Area Forecast Discussion

KEY MESSAGES

- Elevated to near critical fire weather conditions return Tuesday as the hot and dry conditions persist.

- 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.

UPDATE

Issued at 1234 PM MDT Mon Apr 20 2026

The current forecast remains largely unchanged. Elevated to critical fire weather conditions are expected today and tomorrow as humidity values drop below 15 percent and gusty winds 15 to 30 mph occur. Looking at precipitation chances for tomorrow (Tuesday), there will likely be 15 to 20 percent chances over western Wyoming as some advancing moisture moves over the area. The chance for any actual liquid is small (10% or less). The main outcome of any showers or thunderstorms would be gusty outflow winds, mainly in the 30 to 40 mph range, though a gust to around 55 mph is possible. These showers and storms would be mainly for western Wyoming, though spreading chances occur into Wednesday, as well as increasing chances for measurable liquid.

For the snow amounts Wednesday and Thursday, have held off of any highlights for now. Current trends suggest borderline 10 to 12 inches over the western mountains. Given the late April sun, and the two-day duration of the event, impacts are currently looking to be sub-warning.

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 as 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 500mb heights persisting through the weekend.

AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/

Issued at 408 PM MDT Mon Apr 20 2026

VFR conditions will prevail across all terminals through the TAF period. The light breeze of 15 to 25kt that has been seen at nearly all terminals should gradually dissipate shortly after sunset. High clouds will continue to stream over the forecast area tonight into Tuesday morning. Nearly all terminals will see breezy winds of 15 to 25 kt develop by the late morning and early afternoon hours Tuesday. A few afternoon showers cannot be ruled out, mainly the western terminals KRKS, KBPI, KPNA, and KJAC. However, at this time confidence remains low and any precipitation has been kept out of the TAF.

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 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.