textproduct: Cheyenne

KEY MESSAGES

- Snow showers and blowing snow will impact travel in the Arlington/Elk Mountain area through Monday morning.

- A long duration wind event is beginning today. While some breaks or lulls will occur, high winds will be a concern every day through Friday.

- Damaging winds are expected near and in the lee of southeast Wyoming mountain ranges Monday evening through Tuesday evening. Gusts up to 90 mph are expected.

- Cheyenne, Laramie, Rawlins, Wheatland, and Douglas can expect wind gusts up to 75 mph tonight into Tuesday.

- Wind gusts up to 65 mph are expected to spread into High Plains during the day Tuesday.

- A backdoor cold front may bring a brief reprieve from the wind along with a chance for snow showers Tuesday night into early Wednesday before winds pick up again Wednesday.

SHORT TERM /THROUGH TUESDAY NIGHT/

Issued at 400 AM MST Mon Dec 8 2025

Current GOES satellite imagery indicates elevated mid-level mositure associated with a weak vort-max moving through the area this morning. This is helping to boost pressure gradients. Wind gusts of 55 to 65 mph have been ongoing for the last several hours in the typical wind prone areas of southeast Wyoming. In addition, moisture embedded in the northwest flow pattern is forcing some snow shower activity in and near the mountains of southeast Wyoming. The combination of falling and blowing snow is leading to reduced visibility and hazardous travel conditions in the Arlington/Elk Mountain area. Water vapor imagery shows that drier air is beginning to move into the area, so expect conditions to improve by around sunrise if not before. Conditions will remain marginally supportive for wind gusts to around 60 mph along I-80 all through the day today, so decided to extend the High Wind Warning for these areas all the way through the next event (lasting until Friday). Otherwise, expect a breezy to windy day across the area, but the high wind threat should remain confined to the wind prone areas (for now).

The main hazard in the short term is the upper tier wind event expected to begin this evening and last through Tuesday evening. The wind prone areas may not see a break at all before the next event Wednesday, but that is discussed more in the Long Term section below. High wind parameters begin ramping up rapidly after sunset today as the nose of a powerful jet streak aloft moves overhead. We will be in the right exit region of this feature, which will help to support synoptic descent and aid in winds reaching the ground. After midnight, we will have 700-mb winds exceeding 65 knots over much of southeast Wyoming. The typical gradients we often look at to gauge wind potential are about as high as they get. Per the GFS (which is still running a little hot compared to other models), Craig to Casper 700-mb height gradients reach 101 meters Tuesday morning. MSLP gradients from Craig to Bordeaux are sitting between 15 and 20 mb late tonight all the way through the day Tuesday. The MSLP gradients will be enhanced as a surface trough trailing below a strong surface cyclone in the northern Plains moves through the High Plains Tuesday morning. Gradients should peak generally between sunrise and midday Tuesday. In addition to the impressive wind parameters, forecast soundings also look favorable for vertically propagating mountain wave activity. Models are in pretty good agreement showing a strong inversion setting up between 600 and 700- mb, which lines up well with mountain top height here. Forecast wind speeds peak at the inversion level and generally decrease up to about 500-mb which is a good signal for the potential for mountain wave breaking and downslope enhancement in the immediate lee of each of our mountain ranges. All together, the pieces are in place for a high end wind event between about midnight tonight and Tuesday evening. The wind prone areas, especially in the lee of the Snowy and Laramie Ranges (I-25 Bordeaux, I-80 summit/Buford, I-80 Laramie to Elk Mountain), will likely see wind gusts of 80 to 90 mph during the peak of this event. While not necessarily likely, it would not be shocking at this time to see a few gusts in the 95 to 100 mph range. Southeast Wyoming population centers (including Cheyenne, Laramie, Rawlins, Douglas, and Wheatland) will probably peak between 65 and 75 mph, but a few brief gusts exceeding 80 mph cannot be ruled out especially in Cheyenne and Laramie. Once we get some better mixing in place mid to late Tuesday morning, expect strong winds to spread all across the High Plains. For far eastern Wyoming (e.g. Lusk, Torrington, Pine Bluffs) and into western Nebraska, there is potential for gusts 60 to 65 mph mainly during the day on Tuesday. Since this threat won't really begin until Tuesday morning, decided to let the High Wind Watch continue here to wait for more confidence, while all other Wyoming zones further west were upgraded to a High Wind Warning.

