textproduct: Cheyenne

KEY MESSAGES

- Another round of light snow will move through the area this evening through Wednesday morning.

- Most areas can expect between a dusting and an inch of snow, but a few inches will be possible between Rawlins and Cheyenne. - Long term remains active with multiple systems promoting prolonged periods of high winds, light snow and cold but steadily warming temperatures.

SHORT TERM /THROUGH WEDNESDAY NIGHT/

Issued at 330 PM MST Tue Dec 2 2025

Visible satellite imagery shows ample cloud cover across the area this afternoon, streaming out ahead of a weak upper level shortwave sagging southward over the northern Rockies. This is associated with modestly higher surface pressure also moving southward at this hour, which is beginning to decrease the pressure gradient across the mountain barrier and thus weaken the wind speeds. High Wind Warnings should be able to expire on time in a few hours. The surface high will continue to push south this evening as the shortwave aloft promotes some modest lift. Other mechanisms for lift will be weak frontogenesis as the reinforcing cold front pushes up against the Rockies, along with light, shallow surface upslope flow from north to northeast winds. While we have a few mechanisms present for lift, all will be fairly weak, so snowfall rates are expected to be light as well.

Expect light snow to pick up during the late evening hours today and last through Wednesday morning, tapering off by noon. Most of the area can expect between a light dusting and an inch, but there will likely be some higher amounts between Rawlins and Cheyenne and points southward. There is still a bit of uncertainty in this potential. High resolution models are sharply divergent, with some (e.g. 3km NAM) showing barely a dusting for the entire forecast area, while others (e.g. HRRR) show a widespread 2 to 4" along the I-80 corridor. The official forecast sticks close to a blend of the HREF and the ECMWF ensemble which is an average of both scenarios. Leaning on the cautious side, we have issued a Winter Weather Advisory for the higher elevation portions of I-80, including the Arlington/Elk Mountain areas and the I-80 summit. Both of these areas can do well in northeasterly upslope. The Laramie Valley was left out of this expansion of the Winter Weather Advisory, since the low-level northeast winds may cut down on totals in the immediate vicinity of the city of Laramie. However, totals may increase again heading west from the city on the western side of the valley. While the mountains are still expected to receive some light snow tonight, totals will likely be on the very low end of yesterday's expectations. The first phase of the event with moist westerly upslope flow essentially failed to materialize today thanks to some dry air in the mid-levels.

Mostly cloudy skies and a reinforcing shot of cold air will keep temperatures cold on Wednesday after the snow departs. Highs will stay stuck in the 20s for most, with breezy north winds in the morning decreasing as the day goes on. Clouds will clear from northwest to southeast Wednesday afternoon and evening. With winds expected to be light initially, decided to nudge the temperature forecast towards the NBM 25th percentile, and then lowered further in the typical colder spots of Laramie, Saratoga, and Alliance. Temperatures tanking below guidance will be contingent on wind speeds which are expected to creep up in the higher elevations overnight not mixing down to the valley floors.

LONG TERM /THURSDAY THROUGH TUESDAY/

Issued at 330 PM MST Tue Dec 2 2025

Long term looks to remain stuck firmly under northwesterly flow as we see the CWA between high pressure ridging to the southwest and several small troughs to our north to northeast, bringing a pattern that will include breezy winds, periods of precipitation primarily in the mountains but occasionally spilling into the adjacent zones and high plains, and temperatures that should very gradually warm through the end of the period.

Ensemble clusters have been in pretty solid agreement on the overall pattern, with primary differences lying in the strength of the features in the long term, and small nuances in how the ridge or troughs impact one another. Nonetheless, colder airmasses should remain further north and east of us, allowing the region to remain at or just below normal through the weekend, with temperatures then becoming near to just above normal by early next week. Meanwhile moisture will stream across our CWA and allow for several days of precipitation that will primarily be influenced by upslope flow into the the mountains and produce high terrain snow, but some of this might spill over into the adjacent valleys and down to the high plains at times, particularly on Friday into Saturday when moisture will be highest. Finally the low level jet will be just as active as you would expect for December, with the 700mb flow averaging around 50-60 knots for our wind prone locations for almost all of the long term, and downward omega values favorable to bring this flow to the surface, likely prompting even more high wind warnings yet again.

AVIATION /06Z TAFS THROUGH 06Z THURSDAY/

Issued at 1045 PM MST Tue Dec 2 2025

Snow coverage will expand west to east and impact aviation operations across all terminals to varying degrees. This will result in MVFR and/or IFR conditions as CIGs lower and VIS decreases. If heavier snow moves over a terminal, expect aviation conditions to possibly drop to LIFR. Snow should be tapering off sometime around 18Z Wednesday, ending for all terminals by 00Z Thursday.

CYS WATCHES/WARNINGS/ADVISORIES

WY...Winter Weather Advisory until 11 AM MST Wednesday for WYZ110- 112-114-116. NE...None.