textproduct: Cheyenne

KEY MESSAGES

- A messy pattern is anticipated today through much of the upcoming week, allowing for ongoing precipitation chances across the entire CWA. The best chance for precipitation will be Sunday, when a few rumbles of thunder will be possible.

- A Winter Weather Advisory has been issued for the Sierra Madre and Snowy Ranges from 6PM Saturday through 6AM Monday.

- Cool and wet weather is expected to continue into the work week. Possible dry spell come next weekend.

SHORT TERM /THROUGH SUNDAY NIGHT/

Issued at 345 AM MDT Sat Apr 25 2026

Active weather is progged to return to the region starting today and continuing through much of next week. A messy pattern is currently overhead and will continue throughout the weekend as an upper-level low spinning over southern Canada meanders northward with little to no eastward progression. A secondary trough is progged to develop Sunday into Monday across the Pacific Northwest as the primary low remains largely stationary. Model consensus is that this secondary trough will deepen over the western CONUS and finally act to push the stationary Canadian low off to the northeast by late Sunday night into early Monday morning. Initially, with the stationary low, an unsettled, moist pattern persists with continued weak synoptic support. Looking down at 500mb, the vorticity advection associated with the Canadian low is not favorable for propagation and will only spin around the low without advecting it off to the east as wind direction remains largely parallel to the 500mb vorticity maxima surrounding the low. Luckily, as the primary vorticity maxima advects around the west side of the low, the northerly flow induced by the system itself will act to strengthen the vorticity advection, allowing a 500mb shortwave to develop. The positive vorticity advection on the leading edge of the developing shortwave will enable the system to start its northeastward propagation Sunday night into the early morning hours Monday. All the while, an upper- and mid-level ridge developing off the western coast of the CONUS will funnel westerly to southwesterly winds across central California northeastward into the Intermountain West, allowing a plume of Pacific moisture to impact western portions of the CWA as early as midnight Sunday. With this Pacific moisture plume entering the area, NAEFS Mean Integrated Water Vapor Transport suggesting 90th to 97.5th percentile IVT values combined with 90th percentile Precipitable Water values across much of the region, further showcasing the increasing moisture expected into the day Sunday. Additionally, multiple lobes of 500mb vorticity will eject out ahead of the developing trough across the Pacific Northwest, leading to continued synoptic ascent across much of the CWA Sunday into Monday.

The 700mb low associated with the nearly-stationary upper-level low over southern Canada will start to meander northeastward by early Sunday morning, with the low itself weakening and becoming more broad starting this morning and continuing through Sunday morning. As a result, the CWA will see a break from elevated surface winds across the region as 700mb flow remains quite weak without the influence of the Canadian low. 700mb winds turn southwesterly by Sunday morning and southerly east of the Laramie Range, further supporting the advection of Pacific moisture into the CWA. Broad, weak warm air advection at 700mb is expected this afternoon, with the stronger WAA arriving Sunday morning into the afternoon hours. WAA both today and tomorrow will act to support the overall synoptic ascent across the region, with strong ascent expected Sunday with the strong WAA. Strong WAA comes to an end early Monday morning as the next cold front begins to sweep northwest to southeast across the CWA. While the mid- and upper-level flow remains fairly messy, it does not hold a candle to the surface flow expected today and Sunday. For today, northerly surface flow behind a stationary front that slowly meandered southward will flip to easterly by late morning as a surface high develops downwind from the Black Hills of South Dakota. As this high slowly move southeastward, easterly, upslope flow continues across the CWA with a strong, reverse pressure gradient expected along and east of the Laramie Range. Surface pressure is progged to be around 1013mb near Pine Bluffs and 1006mb near the I-80 Summit, a 7mb change across approximately 80 miles. Therefore, the easterly upslope flow expected this afternoon will be a bit stronger than typical easterly flow regimes, likely around 15 to 20mph and gusting over 20mph. As the high continues to propagate southeasterly, southeasterly flow will slowly return to the Laramie Range by early afternoon. This flow will continue to support upslope development along the Laramie Range, so there is around a 35 to 45% chance for ongoing, light precipitation throughout the afternoon hours today. For Sunday, surface flow east of the Laramie Range remains largely south to southeasterly, with southwesterly surface flow developing west of the Laramie Range. With the 90th percentile PWs and IVT across the mountains, significant snow is expected for both the Sierra Madre and Snowy Ranges. With stronger WAA expected east of the Laramie Range, widespread precipitation is anticipated Sunday with chances at and above 80 to 90%. With WAA ongoing earlier in the day, precipitation is expected to fall as primarily rain everywhere outside of the mountains. However, behind the cold front, rain with transitioning to rain/snow before switching over to all snow for everywhere west of the Laramie Range and rain/snow mix east of the Laramie Range by early Monday morning. Significant snow accumulation outside of the mountains is not anticipated at this time, but the rain accumulation should be quite decent, especially with 90th percentile PWs across much of the area. Many locations could see up to and over 0.5 inches of rain Sunday afternoon. West of the Laramie Range, the HRRR is suggesting up to 500 J/kg of MUCAPE, which would enable a few thunderstorms to develop across the region. These storms will put down more precipitation, but over a smaller area. Severe weather is not anticipated at this time. As for the mountains, 6 to 10 inches of snow will be possible throughout the day Sunday, with the potential for over 10 inches in the highest peaks. As a result, a Winter Weather Advisory has been issued for the Sierra Madre and Snowy Ranges from 6PM Saturday to 6AM Monday.

