Area Forecast Discussion

KEY MESSAGES

- Elevated to near critical fire weather conditions are expected today for much of the area given low humidity, gusty winds, and warmer than normal temperatures.

- 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 dew point 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 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 500 mb heights through the weekend. This would favor cooler temperatures and additional chances for precipitation, perhaps even into next week.

AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/

Issued at 1118 AM MDT Tue Apr 21 2026

VFR conditions prevail across all terminals through much of the TAF period. Breezy winds return around the start of the period for nearly all terminals. Winds will be gusting around 15 to 25 knots periodically this afternoon with speeds decreasing shortly after sunset. Mid to high level clouds continue to develop across the region this afternoon. Most locations remain dry today with terminals such as KPNA, KJAC, KBPI, and KCOD being the exception. These terminals have the chance 10-20% to see a brief or nearby shower this afternoon into this evening. A stray thunderstorm cannot be ruled out but confidence is not high in regards to where the most favorable location would be. Any showers that develop nearby a terminals may be capable of producing a strong gusty outflow of 30 to 40 knots. Overall, due to low confidence only VCSH groups have been added to these terminals. Otherwise, winds weaken overnight before increasing around 15Z Wednesday across most terminals. Winds are forecast to be much stronger Wednesday with widespread gusts of 25 to 35 knots to end the TAF period. Mountains will likely remain mostly unobscured through Tuesday with obscuration chances increasing through the day Wednesday in association with a nearing disturbance.

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 Wednesday morning through Wednesday evening for WYZ275-276-280>283-285-287-289-300.