textproduct: Western and Central Wyoming

KEY MESSAGES

- An approaching system will bring moderate snow to the western Wyoming mountains Thursday through Friday morning. The heaviest period of snowfall is expected Thursday night. A rain or rain and snow mix is expected across the valleys and basins of western Wyoming. Winter travel conditions are expected along mountain roads Thursday afternoon through Friday morning.

- Areas East of the Divide will see clouds on Thursday with low chances (20% or less) for occasional light rain.

- Precipitation ends Friday, with warmer temperatures through the weekend.

UPDATE

Issued at 1237 PM MST Wed Dec 31 2025

The ridging of the past few days will be briefly replaced by a weakening midlevel trough beginning Thursday. As noted below, this will return precipitation to areas west of the Continental Divide as early as sunrise, though most of this will hold off until the afternoon. Totals have continued to trend up for the mountains; the heaviest snow is expected over the Teton Range, Snake River Range, southwestern Yellowstone, and the Salt River Range Thursday evening through Friday morning as moisture funnels up the Snake River Plain. If this trend holds, winter highlights may be needed for these areas beginning Thursday afternoon or evening. Rain or a rain/snow mix is still on track for lower elevations of western Wyoming given the general warmth of this system.

DISCUSSION

Issued at 158 AM MST Wed Dec 31 2025

Quiet weather to finish 2025. As has been a common occurrence this winter so far, mild temperatures are in place today as a ridge dominates the western US. Highs today are in the upper-30s to mid- 40s (and around 50F for Johnson/Natrona Counties and near Cody). These values are generally 10 to 15 degrees above normals for December 31st. Besides some breezy west to southwest winds for the usual areas, winds are light today. No precipitation is expected today, with high clouds increasing from the southwest ahead of the next weather system.

Speaking of that weather system, there have been a couple small changes with model projections. The center of the low has shifted slightly north and stays a bit stronger as it moves into the Nevada/Utah area. The changes aren't too major, however, with the main change being some increased snow amounts over the western mountains. That precipitation should begin moving into southwest Wyoming Wednesday night, as early as around midnight (15% chance) but better chances towards sunrise. Snow levels to start are between 6000 to 7000 feet, rising to 7000 feet or greater by the end of Thursday. This should bring snow accumulations above 7000 feet, with snow and rain/snow mix to the lower elevations. Most precipitation chances remain along and west of the Divide, with the best chances over the mountains. Current snow totals for the Teton and Salt River Ranges are generally 4 to 8 inches, but there is some lack of confidence given snow levels and still some uncertainty with storm track. A dusting to half an inch is possible for the lower elevations west of the Divide, mainly for the the valleys like Star and Jackson Valleys.

Past this system, ridging returns, keeping temperatures warm into the weekend, with highs pushing near daily records. A low near the Pacific Northwest tightens the pressure gradient, with gusty winds expected for portions of the area. Both the ECMWF and GFS have a few 50 knot winds at 700mb late Saturday into Sunday, so will have to watch the wind potential for this weekend.

AVIATION /00Z TAFS THROUGH 00Z FRIDAY/

Issued at 330 PM MST Wed Dec 31 2025

VFR conditions expected throughout the period for all locations. Light winds and mainly clear skies outside of gusty winds up to 25kts at CPR. These winds will increase to 30kts after 03Z as the gradient further east remains without the inversion setting up to cap anything aloft. Otherwise, increasing upper level clouds overnight ahead of the next system down to the mid levels by 18-19Z west of the Divide. Rain chances increase after this point in from the southwest with it more of a warm boundary not seeing the snow chances until Friday morning. PROB30 groups expected first at RKS, then BPI/PNA, followed by JAC. There may be impacts at CPR/COD into the next TAF cycle by 00-06Z Thursday evening and overnight. Little impacts as VFR conditions should remain throughout.

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

None.