A 31 year old man riding in the Wyoming Range to the East of Alpine was riding a snowmobile in steep terrain when he triggered a 100 foot by 100 foot slab avalanche. The avalanche flipped his snowmobile and he was pinned under the snowmobile for an hour before being dug out.
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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 31 year old man riding in the Wyoming Range to the East of Alpine was riding a snowmobile in steep terrain when he triggered a 100 foot by 100 foot slab avalanche. The avalanche flipped his snowmobile and he was pinned under the snowmobile for an hour before being dug out. He was pronounced dead at the scene.
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 22, 2:29 AM MST, 6 hours 31 minutes earlier.
Area Forecast Discussion National Weather Service Riverton WY 229 AM MST Sat Dec 22 2018 .SHORT TERM...Today through Christmas Eve night Light snow showers will be ongoing this morning across southern portions of Sweetwater County. Another band is expected to develop before sunrise, from the Owl Creek Mountains to Casper. Snowfall amounts will be an inch or less and end by mid morning. There will remain a slight chance for snow to continue through the day today over the western mountains, but accumulations will remain light. Otherwise, conditions will be quiet today across much of the area. However, gusty west winds will occur across the I-80 corridor. Another fast-moving trough will impact the far west on Sunday. As the trough continues eastward and exits over the Plains late Sunday afternoon, there will be enough jet dynamics (left front quad) and upslope components to keep generating snow over this area through the night Sunday night. There will be a lull in this activity Monday morning, before another weak shortwave moves over late Monday morning into the afternoon. Snowfall amounts will generally be light over a 24-hr period. An additional 3 to 6 inches is expected in the far western mountains Sunday and Sunday night, with 1 to 3 inches in the valleys. Locally higher amounts will be possible in the Tetons and Gros Ventres. Amounts will be slightly lower for Monday. Gusty SW winds will return over the Wind Corridor Sunday, with the passage of the trough. This also looks to repeat Monday, but with winds being about 15 mph lower. Temperatures are expected to be somewhat seasonal, with a more Pacific airmass being in place through the period. The good news is that days are getting longer now. .LONG TERM...Christmas Day through Saturday Overview...A low pressure system will move east across the southwest U.S. and southern Rockies Christmas Day and Tuesday night, then lift northeast across the central Plains Wednesday and Thursday. The heavier precipitation is expected to stay south and east of the area with this system with the best chances of light snow accumulations on Tuesday night into Wednesday. Temperatures will be on the cool side Wednesday through Saturday with most highs in the 20s across the valleys and basins. Discussion...A quick transition from our current zonal flow to a more amplified flow takes shape on Christmas Day as ridge amplifies over the eastern Pacific and upper low digs down the front side of this ridge to near the CA/AZ border by 00z Wednesday. 22/00z ECMWF and GFS are in better agreement with the storm track and timing with ECMWF remaining a bit slower overall. Isolated to scattered snow showers are expected to push north in difluent southerly flow on Christmas Day with GFS more aggressive bringing QPF north into south and central Wyoming than ECMWF. We left the idea of low end PoPs (isolated to scattered snow showers) spreading north and east across the area Christmas Day/night. Surface lee cyclogenesis is expected across NE New Mexico early Wednesday with the surface low slowly lifting across Kansas Wednesday night into eastern Nebraska on Thursday. Precipitation shield NW of surface low is expected to extend westward to near a Casper-Rawlins line on Wednesday and slowly lift north and east through Thursday. Thus, some light snow accumulations are possible mainly in the Casper area on Wednesday, aided by a light N-NE upslope flow. An upstream shortwave is expected dive down the front side of the eastern Pacific ridge, south across the western Great Basin on Thursday into Arizona on Friday, effectively reloading the upper trough. This system will spread chances of snow showers across the west on Thursday and then be too far south of the area to have much impact on Friday. Just beyond this extended period, both ECMWF and GFS are showing a blast of snow and cold across the area on New Year's Eve and a cold start to 2019. && .AVIATION...For the 12Z TAFS through 12Z Sunday West of the Divide...KBPI/KJAC/KPNA/KRKS Routes Some very light snow and lcl MVFR conds may linger through 14z before ending. Some mtn tops will remain obscured through 18z. Otherwise, VFR conds will return Saturday. A new weather system may spread lgt snow into the far northwest corner after 09z Sunday. East of the Divide...KCOD/KCPR/KLND/KRIW/KWRL Routes Between 12z and 18z this morning, some lcl very light snow is possible between KRIW and KCPR with lcl MVFR cigs. Otherwise, expect VFR conds through Saturday night. && .FIRE WEATHER... Light snow across the far west and over central portions this morning. Little to no accumulation expected. Otherwise, gusty SW to W winds return over the Wind Corridor and southern portions today. Mixing heights and smoke dispersal will generally be poor for most areas, but up to good where winds will be gusty. && .RIW WATCHES/WARNINGS/ADVISORIES... NONE. && SHORT TERM...LaVoie LONG TERM...Meunier AVIATION...Skrbac FIRE WEATHER...LaVoie
Hazardous Weather Outlook National Weather Service Riverton WY 232 AM MST Sat Dec 22 2018 WYZ001>020-022>030-231000- 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- 232 AM MST Sat Dec 22 2018 This Hazardous Weather Outlook is for Western and Central Wyoming. .DAY ONE...Today and Tonight. Light snow over the far west and flurries over central portions this morning. Accumulations will stay light. .DAYS TWO THROUGH SEVEN...Sunday through Friday. Sunday and Christmas Eve...Snow expected across the west. Light to moderate accumulations are expected. Light snow possible across the south. .SPOTTER INFORMATION STATEMENT... Spotter activation will not be needed today or tonight.
The national radar mosaic for the moment the first event began.
1 avalanche. Local standard time, as filed.
As the offices recorded each death: direct deaths were caused by the weather itself, indirect ones by something it set in motion.
| Event | Date | Age | Sex | Where | Kind |
|---|---|---|---|---|---|
| Avalanche, Salt River & Wyoming Ranges | 2018-12-22 | 31 | Male | Outside/Open Areas | Direct |
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Wyoming in 2018Every state in 2018This day in weather historyWarnings in Wyoming, December 2018
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: 798159.