A cold front dropped out of Canada and brought heavy snow to portions of western and central Wyoming. The heaviest snow fell in the favored northeasterly upslope areas.
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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 cold front dropped out of Canada and brought heavy snow to portions of western and central Wyoming. The heaviest snow fell in the favored northeasterly upslope areas. Up to 2 feet of new snow fell in the Wind River Mountains with up to 15 inches around Lander, Wyoming. Other notable amounts included 17 inches at Jackson Hole, Wyoming, 10 inches at Hudson, Wyoming and 8 inches near Kaycee, Wyoming.
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 Apr 15, 2:12 AM MST, 1 hour 48 minutes earlier.
Area Forecast Discussion National Weather Service Riverton WY 312 AM MDT Wed Apr 15 2020 .SHORT TERM...Today through Friday night Active weather will be the rule for the next 36 hours or so. The two culprits will be a cold front dropping southeastward across the area and a cold front moving in from north to south. Snow is already ongoing across the west. Snow will spread from north to south across the area as the cold front drops southward through the area. For the most part, the morning looks mainly dry East of the Divide. Even the afternoon hours do not look to bad impact wise as the high April sun angle should keep travel conditions not too bad. That will change tonight as cold air moves in behind the front. In addition, this is when a 700 millibar circulation will drop southeastward across the area and combined with some jet energy, will bring the worst conditions. Most of the models are zeroing in on the period between 6 pm and midnight as the maximum impact with the heaviest snow along with gusty to strong north winds, courtesy of the cold advection behind the front. Later at night, conditions should improve for most areas as the best upper level forcing moves away. At this time, it will transition to more an upslope event. And at this time, it looks to be more of an east to east-northeast flow. This would favor areas like Lander as well as the eastern slopes of the Wind River Range. As a result, we have upgraded the advisory to a warning for those areas. All other locations the highlights look reasonable and will be maintained as-is for the most part. Thursday at this point looks to see gradually improving conditions as high pressure builds in from the north and slowly shuts of the snow and the wind slowly decreases. Temperatures will remain well below normal as well with the fresh snow cover and cold air mass. We will also have the potential for record low temperatures for many locations with the fresh snow cover if the sky can clear. Friday at this point looks to be a dry and chilly day with melting snow as temperatures rise above freezing for most locations. .LONG TERM...Saturday through Tuesday night Saturday looks dry with breezy areas. Highs will be in the 40s and 50s. A weak weather system in the NW flow aloft will pass through the area Saturday night with a few rain and snow showers over the north and northwest. The rest of the area looks dry. The GFS is wetter than the ECMWF model with this system. Will keep low chances in the north and northwest for now. Sunday should be dry for all areas. Isolated mountain snow showers may occur in the western mountains Sunday afternoon and early evening. High temps Sunday will be in the 40s and 50s with a few lower 60s in the basins. Long range models vary Monday and Tuesday with the weather pattern. The GFS has unsettled weather Monday and Tuesday with a trough moving through the four corners and eventually ending up in SE Colorado Tuesday late afternoon into the night. The ECMWF model is drier and keeps the bulk of the trough through Arizona and New Mexico. The NBM precip grids keep Monday fairly dry and then scattered rain and high mountain snow on Tuesday. With the uncertainty this far out will not alter the forecast much and keep Monday fairly dry. Then a chance of rain showers and high mountain snow showers Tuesday into Tue night. Highs Monday and Tuesday will be in the 50s and 60s.