textproduct: Western and Central Wyoming

KEY MESSAGES

- There is high confidence in widespread showers and thunderstorms Friday through Sunday, with occasional dry periods. The greatest chances (80% to 90%) and highest rainfall totals exist across west and northwest Wyoming during this time frame.

- A few thunderstorms could produce gusty 45 to 50 mph winds across central and southern Wyoming from noon to 7PM today.

- Windy conditions are forecast across and around the Wind Corridor on Saturday afternoon with gusts of 30 to 45 mph common. Widespread windy conditions is forecast on Sunday with gusts of 30 to 40 mph across the entire area.

- Lows temperatures in the 30s are becoming increasingly likely much of next week, especially Monday morning, for western Wyoming. Daily afternoon shower and thunderstorm chances exist next week.

UPDATE

Issued at 100 PM MDT Fri Aug 28 2026

Moisture surge continues to pump northeast into the state, with showers and rain continuing. Latest precip numbers continue with better than 70% chance of one inch total accumulation through Sunday for most of the northwest sections. Models are hinting that one of the waves could be an extended period of training somewhere in the NW Parks. This brings some concern for localized flooding, so have posted Flash Flood Watches for the Tetons, Gros Ventres, Greater YNP, the Salts and Wyomings, and some surrounding lower elevations, and along the southwest facing slopes of the Winds through noon Sunday. All are advised to watch for quickly increasing river levels, especially along dry washes and valleys.

DISCUSSION

Issued at 243 AM MDT Fri Aug 28 2026

230AM water vapor imagery shows an upper level high over the southwest CONUS with it's associated ridge axis extending over eastern Wyoming. This ridge has been positioned over western Wyoming the past few days, keeping convection largely diurnally driven and the temperatures hot and above normal. This will not be the case these next few days as Wyoming will be on the upstream side of the ridge in moisture rich southwest flow. A vorticity maximum with accompanying Pacific moisture is on track to reach west and northwest Wyoming around sunrise this morning. This vorticity maximum will be present across northwest portions of the state throughout the day. This means a rainy day is in store for locations such as Jackson Hole, Yellowstone National Park, and portions of the Bighorn Basin. Yellowstone looks to get the most rain today, with 12- hour (6AM-6PM) rain totals upwards to 0.5" forecast. That being said, a few strong showers and embedded thunderstorms could producing moderate to heavy rainfall at times with localized flooding possible. Temperatures across these areas are forecast to be in the 60s to mid 70s due to dense cloud cover and 700mb temperatures of 6C to 8C. This vorticity maximum looks to shift north out of the area after 6PM, allowing for shower chances to drop to around 20% through 9PM/10PM tonight.

By early afternoon, shower and thunderstorm chances increase elsewhere as a weaker disturbance passes overhead. Low level moisture is not as abundant compared to northwest and northern portions, so convection is expected to initiate off the higher terrain of central and southwest Wyoming and trek northeast. There is generally a 20% to 40% chance of showers and thunderstorms for most areas between noon and 7PM. A few thunderstorms could produce gusty 45 to 50 mph winds due to dew point depressions around 45 degrees. Temperatures across southern and central Wyoming will be quite a bit warmer compared to northwest parts of the state with highs in the 80s. These warmer temperatures can be attributed to 700mb temperatures of 12C to 14C degrees.

By late tonight, shower and thunderstorm chances begin to increase across western Wyoming as a shortwave approaches the area. This shortwave is forecast to have more abundant moisture with widespread PWATs above the 98th percentile of climatology from late tonight through midday Saturday. In addition to the abundant moisture, the shortwave will also provide support for a cold front to pass across the state. This front will focus the shower and thunderstorm chances (60% to 90%) across western Wyoming early Saturday morning through the early afternoon before pushing east in the afternoon and evening (30% to 80% chances elsewhere). Winds will also be stronger across the Wind Corridor Saturday afternoon with the presence of a 60kt jet aloft and a tightening pressure gradient ahead of the front. Widespread wind gusts of 30 to 45 mph are forecast in and around the Wind Corridor on Saturday afternoon.

The shower and thunderstorm chances increase once again on Sunday, especially across western and southern Wyoming, as a more potent cold front treks across the state. This cold front is associated with the eastward progression of a Pacific Northwest upper low into Montana. Most areas have a 40% to 90% chance of showers and thunderstorms from midnight Saturday night through Sunday afternoon. All in all, there is high confidence in a rainy Friday through Sunday. From Friday afternoon through Sunday afternoon, there is a 70% to 90% chance of at least 1 inch of rain across west and northwest Wyoming, with the higher chances over the higher elevations. Across southwest and southern Wyoming, the 48-hour rainfall totals will not be as high with only a 50% to 70% chance of 0.5" of rain. Central and northern Wyoming will likely see only a few tenths, at best, during this timeframe. Widespread windy conditions are also forecast with this system on Sunday, with most locations seeing wind gusts of 30 to 40 mph. Drier and cooler air quickly filters in behind the front Sunday evening.

Monday morning is expected to be the coldest we have experienced in awhile, especially west of the Continental Divide. Across the western mountains, the western valleys, Yellowstone National Park, and the Upper Green River Basin, there is a 40% to 90% chance of Monday mornings lows being 35 degrees or less. However, temperatures are forecast to warm up into the upper 60s to 70s by Monday afternoon across those areas as a transitory ridge moves overhead.

Deterministic model guidance begins to differ Tuesday through Thursday on the position of an upper high. One model guidance positions a high over the southeast CONUS, which puts the Intermountain West in strong southwest flow with shortwaves each afternoon. This outcome favors daily shower and thunderstorm chances. On the contrary, another model guidance positions the upper high over the south central CONUS and keeps the greater shortwave forcing out of Wyoming. This outcome would favor less shower and thunderstorm chances across the state. The current forecast maintains something in the middle, with afternoon shower and thunderstorm chance, mainly across the higher terrain of western and southern Wyoming.

AVIATION /18Z TAFS THROUGH 18Z SATURDAY/

Issued at 1203 PM MDT Fri Aug 28 2026

An active period is expected as moisture arrives within southwesterly flow. This will keep scattered showers and thunderstorms going across the area through much of the period. Confidence is highest on impacts across western terminals, including KBPI, KJAC, KPNA, and KRKS. Regardless, all terminals have a chance of seeing this activity; the uncertainty lies more with the timing. All terminals have at least PROB30 groups to account for this. Brief heavy rain may bring occasional MVFR conditions, again with the best chances across terminals west of the Divide. After a relative lull late this afternoon, another round of showers will move in overnight. This will pick up toward the end of the period as it moves to the east. Other than rain, strong outflow wind gusts to 35 knots will be possible with this activity. Low clouds will lead to frequent mountain obscuration through the period, especially across western Wyoming.

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

Flood Watch from 6 PM MDT this evening through Sunday morning for WYZ001-002-012>014-023-024.