textproduct: Western and Central Wyoming

KEY MESSAGES

- A series of weather systems move north across Wyoming Tuesday and Tuesday night increasing shower and thunderstorm chances (30% to 70%). The precipitation ends from south-to-north early Wednesday morning.

- Thunderstorms across southwest Wyoming between 4 PM and 8 PM Tuesday have the potential to create gusty outflow wind of 40 to 60 mph.

- Dry conditions and a warming trend occur through the end of the week ahead of a Friday night cold front. Wind speeds increase from the west to southwest Friday and Saturday.

- Another weather system arrives late in the weekend into early next week, possibly leading to cooler temperatures and a chance of precipitation.

UPDATE

Issued at 1150 AM MDT Tue Sep 22 2026

Midday Tuesday water vapor satellite imagery shows a weak shortwave over eastern Idaho, while a clearly defined stronger shortwave spins near east-central Nevada. Morning convection with the Idaho wave has been light as showers move north across western and central Wyoming. The better chance of more intense and widespread convection comes Tuesday afternoon and evening in association with the stronger shortwave in Nevada. A 60-80kt jet streak ahead of this shortwave moves north through Utah Tuesday afternoon and helps strengthen developing convection across eastern Utah. Moderate to strong mid- level wind shear spreads into southwest Wyoming later Tuesday afternoon leading to increasing coverage and intensity of showers and thunderstorms. SPC has highlighted a marginal chance of severe thunderstorms across the southwest-quarter of the state. While the primary hazard will be outflow wind gusts around 40 to 60 mph between 4 PM and 8 PM MDT, stronger storms could be capable of one-half to one inch diameter hail within the marginal risk. The potent shortwave and associated showers and isolated thunderstorms track north across the state Tuesday evening and overnight leaving only lingering light showers over the far north by sunrise Wednesday. While the intensity of the convection generally wanes after sunset Tuesday, a few thunderstorms east of the Continental Divide could be strong until closer to midnight.

Enough instability and lingering mid-level moisture allows for isolated showers across the far north, mainly over the mountains, Wednesday afternoon. Otherwise, conditions are dry with temperatures around or just a tad cooler than seasonal averages. This changes Thursday and Friday as warmer southwest flow arrives ahead of weather system dropping into the Pacific Northwest to end the work week. Wind speeds increase Friday ahead of this feature and temperatures climb to above normal.

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 /00Z TAFS THROUGH 00Z THURSDAY/

Issued at 351 PM MDT Tue Sep 22 2026

Lingering showers and thunderstorms diminish from the start of the TAF period through 06z. Gusty outflow winds 40 to 60 knots are possible during this time, as well as brief MVFR conditions due to moderate to heavy rain if a shower moves over a terminal. Once rain chances end, light winds prevail overnight. For Wednesday, light showers and towering cumulus will likely develop around the western Wyoming mountains. At this time, not expecting impacts to sites, but near mountain locations (like KCOD) could see some nearby convective clouds or light showers.

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.