textproduct: Western and Central Wyoming

KEY MESSAGES

- Chilly temperatures return again Tuesday morning with lows in the 30s and middle 40s. Clouds will increase from the south through the overnight hours. There will be a 10 to 20% chance for low clouds/fog near Casper Tuesday morning through about 9 AM.

- Shower and thunderstorm chances (40% to 70%) on Tuesday afternoon and evening, with gusty outflow winds up to 50 to 55 mph the main threat through sunset.

- Dry conditions and a warming trend through the end of the week into the weekend with the next system pushing in late Sunday into early next week.

DISCUSSION

Issued at 130 AM MDT Tue Sep 22 2026

IR currently shows an upper level low over Nevada with cooling cloud tops pushing into northern Utah and far southwestern reaches of Wyoming. This will be the ignition for thunderstorm development come later Tuesday afternoon and evening as it pushes northeast through the morning hours. WV shows the main finger of the PFJ extending around a low over the Gulf of Alaska extending into Canada, with a weak finger of 60-70kts around the aforementioned low over Nevada. With not much support, it is forecasted to become more of an open wave as it moves over the CWA in the afternoon and evening. With mostly clear skies for much of the CWA, coupled with recent rainfall, fog development is possible in eastern Natrona County around Casper by sunrise Tuesday morning, but confidence low with small hint of upslope easterly flow by the FV3 sticking with 10-20% chance. Regardless, this will burn off quickly with a slightly warmer afternoon in store than it was Monday by 2 to 5 degrees.

With the approaching system from the southwest, expect scattered rain shower activity with a few isolated thunderstorms to push in from northeastern Utah west of the Divide by 11AM to noon with northward progression through the evening hours. This will extend across the Absarokas and Bighorn Basin by late afternoon exiting into Montana by 7-8PM weakening with radiational cooling towards sunset. The main concern will be with a stronger push of PVA anomaly into western Sweetwater County by 4-5PM extending over the southern Winds into the Wind River Basin by 6-7PM before exiting across Natrona/Johnson Counties to the northeast by 9-10PM. The main threats will be gusty outflow winds up to 50 to 55mph. MLCAPE values are forecasted to increase to 6-700 J/kg by late afternoon with forecast sounding output of shear values over 30kts that will help aid in the stronger winds. Not quite severe is expected, with much of that activity into northern Utah to Uinta County due to stronger aid of peak heating of the afternoon earlier than when it pushes into the RIW CWA. Heavy downpours will not be as high of concern being a bit more progressive than over the weekend with the low becoming more open with its northeastward progression into the upper Great Plains by midnight Tuesday night. It fills with time as well with decreased divergence aloft and ridging builds in from the south.

With that said, a warming trend and dry conditions expected for the rest of the work week into much of the weekend. Above average temperatures in the afternoon by Thursday extending through Saturday ahead of the next system that could affect the upper Rockies by late Sunday from the previously mentioned GOA low. Longer term model solutions aren't in total agreement on its progression to the Pacific northwest and later through the Rockies but something to watch in the coming days for late Sunday into early next week. For now, enjoy the rain chances for Tuesday, as it will be a few days at least until the next decent chance.

AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/

Issued at 430 AM MDT Tue Sep 22 2026

VFR conditions expected throughout the entirety of the period at all TAF sites. Low confidence fog near CPR through 15Z carrying VCFG (10-20%). Otherwise, increasing mid level clouds ahead of the next system with winds around 10-15kts into the afternoon hours. A push of scattered thunderstorms push through the CWA between 18-22Z with another round after 00Z moving southwest to northeast, ending at CPR by 08Z. Gusty outflow winds up to 35-45kts during peak heating of the afternoon and early evening, with some restriction at site during storm activity. Otherwise, mid level ceilings there after into the overnight hours heading into Wednesday morning.

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.