textproduct: Western and Central Wyoming

KEY MESSAGES

- Scattered light rain showers will spread from south central to central Wyoming this evening and into the overnight hours. Rain will have a hard time reaching the ground, but those in Sweetwater, Fremont, and Natrona Counties could see a few brief rain showers (30% chance).

- Temperatures will approach freezing for western valleys and basins around sunrise Monday, with frost likely (70% chance) and a freeze possible (40% chance). Typical cold spots and high elevation valleys like Bondurant have a higher chance of a freeze.

- On Monday morning, light accumulating snow is forecast across northwestern Wyoming for the high mountains above 10,000 ft.

- East of the Divide, windy conditions will develop Monday with a 50% chance of wind gusts in excess of 50 mph in central Wyoming.

- Tuesday morning is forecast to be chilly again, with frost possible in western Wyoming valleys and basins.

UPDATE

Issued at 1234 PM MDT Sun Jun 28 2026

Main considerations for this update were related to wind and cold products. Starting with wind, models are still borderline on the high wind potential Monday. 700mb winds continue to show 40 to 45 knots, just too low for greater confidence. Wind prone places like Outer Drive in Casper, South Pass, and the slopes of the Green Mountains/Rattlesnake Hills could easily see gusts around 60 mph, but widespread high winds do not seem likely at this time. Nevertheless, gusts around 50 mph will be common across the Wind Corridor of South Pass to Casper Monday morning and afternoon. An isolated gust to 60 mph is not out of the question.

For frost, temperatures in the upper-20s to mid-30s occur tonight and Monday night for western valleys and basins. Climatologically, end of June is where these locations typically see their last "spring" freeze. So, although this is not too out of the ordinary, a warm winter and spring has led to an earlier growing season for much of the area. Places of greatest impacts are for the Green River Basin, which should be a bit warmer this time of year, so places like Big Piney and Farson should be aware of frost the next couple nights.

DISCUSSION

Issued at 230 AM MDT Sun Jun 28 2026

Well, the day has finally arrived. On a day I am working, we are not in the outlook for severe weather across western and central Wyoming. In nine days I have worked, there has been at least a Marginal risk on seven of those days. And kudos to the SPC, they were right on yesterday. Thankfully, things are more tranquil right now, with just some areas of light to occasionally moderate rain. And, something else in the mountains, we will talk about that in the discussion.

All in all, today looks not as active. It will feel more like May across areas east of the Divide, and more like April west of the Divide. The bowling ball of an upper level low is now moving from Oregon and into Idaho. Most guidance shows much drier air spreading across much of the area, and as a result any shower activity will be limited. The main area of showers will be across far northwestern Wyoming, with another across southwestern areas. Amounts today should remain on the light side though, generally a tenth of an inch or less. There is also a less than 1 in 5 chance that a shower or storm could develop in eastern Natrona and Johnson Counties as just enough moisture may return. Elsewhere, the chance is less than 1 out of 10. Instability is rather limited, with at most 200 J/kg of CAPE, so any lightning would be limited. The main concern today looks to be fire weather. With the 100 knot jet still over the area, many areas have a greater than 1 out of 2 chance of wind gusts over 25 mph. However, humidity is rather borderline, largely remaining above 15 percent. Cooler temperatures today will help with this as well. So, no Red Flag Warnings today, although Elevated Fire Weather will be likely.

Concerns ramp up tomorrow, and there will be a contrast west and east of the Divide. The upper level low will lift northward into Montana, and drag a trough which will become negatively tilted as it moves across the Cowboy State. This will be the main factor with the weather. In areas east of the Divide, the concern will be wind. I did give thought to a High Wind Watch for the Green Mountains and Natrona County. There will be a decent setup, with a trough mixing across the state. This area will be in the left front quadrant of the jet to enhance downward momentum as well. The 700 millibar winds are still borderline though, generally only peaking out at around 45 knots when I would like the see several 50 knot barbs. The NBM ensemble also only gives at most a 1 in 3 chance of gusts over 55 mph except in the mountains and in areas where criteria is higher. So, we will hold off on any High Wind Watches for now. The strongest wind would not be until Monday afternoon, so we will let the day crew take another look at it. Nevertheless, it will be a windy day across much of the area. As for fire weather, there will be many areas of elevated fire weather. With temperatures still on the cool side, humidity should stay above critical levels. Wind should decrease during the evening as the trough moves away to the east. With the strong downsloping flow, very few places would see a shower or thunderstorm on this day east of the Divide.

