190 FXUS65 KCYS 212143 AFDCYSArea Forecast Discussion National Weather Service Cheyenne WY 343 PM MDT Sun Sep 21 2025
.KEY MESSAGES...
- Breezy conditions and overspreading precipitation continue into Monday as a Pacific system causes widespread rain and cooler temperatures to start the week.
- A cold front and weather disturbance will bring cooler and wetter weather for Tuesday, before a ridge aloft produces drier and warmer weather for Wednesday into the weekend.
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.SHORT TERM /THROUGH TUESDAY/... Issued at 212 PM MDT Sun Sep 21 2025
Showers and storms have been a little more aggressive and eastward moving than anticipated, and the forecast has been updated accordingly. Expectation is that this will continue through this afternoon, with the regional showers and storms weakening later tonight but lingering at least through the evening hours. The approaching Pacific trough and cold front are expected to make their presence known tomorrow with widespread precipitation and gusty winds. Precipitable water values of 0.5-1.0 inch are expected with this system, around 150-200% of normal for this time of year. This should allow for overall rainfall totals starting Monday and continuing just beyond the short term into Tuesday of 0.5-1.0 inch for the CWA, highest along the Snowy and Laramie Ranges. On the note of the Snowy Range, 700mb temperatures continue to descend to around 0 to -1 C as this front makes its way through. With overall QPF values over an inch for the Snowy Range and the expected cold, snow levels should drop to around 9k feet Monday into Tuesday. Forecast currently calls for notable mountain snow for this range, with overall totals around 6-7 inches in the high terrain and the peaks nearing 10 inches. This is nearing advisory level criteria, but being the first system of the year and temperatures having been as warm as they have been, overall accumulations will likely be lower than this. Therefore have held off on issuing an advisory for the snowy range, but we`ll continue to keep an eye on the range over the next update or two in case amounts increase or confidence in accumulations sticking rises.
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.LONG TERM /TUESDAY THROUGH SATURDAY/... Issued at 212 PM MDT Sun Sep 21 2025
Tuesday...The shortwave trough aloft moves across our counties, producing scattered to numerous showers and thunderstorms, along with cooler temperatures due to cloud cover and precipitation coverage.
Wednesday...A warming and drying trend begins as a high amplitude ridge aloft builds across Utah and western Wyoming.
Thursday...Dry weather continues with a warming trend as the ridge aloft transitions over eastern Wyoming.
Friday...Mild and dry weather continues as the ridge aloft moves eastward over the western high plains, and the low and mid levels remain relatively dry.
Saturday...Although a shortwave trough aloft moves across the Four Corners states, clouds and precipitation associated with the trough will remain to the south of our counties. 700 mb temperatures suggest little change in temperatures.
Sunday...Moist southerly flow aloft develops ahead of the shortwave trough aloft over Arizona. There may be enough of an increase in low and mid level moisture to spark isolated afternoon showers and thunderstorms over the Snowy Range and southern Laramie Valley. High temperatures remain similar to Saturday.
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.AVIATION /18Z TAFS THROUGH 18Z MONDAY/... Issued at 1143 AM MDT Sun Sep 21 2025
Areas of showers and some thunderstorms possible today, primarily impacting sites KCYS, KLAR, and KRWL. KRWL has the highest and most likely chance to see precipitation and early rain could even be accompanied by thunder, but only included VCSH at this time. Any precipitation that moves near or over TAF sites could locally enhance winds and make them gusty and erratic. Cloud bases with this activity will be mid level, generally between 5-10k feet, with cloud bases in the NE Panhandle around 15-20k feet and precipitation not likely (though cannot be ruled out 100%, and not high enough to include in TAFs). Breezy day with winds 10-15 knots and gusts 20-30 knots, strongest at WY terminals. Winds lessen tonight. precipitation possible once again tomorrow around or just after the end of the forecast period.
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.CYS WATCHES/WARNINGS/ADVISORIES... WY...None. NE...None.
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SHORT TERM...CG LONG TERM...RUBIN AVIATION...CG
NWS CYS Office Area Forecast Discussion