textproduct: Cheyenne

KEY MESSAGES

- High winds remain possible in the Arlington/Elk Mountain wind prone zone through the morning.

- Another round of high winds remains possible Thursday morning, with a third round possible on Friday.

- Above average temperatures, breezy conditions and a chance of precipitation primarily in the mountains expected through early next week, with a pattern change possible late.

SHORT TERM /THROUGH THURSDAY NIGHT/

Issued at 213 AM MST Wed Dec 31 2025

Mostly quiet for the next with days with gusty winds and mountain snowfall. Upper-level flow will be largely dominated by a building ridge across the Intermountain West today through much of Thursday before a transitional pattern sets up for Friday onwards. For today, upper-level ridging will build into the area leading to predominantly northwesterly flow aloft and clear skies. A weak 500mb vorticity max looks to push into southwestern portions of the CWA this after, so clear skies are expected to turn partly cloudy west to east across the CWA. 700mb flow will remain mostly northwesterly throughout the day, with a brief amplification of the height gradients across and just west of the Laramie Range through about 15Z this morning. A fairly strong surface pressure gradient will set up both across the Arlington/Elk Mountain wind prone zone and the Laramie Range near the Bordeaux wind prone area. The surface gradient across both zones will max out around 4mb, leading to some breezy gap winds across these zones through about 15 to 18Z, when the surface gradient weakens. 700mb flow will be fairly week across these zones and will max out around 40kts. Modest to strong GFS downward omega values should allow some of these 40kt winds to mix down to the surface through the morning hours, with downward acceleration from gravity potentially leading to a few gusts 50+kts in these zones. The High Wind Warning and High Wind Watches remain in effect to cover this early to late morning threat. However, in- house random forest guidance keeps fairly low probabilities of high winds through the morning, but a few gusts 50+ kts cannot be completely ruled out when downward acceleration is considered.

Aside from the gusty conditions today, 700mb temperatures will warm into the 3 to 5C range this afternoon, which is above the 90th percentile according to the NAEFS climatological percentile. With additional downslope warming, today will be another balmy day as temperatures increase into the low- to upper-50s east of the Laramie Range and mid-40s to low-50s west of the Laramie Range. Downslope winds will also lead to drier conditions, so precipitation is not anticipated today, especially with little to no synoptic lift aside from weak 500mb cyclonic vorticity advection. With the dry and gusty conditions, elevated fire weather conditions are expected this afternoon for the I-80 corridor east of the Laramie Range and Cheyenne areas. Did not issue any fire weather headlines as the minimum afternoon relative humidity looks to remain above critical thresholds with only a few gusts 30+ mph possible in this area. However, still use caution if conducting any outdoor burning.

Upper-level ridging continues into Thursday, though an upper-level trough moving into the western CONUS will start affecting the region. Largely northwesterly flow is expected Thursday as the ridge remain aloft, but starts to weaken through the afternoon and evening hours. A fairly strong vorticity maximum looks to eject out ahead of the incoming trough along with a diffuse shortwave, leading to amplified synoptic lift across western portions of the CWA starting Thursday morning. These two factors will act together to start increasing mountain snowfall potential Thursday morning into the afternoon hours. Southwesterly flow at 700mb will further favor upslope development along the Sierra Madre Range and Snowy Range throughout the day Thursday. The NAEFS Mean IVT suggests a brief increase in IVT values 18Z Thursday along the Sierra Madres, increasing confidence in decent snowfall rates for the mountains. NAEFS Mean Precipitable Water values also look to be above the 99th percentile to the maximum percentile across the Sierra Madres from 12Z Thursday through 12Z Friday. Therefore, a decent snowfall event looks to be taking shape for the Sierra Madres, with a current forecast of 10 to 13 inches for the Sierras and 5 to 8 for the Snowy Range. Decided to hold off for now on issuing winter weather headlines to allow day crew to take another look at the overall setup and snowfall potential for the mountains.

