textproduct: Western and Central Wyoming

KEY MESSAGES

- Scattered showers and thunderstorms will move from southwest to northeast across the area today, most widespread west of the Continental Divide. Strong outflow wind gusts of 40 to 60 mph will be possible with this activity through sunset.

- Elevated to critical fire weather conditions are expected for much of central Wyoming through the afternoon. This threat returns again for Monday.

- Light snow is expected across western Wyoming this evening and tonight. Light accumulation is possible for the valleys as snow levels drop (only 20% chance of an inch).

- The unsettled pattern will persist through the week, with mild afternoon temperatures and several chances for moisture. A late week system may bring a more widespread precipitation event and return cold temperatures (15-25 degrees) to lower elevations.

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 /00Z TAFS THROUGH 00Z TUESDAY/

Issued at 504 PM MDT Sun Apr 12 2026

VFR flight conditions are largely expected throughout the TAF period. Isolated showers and thunderstorms in the area of KJAC and KCOD are expected to linger through roughly 01Z/02Z. All other terminals have less than a 15 percent chance of a shower or thunderstorm through 02Z. Gusty 40kt winds are possible at any terminal in or with nearby showers or thunderstorms. Overnight at KJAC, KPNA, and KBPI, there is a 30 percent chance of light snow with the potential (20 percent chance) for MVFR ceilings. Expect mountain obscurations with any light snow. Late in the TAF period, there are light rain shower chances at KRKS (30 percent) and KJAC (15 percent). However, opted to only mention in KRKS TAF at this time given slightly higher confidence.

Gusty winds are expected to diminish by 02Z, at the latest, at all terminals. Winds are forecast to be light through sunrise on Monday. Winds increase again around sunrise/11Z on Monday at KCOD and KCPR. All other terminals become gusty between 16Z and 19Z on Monday. Afternoon wind gusts on Monday are forecast to be between 20kts and 30kts, except at KCPR. KCPR could see gusts between 35kts and 40kts on Monday afternoon.

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 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

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