831 FXUS65 KCYS 232327 AFDCYSArea Forecast Discussion National Weather Service Cheyenne WY 527 PM MDT Tue Sep 23 2025
.KEY MESSAGES...
- A cold front and Pacific storm system will bring much cooler temperatures and unsettled weather Tuesday. Mountain snowfall is expected above 8500 feet.
- A Freeze Warning is in effect for the high valleys west of the Laramie Range Wednesday morning. Freezing temperatures and frost possible.
- A ridge of high pressure aloft will lead to drier and warmer weather for Thursday through the weekend.
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.SHORT TERM /THROUGH WEDNESDAY NIGHT/... Issued at 104 PM MDT Tue Sep 23 2025
Radar still shows fairly good coverage of stratiform precipitation across the southern half of the CWA early this afternoon. As the upper-level low associated with this system slowly moves southeast throughout the day, precipitation will taper off this afternoon from north to south. A Winter Weather Advisory remains in effect for the Snowy Range until 6 PM as areas above 8500 feet could see accumulating snow through the afternoon. Webcams still show snow falling, but as the afternoon progresses, a rain/snow mix will be possible. While precipitation is expected to be stratiform for the most part, cannot rule out a few convective showers/storms for areas further north. Areas further north will see some sunshine later this afternoon, leading to warmer temperatures and perhaps some destabilization which could result in some convection. Most precipitation will clear out of the CWA by the evening hours as the upper-level low enters Kansas.
Clouds are also expected to clear out relatively quick later this evening. Clearing skies combined with calm winds could cause temperatures to tank overnight. Model guidance has done poorly on anticipating the well below average high temperatures during the day Tuesday. With cooler than expected temperatures during the day, it will not take much for temperatures overnight to also drop below model guidance. Went with a blend of the NBM 25th percentile for overnight lows around freezing for areas west of the Laramie Range. A Freeze Watch was already in effect for the high valleys out west, so upgraded to a Freeze Warning with this forecast package to account for the freeze potential. There is a failure mode for temperatures to stay above freezing in these areas overnight. Given the ample low-level moisture from the precipitation, some models show fog developing in the valleys which could keep lows from reaching freezing. Even if some locations do not reach freezing, the ample moisture could at least produce widespread frost which could be damaging to sensitive vegetation. The Freeze Warning is in effect until 10 AM, at which point temperatures will begin to warm up.
Warmer and drier air will begin to push into the CWA Wednesday as a ridge of high pressure sits over the Great Basin. 700 mb temperatures will begin to climb into the upper single digits with much drier air aloft. This will lead to a 10 to 15 degree warm up on Wednesday, with highs returning to the 60s and 70s. The dry air will also keep skies sunny with no chance of precipitation during the day or Wednesday night. Cool and calm conditions Wednesday night will lead to another chilly night for areas west of the Laramie Range.
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.LONG TERM /THURSDAY THROUGH TUESDAY/... Issued at 104 PM MDT Tue Sep 23 2025
An upper level ridge will keep things rather dry starting Thursday. Following the trough that pushed through the Intermountain West, a amplified ridge sets in. The strong subsident flow is expected to suppress any rising motion to decrease any rain/snowfall chances. 700mb temperatures look to remain stagnant between 9 to 11C Thursday through the weekend. So temperatures look to remain the the 70`s in Wyoming with low to mid 80`s in the Nebraska Panhandle. Friday into Saturday, an upper level trough traverses across the Canadian Providences as well and another trough pushing into the southern California coast. The southern trough will inject some moisture into the region however will strengthen the ridge over the intermountain west as the Rex Block sets up. The northern trough will compress the ridge to give us a dry but gusty weekend. Our next precipitation chances after the weekend may come Monday afternoon with another shortwave pushing through the intermountain west.
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.AVIATION /00Z TAFS THROUGH 00Z THURSDAY/... Issued at 527 PM MDT Tue Sep 23 2025
Rain has pushed south a little faster than anticipated but the ceilings are still expected to float between the MVFR and VFR range as the low clouds start to move south as well. by 06z every site should be VFR. Winds generally look to shift to the south by tomorrow with KCDR, KAIA, and KSNY looking a little more southwest in the Panhandle.
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.CYS WATCHES/WARNINGS/ADVISORIES... WY...Freeze Warning from 2 AM to 10 AM MDT Wednesday for WYZ105- 109>111-113-115. Winter Weather Advisory until 6 PM MDT this evening for WYZ114. NE...None.
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SHORT TERM...SF LONG TERM...MM AVIATION...MM
NWS CYS Office Area Forecast Discussion