textproduct: Western and Central Wyoming

KEY MESSAGES

- Periods of moderate to heavy snowfall will continue across western WY overnight and through Saturday afternoon.

- Warm temperatures will subside for a short period as a cold front brings more seasonable temperatures to the state for the weekend.

- Snow showers are possible east of the Divide behind the frontal passage Saturday evening into Sunday morning.

- The end of December and 2025 is looking mild with mostly quiet weather expected at this time.

UPDATE

Issued at 1245 PM MST Fri Dec 26 2025

Snow will continue to move into portions of western WY this afternoon. Temperatures across western valleys have been fluctuating with Jackson seeing some periods of rain or wet snow this morning. Temperatures will continue to drop with precipitation turning over to all snow by sunset. Moderate to heavy periods of snowfall will be possible through the evening with a brief decrease in intensity expected late Friday evening. Snowfall intensifies once again by the morning Saturday and continuing into the afternoon. Most of the forecast remains unchanged with the one exception being the extension of Winter Weather Advisories across the mountains of western WY. This is due to a second round of moderate snowfall that arrives during the morning and afternoon hours Saturday. The second round of snow is forecast to bring another 2 to 6 inches for low to mid elevations with the higher elevations seeing 6 to 10 inches. Otherwise, things remain on track with the frontal passage expected to occur during the morning hours Saturday. Snow showers will be possible east of the Divide post frontal passage which would be during the evening Saturday into the early morning hours Sunday. The forecast for the start of next week into the end of December has not changed. Warmer temperatures return with mostly quiet conditions prevailing as well.

DISCUSSION

Issued at 303 AM MST Fri Dec 26 2025

It was more of the same yesterday. Seven more record high temperatures fell. I was a little warm with my temperatures, but many areas had a nice Christmas afternoon. Today we will begin the transition back into reality as temperatures will trend down some each day, reaching a nadir on Sunday and Monday before rebounding somewhat before the New Year.

Radar is currently showing some showers across northwestern Wyoming. The next Pacific trough and cold front will be approaching the area today and bringing some snow to western portions of the area. This will increase through the day, with the heaviest expected this afternoon and evening as the trough axis passes through the area. One difference with this system is that there will be cooler air in place, so snow levels should drop to the valley floors by this afternoon and bring some snow to the western valleys. As for amounts, the current forecast looks to be largely on target. Most of the areas with the advisories have at least a 4 out 5 chance of 6 inches of new snow or more, The chance of 12 inches or more still looks fairly small, generally less than 1 out of 4. The exceptions are the highest elevations but impacts here would be limited. I do have a couple of concerns though...

One is that decent snow may continue past the 11 pm ending of the advisory. However, most guidance does show the heaviest snow ending by 11 pm, although lighter snow will continue through the remainder of the night. The impacted areas would be in areas with few people though. The other is what happens tonight, especially later tonight as the system moves into southern Wyoming. This includes along Interstate 80. The ground is rather warm given the recent record high temperatures. Colder air could spread in quickly and any snow that falls could melt and then refreeze on roads, possibly bringing a flash freeze. Amounts will not be the problem. Probabilistic guidance only gives at most a 1 in 3 chance of over 2 inches of snow and this is over far southeastern portions of the county where population and impacts are slim to none. This may be better handled with short fuse special weather statements though. A few showers are also possible East of the Divide, but amounts here would be very light.

In addition, we have the concern for wind. Like was stated in the update yesterday afternoon, things continue to look borderline. We do have a few 50 knot wind barbs at 700 millibars, but nothing widespread. The NBM ensemble also keeps the chance of wind gusts past 60 mph generally less than 1 out of 2. The exceptions are the higher elevations of the Green Mountains and the south side of Casper. However, high wind criteria is higher in this vicinity. For now, we will opt for a Special Weather Statement since we feel any high wind gusts would be isolated. Wind should decrease later tonight after the front passes. As for temperatures, they will be above normal once again, with a few records possible again.

The thing that will put an end to the warm temperatures will then move in for Saturday and Saturday night in the form of a Canadian cold Front. It will sweep into northern Wyoming in the afternoon and drop southward through the nighttime hours. We have the usual concerns with these systems. The first is for wind. There is a decent pressure gradient with it as well as good cold advection and northwest flow. This is the classic formula for strong wind gusts in places like the northern Big Horn Basin and Johnson County. The NBM ensembles give around a 1 in 3 chance of wind gusts past 55 mph in the afternoon and evening as the front passes. It would be brief but there is a definite possibility. The other concern is snow. The system is continental in origin, so it does not have a lot of moisture to work with. It is also a fast mover so precipitation would not last a long time. The only location that has any chance of over 6 inches of snow is the Tetons but even here it is only 1 out of 3. As for East of the Divide, some locations have a 1 in 4 chance of an inch of snow. This is largely in areas like Riverton, Lander and Casper where a brief period of northerly upslope may develop later Saturday night behind the front, and around Buffalo. This is far from certain though since these anafrontal snow events tend to be banded and hard to pinpoint. The main concern would be a possible flash freeze with initial snow falling on warm ground and melting before temperatures fall into the teens and even the single digits. Travel could get difficult in some areas later Saturday night. And it will feel MUCH colder Saturday night, as places like Buffalo could be 60 degrees cooler Sunday morning compared to Christmas afternoon.

A period of quieter weather should then move in for the rest of the calendar year as ridging builds over the area. Sunday and Monday look colder but likely only seasonably cold, and a lot depends on snow cover. Areas that don't see much snow from the cold front may end up warmer. Flow then gradually turns more zonal toward the middle of next week, bringing a return of above normal temperatures, but not record breaking ones like we had much of this week.

AVIATION /06Z TAFS THROUGH 06Z SUNDAY/

Issued at 930 PM MST Fri Dec 26 2025

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

Light snow continues to push MVFR conditions at JAC/BPI/PNA/RKS overnight lingering at JAC all day Saturday. Much lower confidence at BPI/PNA/RKS for additional showers after 12Z with low but VFR ceilings lingering. Gusty winds after 18-19Z, highest at RKS up to 25kts ahead of the cold front pushing to 30kts after 00Z as it pushes southeast. Otherwise, JAC should end with the shower activity after 03Z, although lingering over the higher terrain, and thus, mountain obscuration continues throughout the entire period for all locations.

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

Snow showers have ended but lingering around CPR through 10Z carrying VCSH due to lower confidence on station (10-20%). Winds remain elevated at CPR through the entire period peaking at 30kts in the afternoon before diminishing after 02Z as the front pushes through. All other locations will see gusty winds up to 25kts after 16Z ending by around 01Z. Any snow shower activity at COD/CPR will be post frontal after 01-02Z but less moisture to work with, and hence, lower confidence carrying VCSH at this time. Otherwise, mountain obscuration continues with the low but continued VFR ceilings throughout the period.

Please see the Aviation Weather Center and/or CWSU ZLC and ZDV for the latest information on icing and turbulence forecasts.

CLIMATE

Issued at 303 AM MST Fri Dec 26 2025

On Christmas Day, there were 7 more record high temperatures at official climate sites, bring the monthly total to 66. All but one of these record high temperatures occurred in the past 2 weeks. All 9 official climate sites have had the warmest first 25 days of December in station history. The Riverton Airport is 5 degrees warmer than the second warmest period (in 2021) and the Rock Springs airport is 4.8 degrees warmer than the second warmest period (in 1958).

RIW WATCHES/WARNINGS/ADVISORIES

Winter Weather Advisory until 5 PM MST Saturday for WYZ001-002- 012-014-024.