textproduct: Cheyenne

KEY MESSAGES

- Dry conditions expected through Friday alongside critical Fire Weather conditions.

- Moisture and cooler temperatures return for the weekend, with another shot of cooler air to start next week.

SHORT TERM /THROUGH FRIDAY NIGHT/

Issued at 145 PM MDT Wed Sep 9 2026

Weather in the short term is rather benign as the forecast area sits in quasi-zonal flow through at least Friday. Although benign, conditions will be conducive for fire weather. Zonal flow aloft will lead to windy conditions at the surface as a decent MSLP gradient sets up over the western half of the CWA. Even 850 mb CAG to CPR height gradients show a slight response, peaking into the 40 meter range on both Thursday and Friday. Winds aloft during the day will only range from 30 to 35 kts, so while not high winds, 30 to 40 MPH gusts at the surface will be favorable for rapid fire spread. Westerly flow will usher a very dry airmass into the area Wednesday afternoon. This airmass will stick around through Thursday night, leading to low relative humidity. Overnight humidity recoveries both Wednesday and Thursday night will be poor, as breezy conditions keep the surface dry. Thursday will be the driest day with relative humidity falling into the single digits for most of the forecast area. High temperatures will also warm about 5 to 10 degrees compared to Wednesday. Red Flag Warnings are already in place this afternoon through Thursday evening, mainly for Carbon County and the central to northern Laramie Range. The fire weather threat shifts eastward on Friday into Nebraska as a weak disturbance aloft raises mid-level relative humidity over the western zones.

LONG TERM /SATURDAY THROUGH WEDNESDAY/

Issued at 145 PM MDT Wed Sep 9 2026

A cold front should have made its way through the area overnight Friday. The timing is in fairly good agreement between global models with a five degree drop in the morning minimum temperatures compared to Friday. This will translate into a pleasant afternoon with highs in the upper 70s to low 80s. The northerly winds behind the front swap to southeasterly in the afternoon with the return flow. Aloft it is possible that a shortwave trough is passing through the area. This shortwave would provide a little more lift and moisture to perhaps kick off scattered showers and thunderstorms with IVT in the 90th percentile.

Sunday we should start to feel the effects of a new upper level system moving into the Pacific Northwest. Stronger return flow ahead of this system's passage would increase storm potential. Some machine learning models are depicting a risk area on and east of I- 25. Ensemble models have 75 percent of members having CAPE and shear values above climatological average and about 30-50 percent having values above the 90th percentile of climate. In other words the signal for severe weather is starting to show in guidance. A cold front associated with the Pacific system passes through sometime Sunday night into Monday morning.

Post front temperatures cool and a drying trend starts as a ridge builds up again. Return flow possible on Tuesday which could allow more diurnal shower and storm activity. The signal for another system at this range is murky. If no other system turns up in ensembles expect the ridging pattern to persist in the long term.

AVIATION /00Z TAFS THROUGH 00Z THURSDAY/

Issued at 517 PM MDT Wed Sep 9 2026

The cirrus shield that has been moving over the area this afternoon will depart this evening leaving skies clear. Winds are generally gusty over KRWL and KLAR, but are expected to calm in the next few hours with the loss of daytime heating. The same occurs at all other terminals with calm and sometimes variable winds. There is a low confidence signal of patchy fog or low cloud ceilings in some high resolution models for the Nebraska Panhandle terminals. The greatest signal being for KSNY. However, trends have been towards lower relative humidity values at the surface, so TAFs currently do not include fog in the forecast. Tomorrow morning, about 15z, winds pick up again out of the west with gusts to 25-30 knot possible at KRWL, KLAR, and KCYS.

CYS WATCHES/WARNINGS/ADVISORIES

WY...Red Flag Warning until 8 PM MDT Thursday for WYZ419>422-425- 427. NE...None.