textproduct: Cheyenne

KEY MESSAGES

- Precipitation chances return by this weekend, with the possibility of widespread rain on Saturday.

- Daily shower and storm chances continue Monday through the end of the week with slightly above average temperature expected until Thursday.

SHORT TERM /THROUGH SUNDAY/

Issued at 131 PM MDT Fri Aug 21 2026

A bit of uncertainty in the forecast for this afternoon and evening regarding storm chances. Upper-level ridging over the west continues to shift eastward into Wyoming today. This will produce strong subsidence which will work to counteract storms. However, model soundings and mesoanalysis show quite a bit of instability, especially east of the Laramie Range. Satellite thus far has been unimpressive, showing flat topped cumulus fields mainly around Cheyenne and Laramie. A few isolated instances of vertical growth have been observed, but have quickly fallen apart due to the presence of MLCIN. Mesoanalysis does have CIN eroding away within the next few hours, so it is possible that by late afternoon and evening, storms could develop given the instability and lift from a weak upper-level disturbance. Most CAMs aren't too exited about storms today. The HRRR has been the most bullish, but also the most uncertain, flip flopping back and forth between lots of storms and barely any storms. However, newest runs of the HRRR seem to be more believable, showing convection developing this evening over the high terrain and pushing into the panhandle where it strengthens due to higher instability. If this is the case, a severe thunderstorm or two could be possible. Both strong winds and large hail cannot be ruled out in storms with DCAPE over 1000 J/kg and MUCAPE around 1500 J/kg. Any storms that develop will move out of the area by midnight tonight, however, cannot rule out nocturnal convection developing in the panhandle after this. Increased moisture into the area from precipitation as well as weak southeast flow, could cause low stratus and patchy fog east of the Laramie Range early Saturday morning.

The forecast for Saturday looks more certain, with greater chances for precipitation. Another weak shortwave moving through the ridge will provide the needed lift and monsoon moisture for storms to develop. Model soundings show decent instability once again, which could lead to marginally severe storms. Hi-Res guidance shows widely scattered storms developing during the mid-afternoon and continuing through the evening hours. Most hazards will be possible in storms, including heavy rain due to PWATs in the 90th percentile, large hail, and strong winds. Hi-Res guidance does show lingering showers across the area Saturday night, however these should not cause impacts. Similar conditions are expected on Sunday with another round of scattered storms. PWATs and instability are weaker on Sunday, so severe storms are unlikely at this time. Due to less moisture, models are also hinting at lower coverage of storms on Sunday.

LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/

Issued at 131 PM MDT Fri Aug 21 2026

Monday...Coverage of afternoon and evening showers and thunderstorms increases somewhat by an increase in monsoonal moisture and lowering 700 mb temperatures providing less convective inhibition, CIN, compared to Sunday. As is this type of pattern, afternoon convection will be over and near the mountains due to differential heating and orographic effects, with the activity spreading across the rest of the forecast area before dissipation by late evening. Warmer temperatures compared to the previous day due to less cloud cover and convective coverage.

Tuesday...Similar pattern synoptically to Monday with minor perturbations in the flow aloft aiding in lift of monsoonal moisture to produce widely scattered to scattered afternoon convection over and near our Snowy, Sierra Madre and northern Laramie Ranges, with the activity spreading eastward across the rest of the forecast area in the evening. Some lowering of mid level temperatures suggests daytime maximum temperatures will be a little cooler.

Wednesday...The primary change compared to Tuesday, will be a reinforcement of the ridge aloft axis over Wyoming, inducing a return to upslope mechanical lift aiding the areal increase of showers and thunderstorms, especially east of the mountains and along the I-25 corridor and eastward. Slight warming trend with 700 mb temperatures near 13 Celsius yielding high temperatures in the 80s.

Thursday-Friday...Monsoonal moisture becomes a bit more scant with decent westerly flow aloft and with warm temperatures aloft producing more convective inhibition, CIN, to limit development. A slight warming trend continues based on mid level, 700 mb temperature trends.

AVIATION /00Z TAFS THROUGH 00Z SUNDAY/

Issued at 525 PM MDT Fri Aug 21 2026

Tricky aviation forecast for this period, especially across the Nebraska Panhandle with showers and thunderstorms rolling through and the possibility for further development. Do to low confidence on placement and coverage, kept TS out of the TAFs for the most part and expect AMDs if further development occurs. For the southeast Wyoming terminals, scattered showers and storms are pushing southeast across the region and will continue for the next several hours. In any storm activity, winds could become erratic and gusty. There is also the threat for GR in any thunderstorm activity, this could bring additional aviation hazards. After everything clears, with the added moisture and wind direction, VIS and CIG reduction is possible overnight for the Nebraska sites.

CYS WATCHES/WARNINGS/ADVISORIES

WY...None. NE...None.