textproduct: Western and Central Wyoming

KEY MESSAGES

- Elevated to critical fire weather conditions are expected today for most of the area. A Red Flag Warning is in effect for portions of central Wyoming. Similar conditions are expected on Tuesday.

- Strong wind ahead of a cold front will lead to a more widespread fire weather threat on Wednesday.

- A system will bring widespread cooler temperatures and precipitation chances Wednesday through the end of the week. Accumulating mountain snow is expected across western Wyoming.

DISCUSSION

Issued at 407 AM MDT Mon Apr 20 2026

The warming trend continues today as the upper ridge remains dominant over the Rockies. Highs will peak another 5 to 10 degrees warmer than on Sunday, with humidity again dropping to around or below 10 percent for most lower elevations. The main difference today will be slightly increased wind as a subtle shortwave to our north induces a weak surface low across northeastern Wyoming. This will lead to gusts in the 20 to 30 mph range, returning critical fire weather conditions to portions of the Wind Corridor.

The ridge will begin to compress on Tuesday as an upper low over the Pacific moves onto the West Coast. 700mb temperatures of 8 to 10 C will allow for highs to reach the 70s west of the Divide and 80s east, the warmest of this stretch. Another day of elevated to critical fire weather conditions is expected. The difference Tuesday will be an uptick of moisture arriving from the southwest, as well an increasing upper level jet. This should be just enough support for isolated convection across western Wyoming. Given the still dry surface conditions, strong outflow winds appear likely with this activity, though it should be pretty isolated.

The upper low will approach Wyoming Tuesday night, with a cold front moving east through the area beginning Wednesday morning. There has been a notable northward shift in the placement of the low as it moves through, unfortunately for those wanting a widespread moisture event. This will favor western Wyoming for precipitation initially, and then northern Wyoming Wednesday night and Thursday. 700mb temperatures of -6 to -8 C behind the front will allow for mountain snow Wednesday, dropping down to the western valleys by evening. There appears to be enough moisture with this system for decent western mountain accumulation, and winter weather highlights appear increasingly likely. The main concern across most of central and southern Wyoming on Wednesday will be strong southwesterly wind ahead of the front. While there is still some uncertainty on FROPA timing, an afternoon of widespread critical fire weather conditions appears likely (60-70%). The limiting factor here will be humidity as moisture increases. High wind can't be ruled out either, though confidence is lower on that potential for now.

Rain and mountain snow should expand east of the Divide on Thursday, though the best moisture with this system may be displaced north into Montana if trends hold. One glimmer of hope is that guidance is still suggesting a couple of robust waves trailing along the backside of the main low, extending precipitation chances and cooler weather through the end of the week. Ensemble cluster analysis supports this scenario, with anomalously low 500 mb heights persisting through the weekend.

AVIATION /18Z TAFS THROUGH 18Z TUESDAY/

Issued at 1056 AM MDT Mon Apr 20 2026

VFR conditions will prevail across all terminals through the TAF period. A breeze of 15 to 25 knots will develop around the start of the period as most terminals. These winds weaken near sunset with light winds (<10kts) through the overnight into Tuesday morning. Skies remain mostly clear for the period with some fair weather high clouds at times this afternoon and evening. Winds gradually increase near the end of the TAF period with KCOD and KCPR seeing breezy winds develop around 15Z Tuesday.

FIRE WEATHER

Issued at 407 AM MDT Mon Apr 20 2026

Humidity values will again drop to around or below 10 percent for the majority of the area today. A Red Flag Warning remains in effect for portions of central Wyoming that will also see stronger wind gusts this afternoon. Similar conditions are expected on Tuesday. A system will approach the area on Wednesday, with a cold front expected to move west to east through the day. Strong southwesterly wind gusts of 40 to 55 mph are expected ahead of the front, leading to widespread elevated to critical fire weather conditions.

RIW WATCHES/WARNINGS/ADVISORIES

Red Flag Warning until 8 PM MDT this evening for WYZ280-289.