textproduct: Cheyenne

KEY MESSAGES

- There is a Marginal Risk (Level 1 of 5) for severe weather Wednesday with a small sliver of a Slight Risk (Level 2 of 5) from Cheyenne east to Cheyenne. A Marginal Risk of Excessive Rainfall is also in place for Wednesday.

- There is a Marginal Risk (Level 1 of 5) for severe weather for portions of southeast Wyoming and western Nebraska on Thursday. Large hail and damaging wind are the primary hazards.

- Friday will act as a transition day between active weather to more organized active weather Saturday onwards.

- Daily shower and thunderstorm chances expected Saturday through at least Thursday, with the potential for strong thunderstorms Sunday afternoon.

SHORT TERM /THROUGH THURSDAY NIGHT/

Issued at 238 AM MDT Wed Aug 26 2026

Messy, upper-level ridging will continue today as it remains parked across much of the Intermountain West. Westerly flow aloft turns northwesterly through the mid-morning hours. A weak jet develops around 00Z this evening, placing portions of the region broadly in the right entrance region, favoring synoptic lift across much of the CWA. Several lobes of 500mb vorticity will advect around the 500mb high sitting over the Four Corners region and push into southeast Wyoming and western Nebraska by the afternoon hour. These lobes will promote some upper-level forcing across the region as the strongest lobes move through between 21 and 03Z. 700mb flow remains benign with widespread ridging across the western CONUS. Weak 700mb warm air advection is expected between 18 and 06Z this afternoon and evening, leading to weak, lower-level, forcing for ascent. Surface flow will turn southerly to southeasterly through the mid-morning hours, advecting in additional moisture throughout the morning and afternoon hours and providing ascent along the Laramie Range. Showers and thunderstorms are expected to develop between 12pm and 2pm this afternoon, with the potential for an additional push of convection around 00Z when the right entrance region of the upper- level jet moves in. Forecast soundings from the RAP and HRRR suggest around 1500 J/kg of MLCAPE this afternoon and around 2000 J/kg of SBCAPE, along with 30 to 35kts of bulk shear by 3PM. A large portion of the CAPE is present below 0C, increasing the potential for large hail with storms that form this afternoon. DCAPE values remain around 1000 J/kg, favoring increased chances for damaging winds as well. With fairly weak flow throughout the atmosphere, storms motion will be slow this afternoon and forecast soundings suggest Precipitable Water values around an inch with the NAEFS Mean Precipitable Water in the 90th percentile for this time of year. All of this combined with surface temperatures expected to be in the low to upper-80s and dewpoints in the 50s, a favorable environment will be present for strong to severe storms this afternoon. The Storm Prediction Center has highlighted much of the CWA along and east of the Laramie Range in a Marginal Risk (Level 1 of 5) for severe weather, with Cheyenne to Kimball in a Slight Risk (Level 2 of 5) for severe weather. The Weather Prediction Center has also highlighted the region in a Marginal Risk for excessive rainfall this afternoon. Therefore, primary concerns with showers and storms this afternoon will be damaging wind gusts, large hail, and heavy rain, potentially leading to localized flash flooding. Luckily, tornadoes do not look overly likely today.

Another active day is anticipated for Thursday as the upper-level ridge remains in place across much of the Intermountain West. The ridge is expected to amplify Thursday afternoon with northwesterly flow aloft continuing. As the ridge amplifies around 21Z Thursday, a weak jet develops from eastern Montana southeastward into western and central South Dakota. This positioning will broadly place the region in the right entrance region of the jet, but it will be much weaker than what is expected on Wednesday. The ridge will be pushed back to the southeast throughout the overnight hours as an upper- level trough starts to push into the Pacific Northwest by 06Z Friday. Looking down at 500mb, a similar pattern to Wednesday will setup with the high over the Four Corners region funneling moisture into the region and allowing multiple lobes of 500mb vorticity to advect around the high into the CWA. 700mb flow will be quite weak once again Thursday afternoon with broad ridging expected to remain overhead. A diffuse 70mb shortwave looks to push into southeast Wyoming between 06 and 12Z Friday, likely initiating more convection or helping sustain any ongoing convection. One big difference between Wednesday and Thursday will be the significantly stronger 700mb WAA on Thursday, with much of the region east of the Laramie Range seeing modest to strong WAA. A stout surface low pressure system starts to develop between 00 and 03 Friday across northeast Wyoming, favoring increased southerly to southeasterly flow across the region and stronger surface winds due to the increased pressure gradient. This low will move eastward, dragging a weak cold front across the region between 03 and 09Z Thursday night into Friday morning. Stronger 700mb WAA in the afternoon will lead to warmer surface temperatures, in the mid-80s to low-90s across much of the area. Dewpoints will increase into the 50s once more, providing a favorable environment for showers and storms along a line of Cheyenne to Wheatland to Douglas then east into western Nebraska. Forecast soundings from the HRRR and RAP suggest much more instability present Thursday afternoon in western Nebraska, with MLCAPE around 2000 to 2500 J/kg, though 2500 J/kg may be a touch high. SBCAPE skyrockets to around 2000 J/kg and DCAPE increases to 1300 to 1500 J/kg Thursday afternoon. Bulk shear will also be just a bit higher between about 35 and 40 kts in the Panhandle. The biggest question with this setup will be how much the building ridge aloft mitigates any rising motion under the subsequent sinking motion expected under a ridge. Currently, an isolated storm or two could become strong to severe Thursday afternoon with the Storm Prediction Center placing western Nebraska in a Marginal Risk (Level 1 of 5) for severe weather with damaging winds and large hail as the primary hazards. Tornadoes, once again, do not look likely. The Marginal Risk for excessive rainfall is pushed much more to the southeast for Thursday, only including Kimball to Sidney and points southeastward. Flooding does not look overly likely Thursday, but heavy rain may still be possible with Precipitable Water values once again around an inch in the Panhandle.

