textproduct: Western and Central Wyoming

KEY MESSAGES

- Snow continuing in western Wyoming, with a gusty to strong wind in many locations East of the Divide today.

- Above normal temperatures continue East of the Divide, although not as warm as recent days.

- A cold front will bring a chance of light snow Saturday and Saturday night, as well as a return to more typical late December temperatures.

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 /18Z TAFS THROUGH 18Z SATURDAY/

Issued at 1055 AM MST Fri Dec 26 2025

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

Precipitation is underway at KJAC with rain quickly changing over to snow and increasing in intensity early in the forecast period. IFR conditions are likely through much of Friday afternoon into early Friday evening at KJAC as moist, southwest flow persists across the region. Light snow becomes more widespread in the Upper Green River Basin Friday afternoon with MVFR conditions consistently occurring at KPNA and KBPI by around sunset Friday. A heavier band of snow slips southeast late Friday afternoon and evening, eventually reaching KRKS just before 06Z/Saturday. KRKS will see a several hour period of IFR/MVFR snow between 07Z-12Z/Saturday. Snow gradually ends at all but KJAC after sunrise Saturday. KJAC finds a west to northwest flow aloft allowing for continued IFR/MVFR conditions until 18Z/Saturday. Southwesterly surface wind will be 10-20kts at times through the day, with KRKS seeing persistent 18-28kt gusts into Friday evening. Mountains frequently obscured.

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

Moist, southwest flow aloft may allow for a few rain showers to spread into KCOD and KLND Friday afternoon and evening, with a lesser chance at KCPR and KRIW Friday evening. Otherwise, conditions remain VFR at all terminals through the period. Gusty southwest surface wind will remain the primary aviation hazard as all terminals see 20-30kt gusts. A cold front begins to push into northern Wyoming late in the period allowing for surface wind to switch to the north to northwest at KCOD just prior to 18Z/Saturday. Mountain tops obscured.

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 11 PM MST this evening for WYZ001-002-012-014-024.