textproduct: Cheyenne

KEY MESSAGES

- Numerous to widespread showers and thunderstorms Thursday will have the potential to produce torrential rainfall and localized flash flooding. Isolated strong to severe storms are possible.

- Unsettled weather continues through at least Sunday, bringing cooler than average temperatures and daily chances for showers and thunderstorms.

- Isolated strong to severe storms and localized flash flooding will remain possible through Sunday.

- Drier weather and temperatures close to seasonal averages will return early next week.

SHORT TERM /THROUGH FRIDAY NIGHT/

Issued at 130 PM MDT Thu Aug 13 2026

The forecast remains largely on track as concern for torrential rainfall and localized flash flooding continues. Moisture is about as abundant as it gets across our area today. Mesoanalysis indicates precipitable water reaching 1.2" to 1.3" along the I-25 corridor and as high as 1.5" in our eastern zones. Even Carbon County is largely over 1.0" at this time. Per the NAEFS, this is showing up with a return interval of between 2 and 10 years, meaning that precipitable water gets this high once every 2 to 10 years depending on the exact location. In addition, GOES water vapor imagery can help identify a few synoptic features helping to drive today's weather. A more notable upper level shortwave is moving into western Wyoming at this time, while a very subtle vort-max is moving out ahead of it, currently located more or less over the I-25 corridor. The leading feature was driving the showers with a few rumbles of thunder that rolled through southeast Wyoming this morning. In between these two synoptic features, we are starting to see some clearing skies which should aid in destabilization over the next few hours. All together, these observations have improved confidence that numerous to widespread showers and thunderstorms will indeed develop this afternoon, and the main uncertainty remaining is how far east this activity will last.

Conditions remain marginally supportive for a few strong to severe thunderstorms, mainly along and south of the North Platte River where instability is most potent at this time. We have MLCAPE around 500 to 1000 J/kg and 0 to 6KM shear around 30 knots. Lapse rates are fairly paltry, as is typical in a very moist environment like today. So, severe weather really isn't the primary hazard today strong outflow winds and small to marginally severe hail will be possible. The main focus remains on torrential rainfall and localized flash flooding. Storm motions are fairly slow today, and the strong forcing will also support potential for training thunderstorms, allowing multiple rounds of heavy rainfall in the same area. We are already seeing some heavy showers anchoring to the Laramie Range early this afternoon. The existing Flood Watch area remains the area with the best instability, but we will also need to keep an eye on Converse, Platte, Goshen, and possibly portions of Albany county as high resolution models remain fairly aggressive on rainfall totals in this area. The weaker instability in those areas reduces confidence. As storms move east, they will move into weaker instability. PoPs were trended downward in the northern panhandle as high-resolution models are in better agreement showing storms dissipating before reaching there, but the southern panhandle still looks like a better bet for heavy rainfall. Showers and thunderstorms will continue all through the evening, and possibly well into the overnight hours. Isentropic lift will continue all the way until the axis of the aforementioned primary upper level shortwave passes through the area around daybreak Friday. While confidence was too low to make any changes to the Flood Watch now, we may have to consider extending to daybreak, at least in the Nebraska panhandle.

Low clouds and fog will be around most of the High Plains Friday morning, but expect winds to turn westerly from west to east during the morning hours and clear things out more quickly than today. We should get a bit more sunshine Friday morning, allowing temperatures to climb close to seasonal averages, several degrees warmer than today. Westerly flow will spread across the area, but this will not actually be that much drier. Precipitable water remains around the 90th percentile of climatology tomorrow despite a "drier" airmass moving in. Overall storm coverage should be lower tomorrow with weaker forcing expected. The area favored for storms also looks more localized, mainly along the I-80 corridor from Laramie to Sidney, and possibly extending north by 50 to 100 miles or so. While forcing is unimpressive elsewhere, models show a small region of positive theta-e advection creeping in from the south, which could help initiation, and the I-80 corridor looks to have the best instability of the forecast area. So overall, expect lower coverage but similar hazards to today. Parameters remain marginally supportive for a few strong to severe storms, and storms will once again be capable of producing torrential rainfall and localized flash flooding.

LONG TERM /SATURDAY THROUGH THURSDAY/

Issued at 1150 AM MDT Thu Aug 13 2026

Saturday...Moist westerly flow aloft and a weak shortwave trough aloft near peak heating will combine with deep atmospheric moisture supply to produce scattered to numerous showers and scattered thunderstorms in the afternoon and evening, with the greatest areal coverage east of Interstate 25. Aiding in the lift will be low level southeast winds adding the mechanical lift in addition to diurnal heating. PWAT, Precipitable water values look decent for beneficial rainfall. 700 mb temperatures yield highs in the 70s to lower 80s.

Sunday...Ridging becomes a bit more pronounced over Wyoming, producing warmer temperatures aloft which will tend to limit areal coverage of showers and thunderstorms, compared to Saturday. Nevertheless though, the monsoonal moisture will stretch from central Colorado through far eastern Wyoming and western Nebraska, where scattered to numerous showers and thunderstorms will occur in the afternoon and evening. Slightly warmer, but comfortable, temperatures for this time in August.

Monday...A drier pattern ensues and is on tap as the flow aloft turns west northwest and the precipitable water values decrease, due to drying at low and mid levels and downslope southwest winds near the surface. Thus, a much drier day when compared to the weekend. A warming trend begins with more sunshine and warmer mid level temperatures.

Tuesday...Brisk westerly flow aloft prevails, and with a decent amount of low and mid level moisture availability, expect isolated to widely scattered late day showers and thunderstorms, mainly east of Interstate 25 and the Laramie Range. Similar maximum temperatures to Monday based on 700 mb temperatures.

Wednesday...The synoptic pattern looks more like September and early autumn with a deep shortwave trough aloft sweeping across western Montana and Idaho, with west southwest flow aloft over our counties. Right now, we have scattered late day showers and thunderstorms in our gridded forecasts, though with a decent increase in precipitable water values, the moist flow aloft, and low level upslope, along with pattern recognition, believe our POPS and convective coverage will likely need to be increased in the next few days.

Thursday...The high amplitude and progressive shortwave trough aloft moves eastward from western Montana, to the Dakotas and western Nebraska by evening, sending a decent Pacific origin cold front across our counties. There may be enough moisture at low and mid levels for isolated to widely scattered convective coverage, though the biggest change will likely be a return to cooler temperatures and windy downslope west winds, which will likely need to be adjusted in the next few days, if model consistency remains for day 7. If you are looking for an early taste of fall weather, this may be your day.

AVIATION /06Z TAFS THROUGH 06Z SATURDAY/

Issued at 1122 PM MDT Thu Aug 13 2026

A tricky TAF forecast once again due to low CIGs, FG/BR, showers and thunderstorms will continue to cause aviation impacts through the first part of the overnight hours. The primary hazard will be very heavy rainfall producing IFR to LIFR VIS, but there is also the possibility for frequent lightning, gusty winds, and small hail. Be alert for possible AMDs through this forecast period. Expect conditions to trend towards VFR sometime after 14z Friday due to drier air moving in.

CYS WATCHES/WARNINGS/ADVISORIES

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