starting to push into the northern US late Friday into early Saturday, which may push into northern WY between midnight and early morning Saturday. However, models are all of the page still as to the air mass movement. Some guidance shows the air plunging southward east of the divide, with others keeping the main influence across northeast WY. The boundary, however, will then enhance snow chances in the northern WY mountains early Saturday. .LONG TERM...(Saturday through Thursday) Issued at 1219 PM MST Thu Feb 4 2021 The persistent northwest flow will remain over the area for the weekend. This means continued snow showers, mainly across the west and north. This will be aided in part by favorable dynamics, with models showing a strong (+135kt) jet over the area on Saturday and Sunday. Snow amounts and coverage now look very similar to the short term event, and additional winter highlights will likely be needed for the weekend. Forecast guidance continues to show a possible surge of arctic air beginning on Sunday. There is still quit a bit of disagreement with deterministic solutions, but the thinking here is that cold air begins to clip the northeast portion of the CWA on Sunday, with a slow but strong front moving south into central Wyoming through early next week. Regardless, NBM temperatures seemed too warm across northeastern and central areas compared to both GFS and ECM MOS guidance, so have lowered temperatures there Sunday through Tuesday. Currently, the coldest temperatures are progged to be in Johnson county and the Bighorn Basin, where highs could only reach the single digits Sunday through perhaps Wednesday. In summary, will have to see where the guidance goes, but if recent trends hold true much colder temperatures are expected next week, mainly east of the Divide. Wind may be an issue this weekend as a strong 700mb flow and surface pressure gradient come together across southern areas; will have to watch this trend as well. Snow chances will decrease by Sunday night across the west, with a drier trend expected Monday through Thursday. && .AVIATION...(For the 18Z TAFS through 18Z Friday) Issued at 1042 AM MST Thu Feb 4 2021 West of the Divide...KBPI/KJAC/KPNA/KRKS Light snow showers will increase across the west this afternoon, with MVFR/IFR conditions possible after 01z at KJAC. Snow will move south tonight, impacting KPNA and KBPI after 15Z Friday. Frequent mountain obscurations are likely today and tonight. Strong west wind will occur at KRKS through the period. East of the Divide...KCOD/KCPR/KLND/KRIW/KWRL Terminals TAFs will remain VFR through the period, but VCSH is possible at times as snow showers move into western Wyoming and the Bighorn mountains today. These showers will increase tonight, with some mountain obscurations likely. 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 1225 PM MST Thu Feb 4 2021 Cool and breezy northwest flow continues over western and central WY this afternoon for this day between storms. A few snow showers are lingering around the Bighorns and northwest mountains though. Breezy to windy conditions with gusts over 30 mph will continue into the early evening. Clouds are starting to increase from the northwest this afternoon, with moisture increasing quickly this evening. Winter Weather Advisories are in effect for much of the west and northwest as well as the west side of the Bighorns. Snow will start during the evening hours and increase around midnight through Friday morning before starting to taper off. The highlighted mountains will see 6 to 12 inches of snow, while the far western valleys will pick up between 3 and 6 inches. Additional snow will fall from Bondurant to Pinedale, and from Cokeville to Kemmerer. Sweetwater County will also see moderate snow showers Friday. Some of these areas will see blowing snow with winds over 30 mph. Lower elevations east of the divide will largely remain dry, except for the northeast Big Horn Basin and northern Johnson County. Snow bands off the southern parts of the mountains (to the southeast) are also possible. Unsettled northwest flow continues from Friday night into Saturday, with colder air push in from the north on Saturday. && .RIW WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory from 8 PM this evening to 6 PM MST Friday for WYZ001-002-012-013. Winter Weather Advisory from 11 PM this evening to 6 PM MST Friday for WYZ023-024. Winter Weather Advisory from 8 PM this evening to 11 PM MST Friday for WYZ008. && SHORT TERM...McDonald LONG TERM...Myers AVIATION...Myers FIRE WEATHER...McDonald
Hazardous Weather Outlook National Weather Service Riverton WY 1039 AM MST Thu Feb 4 2021 WYZ001>020-022>030-051300- 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- 1039 AM MST Thu Feb 4 2021 ...Winter Weather Advisory for Parts of Western and Northern Wyoming This Evening Through Friday... This Hazardous Weather Outlook is for Western and Central Wyoming. .DAY ONE...Today and Tonight. Scattered snow showers today, especially in the morning and in western Wyoming and the Bighorns. Steadier and heavier snow will move into western and northern Wyoming this evening and early Friday morning. Please see the Winter Weather Advisory for details. .DAYS TWO THROUGH SEVEN...Friday through Wednesday. Friday...Snow continuing in the west and north, tapering off later in the afternoon, though continuing in the Bighorns through the evening. Saturday...A chance of snow. Colder air will move into northeast Wyoming. Strong winds are possible from southwest into southern Wyoming late Saturday afternoon and evening. Monday and Tuesday...Another chance of snow. Much colder temperatures possible, especially east of the divide. .SPOTTER INFORMATION STATEMENT... Spotter activation will not be needed today or tonight. McDonald
The national radar mosaic for the moment the first event began.
4 winter storm. Local standard time, as filed.
Heavy snow fell in the Star Valley. Amounts ranged from 8 inches around Afton to 15 inches near Alpine, Wyoming.
Heavy snow fell in the Salt and Wyoming Range. Some of the highest amounts included 21 inches at the Box Y Ranch and at Commissary Ridge.
Heavy snow fell throughout the Tetons. The highest amount measured was 28 inches on top of the Jackson Hole Ski Resort.
Heavy snow fell in portions of the Jackson Valley. The highest amounts were near Teton Village, Wyoming, where 10 inches of new snow fell. Amounts dropped sharply further south with 2 to 4 inches around the town of Jackson.
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, February 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: 938557, 938558, 938554, 938555.