textproduct: Western and Central Wyoming

KEY MESSAGES

- Scattered showers and thunderstorms today. Best chances will be over western Wyoming (30 to 60 percent chances) and over Johnson/Natrona Counties (15 to 40 percent chances). Gusty winds 40 to 50 mph may occur with any storm, though an isolated stronger gust is possible.

- Warm temperatures through Friday. Shower and thunderstorm chances occur each day, but are limited and mainly across northern and central Wyoming.

- Increasing rain chances into the weekend, with slightly cooler temperatures.

UPDATE

Issued at 1236 PM MDT Tue May 26 2026

The forecast remains on track today. Increasing moisture brings rain showers and thunderstorms to the area. A combination of where the best moisture occurs and cloud cover limiting possible convection, keeps the best chances across far western Wyoming and for Johnson and Natrona Counties. While most of this activity ends between sunset and about midnight, some lingering showers are possible around Johnson and Natrona Counties through the night. Gusty outflow winds are the main hazard with this convection, which could be 40 to 60 mph. Some small hail is also possible, mainly for western Wyoming.

DISCUSSION

Issued at 111 AM MDT Tue May 26 2026

Back when I was a little kid and dinosaurs roamed the earth (it was the 1970s) I had a favorite toy, like many little girls and boys did. And may favorite toy when I was 3 and 4 years old relates to the one of the main driving factors with the weather the next several days. The weather feature I am speaking of is an upper level low that is moving onshore in the Pacific northwest. And that toy I am speaking of is the Sit And Spin. Models have finally started to come into better agreement that the upper level low will, move close to the Great Basin and, sit and spin for a few days.

And the main impact from this, in conjunction with a strong, blocking ridge over the Plains States, will keep southerly flow over the area for the next several days. This will keep temperatures above normal for several days, generally between 5 to 15 degrees above normal. It will also keep rotating a few shortwaves over the area, keeping varying chances and placements of largely diurnal showers and thunderstorms.

And today may be one of the more active days across the area. Radar shows an area of rain and embedded thunder across Utah and northern Colorado slowly moving northward as the shortwave moves north. This will bring the chance of showers and storms today. Model guidance is zeroing in on two locations. One is western Wyoming, Where upper level forcing will be greater with a weak jet streak moving through, this is where the most numerous showers and storms will be. One question is will there be any stronger storms? The Storm Prediction Center has a Marginal Risk of severe thunderstorms across northern Yellowstone. Soundings are showing a decent amount of shear as well. The limiting factor may be cloud cover, especially further south where surface instability could be limited. The highest values (CAPE up to 700 J/Kg and lifted indices of minus 2) are across northwestern Wyoming. So, if any stronger storms develop it would likely be here. Chances here range from a 1 in 3 chance to a 4 in 5 chance with the highest chance in the northern mountains. The main threat would be strong wind gusts given the very steep lapse rates, but some small hail may also be possible. The other areas of concern is East of the Big Horn Range in Johnson and Natrona Counties. Low level south-southeast flow will likely bring some upslope flow to initiate showers and storms. And in this area, the highest instability parameters are further north, although shear is less. Chances here range from 1 in 4 to 1 out of 2, with the highest POPs close to the Bighorn Range. With some cloud cover to start, this could be a later show as well, with storms extending into the evening. Elsewhere, we can't rule out a shower or storm, but with less instability and more cloud cover, the chance is only 1 out of 5 or less. The shortwave will also bring a gusty breeze in some locations, although high wind is not expected.

Less activity is now expected for Wednesday and Thursday, Most guidance is showing much drier air moving in from the south, with precipitable water values falling below climatological normals for much of the southern half of the state. On Wednesday, most convection would occur either in or near the northern mountains where some weak upslope and high level heat source convection is possible. A few showers and storms (about a 1 out of 3 coverage) are also possible across Johnson and Natrona County, with the western boundary close to the 0.5 inch precipitable water line. Thursday looks even drier as the atmosphere dries out even more. And storms on these days would be in the same locations, but only around a 1 out of 5 chance.

It continues to look like Friday or Saturday when we get the plunger out to break up the blockage as another trough finally kicks the low to the east and it opens up into a wave. There are still differing solutions on how far east it can get. A closer pass would obviously bring a better chance of showers and storms, but there is still a fair amount of uncertainty right now. Stay tuned.

AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/

Issued at 1138 AM MDT Tue May 26 2026

A leading shortwave within southerly flow aloft is along the western Wyoming border and moving to the north-northwest late Tuesday morning. Southerly wind 15-30kts has surfaced at a few terminals during the late morning, and other terminals will see this wind mix to the surface by 20Z/Tuesday. Speeds generally decrease to 7-12kts between 02Z-05Z/Wednesday. Breaking the forecast area into thirds from west-to-east, drier air is working northward across the central third, a trend that continues into the evening. Showers will be harder to come by within this sector. Those that do form would be more likely to produce gusty outflow wind 30- 40kts. The western-third has moisture and wrap-around dynamics to generate scattered showers and thunderstorms from 19Z-03Z. KJAC and KBPI have the better chance of seeing a brief shower and outflow wind around 30kts. The eastern-third, including KCPR, can expect an uptick in convective coverage after 21Z/Tuesday owing to increased solar heating and a passing jet streak. Outflow wind gusts to 35kts and a possible brief MVFR period (less than 30 minutes) would be the primary hazards. Convection wanes between 02Z-04Z/Wednesday, leaving drier conditions and departing cloud cover overnight.

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

RIW WATCHES/WARNINGS/ADVISORIES

None.