&& .AVIATION...12Z Issuance VFR conditions will prevail through 18Z at most of the terminal sites. KJAC will see MVFR to IFR conditions today into this evening with improving conditions around 07Z. KCOD will see MVFR to IFR conditions for most of the day into the evening with improving conditions after 08Z. As the snow develops over central and southwest WY this afternoon, conditions will become MVFR to IFR and this will continue through tonight. Some improvement will occur in the north after 03Z as the snow decreases or ends and the ceilings rise. Expect mountains to be frequently obscured most of today and tonight. Please see individual terminal sites for more details. && .FIRE WEATHER... A cold front will move across the state today and bring snow and rain changing to snow across most of the area. Windy conditions will develop across much of the area as well, especially this afternoon and into tonight. Relative humidity will remain above critical levels. Mixing and smoke dispersal will generally range from fair to poor. && .RIW WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory from noon today to noon MDT Thursday for WYZ019-026>028-030. Winter Storm Warning from noon today to noon MDT Thursday for WYZ015-018. Winter Weather Advisory until 6 AM MDT Thursday for WYZ012-013. Winter Weather Advisory from noon today to 6 AM MDT Thursday for WYZ005-007-010-011-016-017-020-022. Winter Weather Advisory until 6 AM MDT Thursday for WYZ014-023- 025. Winter Weather Advisory until midnight MDT tonight for WYZ001- 002-008-009. Winter Weather Advisory until noon MDT Thursday for WYZ024. Winter Weather Advisory until midnight MDT tonight for WYZ003. && SHORT TERM...Hattings LONG TERM...Ross AVIATION...Ross FIRE WEATHER...Hattings
Hazardous Weather Outlook National Weather Service Riverton WY 237 AM MDT Wed Apr 15 2020 WYZ001>020-022>030-160845- 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- 237 AM MDT Wed Apr 15 2020 ...Winter Storm Warning in effect for the Eastern Slopes of the Wind Rivers and Lander Foothills... ...Winter Weather Advisories in Effect for Much of Western and Central Wyoming from Tonight through Thursday Morning... This Hazardous Weather Outlook is for Western and Central Wyoming. .DAY ONE...This Afternoon and Tonight. Snow spreading across the area today from northwest to southeast. Please see winter weather products, statements and forecasts for details. Gusty to strong winds likely this evening across many areas East of the Divide. .DAYS TWO THROUGH SEVEN...Thursday through Tuesday. Thursday...Snow continuing, tapering off in the afternoon and ending at night. .SPOTTER INFORMATION STATEMENT... Weather spotters are encouraged to report significant weather conditions, especially snow amounts and strong winds. Swanson/McDonald
Special Weather Statement National Weather Service Riverton WY 440 AM MDT Wed Apr 15 2020 WYZ004-006-152200- North Big Horn Basin-Southeast Big Horn Basin- Including the cities of Basin, Greybull, Lovell, Powell, Shell, Ten Sleep, and Worland 440 AM MDT Wed Apr 15 2020 ...Occasional snow and wind returning... * WHAT...Periods of snow. Accumulations of 1 to 3 inches, with the highest amounts near Ten Sleep with lesser amounts further north. Winds becoming north and increasing to 20 to 30 mph with gusts to 40 mph. * WHERE...Northeast and Southeast Big Horn Basin. * WHEN...This afternoon and tonight. The heaviest snow is expected this evening. * ADDITIONAL DETAILS...Roads will be slick at times. Visibility will be reduced in snow and blowing snow at times.
The national radar mosaic for the moment the first event began.
6 winter storm. Local standard time, as filed.
Heavy snow fell in at the Jackson Hole Ski Resort. At Raymer, Wyoming, 17 inches of new snow fell.
Heavy snow fell in the Star Valley. The highest amount reported was 8.2 inches at Afton, Wyoming.
A trained spotter reported 8 inches of snow to the north of Kaycee, Wyoming.
Heavy snow fell in along the eastern slopes of the Wind River Range. Some of the most notable amounts included 24 inches at Townsend Creek to 17 inches at Hobbs Park.
Heavy snow fell throughout the Lander, Wyoming foothills. Twelve to fifteen inches of snow was commonplace around Lander, Wyoming including 14.1 inches at the Lander airport.
A trained spotter reported 10 inches of snow in Hudson, Wyoming. Amounts dropped further north to around 3 to 6 inches around Riverton, Wyoming.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Wyoming in 2020Every state in 2020This day in weather historyWarnings in Wyoming, April 2020
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: 886255, 886256, 886259, 886262, 886264, 886260.