textproduct: Western and Central Wyoming

KEY MESSAGES

- Dry and warm continues tonight into Tuesday, with areas of elevated fire weather conditions. Gusty winds (30 mph or greater) occur for the Wind Corridor from South Pass to Casper, and the eastern Absaroka, Wind River, and Bighorn Mountains.

- Light snow occurs over the western mountains starting tonight, continuing through Tuesday. Rain and rain/snow mix for the western valleys.

- A widespread high wind event occurs Wednesday. Periods of heavy snow over the western mountains will create winter travel impacts for mountain passes.

UPDATE

Issued at 131 PM MST Mon Dec 15 2025

Weather highlights have been issued for the Tuesday/Wednesday weather system incoming. The main message continues to be wind, with widespread westerly gusts of at least 30 to 40 mph, and many areas expecting over 50 mph gusts. Moderate to heavy mountain snow Wednesday will also increase impacts over the western mountains, especially for the mountain passes.

For the forecast itself, not too many notable changes were made. Have increased winds slightly across the area Wednesday to be better in line with anticipated dynamics shown between various models. Currently forecasted winds Wednesday evening into Thursday morning may drop off too early, as post-frontal winds may keep gusts going through the night. Will need to evaluate this for future updates.

DISCUSSION

Issued at 138 AM MST Mon Dec 15 2025

An active weather pattern will begin today and continue through the week, as a broad ridge that was in place Sunday flattens and a more zonal flow pattern develops. Conditions today will be somewhat benign for most areas as a result, however there are a few areas that will have gusty winds once again this afternoon. Otherwise, conditions will be dry today with above normal temperatures (especially east of the Divide). Concerns for fire weather will also be in play this afternoon where winds will be gusting over 25mph. RH values will be below 20%, approaching 13% (15% is a critical threshold), across most of the forecast area, but especially east of the Divide. Areas from southern Fremont County to southern Johnson County (including the southern end of the Bighorns), the Upper Wind River Basin and the Cody Foothills should be wary with any kind of burning even though it is December. The record temperatures from last week, coupled with a dry start to the winter season, make conditions conducive for possible erratic fire behavior. Take the usual precautions if planning any burning today. There will be just enough midlevel (700mb-500mb) moisture to produce virga showers/snow flurries this evening over northwestern portions, the central basins and Johnson County as a weak shortwave moves over the area.

Winds will be increasing over the east slopes of the Absaroka, Bighorn and Wind River Mountains after 06Z (11pm Monday) Tuesday due to a tightening 700mb temperature gradient and 700mb winds approaching 50kt. Similar conditions will also develop over the western mountains during this time. These winds look to impact areas along Hwy 120 near Cody and Clark, as well as the Upper Wind River Basin near Dubois and Crowheart. Wind gusts over 50mph are likely by 12Z as these winds downslope off the mountains and into the lower elevations. There is a 50% chance for gusts of 60-70mph to occur, especially near Cody and Clark. These winds will continue through the rest of the morning Tuesday, gradually decreasing but remaining gusty through the afternoon with gusts of 35 to 50mph and spreading through the Wind River Basin. Wind gusts of 35 to 50mph will also develop over the Wind Corridor east of the Divide by 12Z, spreading across the south by midday. Light snow will be possible over the western mountains from early Tuesday morning through Tuesday evening, due to westerly upslope flow. Snowfall amounts up to 3 inches is expected, with locally higher amounts closer to 5 inches possible in the higher elevations of the Tetons. Most of this snow will occur in the overnight/early morning hours. A rain/snow mix to rain is likely in the Jackson and Star Valleys by 12Z Tuesday, continuing through the day and into the evening. Precipitation is likely to end sometime Tuesday night before returning again Wednesday with the approaching storm.

Wind gusts of 30 to 40 mph will continue over the Wind Corridor and the mountains Tuesday night as the next storm system approaches. These winds will increase through the overnight hours, with 700mb winds of 50kt occurring across much of the CWA by 12Z Wednesday. A leeside trough over eastern WY will strengthen during this time, irt the approaching system/cold front and tightening the pressure gradient. Wind gusts up to 60 mph will be possible by this time at wind prone locations, like the south side of Casper, Clark and even South Pass. These winds will continue to increase through the rest of the morning, with much of the forecast area experiencing wind gusts of 35 to 45 mph. Areas east of the Divide have a 50 to 80 percent chance for wind gusts over 55 mph, with areas west of the Divide having a 30 to 60 percent chance. Snow will be increasing over the western mountains Tuesday night as well, with moderate to heavy snowfall possible Wednesday morning. Forecasted snowfall amounts are in the Advisory range (between 6 and 12 inches), with snow tapering off by the evening. The timing of the cold front remains in flux and could be entering northern portions by early afternoon, but it could lag and not reach northern portions until sunset Wednesday evening. This timing will determine whether the stronger winds continue through the afternoon, or begin to decrease as they switch to a more northwesterly direction behind the front. Winds will still be strong behind the front, but are not likely to be gusting to 70 mph and will be decreasing through the overnight hours into Thursday morning.

Conditions will be dry for the first half of Thursday, with gusty winds continuing, especially over southern portions and the Absaroka and Wind River Mountains. Another round of snow will return to western portions by late afternoon, with strong to high winds returning through the overnight hours Thursday night, as another storm system approaches the area. Similar conditions from Wednesday look likely to return with this storm. with snow over the west and widespread strong to high winds through Friday night.

AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/

Issued at 1009 PM MST Mon Dec 15 2025

Not much to update in latest TAF package for overnight. Low clouds and precip still expected to move across KJAC overnight. Starts as VC in the nearby mountains, before reaching the airport around 12Z. Still expecting mixed precip through the morning, with snow changing to rain by 15Z, but a concern for brief FZRA around this changeover period until sfc temps are able to rise enough to bring consistent melting.

Some of this precip may briefly reach the KBPI/KPNA corridor during the morning. Probabilities have improved that this will occur, but timing is smaller around 18Z, and will not last very long, so have swapped to TEMPO groups for this short period.

Gusty winds will start ramping up tomorrow morning at KCOD as llvl jet mixes down to the sfc, gusting to 50kts at times.Other sites like KCPR and KJAC will also see gusty winds, reaching 20 to 25kts after 18Z.

RIW WATCHES/WARNINGS/ADVISORIES

Winter Storm Watch from late Tuesday night through Wednesday evening for WYZ001-002-012-014-015-024.

High Wind Warning until 1 AM MST Wednesday for WYZ002.

High Wind Warning until 11 PM MST Wednesday for WYZ003.

High Wind Watch from late Tuesday night through Wednesday evening for WYZ011-016-025>030.

High Wind Watch from late Tuesday night through Wednesday evening for WYZ019-020-022.