Tuesday evening, we will be looking at a surface cold front pushing through on the front edge of a high pressure system traversing the eastern edge of the Rockies. This will knock down pressure gradients considerably as it moves through, and tilt winds more to a northwest direction instead of due west. This provided enough confidence to break up the event and end the current set of warnings at midnight Tuesday night or earlier (with the exception of the I-80 wind prone areas, which run all the way through). In addition to providing a brief reprieve from the wind, this front will be accompanied by potent frontogenesis. This is likely to produce some banded snowfall Tuesday night into Wednesday morning. Moist upslope northwest flow will impinge on the mountains once again Tuesday afternoon and overnight, so periods of moderate to heavy snowfall can be expected again. Winter headlines may be needed, but the wind threat was the primary forecast challenge to focus on with this forecast package.

LONG TERM /WEDNESDAY THROUGH SUNDAY/

Issued at 400 AM MST Mon Dec 8 2025

The surface high will graze against the Laramie range Tuesday night, but begin to pull out to the east just as quickly as it arrived. By late Wednesday morning, forecast models show a surface trough developing along the I-25 corridor once again, which will help surge pressure/height gradients once again. As this moves eastward Wednesday afternoon and evening, winds will overspread the High Plains once again. Confidence is lower in this event reaching east of the WY/NE border, but another High Wind Watch was posted from Wednesday morning into Thursday morning for much of southeast Wyoming. 700-mb winds climb back up to 55 to 65 knots. The winds will help temperatures climb again and push the arctic frontal boundary likely just to the northeast of us (although Chadron may remain on the cold side of the boundary). Wind parameters during this second phase of the event are nearly as impressive as the first phase, but there is a little bit more spread between model systems at this time.

Thursday and Friday remain a very tricky forecast with the arctic front right on our doorstep. Overall, most models have trended towards the warmer, windier scenario, with more ensemble members in the cluster that keeps the arctic front and associated long-duration snowfall in northeast Wyoming, southeast Montana, and western South Dakota. However, this is still uncomfortably close for an arctic front, as these features can often end up pushing further south and west than models show. In addition, the surface frontal boundary is frequently further to the south and west than the mid-level frontal boundary and associated frontogenesis. Thus, even though the probability for significant snowfall has decreased, this leaves an enormous spread amongst ensembles in the forecast temperatures between Thursday afternoon and Saturday morning, with nearly 20F between the 25th and 75th percentiles for Cheyenne. There is higher confidence that areas from Lusk to Chadron or so will be on the cold side of the boundary. These areas will also have a better chance for significant snowfall as they will be right on the cusp of the stalled band of frontogenesis. Considerable uncertainty remains for this period, so we won't go too deep into the weeds just yet.

Beyond Friday, models are in fairly good agreement showing the ridge amplifying and pushing the baroclinic zone further away from the area. We may finally get a break from the active weather period for the upcoming weekend with above average temperatures likely. However, it's never safe to say that we will get a break from high winds in southeast Wyoming in December at this lead time.

AVIATION /12Z TAFS THROUGH 12Z TUESDAY/

Issued at 434 AM MST Mon Dec 8 2025

VFR conditions are expected for the forecast period. However, strong winds will impact aviation for most of the period. Lingering LLWS this morning will break down as winds mix to the surface. look for wind gusts between 30 and 40 knots in Wyoming today, with gusts 20 to 30 knots in Nebraska. Winds will drop off this evening temporarily, but we are on track for a major wind event Tuesday. Wind gusts of 40 to 50 knots will impact Wyoming terminals towards the end of the TAF period, while Nebraska terminals can anticipate increasing LLWS.

CYS WATCHES/WARNINGS/ADVISORIES

WY...High Wind Warning from midnight tonight to 8 PM MST Tuesday for WYZ101-104-105-109. High Wind Watch from Wednesday morning through Thursday morning for WYZ101-107-118. High Wind Watch from late tonight through Tuesday evening for WYZ102-108-119. High Wind Warning from midnight tonight to midnight MST Tuesday night for WYZ103-107-114-118. High Wind Watch from late Tuesday night through late Wednesday night for WYZ104-109. High Wind Watch from Wednesday morning through Thursday morning for WYZ105-106-113-115-117. High Wind Warning until 11 AM MST this morning for WYZ106-117. High Wind Warning from 5 PM this afternoon to midnight MST Tuesday night for WYZ106-117. High Wind Warning until 5 AM MST Friday for WYZ110-116. High Wind Warning from 8 PM this evening to midnight MST Tuesday night for WYZ113-115. NE...High Wind Watch from late tonight through Tuesday afternoon for NEZ002-003-019>021-054-055-095-096.