textproduct: Western and Central Wyoming

KEY MESSAGES

- After a brief lull this morning, wind gusts of 25 to 45 mph will return across much of the area this afternoon.

- Snow returns to western portions tonight, as the start of a multi-day heavy snow event. Snow expected in the western valleys to start, but will change over to rain by Sunday afternoon. Wind gusts up to 30 mph will occur with the snow Sunday, adding to the already difficult travel conditions over Teton and Togwotee Passes. These winds will increase to 40 mph Sunday night. Snowfall amounts of 18 to 36 inches expected through Monday night.

- Above normal, possibly record high, temperatures, and windy conditions Monday through Christmas Eve.

DISCUSSION

Issued at 210 AM MST Sat Dec 20 2025

As of 07Z, the cold front has reached Casper and Riverton and is expected to reach the Divide in the next few hours. Temperatures at these locations have dropped below freezing, with bands of snow occurring over southern portions of the Bighorn Basin and Johnson County, Natrona County along the US-20/26 Corridor and off the southern end of the Wind River Mountains. Snow will also continue to fall over the Salt River/Wyoming Ranges and the Wind River Mountains through the morning hours with an additional 2 to 4 inches expected. Most of this will fall before sunrise. Rain showers are also expected along the I-80 Corridor shortly, pushing south of the Interstate by 10Z. Temperatures are currently in the upper 30s/lower 40s and are not expected to drop below freezing until 12Z. Winds continue to decrease behind the front, with gusts of 25 to 45 mph continuing across southern portions. These winds will gradually decrease by sunrise this morning, with the east slopes of the Wind River Mountains continuing to gust 45 to 55 mph. This will be a brief lull, as west-northwest winds increase to gusts of 25 to 45 mph by midday. These winds will occur for most areas, except eastern portions of the Bighorn Basin and northern Johnson County. Temperatures will be closer to seasonal levels, but still slightly above normal for this time of December.

Precipitation chances will increase over western portions after 06Z Sunday (11pm tonight), as a plume of Pacific moisture moves over the region. This will be part of an Atmospheric River moving onshore over northern CA today and be a multi-day event. Precipitation will likely start as snow in the Jackson/Star Valleys tonight, changing over to rain by the afternoon. Snow levels will range between 7000 and 8000 ft over the western mountains by 18Z Sunday, with moderate to heavy snow through the day and Sunday night. Precipitable water values will be close to record values with this event. This, coupled with favorable west-southwest upslope flow, will lead to snowfall amounts of 18 to 36 inches through Monday night. The bulk of this will occur through Sunday night, with snow becoming light during the day Monday. Wind gusts up to 30 mph will also occur with the snow, adding to the travel hazard over Teton and Togwotee Passes. One of the challenges with the forecast will be if temperatures drop below freezing in the western valleys Sunday night.

Elsewhere, it will be a windy day again Sunday with southwest winds gusting 25 to 35 mph across southern portions and the Wind Corridor. Exceptions will be portions of Natrona County and southern Fremont County, where gusts of 35 to 45 mph will be common. Locally higher gusts up to 60 mph will be possible over South Pass and Hwy 258 on the south side of Casper. There is a possibility for high wind Sunday night into Monday, as 700mb winds increase to 50kt over the Cody Foothills, South Pass and Natrona County. A cold front will move over areas east of the Divide Monday. No precipitation is expected either ahead or behind the front.

The impacts from the Atmospheric River will continue to wane Tuesday, as a ridge begins to build over the region. This will lead to another day of above normal temperatures (possibly record high temps), with highs in the 40s and 50s. Any precipitation will be confined to far northwestern portions, as the ridge shunts most of the moisture to the north and west. Dry, warm and windy conditions are likely Christmas Eve. Another storm system will impact the CWA on Christmas, with western portions having the best chance for a White Christmas. There is the potential that this will be another windy day, as the flow aloft will be southwesterly.

AVIATION /12Z TAFS THROUGH 12Z SUNDAY/

Issued at 320 AM MST Sat Dec 20 2025

West of the Divide...KBPI/KJAC/KPNA/KRKS Terminals.

Largely VFR conditions are expected through 06Z Sunday as the storm system continues to move away. Local MVFR conditions are possible until around 18Z in vicinity of KRKS as a few showers may occur here. However, areas of light snow may continue to bring occasional mountain obscurations through this morning. Wind gusts to 30 knots will be possible and the best chance in vicinity of KRKS. Ceilings will lower again after 06z tonight as the next system approaches from the west. Most snow will hold off until after 12Z Sunday but we did introduce some in vicinity of KJAC after 09Z Sunday.

East of the Divide...KCOD/KCPR/KLND/KRIW/KWRL Terminals.

Largely VFR conditions are expected through 12Z Sunday. The only exception may be some patchy fog in vicinity KCPR but not enough confidence to include in the forecast. Wind will increase again this afternoon with gusts over 20 knots possible at most TAF sites with the exception of KWRL. Wind should decrease after 01Z tonight at all TAF sites.

RIW WATCHES/WARNINGS/ADVISORIES

Winter Storm Warning until 5 AM MST early this morning for WYZ001-002-012-014-015-024.

Winter Weather Advisory until 5 AM MST early this morning for WYZ013-023-025.