textproduct: Cheyenne

KEY MESSAGES

- Scattered to numerous showers and thunderstorms expected this weekend, with the possibility of widespread rain on Saturday. A few strong to marginally severe thunderstorms possible Saturday afternoon.

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

SHORT TERM /THROUGH SUNDAY NIGHT/

Issued at 158 AM MDT Sat Aug 22 2026

Not many changes made to the previous forecast with a relatively wet and warm pattern expected to continue through the last full week of August. Current surface observations across the region show ample low to midlevel moisture with dewpoints remaining in the upper 50s and mid 60s across the eastern plains. A drier airmass is located over central and south central Wyoming, with dewpoints in the 30s and 40s. Expect this to change today as IR and Watervapor Satellite loop shows the next monsoon moisture plume lifting northeast out of Utah and Nevada at this hour and into Wyoming later this morning. This plume, in addition to a potent upper level shortwave, is forecast to drift eastward around the periphery of the upper level high to our south. This will also flatten the upper level ridge axis currently over the Front Range and result in slightly cooler temperatures. NAEFS still show PWATs between 1.00 (west of I-25) to 1.50 (east) across the region, and may have trended a bit higher compared to yesterday with values approaching a two week maximum between 18z and 00z for late August and early September. Getting some signals for excessive rainfall, especially if any outflow boundary interactions are considered. Kept POP above 40% for most of the area with scattered to numerous coverage of showers and thunderstorms. Not a lot of shear, however, so severe thunderstorms aren't as likely. There is a marginal risk for Severe thunderstorms across the eastern plains of southeast Wyoming and the southwest Nebraska panhandle...mainly for gusty winds. Can't rule out some marginally large hail, but thunderstorms will likely be linear lines and multicell clusters with straight hodographs through the afternoon and occasional periods of weaker shear ahead of the upper level disturbance. Could see some respectable rainfall amounts with short range ensembles showing a good chance of a half inch of rain, particularly along the I-80 corridor, and along/north of highway 20 over east central Wyoming and the northern Nebraska panhandle as the shortwave axis moves east through the region later this evening. Cooler today with highs in the 80s under partly to mostly cloudy skies.

For Sunday, models show some drier air attempting to move into the forecast area through the day due to increasing west to northwest winds behind Saturday's shortwave disturbance. Surface winds are expected to increase a bit out of the west with gusts of 25 to 35 MPH possible, especially across southeast Wyoming. With drier conditions and a lack of forcing, expect shower and thunderstorm coverage to be lower into the evening hours with widely scattered coverage, mainly further south along the I-80 corridor. 0-6km shear is a little more favorable for organized convection though, especially over the southern Nebraska Panhandle. Kept POP between 20 to 35 percent near the Colorado border with POP around 15 percent north of I-80.

LONG TERM /MONDAY 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 /06Z TAFS THROUGH 06Z SUNDAY/

Issued at 1122 PM MDT Fri Aug 21 2026

A relatively calm night is in store with the possibility of lower VIS and CIGs across the Nebraska Panhandle with the additional moisture from Friday's precipitation and wind direction. Then, winds ramp up once again across all terminals by 00Z Sunday with southeasterly to southerly gusts 20 to 25 knots. Another round of showers and thunderstorms look to impact all sites except KRWL starting around 23Z Saturday, therefore PROB30 groups have been added. Look for lower VIS along with gusty and erratic winds in any storm activity if it comes near or over a terminal. Chances persist towards the tail end of this forecast period.

CYS WATCHES/WARNINGS/ADVISORIES

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