textproduct: Cheyenne

KEY MESSAGES

- 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 FRIDAY NIGHT/

Issued at 233 AM MDT Thu Aug 27 2026

Upper-level ridging continues today as an upper-level trough starts to dig into the Pacific Northwest. Models are starting to trend downward in the upper-level flow across the region. However, the 500mb high remains over the Four Corners regions, funneling moisture and 500mb vorticity maxima into the CWA throughout the day today. The 700mb ridge remains in place across the region during the day, but a shortwave will try to nose through Thursday night into early Friday morning, flipping flow to the southwest rather than west to northwest. Modest 700mb warm air advection will be present this afternoon and into the evening hours, enabling low-level forcing for ascent to increase this afternoon. A surface low pressure system attempts to form around 21Z this afternoon, increasing surface pressure gradients east of the Laramie Range. Temperatures this afternoon will increase into the low-80s to low-90s across the region with cloud cover increasing this afternoon. Surface dewpoints will remain in the 50s this afternoon across western Nebraska with much of southeast Wyoming in the 30s and 40s. The lower moisture looks to weaken some of the instability this afternoon, with forecast RAP and HRRR soundings suggesting only around 500 to 1000 J/kg of MLCAPE and SBCAPE. This has decreased significantly from yesterday when forecast models were suggesting 2000 to 2500 J/kg of MLCAPE and SBCAPE. DCAPE values have increased to around 1300 to 1600 J/kg this afternoon, suggesting an increasing threat for downbursts across much of the region. Bulk shear values are coming in a touch lower as well, only around 30kts rather than the 35 to 40kts modeled yesterday. Overall, the severe threat may be more limited in spacial extent. A storm could find a pocket of higher CAPE this afternoon, causing them to strengthen and drop some large hail. The Storm Prediction Center keeps the region in a Marginal Risk (Level 1 of 5) for severe weather with damaging winds and large hail (2+ inches) as the primary hazards. Today looks more likely to see one or two severe storms, but those storms could produce very large hail. Precipitable Water values remain around an inch today, so localized flooding is possible.

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, strengthening just a touch, before starting to move off to the east and tilt towards the northeast. The 500mb high over the Four Corners continues to spin through the afternoon hours Friday, but gets pushed off to the south and east and starts to become less organized Friday night into early Saturday morning. 700mb flow turns westerly Friday with a brief period of elevated height gradients possible between 21 and 06Z. GFS downward omega values remain modest at best, but could be enough to mix some of the stronger winds down towards the surface. High winds remain unlikely at this time, but stronger flow is anticipated across Carbon County where southwesterly surface flow develops and surface pressure gradients increase as a high develops over western Colorado. 700mb temperatures also increase into the 15 to 19C range for Friday as the apex of the trough briefly moves directly overhead. Surface temperatures look to max out in the low- 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. Afternoon minimum humidity values will drop into the 15 to 20 percent range across much of the area, but Red Flag conditions are not anticipated at this time.

LONG TERM /SATURDAY THROUGH WEDNESDAY/

Issued at 233 AM MDT Thu Aug 27 2026

The upper-level ridge gets pushed off to the east Saturday as an upper-level trough digs into the Pacific Northwest. Strong, southwesterly flow aloft develops as height gradients increase between the departing ridge and the incoming trough. The 500mb high will be pushed well off to the east over eastern Texas and Oklahoma, but a large fetch of southwesterly flow is anticipated from the Pacific Ocean, just off the coast of southern California, all the way through the Northern Plains. The 250mb jet streak over western Wyoming looks to develop around 21Z, placing much of the region within the right entrance region of the upper-level jet, favoring dynamically induced lift. 700mb flow will be quite elevated across western portions of the CWA Saturday morning before weakening through the mid-morning and early-afternoon hours. Strong 700mb WAA will be present once more east of the Laramie Range before cooler temperatures arrive ahead of the incoming upper-level trough. Westerly flow is anticipated to return by Sunday morning across the region, favoring slightly drier conditions. Another round of showers and thunderstorms will be possible Saturday, but the best lift arrives on Sunday with the upper-level trough. Forecast sounding from the RAP suggest a stout Inverted-V signature across much of the region, with around 1000 to 1500 J/kg of DCAPE. Therefore, showers and storms on Saturday may be quite gusty with increasing potential for microbursts. Temperatures Saturday will be warm again, in the low-80s to upper-90s across the region. Hottest conditions are anticipated in western Nebraska, where some locations could be pushing 100F.

Sunday onwards looks to remain quite active across the region as upper-level flow become more influenced by the incoming trough. Sunday may be particularly interesting day, weather wise, as the upper-level trough deepens and takes on a more negative tilt as it digs into northern portions of the Intermountain West. Strong 500mb vorticity maxima look to eject across the region, though 700mb WAA remains very low across the region. Dewpoints remain in the 40s and 50s, so another active day looks possible Sunday, especially with the enhanced dynamics from the strong upper-level trough. Once the trough moves through, an open wave develops with southwesterly flow continuing across the CWA. Multiple shortwaves look to push through the flow, so daily precipitation chances are expected to continue through much of the week. Temperatures look to remain seasonable to slightly warm across the CWA.

AVIATION /12Z TAFS THROUGH 12Z FRIDAY/

Issued at 504 AM MDT Thu Aug 27 2026

VFR conditions expected to persist through the 12Z TAF period. Isolated showers and storms are possible this afternoon and evening, but coverage will be low. Confidence is low in any specific terminal seeing a shower or storm. Gusty and erratic winds are expected near any shower or storm this afternoon. A low-level jet will kick in tonight across western Nebraska. Gusty conditions expected to develop at KCDR, KAIA, and KSNY overnight with the low-level jet. Some wind shear will also be possible with the low-level jet.

CYS WATCHES/WARNINGS/ADVISORIES

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