Another potential high wind event for the typical wind prone regions looks possible on Thursday, as 700mb winds increase to around 40 to 45kts. Surface pressure gradients across the Arlington wind prone area and Bordeaux wind prone area will increase early Thursday morning to around 3 to 4mb once again. 700mb will be a bit stronger for this event with slight strong downward omega values being modeled by the GFS as compared to today. In-house random forecast guidance is also pinging this event a bit harder, with probabilities of high winds in the Arlington and Bordeaux wind prones around 40%. Decided to hold off issuing any high wind headlines to let future shifts take another look at models for this event. However, it does look to be quite breezy again Thursday morning. Along with this, downslope warming is expected again, leading to another warm day Thursday with highs in the low- to upper-50s once again east of the Laramie Range and low- to mid-40s west of the Laramie Range.

LONG TERM /FRIDAY THROUGH TUESDAY/

Issued at 213 AM MST Wed Dec 31 2025

No major changes to the long term forecast. Please see previous discussion...

Long term will be semi-active as an upper level low pressure system moving inland from California weakens and moves across the Four Corners region, helping to disrupt the high pressure ridge controlling the area. While this ridge should then re-establish into the weekend, multiple systems will then begin riding the periphery of this feature, helping to begin slowly shifting and weakening it through the end of the forecast period, keeping some sensible weather concerns present for the CWA including winds and mountain precipitation.

As mentioned, an upper level low moving inland will help to disrupt the high pressure ridge holding control of the region in the short term, allowing temperatures to stop their rising trend and hover in the 40's to 50's for highs on Thursday and Friday. Meanwhile we should see another brief increase in gusty winds, but still uncertain if it will be strong enough to warrant a high wind warning for our wind prone locations for Thursday. In house guidance indicates only a maximum of around 50% probability for gusts 58+ mph, and will be mostly gradient driven as 700mb support will be lacking. Still, knowing how our wind prone locations do like to over perform, wouldn't be surprised if we see another another round of products. Friday the 700mb jet should briefly re-strengthen and this combined with favorable surface pressure gradients will bring a higher risk of strong winds for our wind prone locations, this time with a slightly better probability (60-70%). Otherwise, this change should bring a little more moisture to the area alongside westerly to southwesterly flow, allowing for mountain precipitation to develop. Without significant forcing this should mostly be orographically forced in nature, with light to moderate snow in the Snowy and Sierra-Madre ranges. Snowy range may be shadowed by the southwesterly flow, but the Sierra-Madre range is currently forecast to see enough snowfall Thursday into Friday to warrant an advisory with around 6 to 10 inches possible.

Over the weekend and into early next week, the ridge will start to re-establish, leading to a warmer day on Saturday with highs a few degrees warmer than the end of the week, but multiple systems riding the periphery of this feature will help to keep it slowly transient through the end of the forecast period, while also beginning to flatten the feature and keep our weather semi-active. Widespread winds through the end of the period look to remain breezy (gusting 20-40 mph), but in house guidance isn't as excited for any stronger wind events currently. Meanwhile generally westerly to southwesterly flow may fuel some light chances of precipitation in the high terrain, but once again a lack of significant features and lower moisture will preclude significant activity, with general light mountain snow showers expected. Temperatures should start to fall a few degrees each day though, keeping us above average as we move into the first full week of the new year but not a widespread record setting event compared to last week.

AVIATION /12Z TAFS THROUGH 12Z THURSDAY/

Issued at 405 AM MST Wed Dec 31 2025

VFR conditions expected through the 12Z TAF period, with mostly clear skies and breezy conditions. Early morning threats for low-level wind shear expected at KLAR and KCDR. Low-level wind shear should dissipate by 18Z as winds pick up for the afternoon. Gusty winds expected at all terminals, with gusts between 25 and 30 kts possible. Increasing high-level clouds through the evening and into the overnight hours.

CYS WATCHES/WARNINGS/ADVISORIES

WY...High Wind Watch until 11 AM MST this morning for WYZ106-116. High Wind Warning until 9 AM MST this morning for WYZ110. NE...None.