textproduct: Western and Central Wyoming

KEY MESSAGES

- Shower and thunderstorm chances (20% to 50%) increase after 1PM today across much of the area. Frequent lightning and gusty winds will be the main hazards in any thunderstorms, with gusts up to 60 mph possible.

- Confidence is increasing in widespread showers and thunderstorms Friday afternoon through Sunday morning. The greatest chances exist across west and northwest Wyoming late Friday through midday Saturday.

- Near to above normal temperatures through Saturday. Daily shower and thunderstorm chances (20% to 40%) exist the first half of next week with widespread cooler temperatures, including lows in the 30s for western Wyoming.

DISCUSSION

Issued at 247 AM MDT Thu Aug 27 2026

An upper level high over has been rooted over the southwest CONUS over the past few days. The associated ridge axis is currently (230 AM) positioned over far western Wyoming, where it has been for the past day or so. The ridge axis will begin to slowly shift east across Wyoming today and bring another day of widespread warm temperatures. With subtle height rises as the ridge progresses east, temperatures east of the Continental Divide are forecast to be in the high 80s to mid 90s. Western and southern Wyoming will likely see widespread highs in the 80s. However, today's forecasted highs across western Wyoming could be a few degrees too warm due to increased cloud cover this afternoon.

The increased cloud cover is a result of an influx of moisture with a shortwave disturbance on the upstream side of the ridge this afternoon and evening. Much like the past few days, showers and thunderstorms are expected to initiate across the higher terrain of western and southern Wyoming this afternoon and move east. Model forecast soundings are indicating DCAPE values ranging from 700 J/kg across western Wyoming to 1500 J/kg in central and southern Wyoming. Furthermore, dew point depressions across central and southern Wyoming are in the 45 to 55 degree range. Thus, another day of gusty outflows will be possible in any shower or thunderstorm across central and southern Wyoming late this afternoon. A couple gusts could be closer to that 55 to 60 mph mark, but most gusts will be in the 35 to 45 mph range. Unlike the past few days, shower and thunderstorm coverage is expected to be greatest across west and northwest Wyoming. This is due to those areas being in better proximity to the highest moisture content. Showers and thunderstorms are largely forecast from 1PM through at least 10PM, with light rain possible across the northern half of Wyoming until 2AM Friday.

By Friday, the upper level ridge will be positioned over the central CONUS, allowing for flow to be predominately southwesterly. This deep southwest flow will advect deep Pacific moisture into the region as embedded shortwaves traverse the state. Shower and a few embedded thunderstorms will be possible (up to 30% chance) as early as sunrise Friday across northwest Wyoming as the nose of the Pacific moisture arrives. These shower and thunderstorm chances will only increase through the day on Friday as a continuous stream of Pacific moisture advects into the state. Showers and thunderstorms are expected to initiate and be most numerous over the higher terrain in the afternoon and move east/northeast into the lower elevation areas. PWATs are expected to increase across the entire state through the afternoon and evening as southwest flow strengthens. Ensemble guidance indicates that PWATs will increase from the the 90th percentile of climatology in the morning to above the 99th percentile of climatology by Friday afternoon, especially across west and northwest Wyoming. This provides increased confidence in widespread showers and thunderstorms bringing at least a few hundredths of rain for many locations. The increased cloud cover across the state will also limit how warm we get on Friday, with forecasted highs in the 70s and 80s.

The active weather will continue Friday night through Saturday afternoon as a cold front traverses across the area. There will be plenty of available moisture, lift, and support aloft for widespread showers and thunderstorms. The highest chances (90%+) are still across the western half of Wyoming due to remaining in better proximity to the greatest moisture content. The current forecast has anywhere from 0.5" to 1.0" of rain between 6AM Friday through Midnight Sunday morning (42 hours) across Yellowstone, the Teton and Gros Ventre Mountains, the northern Wind River Mountains, and Jackson Valley. Amounts during this same timeframe elsewhere across the state range from 0.01" to 0.40". Showers and thunderstorms are not forecast to be slow moving. However, if multiple showers or thunderstorms with moderate to heavy rainfall rates go over the same area in a short amount of time, localized flash flooding is possible across west and northwest Wyoming.

Showers and thunderstorms are expected to persist Saturday night through Sunday afternoon, although coverage will gradually decrease. This is decreasing trend will largely be a result of westerly flow cutting off the deeper moisture. Flow becomes more westerly and strengthens ahead of a shortwave trough rounding a Pacific Northwest low. This shortwave and an associated cold front is forecast to trek across the Intermountain West Sunday afternoon. This cold front is forecast to come with a "punch" of cold air, especially west of the Continental Divide. There is a 60% to 90% chance of temperatures on Monday morning falling into the 30s across the Green River Basin and the western valleys. For the higher elevations, there is a greater than 90% chance of temperatures falling below to or below freezing on Monday morning.

Ensemble guidance is in consensus that multiple shortwaves will traverse across the state Monday through Wednesday. Moisture does not look to be anything of note at this time so the current forecast holds a 20% to 40% chance of showers and thunderstorms each afternoon Monday through Wednesday. Temperatures also look to be near to below normal for the end of August and the start of September.

AVIATION /12Z TAFS THROUGH 12Z FRIDAY/

Issued at 529 AM MDT Thu Aug 27 2026

VFR flight conditions are forecast through 12Z Friday, with increasing mid to high level clouds. Showers and thunderstorms will develop across the higher terrain of western and central Wyoming after 19Z/20Z and shift east through the afternoon and evening. Convection will be scattered today, with a 30 to 40 percent chance of showers and thunderstorms at most terminals so maintained PROB30s at this time. Shower and thunderstorm chances reach KJAC, KCOD, KBPI, and KPNA as early 20Z/21Z followed by KRIW, KLND, and KWRL around 23Z/00Z. There is a reasonable amount of uncertainty whether convection will maintain itself to reach KCPR, but chances are high enough (30 percent) to introduce a PROB30 group beginning at 03Z. An additional round of light rain at KJAC is forecast for a few hours after sunset. Lingering light showers cannot be ruled out in the area of KBPI and KPNA after sunset as well. KRKS has less than a 20 percent chance of seeing a shower or thunderstorm. Thunderstorms will be capable of gusty 35 to 40 kt outflow winds, with a gust over 50 kts possible.

Outside of any showers or thunderstorms, winds are forecast to remain 10 kts or less throughout the TAF period at most terminals. KRKS and KPNA are the exceptions with a few hours of late afternoon breezes around 20kts.

Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for the latest information on smoke, icing, and turbulence forecasts.

RIW WATCHES/WARNINGS/ADVISORIES

None.