textproduct: Western and Central Wyoming

KEY MESSAGES

- Rain continues over far northern and northwestern portions early this morning, spreading to the south and east toward sunrise this morning. Rain showers and thunderstorms become widespread across the state Thursday.

- Light snow is expected across the western and northern mountains to include Yellowstone National Park today, with amounts of 4 to 8 inches expected in the higher elevations. Lower amounts of 2 to 4 inches expected over the passes.

- High confidence in warm temperatures Saturday through Memorial Day, with highs in the 70s and 80s. Late afternoon showers are possible Sunday and Monday afternoons west of the Divide, mainly for the Wind River Mountains (10-20%).

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 irt 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 /12Z TAFS THROUGH 12Z FRIDAY/

Issued at 430 AM MDT Thu May 21 2026

VFR conditions at all TAF sites to start the period, except KCOD, which is expected to drop to LIFR/IFR. Rain shower activity continues across the northwest portions of the state, impacting KJAC and KCOD. This activity is expected to reach KPNA/KBPI around the start of the TAF period, and across the Divide towards 15Z. A cold front has pushed southward through the Bighorn Basin and KCPR this morning. Wind gusts of 20 to 30 kt will impact most sites between 15Z amd 00Z in the wake of this front.

Thunderstorms develop with the aforementioned frontal boundary by 19Z at KBPI/KPNA/KRKS and pushing to KCPR by 21Z. Development east of the Divide should be to the southeast of KRIW/KLND, and have been left out of the forecast. These develop around 20Z and will be close enough to affect approaches. Otherwise, mountain obscuration will be in place through the day with improving conditions occurring from west to east after 00Z. Winds diminish towards sunset, as ceilings lift and conditions improve with the shower activity diminishing and pushing east. Fog will be in possible late in the period toward sunrise as skies clear after 06Z.

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.