textproduct: Western and Central Wyoming

KEY MESSAGES

- Light rain showers producing outflow wind gusts 35 to 45 mph fade late Sunday evening, except over north-central Wyoming where the showers, with less wind, linger overnight.

- Intermittent light precipitation persists in the far west valleys overnight where rain changes to snow. Valley snowfall will generally be less than one inch (only a 20 percent chance of an inch).

- Elevated to critical fire weather conditions occur Monday afternoon in central Wyoming, mainly across Fire Zones 280 and 283.

- The pattern remains unsettled through the week, with mild afternoon temperatures and several chances for moisture. A late week system may drop southeast from Canada and provide a better chance of widespread precipitation while generating much colder temperatures (overnight lows 15-25 degrees).

UPDATE

Issued at 1233 PM MDT Sun Apr 12 2026

Current satellite imagery shows a growing CU field and a few showers beginning to develop across western Wyoming as a shortwave ejects off the upper low to our west. Diurnal heating will lead to MLCAPE values peaking in the 100-300 J/kg range over the next few hours. This will expand convective development from west to east across the area, with the most widespread coverage across western Wyoming given increased instability and a more favorably sheared environment. Like yesterday, the main concern will be strong outflow wind gusts given the still dry, well-mixed boundary layer (forecast DLCAPE values of 400-800 J/kg). This activity will wane with sunset.

Fire weather is the other concern today, and recent forecast trends have increased confidence for reaching critical conditions across much of Natrona County; a Red Flag Warning is now in effect there through sunset.

Colder air and the next wave ahead of the low will quickly push into western Wyoming this evening. This will lead to a quick shot of light snow across the west tonight, including a trace to a half inch across the western valleys by sunrise.

DISCUSSION

Issued at 130 AM MDT Sun Apr 12 2026

We are now well into April. And this means we are now climatologically the wettest time of the year, the months of April, May and June. This is usually when we receive our best rains and moisture laden snows, to build up the water for the drier summer and early fall months. These three months we receive on average anywhere from 30 to as much as 53 percent of our annual precipitation. And we definitely need it this year. Only Greybull is above normal with precipitation this year. The remainder of the area is anywhere from 25 to 80 percent of normal. Riverton, Lander, Buffalo and Casper have received less than half of the average amount of precipitation this year, with Riverton and Buffalo only at around a quarter of normal. The good news is, we will have a few chances of precipitation through the period.

As I write this around 1 am, the radar is largely quiet. Today will be another day of scattered showers and thunderstorms as another shortwave crosses the area. Precipitable waters, especially East of the Divide, are around 25 percent less than yesterday though. So, the vast majority of showers and storms would be West of the Divide today. As for stronger storms, there is a marginal risk across roughly the western third of the area. And given the inverted V soundings across the area, the main threat, like yesterday, would be strong wind gusts over 50 mph. There is another concern East of the Divide. The 700 millibar winds are stronger East of the Divide, approaching 40 knots in some locations this afternoon. Humidity will also be rather low, falling below 20 percent. However, ensemble forecasts give at most a 1 out 2 chance of relative humidity falling to 15 percent or under and only for an hour of so. So, critical fire weather looks unlikely. However, elevated fire weather looks likely across much of Sweetwater, Fremont, Natrona and Johnson Counties this afternoon. There will also be some snow in the higher elevations, with the heaviest in the Wind River Range. The chance of over 6 inches is rather small though, at most a 1 in 3 chance and this over the highest elevations where impacts are limited.

The chance of showers continues Monday as well, although somewhat less moisture should lead to a smaller coverage and largely West of the Divide as well. Convection should reach a nadir on Tuesday with only isolated showers across the area. The one fly in the ointment is an upper level low passing across Colorado that was showing a decent amount of QPF across southern Wyoming. Recent model trends have pushed the system further southward and POPs were lowered as a result, At this time, any showers from this would be confined to the far south with a greater than 1 in 3 chance of a tenth of an inch or rain confined to areas south of Interstate 80. Temperatures through Tuesday and even Wednesday will continue to average above normal.

Then heading into the end of the week, we have the chance of something we have needed for a while, a chance of a decent precipitation event across much of the area. This comes courtesy of an upper level low moving into British Columbia and then moving into the northern Rockies for Thursday and Friday. My gut feeling, given the fast bias of the models for Pacific systems, is that this would start more Wednesday night or Thursday, with Wednesday largely dry. This looks to be a slower moving system with a good amount of moisture that could, emphasis on COULD, bring a good rain and snow to much of the area. There are still fairly substantial differences with details in regards to the movement of the upper level low and any lee cyclogenesis, and this leads to differences in placement of the best upslope flow and placement of the heaviest precipitation. So, I will not even attempt to pinpoint details this far out. This will be a cooler system as well, with 700 millibar temperatures falling to minus 10 or lower, dropping snow levels to valley and basin floors Thursday night. Ensemble guidance gives at least a 2 out of 3 chance of at least and inch of snow across much of the area from Thursday through Friday night, with similar chances of at least a quarter of an inch of precipitation through the period. It is still several days out but things look somewhat promising right now, keep your fingers crossed.

And the final concern is for a freeze. Yes, it is only mid April no one should be planting gardens or crops yet; longtime residents know better. However, many trees have bloomed and many flowers are out. This could be a concern as early as Thursday night with the snow. The real time of concern may be Friday night, especially if the snow ends earlier and there is some clearing. Early ensemble guidance gives at least a 2 out of 3 chance of low temperatures below 25 degrees in the lower elevations by Saturday morning, with some areas having a 1 in 2 chance of lows below 20. A lot depends on how much snow falls and if there is any clearing, but a lot of early blooming plants will likely have a tough couple of nights toward the end of the week.

AVIATION /06Z TAFS THROUGH 06Z TUESDAY/

Issued at 955 PM MDT Sun Apr 12 2026

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

Moisture and embedded shortwaves continue to rotate northeast across the region overnight. The best chance for light snow and/or rain along with brief MVFR conditions at KJAC comes before 10Z/Monday, and before 12Z/Monday at KPNA and KBPI. VFR conditions then prevail at all terminals through at least mid- afternoon Monday when daytime heating leads to another round of scattered light rain showers until around 03Z/Tuesday. Surface wind 12-25kts becomes commonplace between 16-18Z/Monday and continues until around 01Z/Tuesday. Outflow wind gusts will be less than those seen over the weekend, with gusts 25-35kts. The exception will be KRKS where wind gusts 32-42kts are possible given temperature- dew point spreads. Mountain tops frequently obscured.

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

Light showers fade Sunday evening but a few showers linger until 12Z-15Z/Monday. Expect little more than a few outflow gusts around 30kts. Surface wind speeds begin to increase by 12Z/Monday at KCPR and KCOD and between 14Z-18Z/Monday at all but KWRL. Another shortwave within a broad trough across the northwest US nears northwest Wyoming Monday afternoon. This leads to another round of isolated light showers accompanied by outflow wind gusts 35-45kts between 21Z/Monday and 03Z/Tuesday. All terminals remain VFR with the primary aviation concern centering on the gusty convective outflow wind. Mountain tops occasionally obscured.

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 130 AM MDT Sun Apr 12 2026

A combination of above normal temperature, humidity falling to between 15 and 20 percent and a gusty west to southwesterly wind will bring elevation fire weather roughly along and east of a Rock Springs to Riverton to Casper line this afternoon. Elevated fire to possibly critical fire weather is possible again on Monday with lower dew points and continued gusty wind, but somewhat lower temperatures.

RIW WATCHES/WARNINGS/ADVISORIES

None.