textproduct: Western and Central Wyoming

KEY MESSAGES

- A Canadian cold front will drop southward across Wyoming today and tonight, bring gusty wind, a period of snow and sharply colder temperatures.

- Sunday and Monday will be the coldest in a while, with temperatures near to somewhat below normal for late December.

- Much of next week looks rain and snow free with a return to above normal temperatures.

DISCUSSION

Issued at 304 AM MST Sat Dec 27 2025

Much of Wyoming is about to get a slap across the face. And that slap across the face is the reality of winter in Wyoming usually is. If you don't like cold weather, it has been a charmed life over the past 2 weeks, with most locations 15 to as much as 22 degrees above normal. We started cooling yesterday, and that will continue today. But the slap will really hit tonight and into the Sunday and Monday.

We do have some snow falling largely across the western mountains. There is also some across eastern Sweetwater County. The last round of precipitation will occur with the arrival of the next system, a Canadian cold front that will drop across the area today and tonight. This front will have three things to talk about: snow, wind and colder temperatures.

As for snow, there should not be a lot of it. As with most Canadian or Arctic fronts, there is little moisture with it. As we look into the probabilistic realm of ensembles, the only are with a greater than 1 in 2 chance of 6 inches or more of snow starting at 5 am is the Tetons, with most locations having less than 1 in 10 chance. The chance of 3 inches is higher but again, only in the mountains for the most part. We do have winter weather advisories and we will leave these up, mainly for travel over the passes. As for the lower elevations, other than the western valleys, the chance of 2 inches or more of snow is at most 1 out 4, and that is the places like Sinks Canyon and south of Wyoming boulevard where there could be a brief period of upslope enhancement. Chances of an inch or snow do increase to as high as 3 out of 5 through in a crescent from Johnson County to Casper to the Wind River Basin to the Cody Foothills. This snow will be of the anafrontal variety, occurring behind the front. The best chance would be from the afternoon into the night time hours. The system is a fast moving one though, with all snow likely done by sunrise Sunday. With the light amounts of snow, no further highlights will be issued at this time.

Now we move on to wind. There will be a gusty west to southwest wind ahead of the front, but with 700 millibar generally remaining below 50 knots, any high wind gust would be isolated. It could warm things up a bit, and it is not out of the question that a place like Riverton, which has low record highs, could set another one today. The concern for wind then shifts the northwest flow / cold advection locations post frontal, first in places like Buffalo and Greybull in the afternoon. then into central Wyoming after sunset. LIke pre frontal, mid level wind does not support high wind. However, probabilistic guidance does show around a 1 in 2 chance of wind gusts past 50 mph in the favored areas after the frontal passage. This would be a brief period of stronger wind, generally less than 6 hours. We will not issue any wind highlights for now, but may issue a Special Weather Statement, especially for Johnson County where the wind may be the strongest with a better chance of some accumulating snow.

And now on to temperatures. There is a name for the temperatures that will be found behind the front, seasonable. Lows Sunday and Monday night will be fairly close or somewhat below seasonal averages, but fairly typical for the last days of December. It will feel quite cold though, that slap in the face compared to mild weather we have had over the past couple of weeks. Some portions of northern Wyoming will have around a 1 in 3 chance of low temperatures below zero, especially areas that get some snow this afternoon and evening. It will feel below zero though with the gusty wind, but not cold enough for wind highlights. And there is another concern. With the recent warm temperatures, the ground is fairly warm. This is a fairly good setup for a flash freeze with the snow initially melting on roads and rapidly falling temperatures behind the front.

Cold temperatures will stick around into Sunday and Sunday night. But for those people who don't like cold weather, there is good news. Northerly flow will start to turn more zonal and bring in milder air from the Pacific. And, once again, lead to another period of above normal temperatures. It will not be as warm as before Christmas, but temperatures 10 to 15 degrees above normal may appear as early as Tuesday and almost certainly by Wednesday into the rest of the week. This also looks like a dry pattern. The next chance of precipitation would not arrive until the end of the week in the form of a Pacific trough, but details this far out are still difficult to nail down.

AVIATION /12Z TAFS THROUGH 12Z SUNDAY/

Issued at 431 AM MST Sat Dec 27 2025

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

Snow continues at KJAC for most of the day today, with low cigs and variable vis expected. Snow has had trouble getting into KBPI/KPNA overnight, but low clouds and fog have been drifting in the vicinity, and will continue the next couple hours. KRKS will see some vc showers after 00Z, but chances remain low for the moment, so no addition in TAF. All sites see gusty winds this afternoon, gusting 20 to 30kts.

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

Conditions today will be VFR with breezy southwest winds gusting 15 to 20kts, reaching near 30kts at KCPR. The front barrels through after 00Z, bringing a low chance for precip at KCOD/KWRL, but a better chance for brief snow showers at remaining sites the rest of the night. North winds behind the front gust 20 to 30kts through 12Z/28.

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

CLIMATE

Issued at 304 AM MST Sat Dec 27 2025

Although it was not as warm as on Christmas Day, it was still warm enough for 4 more record high temperatures, putting the monthly total up to 70, with 69 occurring in the past two weeks. Through December 26th, all 9 major climate sites except Buffalo are at least 10 degrees fahrenheit above normal so far the month, with the most anomalous being the Riverton airport which is 17.7 degrees fahrenheit above normal for the month.

RIW WATCHES/WARNINGS/ADVISORIES

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