A feed of Pacific moisture brought a long lived snow event to the western mountains between Christmas and New Years Day. New snowfall amounts approached 2 feet in the Tetons as well as the Salt and Wyoming Range.
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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 feed of Pacific moisture brought a long lived snow event to the western mountains between Christmas and New Years Day. New snowfall amounts approached 2 feet in the Tetons as well as the Salt and Wyoming Range.
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 27, 3:43 PM MST, 6 hours 17 minutes earlier. Its key messages:
Area Forecast Discussion National Weather Service Riverton WY 343 PM MST Fri Dec 27 2024 .KEY MESSAGES... - The first of an onslaught of weather systems keeps snow going across western Wyoming today, with a lull tonight before increasing again Saturday morning. - The second set of weather systems really gets going Saturday morning and will bring feet of snow to western mountains, around a foot to western valleys, and minor snowfall amounts for portions east of the Continental Divide. Snow ends Monday afternoon from west to east. - Temperatures remain well above normal east of the Continental Divide through Sunday, but cool next week. Temperatures will remain slightly above normal west of the Continental Divide through Sunday and close to normal next week. && .DISCUSSION... Issued at 237 PM MST Fri Dec 27 2024 There will be a stark contrast in weather conditions west compared to east of the Continental Divide for the next 3-4 days. Snow began in western Wyoming late this morning and is ongoing. This will continue through Monday. For western mountains and valleys snow will be falling/accumulating consistently until Monday afternoon, with little break in between. Temperatures look to warm enough Sunday afternoon (highs upper 30s) for a possible (40%) mix of snow/rain in Jackson Valley/Star Valley. This is likely (70%) to limit snowfall accumulations Sunday afternoon in these valleys. The main complexity with this forecast is the long duration of snow that will occur (still 72 hours). Let's start off with moisture since this is slam dunk part of the forecast. Taking a look a PWAT's it is no surprise snowfall amounts will be high from this long duration winter event. On average PWAT's will be around 0.25-0.35" through Monday morning. For the remainder of the period from today through Monday moisture will be plentiful (PWAT's 0.25-0.4" this falls within the 90th percentile) across the area. One may surmise that this would lead to substantial snowfall accumulations across the forecast area, but the issue is each weather system will be progressive moving across the area from west to east, so mountain shadowing/downsloping will be prevalent. This will keep most of the low-level moisture west of the Continental Divide as lee-side downsloping dries/warms the low-levels. The opposite will occur on the windward (west) side of the mountains, with persistent moist upslope flow dumping all the moisture/snow west of the Continental Divide. This afternoon radar returns and model guidance indicate a slight shift southward in the heaviest snow. This has also been noted by looking at webcams at Jackson compared to Afton. At Afton visibility has been less than a mile since snow began late this morning, but Jackson has only dropped to around 3 mile visibility so far. On radar reflectivity has been noticeably lower around Teton Pass and to the north toward YNP. The current Winter Storm Warnings and Winter Weather Advisories remain in effect until 06Z (11 PM) tonight. Winter Storm Watches have been issued for these same zones and a few additional zones (Absaroka Mtns, East Wind River Range, and Upper Green River Basin Foothills) once the current highlights expire at 11 PM tonight as snow will continue and become heavier this weekend into Monday. Near the end of the event snow will spread east of the Continental Divide and Winter Weather Advisories may be needed for Casper Mountain and the Bighorn Mountains. Snowfall ratios will be fairly high as snowfall efficiency will be enhanced due to favorable temperatures aloft. The dendritic growth zone is likely (80%) to be deep and well within the cloud layer for the majority of the period (Today-Monday). The exception is on Sunday as WAA increases and brings in warmer air that will drop ratios for a good 12 hour period. For all the ski lovers out there this will lead to a surplus of fresh powder over this holiday weekend. Wind will be a key factor through this weekend as well. There certainly will be drifting of snow and blowing snow at times from through Monday. The windiest time period will be Saturday through Monday. Beyond Monday it will be cooler and mostly dry as the strong weather systems push east. The upper-level pattern should become more zonal and moisture is expected to drop substantially, but some lingering snow showers remain possible (40%) across western WY through the middle part of next week. By the latter half of next week model guidance has come into better agreement that an amplified ridge will develop over the region, which would bring back the unseasonably warm temperatures and dry conditions. && .AVIATION /00Z TAFS THROUGH 00Z SUNDAY/... Issued at 342 PM MST Fri Dec 27 2024 West of the Divide...KBPI/KJAC/KPNA/KRKS Terminals. Snow will decrease some this evening, with a relatively short period of improved flight conditions overnight compared to what occurred this afternoon. However, the next round of snow will move into the area in the morning, bringing decreasing conditions once again. At KJAC, winds will also increase with the push of snow, with gusts up to around 25 knots by late morning, continuing through the afternoon. East of the Divide...KCOD/KCPR/KLND/KRIW/KWRL Terminals. A cloudy sky overnight. Winds will pick up in the morning to early afternoon Saturday. KCPR will be the windiest, with gusts up to 35 knots. No precipitation expected, though KCPR and KLND will carry occasional 15 percent chances of light snow Saturday morning. Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for the latest information on icing and turbulence forecasts. && .RIW WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory until 11 PM MST this evening for WYZ001-013-014. Winter Storm Watch from 11 PM MST this evening through Monday morning for WYZ001-002-012>015-023>025. Winter Storm Warning until 11 PM MST this evening for WYZ012- 023-024. && DISCUSSION...Rowe AVIATION...Wittmann
Hazardous Weather Outlook National Weather Service Riverton WY 847 PM MST Fri Dec 27 2024 WYZ001>020-022>030-281400- Yellowstone National Park-Absaroka Mountains-Cody Foothills- North Bighorn Basin-Southwest Bighorn Basin-Southeast Bighorn 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- 847 PM MST Fri Dec 27 2024 ...Winter Storm Warnings and Advisories Posted for the Most of the Western Mountains and Valleys through Monday Morning... This Hazardous Weather Outlook is for Western and Central Wyoming. .DAY ONE...Tonight. After a brief break, snow begins to steadily increase across far west Wyoming toward sunrise Saturday. .DAYS TWO THROUGH SEVEN...Saturday through Thursday. Saturday through Monday...Several rounds of snow, heavy at times, will impact the western mountains and valleys. Windy conditions will lead to blowing and drifting snow at times. Travel impacts are likely, especially west of the Continental Divide. Please see the winter weather statements and forecasts for details. .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.
2 winter storm. Local standard time, as filed.
Heavy snow fell in the Tetons. Some notable amounts included 18 inches at the Grand Targhee SNOTEL site and 16 inches at the Jackson Hole Ski Resort.
Heavy snow fell throughout the Salt and Wyoming Range. The highest amount recorded was 23 inches at the Snider Basin SNOTEL site.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Wyoming in 2024Every state in 2024This day in weather historyWarnings in Wyoming, December 2024
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: 1227499, 1227500.