textproduct: Western and Central Wyoming

KEY MESSAGES

- Scattered showers and thunderstorms are forecast (30 to 70 percent) roughly in a line from Jackson, along the Owl Creeks, to Casper and north through 8PM this evening. The greatest thunderstorm coverage is expected across the Bighorn Basin.

- Temperatures will continue to warm into the upper 50s to low 70s with gusty 25 to 40 mph winds.

- Warmer temperatures are forecast this upcoming week with highs in the 70s and 80s by Tuesday. Afternoon shower and thunderstorm chances exist Monday and Thursday, mainly along and east of the Continental Divide.

UPDATE

Issued at 107 PM MDT Sun May 31 2026

19Z water vapor imagery shows the upper level low over far northeast southeast Montana and a vorticity maximum entering western Wyoming. As the low and trough axis shifts further into Montana, a bulk of the associated mid-level moisture (dense cloud cover) will go with it this afternoon. As of 18Z, the bulk of the mid-level moisture is located north of a line from Jackson, along the Owl Creeks, to Midwest. It has been fairly sunny this morning along this arbitrary line and into the Wind River Basin and Natrona County, so the atmosphere has been, and will continue, to destabilize this afternoon. There will be just enough support aloft with the vorticity maximum, mid level moisture, and instability along this line for diurnal shower and thunderstorm development. Convection will shift north along the main moisture boundary this afternoon and evening, with the greatest thunderstorm potential across the Bighorn Basin. There is a fair amount of uncertainty in thunderstorm development across the Wind River Basin and Natrona County due to dry mid-level air quickly moving in. If something is able to develop in these areas, the most likely timeframe is between 1PM and 5PM. Otherwise, wind gusts of 25 to 40mph, especially the Wind Corridor, will continue to be common through sunset as the vorticity maximum passes over.

Clouds will quickly clear out and winds will become light after sunset tonight, giving way to sufficient radial cooling. Fog is forecast to develop late tonight through Monday morning across the Bighorn Basin, Yellowstone National Park, and Jackson Valley. These locations will be prime for fog development due to rain potential this afternoon and having rain on Saturday that was not able to dry out due to the cloud cover. If winds stay higher than what is forecast, clouds linger later into the night, or if there is more afternoon sun and less rain, the potential for fog development is much lower. Fog should clear out once the sun comes up on Monday morning.

DISCUSSION

Issued at 1235 AM MDT Sun May 31 2026

As expected, areas west of a Cody-to-Rock Springs line had the highest amounts of precipitation since 7am Saturday ranging between 0.15" to 0.70". Roughly add another 0.20" to include the precipitation that was occurring earlier Saturday morning/Friday night. Showers will be mainly confined to western and northern portions of the CWA early this morning as the upper low continues to slowly track toward the northeast. An area of showers will continue over southern portions of the Jackson Valley/northern portions of Star Valley and into the Upper Green River Basin, with additional showers from southern MT moving over YNP and the rest of the Jackson Valley around 10Z this morning. Showers and thunderstorms developed over far northern portions of Johnson County around 05Z and have been backbuilding toward Kaycee through 06Z. This activity will continue to track westward over the Bighorns through 12Z this morning.

Showers will become concentrated over northern portions after sunrise this morning as the upper low moves over the Black Hills and pivots over far eastern MT through the day. Any showers over the Wind River Basin and Natrona County will be isolated and conditions will remain dry elsewhere in the CWA. Precipitation amounts will be much lower with these showers, ranging between 0.10" and 0.20" through the day. Snow levels will stay around 9000-10000ft, with lower levels around 7500 over YNP and the Absarokas. A brief heavy downpour cannot be ruled out, especially in the Bighorn Basin, but is not expected. Precipitation will end from west to east through the evening. Otherwise, wind will be the main feature today with gusts of 25 to 35 mph developing over areas west of the Divide after 15Z and spread into Natrona County by 18Z. Similar winds will develop near Dubois and Crowheart after sunrise and spread down the basin toward Riverton. These winds will decrease across the area in the evening, lingering the longest in the Wind River Basin (which should finally end around 07Z Monday).

Isolated showers and thunderstorms will be possible Monday, as a shortwave moves over the Cowboy State. Winds aloft will be southwesterly as a trough develops over the Northern Rockies from the remnants of the upper low. Most of the convection looks to be isolated across the CWA, occurring along and east of a line from the Bighorns to western Sweetwater County. An additional area of isolated showers will be possible over far northwestern portions. Wind gusts up to 45 mph will be the main threat, as instability will be pretty modest between 200-500 J/kg. Tuesday and Wednesday look to stay mainly dry, with west-southwest winds aloft keeping any potential convection over far eastern portions of the state. Showers and thunderstorms will be possible again Thursday, with dry conditions returning for Friday. Temperatures will be above normal from Tuesday to Friday, with highs in the upper 70s into the 80s. Hot and dry conditions look to return for next weekend.

AVIATION /18Z TAFS THROUGH 18Z MONDAY/

Issued at 1200 PM MDT Sun May 31 2026

The large upper-level low is lifting north into Montana today, with the southern flank continuing to wrap moisture across the northern half of WY for isolated to scattered showers and thunderstorms. With the colder mid-level air, ceilings have been lower than normal; thus, occasional MVFR conditions will continue through about 01/03Z with the showers and storms this afternoon and evening. KJAC/KCOD/KWRL have the best chances of showers and storms today, with KRIW/KCPR right on the edge for about 15-20% chance. Otherwise from central into southern WY, VFR conditions with partly cloudy to mostly sunny skies and gusty west winds of 20-35 kts. The Bighorn Basin and Johnson County will see gusty north winds develop this afternoon, which then pushes into the Wind River Basin and Natrona County during the evening hours. Showers will linger over northern WY after midnight (01/06Z) with the northern WY mountains obscured.

Based on the recent precipitation from KJAC to the Bighorn Basin, expecting low clouds and possibly fog to develop overnight. Have included low visibilities and ceilings in KJAC/KCOD/KWRL starting about 01/08Z through mid-morning.

West-southwest flow then follows Monday morning with the upper- level flow in eastern Montana. A weak shortwave trough is shown by models to move from NE NV into northern UT and southwest WY Monday morning, increasing clouds and potentially bringing isolated showers to west-central WY Monday afternoon. Gusty west-southwest winds are expected again for most TAF sites Monday, especially with stronger upper-level flow over the area.

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

RIW WATCHES/WARNINGS/ADVISORIES

None.