textproduct: Western and Central Wyoming

KEY MESSAGES

- Active weather west of the Divide overnight with above average temperatures east with near record highs for Thursday as well.

- An approaching weather system brings more snow to the western mountains and strong to high wind from South Pass and Muddy Gap through Casper.

- Another weather system follows on Friday, with seasonable temperatures likely for the weekend and into next week.

UPDATE

Issued at 1220 PM MST Wed Dec 24 2025

No major changes to the forecast for the next 24 hours or so. EFI/SOT is highlighting portions of western Yellowstone (Pitchstone Plateau and the northwest corner) for snow, so have upped amounts slightly there, but caution doing too much as models seem to be overdoing snow with many systems so far this season. Also continued to drop precipitation chances east of the Divide as high-resolution models correctly have precipitation struggling to make it over the mountains.

DISCUSSION

Issued at 212 AM MST Wed Dec 24 2025

Twas the shift before Christmas, and all through the weather station, meteorologists were looking at observations from across the nation. Combined with weather models, radar and data from satellite, trying to bring forecasts for travelers through the day and night. And on the inside of the humble Riverton weather abode, there were difficult forecast decisions to be made at it showed. Another Pacific weather system was approaching from the west, And some of the possible travel impacts made the forecaster stressed. Snow was likely over some of the higher mountain passes, and strong wind could slow travel to speeds as slow as molasses. And hopes of a White Christmas for most would be dashed, as recent mild temperatures are not expected to crash.

Now back to your regularly scheduled weather discussion. Things are largely quiet right now, as they were much of yesterday. The main story today continues to be the abnormally warm temperatures, as much as 30 degrees above normal. Casper had their third warmest December high temperature in station history yesterday. We are now up to 53 record highs this month at our 9 official climate sites. Seven of our official sites are having the warmest first 24 days of the month in their stations history (including Lander, which has records dating back 134 years). Riverton is more than 4 degrees above the second warmest period. And the two stations that aren't (Casper and Buffalo) are ranked 2nd and 3rd. And with southwest flow continuing today, we will likely see more record high temperatures this afternoon. As for precipitation, a few showers will develop west of the Divide, but nothing of note, at least until around sunset.

Things get more active tonight. We had two decisions to make tonight in regards to potential highlights, one for wind and one for snow. We will start with wind. Part of the reason it has been so warm is the strong southwest wind, which has been at times very strong. We will have a decent setup for strong wind again today. The pressure gradient will tighten ahead of an advancing Pacific cold front and trough. The 700 millibar winds are expected to increase to 50 to 60 knots ahead of the system. We will also have the right front quadrant of an 100 knot jet streak providing some downward forcing. In the realm of probabilistic guidance, areas from Muddy Gap through Casper look to have at least a 2 in 3 chance of exceeding gusts of 55 mph. So, we went ahead and upgraded the Watch to a Warning and added a couple of zones. We added Casper Mountain for one, with at least a 1 in 2 chance of gusts past 65 mph. The other zone was a bit of a tougher decision.

This is the eastern slopes of the Wind River Mountains. We thought about a Winter Weather Advisory instead. However, southwest flow is more conducive to western portions of the range. We also thought about impacts. The main road in this area, South Pass, only has around a 1 in 4 chance of 2 inches of snow or more. And with 700 millibar temperatures expected to remain above zero Celsius through most of tonight, it would be mainly rain for precipitation. With the busy holiday travel day, we felt the main impact would be high wind. So, we went with high wind. There could be some blowing snow problems as well though, especially Christmas morning as somewhat cooler air moves in. There will likely be some advisory amounts of snow in the higher elevations, but impacts there this time of year would be rather limited.

Now for the snowy side of the system. Steadier precipitation will move in this evening as the front and better upper level forcing approach the area. The 700 millibar temperatures should remain above zero Celsius through around 8 pm tonight, when the arrival of the front begins to lower the levels. The real drop doesn't come until around sunrise Christmas morning though, when they fall to around minus 3 Celsius, putting snow levels around 7000 feet. This should keep snow levels above the valley locations, except possibly toward the end of the event when there could be a small accumulation. The main impacts would be the passes, especially Togwotee Pass with its almost 10000 foot elevation. Here, as well as Teton Pass, with at least a 1 in 2 chance of 6 inches or more of snow, we have hoisted Winter Weather Advisories. And, given the favorable upslope flow, added on for the western Wind River Range as well. If this was a random day, we may have held off. However, given the holiday travel concerns, along with some gusty wind bringing blowing snow, we went ahead and issued. The heaviest snow would fall between midnight and noon on Christmas day, when the trough axis passes and the best jet dynamics move through. And finally, some models are indicating negative lifted indices in western Wyoming, so we can't rule out a stray thunderstorm Christmas afternoon.

Otherwise, Christmas Day looks to be another well above normal day temperature-wise, with more record highs possible. There could be a few showers, but the downsloping flow should keep most areas east of the Divide mainly dry. Wind should decrease somewhat in the afternoon as the system moves away. And as a result, the chance of a white Christmas is basically zero.

Another system will be on this one's heels for Friday. This one has somewhat cooler air with it and should put an end to the record highs for most locations. But not during the day on Friday, when we may have one more day of record highs. As for the next system, this one has more jet forcing with it and as a result precipitation looks to be more of the banded variety and hard to pinpoint. With the cooler air with this system (cooler, but not cold, especially by Wyoming standards), there could be some snow in the valleys as 700 millibar temperatures of minus 5 Celsius put snow levels at 6000 feet. And east of the Divide, there could be strong wind again, although high wind is more questionable.

We will finally put an end to the warm weather on Saturday night and Sunday, as a cold front drops out of Montana and brings some more typical December weather. However, the air is not terribly cold and with the lack of snow cover, temperatures will only fall back to near normal levels. The front could also bring some snow showers along and behind its passage. However, moisture is limited so any accumulations look minor. High pressure should then bring dry and more seasonable weather for early next week and possibly into the start of 2026.

AVIATION /06Z TAFS THROUGH 06Z FRIDAY/

Issued at 930 PM MST Wed Dec 24 2025

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

Light rain but VFR conditions to start the period at JAC/BPI/PNA with low ceilings and little restriction to visibility. Periods of a more steady rain after 08-13Z that will bring MVFR conditions at these locations pushing to RKS between 13-17Z. Any rain and restricted conditions last through 18-19Z before dissipated and lifting to VFR the remainder of the period. Otherwise, winds 10kts or less but with wind shear aloft that will mix down after 18-19Z with daytime heating through about 00-01Z. Light winds and mid level ceilings there on out into the overnight hours through Friday morning.

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

VFR conditions and dry weather expected to the east but with stronger winds remaining elevated overnight gusting up to 20-25kts. Strongest winds between 19-01Z with daytime heating and mixing with mid level ceilings throughout the period, up to 30kts at CPR/LND. Winds diminish with radiational cooling there after with lingering high clouds remaining.

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

RIW WATCHES/WARNINGS/ADVISORIES

Winter Weather Advisory until 5 PM MST Thursday for WYZ012-014.

High Wind Warning until 11 AM MST Thursday for WYZ015-019-020- 022.