textproduct: Western and Central Wyoming

KEY MESSAGES

- Winds have decreased this evening, but will remain gusty across the area tonight with gusts of 30 to 40 mph.

- Snow intensity increases this evening across the western mountains with western valleys seeing periods of rain/snow showers. Winter travel conditions are expected across all western mountain passes due to snow and wind.

- A cooler, more active weather pattern is favored Friday through the upcoming weekend.

UPDATE

Issued at 130 PM MDT Wed Apr 22 2026

A few things to update regarding the forecast. Firstly, stronger than expected winds have been blowing across much of Natrona County this morning. Numerous observations of winds gusting near 65-70 mph with the Casper airport recording a peak gust of 67 mph. As a result of these strong winds, High Wind Warnings have been issued for Natrona County including Casper Mountain through this evening. These strong gusty winds may linger into the late evening and early morning hours. Locations such as Casper and the Cody Foothills have the best chances of seeing these gusts persist. Other areas will see winds of 40 to 55 mph through the evening before decreasing after sunset. Red Flag Warnings remain in place for nearly all zones east of the Divide with no changes expected. Showers and a few thunderstorms have begun developing and will continue to develop over western WY this afternoon and evening. Due to colder temperatures in association with the passing cold front some localized snow squalls cannot be ruled out mainly west of the Divide.

The other change is a slight shift in QPF amounts especially across central WY mainly during the Thursday into Friday morning period. Hi-res models are showing a less favorable setup for any prevailing precipitation to occur. That being said there still does look to be a chance for some showers as the second cold front passes through Thursday evening into Friday. A period of favorable dynamics for portions of Johnson and Natrona County looks possible during this time. As a result, there are increasing chances for some prevailing precipitation to occur possibly in the form of snow as colder air follows in behind the frontal passage. A slushy inch or two of wet snow cannot be ruled out across Johnson and Natrona County by the time the sunrises on Friday. Otherwise, the previous forecast remains on track.

DISCUSSION

Issued at 323 AM MDT Wed Apr 22 2026

Satellite water vapor imagery at 09Z/3AM shows an upper level low circulating over northern California/Nevada with southwesterly flow over Wyoming. An associated surface low is located over northeast Idaho with a cold front over western Utah. This system will be our "weather maker" as it ejects into Montana today, bringing critical fire weather conditions, widespread wind, and precipitation chances.

The pressure and temperature gradient will tighten through the day today as the cold front approaches from the west. Additionally, an 80kt to 100kt upper level jet will be present across the Wind Corridor as the low shifts into Montana. This will result in widespread strong and gusty southwest winds a majority of the day. Southwest winds will quickly ramp up between 9AM and 10AM this morning as deep mixing begins. Widespread wind gusts of 30 to 50 mph can be expected (90%+ chance) across most low elevations. Wind prone locations could see occasional gusts of 60 mph or greater, especially in the hour or two ahead of the frontal passage. There are some indications of a mountain wave breaking over the eastern slopes of the Wind River Mountains in the morning to early afternoon hours. Should this occur, wind gusts of 50 to 70 mph are possible across the eastern slopes of the Wind River Mountains and potentially making it around Lander and Fort Washakie. The cold front is forecast to traverse the state between 2PM and 6PM today, with wind gusts remaining in the 30 to 40 mph range for a few hours behind the front due to the temperature gradient.

The strong and gusty winds mentioned above in combination with dry air ahead of the cold front will create critical fire weather conditions for all areas east of the Divide. Minimum relative humidity values are forecast to be in the 10 to 13 percent range this afternoon. A Red Flag Warning is now in effect from 9AM to 8PM today. Behind the cold front, relative humidities are forecast to increase to a 15 to 25 percent range through sunset. The expected strong winds behind the front will keep conditions favorable for erratic fire behavior despite minimum relative humidities likely being above Red Flag Criteria (15 percent or less) from 5PM to 8PM.