LONG TERM /MONDAY THROUGH FRIDAY/

Issued at 345 AM MDT Sat Apr 25 2026

A cold and wet start looks to be in the cards for our Monday. Temperatures start in the upper 20s to low 30s. Snow showers are likely, that turns to mostly rain in the afternoon. The mountains will hold on to freezing temperatures, therefore snow can be expected there on the western upsloping faces. A general troughing pattern will keep the area overcast for most of the day with a few breaks in the afternoon east of the mountains. Some instability may build to allow a few thunderstorms, yet MUCAPE is expected to be limited to below 500 J/kg. Overnight, temperatures dip back down to near freezing allowing another period for rain to transition to snow. Amounts outside the mountains remain low, from a trace to perhaps a half inch in a few overachieving spots in the northern parts of our CWA. Tuesday looks much the same as Monday, however a shortwave trough is set to pass over and give us a better chance of widespread precipitation, particularly in the early morning hours. Winds may increase during this timeframe, with an in-house machine learning model highlighting wind gusts of 40 to 50 MPH being possible in the wind prones. Yet again CAPE may be enough to promote a few thunderstorms in the afternoon.

The shortwave quickly departs our area by Wednesday, giving an opportunity for a weak upper level ridge axis to build in, reducing ascent and widespread precip. Showers may still occur in the afternoon and evening hours, but QPF outlooks not quite as high as it was Tuesday. Another shortwave could make it's way into our area as a parting gift from the upper level trough that been in place to our north for the better part of a week. Increasing PoPs will be attributed to this disturbance Thursday and Friday, along with an artic cold front passage. The outlook for the weekend is for a few days of ridging which may allow high temperatures to increase into the 60s and 70s.

AVIATION /06Z TAFS THROUGH 06Z SUNDAY/

Issued at 1152 PM MDT Fri Apr 24 2026

Low ceilings, down to 1 kft, are being observed at KCDR, KAIA, KBFF, KCYS, and KSNY. Winds at KRWL and KLAR are expected to increase to 35-40 kts from the west during the early morning hours and persist through the day. NE Panhandle will have weak winds from the east, while KCYS will likely see winds out of the southeast. Periods of MVFR conditions are likely at the NE Panhandle terminals and KCYS through the day, especially in the morning hours, as warm air advection on top of a shallow cool layer sustains a low deck of stratus clouds. Ceilings may lift around 16z through 0z to bring terminals into VFR, except for KCDR which have shower activity continuing throughout the day. After 0z a mid level disturbance starts moving in from the southwest, increasing precip chances and lowering ceilings.

CYS WATCHES/WARNINGS/ADVISORIES

WY...Winter Weather Advisory from 6 PM this evening to 6 AM MDT Monday for WYZ112-114. NE...None.