textproduct: Western and Central Wyoming

KEY MESSAGES

- Not quite as hot today with isolated to scattered showers and thunderstorms (a 1 in 5 to 1 in 2 chance), with the most numerous storms in western Wyoming.

- A better chance of showers and thunderstorms for Thursday, along with temperatures continuing to lower somewhat.

- Remaining active into early next week. The most numerous storms will be in the west through Saturday, with the best chances moving eastward following that.

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, avenging 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 /12Z TAFS THROUGH 12Z THURSDAY/

Issued at 355 AM MDT Wed Jul 15 2026

Largely VFR conditions are expected through 12Z Thursday. There is a less than 15 percent chance of a shower in vicinity of KJAC until 14Z. Increasing moisture will bring the chance of showers and thunderstorms this afternoon and evening (roughly between 20Z and 04Z) at all TAF sites with the exception of KCPR where the chance of a shower or storm in less than 10 percent. The PROB30 groups were continued at all sites due to uncertainty in pinpointing the storms. The one site we had a thought of prevailing thunder was in vicinity of KCOD. However, with the chance around 40 percent, we decided to keep the PROB30 for now. All convection should end by midnight with VFR conditions after that. Wind should remain at 14 knots or less except in and around any shower or thunderstorm where wind gusts to 30 to 40 knots are possible.

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

RIW WATCHES/WARNINGS/ADVISORIES

None.