textproduct: Cheyenne

KEY MESSAGES

- A High Wind Warning is in effect from 11 PM tonight through 11 AM Monday for Arlington, Bordeaux, and the Laramie Summit wind prone locations.

- Generally light mountain snow expected for the Sierra-Madre and Snowy ranges tonight through tomorrow morning.

- A High Wind Watch has been issued for most of the CWA beginning late Monday, with portions lasting through late Tuesday, while much of the high terrain and adjacent zones of Wyoming will stay in a watch through early Thursday.

- Uncertainty remains in the forecast between late Wednesday through Friday due to an arctic cold front that will stall very near or over our area. A small shift in the front location will mean wildly different outcomes.

SHORT TERM /TONIGHT THROUGH MONDAY/

Issued at 259 PM MST Sun Dec 7 2025

This morning's high wind warning was a bust as winds struggled to reach criteria across the gaps of our windy prone locations. That being said, decided to err on the side of caution and issued another high wind warning, once again for our wind prone locations of Arlington and Bordeaux but also included the Laramie Summit from 11 PM tonight and continuing through 11 AM Monday. A quick moving shortwave should promote 700mb pressure gradients from Craig to Casper in excess of 60 meters, and near surface gradients of 65-75 meters, aided by a 700mb jet of around 50-60 knots and favorable downward Omega values. Otherwise tonight into tomorrow morning we should see some light snow showers moving across the mountains of the Sierra-Madre and Snowy Ranges from this quick passing system, with amounts generally sub-advisory outside of the highest peaks, but just low enough that an advisory didn't feel necessary, particularly after the dumping of snow these mountains just got.

Moving into Monday during the morning and beginning of the afternoon, we'll see highs jump back into the 40's to 50's east of the Laramie Range as warmer air overspreads the region and skies remain mostly clear. The aforementioned High Wind Warning will expire by 11 AM, but don't be surprised if winds linger just under or even around high wind thresholds during the early afternoon hours as pressure gradients just barely decline below the level we'd like to see for high winds. And with an even stronger wind event right on the heels of this warning, this will be a temporary respite at best.

LONG TERM /MONDAY NIGHT THROUGH SATURDAY/

Issued at 415 AM MST Sun Dec 7 2025

There may be a brief break in the high wind potential Monday afternoon or early evening, but wind parameters begin to ramp up dramatically during the evening hours. A much more powerful upper level low will race in from the northwest on the nose of a 150+ knot jet streak aloft. While its track should remain well to our north, it will send MSLP and low-level height gradients surging. By daybreak Tuesday, LREF median 700-mb winds exceed 65 knots over much of southeast Wyoming. The GFS indicates Craig to Casper 700-mb height gradients reaching 90 meters, which is a fairly exceptionally high value. The GFS continues to run a little hot compared to most other models, but this is still work a discussion. The model consensus scenario still supports a mid to upper tier wind event beginning late Monday evening and continuing through the day Tuesday. We will also be located in the right exit region of the upper level jet streak, which supports large-scale descent and should help get strong winds down to the surface. Forecast soundings show a fairly strong inversion between about 600 and 700-mb, which is just a little above mountain top height for our area. Winds fairly constant through and above the inversion layer suggest the potential for vertically propagating mountain wave activity which could enhance surface winds in the immediate lee of the Snowy and Laramie ranges. Confidence is very high in high winds for the wind prone and adjacent zones, even though we are still a few days out still. This event has the potential to be an upper tier event, meaning the wind prone areas could see gusts of 90 mph, although confidence in reaching that mark is medium at this time. For now, the official forecast was nudged towards the NBM 90th percentile to get a mention of 75 to 80 mph, which has fairly good confidence.

A strong stationary frontal boundary will be stalled underneath the jet stream aloft during much of the week ahead. It's exact position is expected to waffle back and forth, surging southward behind the passage of shortwave troughs aloft, and then pressing northward again in between shortwaves. Once the first shortwave trough axis passes through Tuesday afternoon or evening, we will see the boundary push southward. Pressure gradients will begin to fall off slightly Tuesday evening into early Wednesday as a surface high traverses over the western edge of the High Plains. Even so, the GFS has high wind parameters minimizing early Wednesday morning at values still supportive of marginal high winds for the Arlington/Elk Mountain area. If the surface high manages to push up against the Laramie range, we should see a break in winds at Bordeaux and the I- 80 summit, but Arlington could continue straight on through. At the same time, the front pushing southward will bring stronger frontogenesis into the area, kicking up chances for rain and snow showers Tuesday night into Wednesday morning.

Most models then show the ridge amplifying once again Wednesday morning, nudging the frontal boundary back to just northeast of the area, and sending wind speeds surging once again. This second period for wind on Wednesday into Wednesday night has lower confidence, but currently has similar high-end potential to the earlier event Monday night into Tuesday. The more the ridge amplifies, the higher wind speeds could get during this period.

After Wednesday, model consensus collapses. While essentially all ensemble members agree that we will remain in an active northwest flow pattern, there are subtle differences in the strength and amplitude of the upper level ridge over the western CONUS. Just a small difference in this feature would shift the location of the stalled frontal boundary by a few hundred miles, and lead to wildly different outcomes for our local weather. The weaker ridge scenario, generally supported by the GEFS, would allow for the arctic front to push right up against the Laramie Range by Thursday morning, sending temperatures plummeting for both Thursday and Friday. In addition, intense frontogenesis is expected to remain along the stalled frontal boundary, supporting moderate snowfall wherever this ends up. If the front stalls over our area, there is the potential for significant snowfall with strong forcing stalling for a day or two over the same area. The other scenario features a slightly more amplified ridge, and is generally supported by the ECMWF ensemble. This would lead to much warmer and drier conditions for most of the area, but also come with an extension of the high wind event into Thursday. The colder scenario would lead to highs in the teens and snow on Friday for most of the High Plains, while the warmer scenario would mean highs in the 40s or even 50s and strong winds. Ensembles are split nearly 50/50 at this time, so the official forecast splits the difference. Past experience suggests that the arctic front usually wins in these scenarios, but that is not enough to push the needle just yet. We would like to see a little bit more model consensus before committing to one scenario or the other.

AVIATION /18Z TAFS THROUGH 18Z MONDAY/

Issued at 1027 AM MST Sun Dec 7 2025

VFR conditions expected over the next 24 hours. CIGs will generally be at mid to high levels or clear by tomorrow morning, with SCT to BKN skies dominating most sites. Winds breezy most sites at 10-25 knots, with KLAR and KCYS seeing much stronger speeds in the 30-40 knot range both today and again tomorrow. Also expecting low level wind shear most sites between 04-15Z with speeds up to 50 knots.

CYS WATCHES/WARNINGS/ADVISORIES

WY...High Wind Watch from late Monday night through Tuesday afternoon for WYZ101-102-108-119. High Wind Watch from Monday evening through late Wednesday night for WYZ103. High Wind Watch from Monday evening through late Wednesday night for WYZ104-105-107-109-113>115-117-118. High Wind Warning from 11 PM this evening to 11 AM MST Monday for WYZ106-110-116. High Wind Watch from Monday afternoon through Thursday morning for WYZ106-110-116. NE...High Wind Watch from late Monday night through Tuesday afternoon for NEZ019-020-054-095-096.