textproduct: Western and Central Wyoming

KEY MESSAGES

- Scattered showers and thunderstorms are forecast this afternoon and evening across western and northern Wyoming. Localized heavy rainfall and gusty winds are possible in any thunderstorms.

- More shower and thunderstorm chances Thursday through Saturday for western and northern Wyoming. This potential becomes more widespread across the state Sunday through the middle of next week.

- Hot temperatures are expected through Sunday with highs in the upper 80s to upper 90s.

UPDATE

Issued at 1200 PM MDT Wed Jul 15 2026

The forecast for today is on track with showers and thunderstorms over western and northern Wyoming as a shortwave traverses overhead. As of 18Z/12PM, the shortwave is located over eastern Idaho and will continue northeastwards within the southwesterly flow aloft. Across the western valleys, morning cloud cover is expected to limit the overall coverage of thunderstorms early this afternoon. Shower and thunderstorm coverage should be greatest from the Gros Ventres and Wind River Mountains to the Absarokas and Yellowstone due to favorable orographics and sufficient daytime heating. Thunderstorms then move into the Bighorn Basin and upper Wind River Basin after 3PM. A few thunderstorms could become severe across the northern Bighorn Basin due to proximity to the shortwave and over 1,000 J/kg of BLCAPE. With DCAPE values around 1,200 J/kg, gusty winds up to 60 mph will be the primary severe threat. There is an additional threat for localized heavy rainfall, but as mentioned in the morning discussion, the flash flooding threat is on the lower end due to the storms moving. Thunderstorms will begin to diminish in coverage after sunset, with only lingering showers and thunderstorms through 1AM along the shortwave axis from the northern Bighorn Mountains to southern Lincoln County. Otherwise, the forecasted shower and thunderstorm chances continue Thursday through the middle of next week.

DISCUSSION

Issued at 133 AM MDT Wed Jul 15 2026

I am coming off of a short break. When I left Sunday morning, I was talking about all time record high temperatures. And we had several across the area. What a difference 72 hours makes. Now, we are talking about a much more moist atmosphere and the potential for heavy rain and possible flash flooding over the next several days. The reason is that the monsoon is now here.

We had a few showers out there yesterday and a couple of light ones this right now, but for the most part most of the action is in Montana right now. Most of the models, both the synoptic and convective ones, have the area of main action across the northwestern half of the area, largely west and north of a Buffalo to Riverton to Evanston line. And, all models show the most numerous storms over the northwestern Bighorn Basin and the Absarokas, where the combination of a passing shortwave and some low level easterly upslope flow will bring more numerous storms. The big difference today is the amount of moisture in the atmosphere. Climatologically, precipitable water values are the highest around this time, averaging around 0.60 inches in Riverton. Today, some of these will exceed this by 150 to 175 percent, especially in the aforementioned Bighorn Basin where values may climb as high as 1.30 inches, close to 200 percent of normal. Instability parameters are also decent here, with lifted indices of minus 4 and CAPE over 1000 J/Kg, so we could see a stronger storm as well. The main threat will still be heavy rain though. If there is one thing against flash flooding, it is that there some decent flow at 500 millibars so the storms will be moving somewhat. This looks like a diurnal event, with the vast majority over by sunset and almost all done by midnight. And, it will be another hot day. Probably not record breaking, but some of the hotter locations could approach 100 degrees again this afternoon.

At this time, Thursday looks fairly similar to today, with mainly diurnal showers and thunderstorms and in roughly the same locations. The deeper moisture may press a little further to the east, but areas like Casper and Rock Springs continue to look mainly dry. Precipitable water values also look fairly similar, generally 150 to 175 percent of normal across the northwestern half of the area, along with easterly upslope, and the maximum chance of convection in the easterly flow upslope locations. I think the chance of local flooding may be greater on this day though, since flow in the 700 to 500 millibar layer looks lighter, so storms would be slower moving. Also, temperatures should continue to slow downward trend, although it will still be above normal with widespread 80s and 90s for highs.

The latest guidance now shows ridging building back over Wyoming Friday and Saturday, with heights 500 millibar heights rising anywhere from 20 to 40 meters. Precipitable water values also drop about 10 to 20 percent, but this still averages around 150 percent above normals. The result will be somewhat less coverage of storms and the main areas of storms being pushed a bit further to the west, although all locations have at least some chance. The emphasis will again be on easterly upslope locations (noticing a pattern here). The mean 700 to 500 millibar flow is also stronger, so the threat of flooding may decrease a bit with better steering flow and a slightly, emphasis on slightly, less moist atmosphere on these days. Temperatures will also increase somewhat on these days, with some 100s again possible in the eastern Bighorn Basin.

The main chance of storms may finally begin to shift East of the Divide on Sunday as the main area of moisture moves eastward as the core of the ridge moves southeastward and moisture can be pushed further east. There is still a bit of a spread on exact timing of this happening and it is impossible to pinpoint a more active day this far out. However, the eastern portions of our area may finally begin to get some needed moisture next week. As for temperatures, they look to remain above normal but more cloud cover and the core of the ridge moving away should keep record high temperatures away for now.

AVIATION /18Z TAFS THROUGH 18Z THURSDAY/

Issued at 1045 AM MDT Wed Jul 15 2026

Midlevel cloudiness beginning to move into western WY currently, with a few showers right along the WY/ID border moving east. This initial line will only bring a few showers into the vicinity of KJAC through 21Z, with isolated thunder possible. As this are moves east, more numerous showers and thunderstorms will build for all remaining sites except KCPR. As thunderstorms will be smaller in nature, confidence in impacting specific airports is decreased, but PROB30 notation should still cover modest chances well. Highest thunderstorm chances look to be in the KCOD/KWRL areas after 21Z, so have put a more predominant forecast in, with TEMPO groups for lower cigs and gusty winds. Latest wind profile notes that some thunderstorm gusts could reach 50kts this afternoon. Once daytime heating fades, precipitation will decrease quickly, with mostly clear skies overnight, with only winds from remnant outflows possible. Another round of peak heating thunderstorms expected again on Thursday.

RIW WATCHES/WARNINGS/ADVISORIES

None.