textproduct: Cheyenne

KEY MESSAGES

- There is a Marginal Risk (Level 1 of 5) for severe weather on Friday with damaging winds (60+ mph) and large hail (1+ inch) possible with the strongest storms.

- There is a Marginal Risk (Level 1 of 5) for severe weather on Saturday with strong, damaging winds (70+ mph) and large hail (1+ inch) as the primary hazards.

- Slightly above average temperatures, breezy conditions, and lower coverage of thunderstorms expected by the middle of next week.

SHORT TERM /THROUGH SATURDAY NIGHT/

Issued at 137 AM MDT Fri Aug 28 2026

Upper-level ridging will amplify this afternoon into the early evening hours before starting to tilt northeasterly through the overnight hours into early Saturday morning. These changes are caused by a stout, upper-level trough starting to move into the Pacific Northwest, forcing the ridge eastward and tilting the apex towards the northeast. Northwesterly flow aloft will turn westerly then southwesterly between 15 and 03Z today with a fetch of southwesterly flow from the Pacific Ocean developing. The 500mb high that has been circulating around the Four Corners region will start to be pushed easterly between 21 and 03Z as the upper-level flow becomes dominated by the incoming upper-level trough. A few lobes of 500mb vorticity will advect into the CWA through the morning and afternoon hours before becoming cutoff from the 500mb high early Saturday morning. 700mb flow remains westerly across much of the region with southwesterly flow expected over Carbon County. A shortwave trough will traverse through the region from 21 to 03Z this afternoon and evening, bringing with it increasing 700mb height gradients and a stronger low-level jet. Modest 700mb warm air advection will accompany the shortwave between 21 and 03Z. GFS omega fields suggest some downward omega values along and east of the Laramie Range, acting to dry out the surface with downslope warming and drying. Not only will downslope warm and dry out the surface, it will likely prevent significant showers and thunderstorms from forming this afternoon. Currently there is around a 25 to 40% chance of showers and storms forming this afternoon. While some of this precipitation may reach the ground, there will be an increased threat of gusty showers due to the dry surface with an Inverted-V sounding in forecasts from the RAP. Most of the instability will remain off to the east where moisture will be higher. With DCAPE over 1300 J/kg, gusty showers will be likely this afternoon. The Storm Prediction Center has just introduced a Marginal Risk (Level 1 of 5) for severe weather today with the primary hazards being damaging winds (60+mph) and isolated, large hail across western Nebraska (1+ inches). With the brief strengthening of the ridge overhead, surface temperatures will be quite warm, in the mid-80s to low-100s. With downslope drying, afternoon humidity values will be in the 15 to 25 percent range, leading to elevated fire concerns. Luckily, winds look to remain below critical thresholds, despite the gusty conditions anticipated in western portions of the region.

Upper-level ridging will finally push east out of the region on Saturday as the incoming, upper-level trough forces a more dynamic pattern in the western CONUS. Strong, southwesterly flow will develop in the upper-levels Saturday afternoon as the upper-level trough approaches the region and height gradients increase as the ridge is slower to move off. An 85 to 90kt jet streak is anticipated to develop across north central Wyoming by 21Z, leading to portions of the region placed in the right entrance region of this jet, a favorable location for dynamically-induced lift. The upper-level jet will continue to get stronger through Saturday night into early Sunday morning as the trough digs into the Pacific Northwest and Intermountain West. Southwesterly 500mb flow will keep the fetch of moisture from the Pacific Ocean in place throughout the day, with stronger and larger vorticity maxima traversing through from southwest to northeast. Southwesterly flow will continue at 700mb with the low-level jet strengthening around 21 to 03Z before decreasing in magnitude overnight and increasing again for Sunday morning. A diffuse 700mb shortwave will move overhead between 21 and 03Z, leading to low-level lift across the region. A surface low pressure system will develop ahead of the main system across western South Dakota, increasing surface pressure gradients and bringing a weak cold front through the region, acting to initiate convection in the afternoon hours. Convective parameters look better for Saturday, especially with the increased forcing across the region. Forecast soundings from the RAP suggesting SBCAPE around 1400 J/kg with MLCAPE around 700 J/kg. DCAPE remains strong, due to drier conditions at the surface, around 1000 J/kg. Bulk shear increasing to around 30kts with favorable speed shear throughout the atmosphere. Severe weather could be possible, though the primary threat at this time looks to be damaging winds. The Storm Prediction Center has placed portions of the region within a Marginal Risk (Level 1 of 5) for severe weather Saturday afternoon with an intensity level 1 for the wind threat. This means that storms that do form in the afternoon could produce wind gusts over 70mph, though coverage may be lower. Surface temperatures will be warm once again, in the low-80s to mid-90s.

