textproduct: Cheyenne

KEY MESSAGES

- Severe weather chances will persist through Monday. All modes of severe weather will be possible on Sunday and Monday, including large hail, damaging winds, and an isolated tornado.

- Hot temperatures and drier conditions are expected by mid-week.

SHORT TERM /THROUGH SUNDAY NIGHT/

Issued at 230 PM MDT Sat Jul 5 2025

Current KCYS radar shows storms lighting up along and west of the Laramie Range. A cumulus field developed here earlier in the day, and is the area where storms continue to pop up thanks to forcing from an upper-level shortwave. Storms will continue through the afternoon and into the early evening hours, however, Hi-Res guidance has really toned down coverage and intensity of storms across the area. Newer runs of the GFS show a sub-severe environment across the CWA. For the most part, MUCAPE values are below 1000 J/kg with decent shear. Hail will be possible, but likely not severe given these parameters. Cannot rule out severe wind gusts in storms just yet given the dry surface across much of the CWA. Inverted-v soundings show over 1000 J/kg of DCAPE, indicating the strong wind threat in both showers and thunderstorms. Storms will push further eastward through the afternoon, eventually leaving the CWA and/or dissipating later this evening. Heading into the overnight hours, conditions should remain relatively quiet. However, cannot rule out a Dawes County clipper as Hi-Res guidance shows storm clusters in South Dakota which could be in the vicinity of Chadron depending on the track. Per the RAP, there will be a little bubble of elevated surface instability around Chadron overnight that could support a storm.

A weak disturbance moving through the flow aloft tomorrow will trigger another round of afternoon showers and thunderstorms. A quick look at model soundings and Hi-Res guidance shows a more favorable environment for severe storms. MUCAPE in the Nebraska panhandle is generally around 1800 J/kg with around 35 kts of effective shear. This will lead to a large hail threat coupled with a strong wind threat due to DCAPE values over 1000 J/kg. Also cannot rule out an isolated tornado in the Nebraska panhandle with MLCAPE values around 1200 J/kg and SFC-3km SRH values around 100 m^2/s^2. Hi-Res guidance has storms developing over the high terrain early in the afternoon, pushing east into the panhandle by mid-afternoon. Currently, most Hi-Res guidance has the strongest storms south of the North Platte River Valley. This is also where the majority of the Slight Risk from SPC lies in the CWA. Most storms will move out of the area by the evening hours.

LONG TERM /MONDAY THROUGH SATURDAY/

Issued at 358 PM MDT Sat Jul 5 2025

The upcoming work week will be bookended by stormy weather patterns, while dry and hot weather will dominate the middle part of the week.

Picking up on Monday, a compact upper level ridge will remain parked over the Four Corners states, allowing for a parade of shortwave troughs to continue to move over the top of it. The dryline is expected to remain parked more or less over the Laramie Range once again on Monday. Moist southerly low-level flow will be present in the morning, but the low-level wind and pressure patterns will be fairly complicated moving into the afternoon hours. Guidance depicts a weak surface low trying to develop near Laramie county, while a high to the north may push northeast winds into our northern/eastern counties. The result will likely be numerous trigger points for scattered afternoon thunderstorms across the High Plains. In addition, plentiful moisture and steep lapse rates will likely put ample instability in place. Modest overrunning and vorticity advection aloft will provide some forcing. While all of this points towards strong to severe thunderstorms, the main piece working against this will be the possible presence of a significant cap. Models show fairly substantial CIN in place, particularly over the Nebraska panhandle. This will be the main failure mode to watch for in the coming days, but if we manage to see storms break through the cap, there will be the potential for strong to severe thunderstorms with all hazards possible.

The upper level ridge will amplify heading into Tuesday, bringing much drier air into most of Wyoming. This will decrease storm probabilities for Tuesday and Wednesday at least, but a few high based showers and thunderstorms can't be ruled out. Attention midweek will shift to hot temperatures as 700-mb temperatures push towards +16C to +19C across the area, peaking on Wednesday. Highs will be some 5-10F above average for Tuesday through Thursday. Wednesday will be the hottest day, with widespread 90s, and a good chance at 100F in the typical low elevation hotter spots such as Torrington, Scottsbluff, and Chadron. Thursday will be a transition day as a shortwave trough nudges the ridge down to the south. Expect plentiful moisture to return to the middle to upper atmosphere, but the low levels will remain fairly dry. This points to possible scattered thunderstorms with a dry microburst potential before a surface cold front plows through the area late Thursday or early Friday. Expect much cooler temperatures on Friday with an increase in possible shower and thunderstorm coverage.

AVIATION /00Z TAFS THROUGH 00Z MONDAY/

Issued at 538 PM MDT Sat Jul 5 2025

Isolated thunderstorms will continue through the next few hours, and may bring a brief VIS drop, lightning, and erratic winds to area terminals. Most of this activity should wane by about 03z, but a few storms may continue near KCDR for several more hours. There is a slight chance for a strong storm to impact KCDR near midnight, which is handled with a PROB30 group at this time due to low confidence.

Expect clearing skies and occasionally variable winds overnight and into Sunday morning. Another round of scattered thunderstorms will develop after noon on Sunday and bring the chance for more impacts due to lightning, heavy rainfall, and strong gusty winds. Isolated large hail will also be possible with Sunday's storms.

CYS WATCHES/WARNINGS/ADVISORIES

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