textproduct: Cheyenne

KEY MESSAGES

- High Wind Warnings are in effect for the typical gap winds areas through Tuesday afternoon.

- Another round of localized high winds is possible very early Wednesday morning into Wednesday afternoon. High Wind Watches have been issued for the typical wind prone locations.

- A third round of localized high winds is possible early Thursday morning through Thursday afternoon.

- Above average temperatures and breezy conditions expected through the weekend, with a chance of precipitation primarily in the mountains to end the week.

SHORT TERM /THROUGH WEDNESDAY NIGHT/

Issued at 218 AM MST Tue Dec 30 2025

Mostly quiet for the next several days as dry, upper-level, northwesterly flow dominates the region. An upper-level ridge will begin to build across the southwestern CONUS today through early Wednesday morning, then begin moving over the region by Wednesday afternoon, resulting in clearing skies and warming temperatures. The pattern at 500mb is very similar to the upper-level pattern. A couple bands of moderate cyclonic vorticity advection will push through late this morning through the overnight hours. However, dry conditions and minimal forcing aside from the CVA will prevent any precipitation with this passage, though a period of increasing cloud cover is expected this afternoon through the overnight hours thanks to the marginal lift associated with the bands of CVA. 700mb winds are increasing early this morning and will peak around 09 to 12Z this morning, maxing out around 40 to 45kts across the Laramie Range. With modest GFS downward omega values across the Laramie Range, general over-performance of winds recently, and in-house random forest guidance showing probability of high winds around 60% at Arlington/Elk Mountain, 40% at Bordeaux, and 35 to 40% for the I- 80 Summit zone, the High Wind Warnings look good and will remain in effect through 18Z and 21Z today. 700mb temperatures between -2 and 0C today will be fairly typical for this time of year, according to the NAEFS climatological percentile. However, downslope warming should lead to temperatures slightly above average, especially east of the Laramie Range where downslope warming effects will be maximized. Expect high temperatures in the mid-40s to low-50s east of the Laramie Range and low- to mid-40s west of the Laramie Range, with increasing cloud coverage through the morning hours. Mostly seasonable overnight lows are expected, with lows in the mid-teens to mid-20s expected.

For Wednesday, the building upper-level ridge will move over the CWA through the morning and afternoon hours. A weak swath of 500mb CVA will moves through the ridge Wednesday morning and afternoon, mainly across western portions of the CWA. Cloud cover should increase west of the Laramie Range as this CVA moves through, though precipitation is not expected due to the most dry conditions. The next system will start to move into southern California late Wednesday into early Thursday morning, more details on this in the long term discussion, leading to cloud cover expanding eastward by 06Z Thursday. 700mb winds remain fairly calm through the day Wednesday, but the surface pressure gradient will begin to increase between 06Z through 09Z early Wednesday morning as a low pressure system develops off the Black Hills in western South Dakota. This pressure system will dive southwesterly off the Black Hills and increase pressure gradients along the Laramie Range to around 3 to 4mb between 09 and 18Z Wednesday morning. 700mb wind support is not really there, as the 700mb flow remains around 30 to 35kts. With these surface gradients and deepening surface low to the east, gusty conditions are expected along and just downwind of the Laramie Range, with breezy conditions expected along the majority of I-80 in the CWA. 700mb Craig to Casper gradients increase into the upper-50s with as 700mb gradients increase slightly as the low pushes through. With modest downward GFS omega values near the Arlington/Elk Mountain wind prone region, gusty winds will be possible from about 06 to 15Z Wednesday. With this fairly marginal setup and lower confidence for a gradient- driven event, decided to issue High Wind Watches and let day crew take another look at future model runs to determine if an upgrade is necessary.

700mb height gradients start to increase late Wednesday night into the early morning hours Thursday behind the departing surface low, increasing 700mb winds to around 40kts across western portions of the CWA and the Laramie Range. With modest GFS downward omega values again, breezy to gusty winds are expected to continue across western portions of the CWA and along the Laramie Range. 700mb temperatures will increase into the 2 to 4C range throughout the day, a jump back into the 90th percentile according to the NAEFS climatological percentiles. With added warming from downslope flow earlier in the day and 700mb temperatures in the 90th percentile, surface temperatures will warm nicely on Wednesday. Highs east of the Laramie Range will be in the low-50s to low-60s and low- to mid- 40s once again west of the Laramie Range. Overnight lows will be warmer Wednesday into Thursday thanks to the downsloping winds and warmer 700mb temperatures. Expect morning lows on Thursday in the mid-20s to upper-30s.

LONG TERM /THURSDAY THROUGH MONDAY/

Issued at 218 AM MST Tue Dec 30 2025

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

A relatively calm long term forecast period is expected, as high pressure ridging brings above normal temperatures and dry conditions on Wednesday, but a quick moving system from off of California will disrupt this pattern beginning Thursday and continuing into the the weekend, helping to bring a bit more breeziness and mountain precipitation to the region.

Wednesday will be a benign day as high pressure ridging controls the region and we see above normal temperatures and dry conditions, but clouds will be building as moisture begins increasing across the area. On Thursday an upper level low will move inland across California and then across our region through Friday, disrupting the ridge and bringing mountain precipitation alongside breezy winds. In house guidance indicates the potential for high winds to return to our wind prone locations, with Arlington seeing peaks of around 50- 65% probability for gusts 58+ Thursday through the weekend. Meanwhile we'll see a moisture plume move across the region, but with a lack of significant forcing the bulk of this activity should be driven by orographic enhancement via southwesterly flow, leading to mostly mountain precipitation in the form of high elevation snow. And overall QPF amounts aren't overtly impressive, so while some fresh snow will be welcome for the area, overall accumulations shouldn't be on the high side. After this system moves across, ridging should re-establish into Saturday, but another quick moving system should help to flatten this feature out while bringing another chance of breezy winds as the jet begins to settle over the area. Meanwhile our temperatures should stay relatively similar through the period without a stronger cold airmass to interrupt, leading to continued above normal highs with temperatures east of the Laramie Range in the 50's to 60's, and to the west in the 40's. The new year will be starting off similarly to how our Christmas went, with warmth and wind.

AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/

Issued at 401 AM MST Tue Dec 30 2025

VFR conditions expected for the 12Z TAF period with mostly clear skies and gusty winds. Early morning hours could see some low-level wind shear at KCYS, KLAR, and KCDR, but is expected to dissipate by 18Z as winds start to increase at the surface. Clear skies early before a few high-level clouds move into the region. Primary aviation concerns will be low-level wind shear this morning and gusty winds by midday.

CYS WATCHES/WARNINGS/ADVISORIES

WY...High Wind Warning until 11 AM MST this morning for WYZ106. High Wind Watch from late tonight through Wednesday morning for WYZ106-116. High Wind Warning until 1 PM MST this afternoon for WYZ110-116. High Wind Watch from this evening through Wednesday morning for WYZ110. NE...None.