The concern in the west shifts to a wintery one, as heavier precipitation develops as flow turns westerly behind the trough passage and still somewhat moist upslope kicks in. New guidance has also trended a bit cooler Sunday night and Monday, with 700 millibar temperatures falling as low as minus 3C when best orographics move in behind the trough. This could drop snow levels down to 7000 feet at times, and I would not rule out even see some wet snowflakes in the Jackson Valley Monday morning. Most locations above 8000 feet have at least a 1 in 2 chance of at least an inch of snow, with a greater than 1 in 2 chance of over 3 inches above 9000 feet in the Tetons and Yellowstone Park. The highest locations of these locations (above 11000 feet) even have a 1 in 2 chance of 6 inches or more. As for travel problems, they shouldn't be too bad as most of the snow should fall during the day and being only a week past the solstice, the snow would have trouble sticking on most roads. However, we are at the peak of tourist season. Anyone visiting from out of state should be aware it can snow during any month of the year in Yellowstone and the Tetons, so be prepared for wet and cold weather if you are venturing there on Sunday or Monday.

I was watching the 70s detective series Columbo yesterday, and as he would say there is "Just One More Thing." And that concerns the potential for frost. Recent model trends have shown more clearing today and tonight, especially in the southern zones. With the chilly air mass still in place, this will be the night to watch. The NBM ensemble gives a greater than 1 in 2 chance of temperatures below 32 degrees in much of the Green River Basin as well as southern Lincoln County and even in the Star and Jackson Valleys. Sky cover will be the X factor though. We may need some highlights for tonight or Monday night.

For Tuesday through much of next week, the reasoning remains the same as yesterday. Wyoming will be stuck between a trough over the western United States and strong ridge to the east, which should bring record heat to the eastern half of the country. That means we will be along the path of shortwaves that will bring chances of convection each day. We are still in low confidence in exact timing of the waves and placement of the heaviest precipitation though. With flow turning more southwesterly, temperatures will recover to near to somewhat above normal but no extreme heat is expected. It will also remain rather breezy and with low dewpoints expected, fire weather may also be a concern for much of next week.

AVIATION /00Z TAFS THROUGH 00Z TUESDAY/

Issued at 421 PM MDT Sun Jun 28 2026

VFR conditions are expected to prevail across nearly all terminals through the TAF period. Wind gusts of 25 to 35 knots will continue at the start of the TAF period, decreasing after sunset with a breeze of 10 to 15 knots through the overnight hours into Monday morning. Most terminals will remain dry, with a few terminals such as KRKS possibly seeing a brief light rain shower between 02Z and 08Z Monday. Other terminals such as KJAC, KPNA, KCOD, and KWRL see precipitation chances develop later Monday morning into the early afternoon. Winds increase across all terminals between 14Z and 16Z Monday with speeds of 15 to 25 knots and gusts of 25 to 35 knots. However, terminals such as KCOD and KCPR may see stronger winds with gusts of 40 to 45 knots. These gusty winds are expected to prevail through the end of the TAF period. Mountain obscuration is expected to persist across the western mountains. Expect turbulent winds over the mountains. LLWS is not expected at any terminal, however areas north of KCOD could be impacted.

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

FIRE WEATHER

Issued at 230 AM MDT Sun Jun 28 2026

A combination of a gusty wind and low humidity will bring elevated fire weather to many locations east of the Continental Divide this afternoon. Relative humidity may fall into the teens at times, but remain above critical levels. On Monday, wind gusts to around 50 mph are possible in Fremont and Natrona Counties with a gusty wind in most locations along with humidity dropping to around 20 percent in many locations east of the Continental Divide.

RIW WATCHES/WARNINGS/ADVISORIES

None.