LONG TERM /FRIDAY THROUGH TUESDAY/

Issued at 238 AM MDT Wed Aug 26 2026

A brief reprieve from scattered thunderstorms is anticipated Friday as the upper-level start to transitioning to another active pattern. The upper-level ridge remains in place Friday, though starts to move off to the east and tilt towards the northeast Friday night into early Saturday morning. The 500mb high over the Four Corners continues to spin through the afternoon hours Friday, but gets pushed off to the south and east Friday night into early Saturday morning. 700mb flow turns more westerly Friday, as the ridge starts to weaken and move out of the region. A brief period of increased height gradients at 700mb will promote slightly stronger 700mb winds, with GFS Omega field suggesting modest downward motion along and east of the Laramie Range Friday morning through mid-day. Much as is expected for Wyoming during the year, the slightly stronger 700mb flow and increased downward omega values will lead to stronger surface winds, especially across Carbon County where strong southwesterly flow is anticipated to develop. ALl areas have less than a 30% chance at high winds during this period, but gusty winds look quite likely. 700mb temperatures also increase for Friday as the apex of the trough moves directly overhead then off to the east. 700mb temperatures will warm into the 15 to 19C range Friday afternoon. Surface temperatures look to max out in the upper-80s to upper-90s in all locations east of the Laramie Range. These very warm temperatures combined with gusty downsloping winds along and east of the Laramie Range, as well as minimal precipitation chances, will lead to elevated fire weather conditions as afternoon minimum humidity values drop into the 15 to 20 percent range across much of the area. Red Flag conditions are not anticipated at this time, but very dry and windy conditions are expected for the afternoon hours.

Saturday onwards will be dominated by the upper-level trough moving into the Pacific Northwest Friday through the weekend. Active weather looks to continue Saturday onwards with the much more progressive upper-level flow. Daily, scattered to numerous showers and storms are expected Saturday and Sunday afternoons as the upper- level trough pushes into the region, increasing synoptic forcing. Sunday looks particularly interesting as the upper-level trough starts to become negatively tilted over central Montana and a strong jet develops from eastern Montana southeastward through western Nebraska. Much of the region will be in the right entrance region of the strong, upper-level jet, favoring much stronger forcing across the region Sunday afternoon. While this setup is still several days out, long range models suggest decent 700mb WAA across the region Sunday afternoon. When combined with the strong, upper-level jet, storms could become quite strong Sunday afternoon. Details for this setup will become clearer over the coming days. Active weather will continue through the end of the long term period with daily shower and thunderstorms chances across the region. Surface temperatures will be quite warm Saturday before cooling off Sunday. More seasonable temperatures expected Monday through the end of the long term forecast period.

AVIATION /18Z TAFS THROUGH 18Z THURSDAY/

Issued at 1104 AM MDT Wed Aug 26 2026

Showers and thunderstorms are expected to move into the area later this afternoon trhough the evening. All terminals except KCDR have the PROB30 designation. These stroms may be strong to severe and are capable of producing gusty damaging winds and large hail. These storms may cause temporary VFR conditions. Otherwise, IVR conditions are expected for this TAF period.

CYS WATCHES/WARNINGS/ADVISORIES

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