textproduct: Western and Central Wyoming

KEY MESSAGES

- A mainly dry and cooler day today with diminishing wind.

- Light to moderate snowfall rates overnight Tuesday night into Wednesday across northwest WY. Limited impacts focused along mountain passes with 1 to 4 inches across Teton and Togwotee Passes expected.

- Confidence continues to increase (60 to 80% chance) that a Winter weather system will impact the region Friday into Sunday. Details on timing and placement of the heaviest snow remains uncertain (20 to 40% confidence), especially on Saturday and Sunday.

UPDATE

Issued at 1000 AM MST Tue Nov 25 2025

There has been little to no change to the forecast. Everything remains on track with the shortwave pushing through tonight and snowfall amounts remain consistent with the previous forecast. Snowfall will be focused across the northwest WY mountains, generally 2 to 5 inches across most peaks. Isolated favored west- facing slopes in the Tetons and Absarokas, most notably along the eastern boundary of YNP, could see an isolated 6+ inches of snow. Due to how isolated those higher values would be, and given that impacts to mountain travel corridors will be minimal, have opted not to hoist any highlights.

With the cloud cover Wednesday morning, expect low temps to be a few degrees warmer than they were this morning. The cloud cover should also prevent fog development, so have not included any fog mentions in the forecast for Wednesday morning. Beyond Wednesday, the forecast remains on track with confidence regarding the post- Thanksgiving storm continuing to increase.

DISCUSSION

Issued at 230 AM MST Tue Nov 25 2025

A cold front has moved through Wyoming and most of us are getting a slap across the face called reality, A.K.A. what the weather usually is late November in the area. We have been living a charmed life through most of the eleventh month of the year, with most of our main climate sites having the warmest first 24 days of the month (8 of the 9, the only one that isn't is Buffalo), in many cases more than 10 degrees above normal. This will be the coolest day in a while, but by late November standards, not too bad. Most locations will only see temperatures near to slightly below normal, although it may feel colder given the recent mild temperatures. The other issue will be a gusty wind, mainly this morning and mainly in the favored cold advection / northwest flow locations like northern Johnson County. There have been isolated gusts over 60 mph Monday night. These winds should decrease through the morning as the pressure gradient decreases as the front moves away. Any light snow showers should end by sunrise with mainly dry conditions continuing through this evening.

The next system, a shortwave will move into northwestern Wyoming late tonight. This system does not have a ton of moisture to work with. However, one thing that gives me a bit of concern is that it will have jet energy in the form of an 120 knot jet streak moving through Wednesday morning which would maximize the efficiency of the system. As for potential highlights though, we have decided not to. The chance of 6 inches of snow or more in the mountains for most locations is less than 1 out of 4 through Wednesday night. The one exception is the western Absarokas, where the chance is generally around 1 out of 3, maxing out at 1 out of 2 in a small area. However, this area is in an area with no roads and as a result, basically no impacts. The day shift can monitor in case amounts increase, but this looks like the only location that would need highlights. There is good model agreement in timing, in the steadiest snow falling between 2 am and 2 pm. As for the valleys. temperatures will be cold enough for snow everywhere. There is a greater than 3 in 5 chance of an inch of snow in the Jackson and Star Valleys, but the chance of 3 inches is less than 1 out of 6. Out there, they need snow badly and it would be welcomed. The lower elevations East of the Divide would have few impacts, although a few showers may occur in the northern Bighorn Basin and around Casper on Wednesday afternoon.

Turkey day looks relatively quiet at this point. There will be some orographically enhanced snow showers across the western mountains, but any potential accumulations look to be on the light side. Most locations will have a fairly nice day with dry conditions and another day of above normal temperatures with some locations approaching 50.

Then the interesting stuff moves in starting Friday. The first is in the form of a cold front dropping southward into the state starting Friday morning and continuing into early Saturday morning. Deterministic guidance has come into somewhat better agreement this morning showing the front dropping into northern Wyoming Friday afternoon and exiting Saturday morning. Precipitation with this system looks largely anafrontal, with the highest rates occurring Friday evening as the moisture encounters a jet couplet moving across Wyoming. With 700 millibar temperatures initially around minus 4 in eastern portions of the area, precipitation may start as rain in places like Buffalo, and this could freeze Friday night as the colder air moves in, bringing slick roads. This still looks to be the best chance so far of the first accumulating snow across areas East of the Divide, with many locations having a greater than 1 in 2 chance of an inch or snow by Saturday. The chance of 3 inches looks fairly low though, at most 2 out of 5. With north to northwest flow behind the front, the best chance of this would be the northwest upslope flow locations, like the southern Bighorns and Thermopolis. There is more uncertainty on the other factor, a second spoke of energy that will may move in from the south and combining with another cold front, this one of Canadian origin, and may bring another round of snow. The deterministic models are split on this, as are the ensembles, with some bring a few more inches of snow, mainly to central and southern Wyoming and others keeping the impacts mainly south of Wyoming.. This does not look like a huge storm but given the travel implications over the holiday weekend we have to watch this closely. Hopefully, this will resolve itself over the next few days. And, behind this second cold front will be the coldest air so far this season. The 700 millibar temperatures will fall as low as minus 18, which could bring some below zero low temperatures Sunday or Monday night, especially if there is some snow on the ground. At this point, it does not look record breaking, but it will feel cold after all the mild weather through most of November.

AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/

Issued at 1028 AM MST Tue Nov 25 2025

VFR conditions prevail across all terminals to start the TAF period. Winds remain light through much of the period. Mid to high level clouds will continue to work their way across the region throughout the day Tuesday with ceilings expected to remain VFR. Another disturbance moves into the area for Wednesday morning. Light snow will be possible across some terminals with the best chances being at KJAC. Precipitation looks to move in around 09Z Wednesday with prevailing snow starting later in the morning through the end of the period. Periodic MVFR to possible IFR conditions may be possible depending on the intensity of the snow showers. KPNA may see a brief shower or two during the mid to late morning Wednesday. KBPI and KRKS have much lower chances but still a very brief isolated shower cannot be ruled out. Other terminals east of the Divide such as KCOD, KWRL, and KCPR may see a few showers starting after 13Z through the end of the TAF period. Due to lower confidence at these terminals PROB30 groups are in place with prevailing lines possible if confidence increases. Winds increase along with the precipitation entering the area. Most terminals will see a slight increase with winds around 10 knots at times. KRKS and KCPR may see stronger winds of 15 knots with gusts of 20 to 30 knots possible. Mountains are expected to see obscuration begin by the early morning hours Wednesday and likely persisting through the end of the period.

RIW WATCHES/WARNINGS/ADVISORIES

None.