textproduct: Western and Central Wyoming

KEY MESSAGES

- Showers and thunderstorms will continue across much of the area through 5PM/6PM MDT. Thunderstorms will be most numerous across Sweetwater and Natrona Counties this afternoon. Periods a rain/snow mix will be possible across many low elevation areas.

- Light snow will be coming to an end across the western mountains this afternoon but will persist across the northern Bighorns through roughly 7PM/8PM MDT. The greatest snow amounts will be across the northern Bighorns.

- There is high confidence that temperatures will warm into the 70s and 80s Saturday through Monday (Memorial Day). Late afternoon showers are possible (10-30% chance) Sunday and Monday afternoons, mainly across western Wyoming.

UPDATE

Issued at 1236 PM MDT Thu May 21 2026

The forecast is on track for the remainder of the day with widespread precipitation and thunderstorms along and behind a cold front. As of noon MDT, radar shows two focus areas of precipitation. The first is exiting Johnson and Natrona Counties, where an area of diffluence aloft is at ahead of the shortwave trough axis. As the shortwave trough axis progresses east early this afternoon, light rain associated with this focus area will also progress eastwards. The second focus of precipitation and thunderstorms is along the cold front and shortwave axis. This area of showers and thunderstorms is roughly located from Hiland to Rock Springs. Showers and thunderstorms will traverse east along the front, with thunderstorms becoming more numerous over Sweetwater and Natrona Counties through 4PM/5PM MDT. This is a result of increased instability (CAPE values of ~500 J/kg and mid-level lapse rates of 8.0 C/km) ahead of the front from late morning cloud breaks.

Behind the front, scattered light showers, and a few rumbles of thunder, are forecast through 5PM/6PM MDT. With snow levels dropping to between 6,500 ft AGL and 7,500 J/kg directly behind the front, low elevations could see a rain/snow mix during this time with no accumulation expected. Higher elevations of western and northern Wyoming, especially the northern Bighorns, will see all snow. Winter travel conditions are possible over all mountain passes this afternoon. Most will remain dry overnight as the system pushes to the east. The exceptions to this are Johnson and Natrona Counties where a light rain/snow mix is forecast through 2AM Friday as moisture wraps around the low. Gusty north winds will also be present behind the front this afternoon and evening, with the gustiest locations being in and around Buffalo.

DISCUSSION

Issued at 115 AM MDT Thu May 21 2026

Rain showers have moved over northwestern portions this morning, along and north of a roughly Jackson-to-Cody-to-Lovell line. The overall forecast remains on track, with timing being the main difference today. Snow levels will drop to around 7000 ft behind the cold front through 12Z this morning. The front is expected to extend from Evanston-to-South Pass-to-Thermopolis-to-Casper by 12Z. A leeside low will develop along the front in the Wind River Basin by this time and push eastward toward the Fremont/Natrona County line around 16Z. The cold front extending from the low will have passed through Rock Springs/Green River by this time as well and continue its trek eastward. Winds over the southern half of Natrona County will turn southwesterly in relation to the sfc low, turning more westerly by 21Z, and eventually northerly, as the front exits the CWA toward eastern WY. Precipitation will be widespread across the CWA today, with snow levels dropping as low as 6000 ft. Lower elevations can expect rain or a rain/snow mix through the day. Thunderstorms will also be possible this afternoon, with areas along and south of a Casper-to-South Pass- to Kemmerer line having the best chances. Western portions of the CWA could have some isolated embedded lightning strikes, as showers will be a bit more scattered over this area this afternoon. Precipitation will quickly end from west to east late this afternoon into the evening as the storm makes its way over western portions of SD and NE. Precipitation will linger over Johnson and Natrona counties the longest, ending as early as 06Z Friday. A couple of CAMS have light precipitation continue through the rest of the night. QPF amounts are highly varied, with areas west of the Divide receiving 0.05" to 0.15" and areas east of the Divide ranging as low as 0.05" to 0.20". The Bighorn, Absaroka and Wind River Mountains look to receive up to 0.50", which will help with some late season snowfall before summer sets in next month.

Temperatures rebound Friday, rising 5 to 15 degrees warmer than today. Isolated showers will be possible over the western mountains after 21Z and end by sunset. Saturday looks to be a nice start to the holiday weekend, with highs in the 70s, mostly clear skies and generally light winds. Temperatures in the 70s and 80s will be in place Sunday and Monday, with elevated to critical fire weather conditions possible for portions of Johnson County and the Bighorn and Wind River Basins Monday afternoon. Late afternoon showers and possible thunderstorms will be possible Sunday and Monday as well. Winds will turn more southerly by Tuesday, as a storm system drops southward over the PACNW. Moisture will increase over the Cowboy State as well, with Gulf moisture possibly making its way into areas east of the Divide. This looks to be the next day for widespread precipitation chances and possibly strong thunderstorms.

AVIATION /18Z TAFS THROUGH 18Z FRIDAY/

Issued at 1145 AM MDT Thu May 21 2026

Today's passing weather system is bringing widespread rain to lower elevations, and snow to mountains (along with obscured terrain). Intermittent MVFR conditions will be common, but most locations be VFR for the majority of the afternoon and evening, albeit with multiple mid cloud layers and occasional precipitation.

Winds will also be gusty as the cold front pushes through from west to east this afternoon, leading to shifting wind direction and gusts of 25 to 35 kt. There have been a few isolated strikes of lightning with the strongest showers along the front, but widespread lightning is not forecast today. Nevertheless, remain vigilant if outside, knowing that the stronger showers today could briefly become thunderstorms with lightning.

Around sunset, a majority of precipitation will have moved on to eastern Wyoming, and the scattered showers in the wake of the front will dissipate. CPR has the best chance of keeping a light rain-snow mix well in to the early morning hours Friday. Skies clear from west to east throughout the morning hours Friday, before scattered mid-level cumulus redevelop Friday afternoon

RIW WATCHES/WARNINGS/ADVISORIES

None.