textproduct: Western and Central Wyoming

KEY MESSAGES

- Above normal to record high temperatures Tuesday and Christmas Eve.

- Southwest winds, with gusts of 30 to 40 mph, will be occur Tuesday and Christmas Eve 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.

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 eat 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 WEDNESDAY/

Issued at 930 PM MST Mon Dec 22 2025

VFR conditions expected throughout the entirety of the period. Some lingering showers near KJAC carrying VCSH to start before it exits to the northeast. Otherwise, some gusty winds near KLND off the Wind River Mountains have resulted in some wind shear overnight before diminishing before sunrise. Winds increase once again at KCPR/KCOD/KRKS gusting up to 25kts with daytime heating and mixing to the surface. Ceilings lift from the mid levels to upper levels through the afternoon across the entire CWA with dry conditions expected for Tuesday. With the recent rainfall at KJAC Monday, expect fog to develop Tuesday night about the end of this period but certainly into the next TAF cycle for Wednesday morning. Confidence low at this point 24 hours out (10-20%) but something to consider in the coming forecasts.

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.