textproduct: Western and Central Wyoming

KEY MESSAGES

- Mainly quiet night ahead with above normal to record high temperatures Christmas Eve Day.

- Southwest winds, with gusts of 30 to 40 mph, occur Christmas Eve Day over the Wind Corridor (eastern Sweetwater County to southern Johnson County) and the east slopes of the Wind River, Absaroka and Bighorn Mountains. Locally higher gusts up to 55 mph possible in the more wind prone locations. - Valley rain/mountain snow will develop by the afternoon Christmas Eve and continue into the day on Christmas.

- High wind with gusts around 60 mph will be possible Christmas Eve night into Christmas morning from South Pass to portions of Natrona County, including the Casper area.

UPDATE

Issued at 1140 AM MST Tue Dec 23 2025

No major changes with the forecast through the next few days, as windy and warm conditions remain in place. Have added a High Wind Watch for the Wind Corridor for late Wednesday night into Thursday morning. 700mb winds are forecast around 50 or 55 knots, with a favored southwest flow. Gusts 50 to 60 mph are likely during this time, with wind prone areas (like Outer Drive in Casper or South Pass) likely seeing the highest values. Outside these highlighted areas, it will be at least breezy. Moisture incoming to western Wyoming brings snow (snow levels above 8000 feet) and lower elevation rain. Have held off on any winter highlights for the mountains for now, as confidence is not quite high enough in the amounts. For Thursday, have reduced rain chances a bit east of the Divide, as with this flow pattern precipitation has difficulty getting over the mountains.

For this forecaster, a White Christmas is having enough snow on the ground to cover the (dead) grass. But whether you use my definition or the one in the full discussion below, lower elevations will not see a White Christmas.

DISCUSSION

Issued at 112 AM MST Tue Dec 23 2025

Light snow will continue over far northwestern portions this morning and end before sunrise. This will be the last of the snow that occurred across western portions about 48 hrs ago due to the Atmospheric River. A broad ridge will build over much of the Intermountain West today, pushing the Pacific moisture over the PACNW. This will lead to a southwest flow pattern aloft and unseasonably warm temperatures today and Wednesday. Gusty southwest winds will continue in the same areas from Monday as well, namely the Wind Corridor (eastern Sweetwater County to southern Johnson County) and the east slopes of the Wind River, Absaroka and Bighorn Mountains. Gusts of 30 to 40 mph will be common in these areas, with locally higher gusts up to 55 mph possible. These winds will be slightly stronger Christmas Eve, with gusts of 40 to 50 mph and locally higher gusts up to 65 mph. Above normal to record high temperatures will continue in these areas with the gusty winds, with 50 degree readings common across Sweetwater and southern Lincoln Counties and east of the Divide. Riverton, Lander, Natrona and southern Johnson counties could reach 60 degrees, with the latter locations having the best chances. Expect these temperatures to return Christmas Eve, with more locations east of the Divide having better chances of reaching 60F. Conditions will be dry today, with a slight chance for virga showers over Sweetwater County this evening and flurries of snow over the Wind River and Gros Ventre Mountains and the Salt River/Wyoming Ranges late tonight. Fog will be possible tonight in the western valleys, but it looks like skies will be mostly cloudy to overcast.

A longwave trough will be in place over the EPAC tonight into Christmas Eve with a closed low eventually developing by Christmas. The trough will progress very little eastward today through Christmas due the ridge, resulting in shortwaves ejecting over the West Coast, the Great Basin and Northern Rockies. The first of these shortwaves will reach western portions of the Cowboy State by the afternoon Christmas Eve, bringing valley rain and mountain snow. Snow levels will range between 8000 and 9000ft, dropping to around 7000ft late in the afternoon on Christmas. This looks to be a repeat of last Sunday/Monday, with 0.50" of rain and 8 to 16 inches of snow in the mountains. High Wind Watches may be needed Christmas Eve night for South Pass and Natrona County, as 700mb southwest winds increase to 50-60kt by 06Z Thursday. These winds will decrease through the afternoon Christmas Day, as a cold front moves over the area. This will make it a not-so- pleasant Christmas for those in the Casper area and the rest of the Natrona County. In summation, rain expected for western areas below 8000ft but will be a good day for the ski slopes. The caveat here will be wind gusts of 30 to 40 mph Christmas morning. Wind gusts of 30 to 50 mph over the Wind Corridor Christmas Eve into Christmas morning, with gusts around 60 mph across portions of Natrona County. So a White Christmas is not expected this year. A White Christmas, in this forecaster's opinion, is when snow falls Christmas Eve night and/or Christmas morning. Snow on the ground that is a couple of weeks old isn't very special and by this definition we could have a White Christmas from as far back as Thanksgiving.

The Pacific upper low looks to finally move onshore over northern CA by Friday, Ejecting most of its energy and moisture, as well as weakening the ridge, in the process. A separate system begins to drop southward from Canada, marking an end to the unseasonable "hot" streak. Chances for snow in the western valleys increase by this time, along with chances for precipitation across southern portions. There is even a chance for snow occurring over far northern portions of the CWA Friday night into Saturday with the passage of the Canadian cold front.

AVIATION /06Z TAFS THROUGH 06Z THURSDAY/

Issued at 930 PM MST Tue Dec 23 2025

VFR conditions expected throughout the period for all locations. Winds have diminished to 10kts or less for the overnight hours except for remaining elevated at CPR with a 18kt breeze. Increasing upper level clouds into Wednesday ahead of the next system lowering to the mid levels west to east 20-00Z. Light rain expected at JAC by 20Z pushing to BPI/PNA by 02Z but with less confidence carrying VCSH. Restricted visibility and lower ceilings possible to MVFR at JAC after 02Z carrying a tempo through the end of the period with a 20-30% confidence level IAW much of the hi-res data. Otherwise, winds increase with the system after 00Z gusting up to 25kts east of the Divide along with RKS, highest at CPR during the afternoon up to 35kts. These will remain elevated into the overnight hours into Christmas morning as well.

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

High Wind Watch from Wednesday evening through Thursday morning for WYZ019.

High Wind Watch from Wednesday evening through Thursday morning for WYZ020.