textproduct: Western and Central Wyoming

KEY MESSAGES

- Isolated virga showers will continue to stream northward through the rest of the evening, ending shortly after midnight. Skies will clear through the rest of the night, with mostly clear skies for most locations by sunrise Wednesday morning.

- Strong wind ahead of a cold front will lead to a more widespread fire weather threat on Wednesday. A Fire Weather Watch is now in effect for locations east of the Continental Divide.

- Rain and mountain snow is expected across western Wyoming on Wednesday. A Winter Weather Advisory is now in effect for the western mountains Wednesday through Thursday night.

- Cooler temperatures and precipitation chances extend to the rest of the area Thursday and Friday.

UPDATE

Issued at 1151 AM MDT Tue Apr 21 2026

Forecast remains similar to previous. Have adjusted precipitation timings for tonight, with the main push of moisture (and thus rain/snow chances) holding off until about 16Z (10am) Wednesday, though some light stuff could start as early as tonight. Dynamics still favors mid-afternoon Wednesday into Wednesday night as the period of greatest snowfall for the western mountains. For highlights, will keep them as is. There was thought of adding the Absaroka or Wind River Ranges. However, most notable snowfall occurs above 9000 feet, and for the Absarokas, it is mainly for the far western range. Highlights could still be added if snow amounts trend a bit higher or snow levels drop some.

For today, very dry and breezy conditions. Looking at wind, the larger threat will occur with western virga or light rain showers this afternoon and evening. Outflow gusts would likely be 40 to 50 mph given the dewpoint spreads, though a gust up to 60 mph is not out of the question. For wind Wednesday, the threat is widespread, with gusts 30 to 55 mph. Some isolated areas to around 60 mph are possible, but will keep Fire Weather Watches to cover this threat as confidence in widespread 60 mph winds is lower.

DISCUSSION

Issued at 427 AM MDT Tue Apr 21 2026

Temperatures will reach their peak of this warm stretch today as the ridge continues its progression over the region. 700mb temperatures of 8 to 10 C will allow for highs to rise into the 70s west of the Divide and 80s east. Along with this, yet another day of elevated to critical fire weather conditions is expected. The difference today will be an uptick of moisture arriving from the southwest, as well as an increasing upper level jet. This should be just enough support for isolated convection across western Wyoming, moving from south to north this afternoon and evening. Given the still dry surface conditions (T/Td spread of 40 to 50 degrees), strong outflow wind gusts appear likely with this activity, though it should be pretty isolated.

The upper low will approach Wyoming tonight, with the accompanying cold front moving west to east across the area beginning Wednesday morning. Ahead of the front, southwesterly wind will ramp up as a strong surface low develops to our northeast. This will be supported further by an encroaching 100 knot upper jet. With a still dry boundary layer, this will lead to at least a few hours of widespread critical fire weather conditions beginning late Wednesday morning. The question will be how long these conditions will last before the front passes and humidity increases. Regardless, wind of 40 to 55 mph will certainly support quick fire spread with any new starts, and a Fire Weather Watch is now in place for locations that have critical fuels. There is also a 50 to 60 percent chance of a couple of hours of wind gusts reaching high wind criteria (at least 58 mph) just ahead of the front, especially across the Wind Corridor from Rock Springs to Casper.

Meanwhile, rain and mountain snow will start across western Wyoming by late Wednesday morning. Initial westerly midlevel flow and a steady stream of moisture up the Snake River Plain will support decent snow rates across the mountains, most notably the Tetons which could see a quick 6 to 12 inches through Wednesday night. Accounting for additional snow expected on Thursday, a Winter Weather Advisory is now in effect for the Tetons and the rest of the western mountains. Snow levels will drop to the western valley floors Wednesday evening, though accumulations are mostly expected to be under 2 inches.

Rain and mountain snow will spread east of the Divide Wednesday night through Thursday. Unfortunately for those of us wanting a drought busting precipitation event, the main low with this system is still expected to pass to our north, displacing the best moisture into Montana. Northern Wyoming will accordingly be most favored on Thursday, as well as the far western mountains that will benefit from favorable orographic flow. However, there will be a second chance, at least for those east of the Continental Divide: while this first midlevel low will move away on Thursday, another one will follow quickly Thursday evening. This will bring additional precipitation chances through Friday. The caveat with this is a familiar one; moisture content is looking fairly low, and forecast accumulations are generally only a tenth or two east of the Divide, with little to none across southwestern Wyoming. With snow levels dropping to the basin floors Thursday night, some of this may fall as snow east of the Divide.

Further out, ensemble cluster guidance continues to support lower 500mb heights through the weekend. This would favor cooler temperatures and additional chances for precipitation, perhaps even into next week.

AVIATION /06Z TAFS THROUGH 06Z THURSDAY/

Issued at 944 PM MDT Tue Apr 21 2026

West of the Divide...KBPI/KJAC/KPNA/KRKS Terminals

A strong weather system will move into the area over the next 24 hours bringing strong wind and precipitation with it. A few rain showers and a thunderstorm remain possible (20-30%) around KJAC until 08Z, with more showers moving in by 14Z. Convective bands of rain changing to snow will push into the area Wednesday afternoon, with impacts at KBPI, KPNA, and KJAC. Conditions will drop to MVFR with the convective bands at KJAC Wednesday afternoon. There will be thunderstorms Wednesday afternoon across western Wyoming, so PROB30 groups have been added for the aforementioned terminals. Rain should change to snow at KJAC quickly Wednesday afternoon, especially in heavier showers. Prevailing snow will begin at KJAC late Wednesday evening by 05-06Z/Thurs, with IFR conditions expected. Mountain obscuration will continue at times tonight into Wednesday morning, becoming prevalent Wednesday afternoon. Wind will increase quickly by mid-morning Wednesday and will be strong (15-25 knots, with gusts of 25-35 knots). Stronger wind will occur at KRKS, with gusts of 40-45 knots from 18-03Z.

East of the Divide...KCOD/KCPR/KLND/KRIW/KWRL Terminals

A strong weather system will move into the area over the next 24 hours bringing strong wind to terminals, beginning by mid-morning Wednesday. No precipitation is expected over the next 24 hours, with chances below 10% at all terminals. Wind will be strong across the area through Wednesday evening. On average wind will be 20-30 knots, with gusts of 30-40 knots, but higher gusts will be possible (30- 40%) at KCPR and KLND. At KLND mountain waves are possible Wednesday morning as well as late Wednesday afternoon into Wednesday evening, which could result in wind gusts around 60 knots if the mountain waves break over the terminal. If this looks more likely for the 12Z issuance a TEMPO may be needed to highlight this wind threat.

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

FIRE WEATHER

Issued at 427 AM MDT Tue Apr 21 2026

Warm, dry, and breezy conditions will continue to support near- critical fire weather conditions today for much of the area. Wind will again be the question mark on if and where conditions can reach critical criteria. Wind will not be a question mark on Wednesday. Strong southwesterly gusts of 40 to 55 mph will be widespread as a cold front approaches from the west. This will support critical fire weather conditions before humidity values increase behind the front. Cooler and wetter conditions are then expected Thursday into the weekend, though breezy conditions will persist across the area.

RIW WATCHES/WARNINGS/ADVISORIES

Winter Weather Advisory from noon Wednesday to 11 PM MDT Thursday for WYZ001-012-024.

Fire Weather Watch from 9 AM MDT Wednesday through Wednesday evening for WYZ275-276-280>283-285-287-289-300.