textproduct: Cheyenne

KEY MESSAGES

- There is a Marginal Risk (Level 1 of 5) of severe weather across portions of the region along and east of the Laramie Range. Large hail and damaging winds will be the primary hazards.

- Drier conditions start to return Wednesday as the upper-level ridge strengthens across the Intermountain West increasing fire weather concerns.

SHORT TERM /THROUGH WEDNESDAY NIGHT/

Issued at 159 PM MDT Tue Aug 18 2026

This morning the forecast area was pretty clouded over limiting the amount of diurnal instability and decreasing the chances for the severe thunderstorms this afternoon. The 12z and later runs of the Hi-res guidance were far from enthusiastic about convection later on this evening. The RAP had about of 1000 joules of SBCAPE and maybe 500 joules or less of MLCAPE depending on the area. The HRRR and the RRFS were a little bit more generous with the CAPE and having around a 100 more joules in each category. However, with a cloudy morning that never really cleared out except for a few pockets, the amount of CAPE depicted by the models may even be overdone despite how meager those values are. Also displayed by the models were lobes of "quick" moving vorticity and a brief window of strong warm air advection over the Panhandle. So despite the meager environmental conditions we may still have enough forcing to produce some embedded thunderstorms the late afternoon/evening but outside of a brief wind gusts over 50-60mph. No other parameters are really expected to reach severe criteria. Even with the Bulk shear being 30 to 40 knots this Marginal Risk of severe thunderstorms may not pan out the way everyone thought. These showers are moving fairly quickly but they are struggling to hold themselves together outside of the mountains as they move east past i-25 and little precipitation makes it to the surface.

The upper-level ridge continues to build across the Intermountain West on Wednesday, leading to warmer and drier conditions once more. Northwesterly flow aloft develops for Wednesday, allowing multiple lobes of 500mb vorticity to traverse overhead, resulting in sporadic synoptic forcing for ascent. Northwesterly flow will persist at 700mb leading to drier conditions along and east of the Laramie Range as downslope warming and drying take hold. The terrain-induced dryline returns Wednesday and quickly pushes well to the east, fueled by the stronger 700mb flow advecting drier air eastward. Precipitation chances will be limited to none for most locations across the region. Models have really trended down the chances for precipitation across the Panhandle tomorrow compared to the overnight runs. Model guidance favors dry and breezy conditions as we maintain westerly flow aloft. Elevated to near-critical fire conditions are anticipated to develop across Carbon County where surface winds return to more "normal" speeds and afternoon minimum humidity values drop into the 10 to 15 percent range. Decided not to issue any Fire Weather headlines this morning due to low confidence in achieving 3 consecutive hours of Red Flag conditions and due to the fairly limited coverage of any critical fire conditions.

LONG TERM /THURSDAY THROUGH TUESDAY/

Issued at 159 PM MDT Tue Aug 18 2026

Thursday...Ridging becomes more pronounced with a relatively dry airmass, at low and mid levels becoming more prevalent, eradicating any chances of showers and thunderstorms under northwest flow aloft. 700 mb temperatures near 17 Celsius will yield maximum temperatures in the 80s to lower 90s.

Friday...The mid level, 500 mb, or about 18,000 feet MSL, ridge axis moves to a Grand Junction, Colorado to Great Falls, Montana axis, with its dominance continuing across our forecast area of southeast Wyoming and western Nebraska, continuing the dry conditions for our neck of the woods. Warming trend continues as 700 mb temperatures rise to near 19 Celsius, producing maximum temperatures from the upper 80s to mid 90s.

Saturday...With the upper ridge axis, near 500 mb, or 18,000 feet MSL, transitioning into the western Great Plains states from the Dakotas southward to eastern Colorado, west southwest flow aloft will develop over our counties, helping the pseudo monsoonal moisture to creep back into our forecast area from western Colorado through primarily our western counties west of I-25. Afternoon thunderstorms will be most prevalent across our Snowy, Sierra Madre and southern Laramie ranges, with evening thunderstorms, isolated to widely scattered, spreading across our entire forecast area, with of course the greatest areal coverage over our mountainous zones due to differential and orographic effects. With additional cloud cover and precipitation coverage, high temperatures will be tempered somewhat despite the warm mid level temperatures.

Sunday...More scattered beneficial showers and thunderstorms will occur in a carbon copy type day compared to Saturday, with broad northwest flow aloft over southeast Wyoming and western Nebraska, and pseudo monsoonal moisture over the counties. Carbon copy day temperature wise to Saturday, for the aforementioned reasons from Saturday.

Monday...Looks like the best chance for measurable rainfall, of 0.01 inch or more, with scattered to numerous afternoon and evening showers, and scattered thunderstorms due to increased monsoonal moisture, light steering winds and PWATs, Precipitable water increases. Slight cooling in maximum temperatures due to lowering of mid level temperatures and additional cloud and precipitation coverage.

Tuesday...Ridging aloft amplifies over the Rockies, though with monsoonal moisture trapped under the ridge from western Colorado through the western half of Wyoming, and to a lesser coverage over eastern Wyoming and western Nebraska, expect to see another carbon copy type day with scattered to numerous showers, and scattered thunderstorms during the afternoon and evening hours. Similar maximum temperatures compared to Monday, with clouds and precipitation coverage tempering highs, with readings peaking i the 80s to lower 90s.

AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/

Issued at 1204 PM MDT Tue Aug 18 2026

Primary challenges include ongoing showers as well as timing, intensity and coverage of afternoon and early evening showers and thunderstorms. A series of shortwave troughs aloft, also known as an atmospheric perturbation, will move southeastward in northwest flow aloft over the aviation district.

The primary shortwave trough aloft will affect the terminals and aviation area from late afternoon through early evening, producing scattered showers and isolated thunderstorms, with some of the stronger storms producing winds gusts to 45 knots with isolated strong thunderstorms, especially east of the Laramie Range and the I-25 corridor, producing a few wind gusts in excess of 50 knots. Showers and thunderstorms will exit the forecast area by 06Z with clearing skies and lessening winds.

Wyoming TAFS...VFR prevails through the TAF period. High confidence in the latest consistent HRRR timing of showers and thunderstorms, as well as the latest 12Z NAM run. Confident enough with timing of the HRRR to go with TEMPO groups at KRWL, KLAR and KCYS, from 22Z to 00Z, 23Z to 01Z, and 00Z to 02Z, respectively, with occasional MVFR due to visibilities and low VFR ceilings, as well as erratic winds and some gusts from the stronger storms up to 45 knots, with a few storms in the aviation district supporting wind gusts in excess of 50 knots. During the evening hours and overnight, expect decreasing cloud cover with ceilings and visibilities becoming unrestricted.

Nebraska TAFS...VFR prevails through the TAF period. High confidence in the latest consistent HRRR timing of showers and thunderstorms, as well as the latest 12Z NAM run. Confident enough with timing of the HRRR to go with TEMPO groups at KCDR, KAIA, KBFF and KSNY, from 23Z to 02Z, with occasional MVFR due to visibilities and low VFR ceilings, as well as erratic winds and some gusts from the stronger storms up to 45 to 50 knots, with a few storms in the aviation district supporting wind gusts in excess of 50 knots. During the evening hours and overnight, expect decreasing cloud cover with ceilings and visibilities becoming unrestricted. -Rubin

CYS WATCHES/WARNINGS/ADVISORIES

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