textproduct: Cheyenne

KEY MESSAGES

- Isolated strong to severe thunderstorms are possible over the High Plains through the evening hours Thursday.

- Expect hotter weather on Friday with scattered high based showers and thunderstorms, bringing a chance for gusty winds.

- Daily chances for afternoon and evening showers and thunderstorms continue through at least the middle part of next week.

SHORT TERM /THROUGH FRIDAY NIGHT/

Issued at 215 PM MDT Thu Aug 27 2026

Another potent upper level ridge is building in over the southwest today, with our area on the periphery. Temperatures are warmer than yesterday across the area as the ridge amplifies. While clear skies remain over most of the area, typical diurnal cumulus are building over the higher terrain of southeast Wyoming, and the Black Hills of South Dakota. The environment for severe storms is fairly marginal on the Wyoming side, but more potent as you move eastward into Nebraska. In Wyoming, MLCAPE is around 500 to 1000 J/kg (higher right on the state line), with some modest capping still in place, and deep layer shear around 25 to 35 knots. In Nebraska, we have MLCAPE pushing 1500 to 2000 J/kg especially in the eastern row of counties in the Chadron to Sidney corridor. Vertical wind shear is also stronger, around 35 to 40 knots. The cap is expected to keep storms fairly isolated today, with lower coverage than the last few days. However, this may not limit the intensity of storms that manage to develop. Development will likely be anchored to the higher terrain, with storms moving generally southeastward from there. Of particular concern though is the potential for a right-moving supercell thunderstorm to drop out of South Dakota. While the environment is not quite as explosive as last Friday (8/21), there is potential for a similar setup today. Right-moving supercell vectors are nearly due north to south, indicating that if a sufficiently strong develops off of the Black Hills in South Dakota, it could move due south into the Dawes, Box Butte, and possibly counties further south too. Overall, today is a conditional threat with a slightly lower probability of occurrence, but high intensity ceiling. A few storms may linger into the evening hours, but we should be done by 11PM to midnight.

The flow aloft will turn southwest Friday as the upper level ridge axis shifts to the east. A surface trough positioned along the WY/NE stateline will mark a dryline as westerly to southwesterly flow spreads into the west, and moist southerly flow remains in place to the east. This feature will advance eastward through the day, pushing the most potent environment for strong to severe thunderstorms off to our east, though we will need to watch for the dryline progressing slower than modeled, which has occurred frequently recently. Southwest flow will open the door to a more favorable monsoon tap. Forecast soundings show a somewhat dry, well- mixed boundary layer, but plentiful moisture moving in aloft for tomorrow. We'll have a little bit of forcing with a vort-max pushing around the upper level ridge, which should support another round of scattered showers and thunderstorms. Expect this activity to be high- based, with a lower overall potential for strong to severe thunderstorms. However, storms will have the potential to produce strong, gusty winds. Temperatures will also be quite warm Friday, with 700-mb temperatures peaking around +14C to +17C. No record highs are currently forecast, but Cheyenne and Laramie have forecast highs within about 2 degrees of daily records.

Saturday

The monsoonal moisture tap returns under southwest flow aloft. With adequate low and mid level moisture, as well as decent PWAT, precipitable water, values, and a passing shortwave trough aloft in the afternoon, we anticipate scattered to numerous showers, and scattered thunderstorms in the afternoon and evening, mainly south of a Rawlins to Scottsbluff line. Slightly cooler compared to Friday based on the 700 mb temperature trends.

Sunday...Southwest flow aloft increases in response to a shortwave trough aloft moving northeastward from eastern Montana southward into eastern Wyoming. Although PWAT values remain about the same as on Saturday, afternoon and evening shower and thunderstorm coverage will be less than Saturday, with more orographic type convection for our southwest counties in and near the Snowy and Sierra Madre Ranges. A bit cooler based on mid level temperatures.

Monday...The moisture plume of monsoonal moisture is shunted a bit further south, over our southern counties, and coverage will be less with weak shortwave ridging aloft over our counties. Greatest areal coverage for convection will be south of a Rawlins to Scottsbluff line. The slight cooling trend continues.

Tuesday...A progressive shortwave trough aloft will pass Monday night, producing scattered showers and some thunderstorms. Some drying will occur in the wake of the shortwave trough passage, for producing a nearly dry forecast for Tuesday afternoon and evening. 700 mb temperatures rise slightly, corresponding to a rise in surface maximum temperatures.

Wednesday...Brisk southwest flow aloft returns with the monsoonal moisture stream overhead, and our current scattered afternoon and evening POPS may need to be increased in the next few model runs. Temperatures about the same as on Tuesday.

Thursday...Drier air infiltrates the region, thus only isolated to widely scattered late day showers and thunderstorms expected for the Snowy and Sierra Madre Ranges, and nearby locations, with dry conditions elsewhere. 700 mb temperatures suggest little change in high temperatures.

AVIATION /18Z TAFS THROUGH 18Z FRIDAY/

Issued at 1135 AM MDT Thu Aug 27 2026

Ridging aloft will continue across the northern and central Rockies with surface low pressure developing across central Wyoming this afternoon. A few low level convergence boundaries will develop from Douglas to Chadron, as well as from Douglas to Sidney this afternoon. Isolated to widely scattered afternoon and evening thunderstorms will develop to the south of a Laramie to Wheatland, to Scottsbluff to Sidney line, with a few thunderstorms also possible across the northern Nebraska Panhandle.

Wyoming TAFS...Confidence is high on VFR through the period. Expect scattered high based clouds from 10000 to 12000 feet AGL through early evening, before dissipation. Spatial confidence is minimal, though with persistence from the past few days, feel enough confidence to include VCTS at KLAR and KCYS from late afternoon through early evening, with VCSH at KRWL. As is typical, expect wind gradient gusts to 23 knots through sunset. Gradient wind gusts to 20 to 30 knots developing at KRWL and KLAR after 15Z Friday.

Nebraska TAFS...Confidence is high on VFR through the period. Will see scattered high based cumulus field developing this afternoon and continuing through sunset. Although the recent runs of the HRRR show little if any convective development, with several low level boundaries in the area, decent CAPE values and bulk shear, and a marginal risk of severe thunderstorms from the Storm Prediction Center, felt it prudent to include VCTS in the TAFS from late afternoon through early evening, and we will update the TAFS as convection develops. Expect typical gradient wind gusts to 25 knots through sunset, with the low level jet developing from roughly 06Z to 12Z, producing south winds gusting to 25 to 35 knots at the sites, with the best probability for these gusts at KCDR and KAIA.

CYS WATCHES/WARNINGS/ADVISORIES

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