LONG TERM /SUNDAY THROUGH THURSDAY/

Issued at 137 AM MDT Fri Aug 28 2026

Active weather pattern likely to continue Sunday into early next week as Pacific jet energy and an associated upper level disturbance moves northeast across Colorado and Wyoming later on Monday. Models show an 100 knot jet max lifting north across the Pacific NW region and mainly near the Wyoming and Montana border Sunday afternoon. This jet is associated with a pretty strong upper level trough moving eastward near the US and Canadian border, which may bring some early season snowfall to the mountains across Montana and the Yellowstone area. This jet max is forecast to clip the area with models showing decent upper level difluence. Convective parameters looks suitable for widely scattered or scattered thunderstorms along the I-80 corridor, and more isolated north of I-80 as some drier air enters Carbon, Converse, and Niobrara county. MLCAPE between 400 to 800 j/kg and straight hodographs with 30-40 knots of shear favor linear segments and locally strong gusty winds. MLCAPE and SBCAPE are closer to 1500 j/kg across portions of western Nebraska, so the central and southern Panhandle have the higher potential to see a few strong to severe thunderstorms Sunday afternoon and evening. Sunday afternoon will also be pretty windy with the upper level trough not far too our north...expect wind gusts of 35 to 45 MPH, mainly north of I-80. For Monday, severe weather is not expected with lower CAPE values and too much midlevel shear (60+ knots). However, with an upper level disturbance lifting northeast out of the desert SW, another round of showers and thunderstorms are possible. This will greatly depend on the speed and location of the disturbance. The ECMWF is currently more progressive with the shortwave feature, showing it moving into the area nearly 6 to 12 hours earlier compared to the GFS and Canadian. Increased POP up to 50% for the I-80 corridor with ensembles showing some pretty good total QPF amounts, but kept POP lower further north towards the North Platte River Valley. Temperatures will be seasonable with highs in the upper 70s to upper 80s, but also noticeably cooler compared Friday and Saturday.

For the rest of next week, all models show southwest flow aloft developing over the Front Range as a series of late summer fall- like cold fronts move into the Pacific NW coast and as far south as northern California. Not expecting this cooler air to make it into Wyoming this early, but breezy conditions are expected, especially across southeast Wyoming, with temperatures a few degrees above average for early September with highs in the mid 70s to mid 80s for southeast Wyoming, and around 90 for western Nebraska. Precipitation is uncertain since models are struggling to resolve a pair of shortwaves on the southeastern quadrant of the main upper level trough near the Pacific coastline. With timing highly uncertain, POP were kept between 10 to 20 percent. Ensembles do not show PWATs lowering substantially next week, so can't rule out at least isolated convection across the area.

AVIATION /12Z TAFS THROUGH 12Z SATURDAY/

Issued at 545 AM MDT Fri Aug 28 2026

Upper level ridge axis will drift east over the area today with increasing westerly winds across southeast Wyoming. Rain showers and widely scattered thunderstorms will develop across the mountains and push east across the high plains later this afternoon.

HAZARDS/WEATHER TRENDS: VFR conditions will prevail over the next 24 hours for all terminals. Windy conditions at KRWL and KLAR after 17z today with gusts up to 35 knots. Rain shower activity and some embedded thunder possible, but coverage of thunderstorms is uncertain at this time. Shower and thunderstorm activity may result in brief strong wind gusts at times, but MVFR or lower conditions appear unlikely at this time due to high cloud bases.

CYS WATCHES/WARNINGS/ADVISORIES

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