The final component of this weather system will be the precipitation chances along and behind the cold front. Because of the Pacific origin of the system, there will enough available moisture to bring accumulating mountain snow and low elevation rain and snow to the west. Through late Thursday night, there is an 80 to 95 percent chance of at least 8 inches of snow for elevations above 7,500 feet across the western mountains. Chances of 12 inches or more are in the 40 to 70 percent range and confined to the Tetons. Gusty winds of 30 to 50 mph will also be common. Given the slightly lower confidence in widespread 12 inches or more of snow and the higher sun angle, opted to maintain the Winter Weather Advisory. The Absaroka Mountains have been added to the Winter Weather Advisory with an 80 to 90 percent chance of snow accumulations of 6 inches or more and gusty 50 to 70 mph winds. Winter travel conditions are expected with the snow and gusty winds across all western mountain passes. There will also be enough instability (up to 500 J/kg of CAPE) to support some instances of thundersnow. As for Jackson Valley and Star Valley, precipitation will remain as rain most of the daylight hours today before changing over to snow after sunset when snow levels drop below 6,000 feet.

Precipitation will largely be focused across the west today through at least mid-day Thursday due to the low passing north of Wyoming. On Thursday afternoon, a shortwave is forecast to drop down from Canada and provide support for another front to traverse the state. This front is forecast to bring cooler temperatures and precipitation. Precipitation will finally push east of the Divide late Thursday through most of Friday, first as rain across low elevations. Rain will quickly change over to snow overnight Thursday into Friday with 700 mb temperatures behind the front being in the minus 6 Celsius to minus 10 Celsius range. However, snow amounts are forecast to be minimal by Friday night with less than a 40 percent chance of 2 inches of snow for the basins.

By Saturday, the above normal temperatures that we have been experiencing will be a thing of the past. Lower 500mb heights are forecast across Wyoming Saturday as the previously mentioned upper level low sits itself over southern Canada. By late Saturday, ensemble guidance is in consensus that an associated longwave trough will develop over the western CONUS with embedded passing shortwaves. There are also indications that upper level troughing and embedded shortwaves, will keep an almost constant fetch of moisture into the Northern Rockies. If this comes to fruition, a more active period of more widespread precipitation is favored late Saturday into early next week.

AVIATION /00Z TAFS THROUGH 00Z FRIDAY/

Issued at 434 PM MDT Wed Apr 22 2026

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

The broad upper-level trough has been slowly progressing eastward across the region this afternoon. Scattered brief IFR/MVFR rain and snow showers persist through at least mid-evening within an increasing unstable environment given colder air aloft. A period of more widespread precipitation is expected at KJAC late Wednesday evening through early morning Thursday. IFR/MVFR conditions anticipated at KJAC between about 04Z-16Z/Thursday as shortwave energy pushes across the area. After a brief respite, convective showers develop within the cold pool and push southeast on the backside of the trough Thursday afternoon. PROB30 has been included late in the period at all but KRKS to account for these showers. Westerly surface wind gusting 25- 35kts continues until 01Z-03Z/Thursday before slowing slightly for the overnight hours. All terminals to see 20-30kts westerly wind beginning late Thursday morning on the backside of the trough. Mountain tops obscured throughout.

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

Wind remains the main aviation concern through the period. West surface wind gusting 35-50kts persists until 02Z-03Z/Thursday, before slowly decreasing to 25-40kts overnight. Isolated weak convection is mainly limited to the Wind River and Bighorn Basins this evening and again Thursday afternoon. Impacts through 18Z/Thursday would be limited, so no TEMPO or PROB30 groups with any terminals. Surface wind to become more west- northwest on the backside of a departing late Thursday morning shortwave. This will favor the strongest gusts at KRIW during the late morning and afternoon. KCOD and KWRL to both see northwest to north wind by around midday Thursday as a surface cold front begins to make its way south. Weak near-surface upslope flow leads to a 30-50 percent chance of MVFR rain showers at KCOD late in the day. Similarly, the northwest flow aloft could provide a shot of brief showers late in the day at KRIW and KLND.

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

FIRE WEATHER

Issued at 323 AM MDT Wed Apr 22 2026

Warm, dry, and windy weather will cause critical fire weather conditions east of the Divide today ahead of an approaching cold front. East of the Divide and ahead of the cold front, relative humidity values are forecast to be in the 10 to 15 percent range with widespread southwesterly gusts of 35 to 55 mph. Occasional gusts of 60 mph or greater are possible, especially for wind prone locations. The cold front is forecast to trek across the area between 2PM and 6PM today, with relative humidity to be in the 15 to 25 percent range behind the front. Winds will remain gusty through sunset. Elevated fire weather conditions are expected across southern Wyoming today as well. Should a fire start, especially ahead of the cold front, erratic fire behavior and rapid fire spread is expected.

RIW WATCHES/WARNINGS/ADVISORIES

Winter Weather Advisory until 11 PM MDT Thursday for WYZ001- 002-012-024.