textproduct: Western and Central Wyoming

KEY MESSAGES

- Increasing and lowering cloud cover through the day as the next weather system approaches.

- Snow begins for the western Wyoming mountains Thursday afternoon lasting into the day Friday.

- The heaviest period of snowfall will be Thursday evening into early Friday morning. Wintry travel conditions are expected on mountain passes.

- Basins east of the Continental Divide will largely stay dry during this weather system. There is a 10% chance for occasional light rain.

- Additional snow is likely (70% chance) by Sunday night/Monday morning for the western mountains and valleys.

DISCUSSION

Issued at 117 AM MST Thu Jan 1 2026

Mid to high level clouds will continue to increase from the west- southwest this morning, as an upper level low moves onshore over central CA. Precipitation chances will increase across areas west of the Divide through the day and into tonight, as the low moves over the Great Basin. The forecast challenge this afternoon into the evening will be whether precipitation falls as snow, a rain/snow mix or freezing rain. Southern portions, such as Kemmerer, Rock Springs and Farson, will have a snow to rain/snow mix by 21Z with snow levels staying around 6500ft. Similar conditions are expected in the Jackson/Star Valleys. Temperatures are expected to rise above freezing (35F to 37F) in the afternoon, with only a 10 to 20% chance of staying below freezing through 00Z. Snow levels will stay around 6200ft by this time in the Jackson Valley and toward Alpine, with the southern portions of the Star Valley starting at 6800ft at 00Z and dropping to 6400ft by 06Z Friday. A rain/snow mix or very wet snow is expected as a result, with sfc temperatures being at or just above freezing through much of the night. There is a 30 to 40% chance for freezing temperatures in the city of Jackson and the rest of Star Valley. Snow is more likely in foothill locations like Teton Village, as well as the rest of Jackson Valley north of Jackson. Regardless, accumulations will be more muted as snow ratios will be closer to 8:1 due to the Pacific airmass from the upper low. Will issue a Winter Weather Advisory for the Tetons/Gros Ventres and Salt/Wyoming zones with most areas receiving up to 8 inches through Friday. Locally higher amounts up to 16 inches will occur in the Tetons and the Salt River Range. Will opt for the Advisory vs a Warning due to the more localized higher amounts.

Precipitation east of the Divide will mostly be isolated, with foothill locations like Lander, Dubois and Cody having a 20 to 40% chance. Rain is more likely to occur, with Dubois having the better chance for snow due to its higher elevation. Temperatures are expected to stay above freezing across I-80, but slick spots cannot be ruled out. However, precipitation amounts are expected to remain very light so not overly concerned with this hazard.

Snow will continue over the western mountains through Friday morning, gradually decreasing through the afternoon, as the upper low moves over the Central and Southern Rockies. Any precipitation east of the Divide and over southern portions of the CWA will be isolated and (relatively) short-lived. Areas near Green River/Rock Springs and Wamsutter look to have the best chances these showers late in the morning to early afternoon.

A transitory ridge will build back over the region during the day Friday, as a strong closed upper low moves over the EPAC toward the West Coast. Dry conditions and above normal temperatures will be in place once again as a result. Strong to high winds could occur over the Wind Corridor Sunday night into Monday morning, as the ridge transitions eastward and increasing the southwest flow aloft. This in turn will lead to a leeside trough to develop over eastern WY, tightening the sfc pressure gradient. The first round of snow could also return to western portions during this time as well, as the first shortwave from the upper low moves over the region.

AVIATION /18Z TAFS THROUGH 18Z FRIDAY/

Issued at 1000 AM MST Thu Jan 1 2026

VFR conditions to start the period as rain/snow pushes in from the west. A mix to just snow at JAC through the period lowering to MVFR conditions after 21Z. This will spread to BPI/PNA after 22Z with possible IFR at PNA by Friday morning around 12Z. RKS will see snow chances most likely during 07-13Z with MVR conditions. Lowest chances east of the Divide at LND/COD/CPR after 23-03Z and overnight through 12Z but low confidence (10-20%) carrying only VCSH. Otherwise, gusty winds at CPR, strongest after 23Z diminishing by 12Z Friday morning. RKS will see gusty winds Friday morning after 13Z with all other locations expected to be 10kts or less for the entirety of the period.

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 from 2 PM this afternoon to 5 PM MST Friday for WYZ012-024.