textproduct: Western and Central Wyoming

KEY MESSAGES

- One more hot day with highs around 100 in the warmer spots. A few showers and thunderstorms will be around, mainly in and near the mountains and in southern Wyoming.

- Deeper monsoonal moisture returns Tuesday and brings a better chance of showers and thunderstorms, especially in western Wyoming.

- Coverage of showers and thunderstorms peaks on Wednesday and Thursday, with very heavy rain possible from any storm, along with potential for flooding.

UPDATE

Issued at 1242 PM MDT Mon Jul 20 2026

The forecast and key messages remain largely unchanged. Today, isolated showers and storms will be possible around the mountains and across southern Wyoming (generally around and south of I-80). A boundary also pushes south through the area during the day, bringing a gusty north to northeast wind shift to locations east of the Continental Divide. One addition to the forecast was for the introduction of smoke the next couple days, as smoke from Oregon/Washington sinks southward into the state with this boundary moving through. Attention then remains focused on the monsoon moisture for Wednesday as models continue to support high-end moisture values across the area.

DISCUSSION

Issued at 139 AM MDT Mon Jul 20 2026

It was finally fairly quiet on a night shift, with only very isolated showers over Johnson County and the Wind River as I write this. These should be gone over the next couple of hours. And for the most part, the morning should be dry.

We have two issues to deal with this afternoon. The first is the one we have been talking about ad nauseam for the past five days, the monsoonal moisture and the potential for convection. For the most part, the deepest moisture will remain south of the area over the next 24 hours. This, plus some warmer air at the mid levels should help cap the atmosphere somewhat. This should keep shower and thunderstorm coverage fairly sparse. Precipitable water values remain rather high though, generally about 150 percent of normal, approaching 180 percent in Sweetwater County. This is where the best chance of convection will be, but even here it is only around a 1 in 4 chance for the most part. As for heavy rain and potential flooding, the Excessive Rainfall Outlook is still out of the area. I could see a few heavier storms and the chance of flooding is not zero. However, since the storms would be isolated and this area has seen little rain since the monsoon started, the chance is low. The moisture deepens later at night, but with the instability limited this would likely only be showers.

The second issue is the heat. There are a few locations that have had the warmest string of high temperatures in station history over the 9 days (since last weekends heat wave began). And, we will have one more hot day today. High temperatures look similar to yesterday, with the warmer spots in the Bighorn Basin, like Worland and Greybull, having a 1 in 2 chance of highs of 100 or higher. Elsewhere, like yesterday, highs in the 90s will be almost certain in locations below 6200 feet, with 80s in the rest of the populated areas.

The monsoon really makes itself felt starting on Tuesday. Precipitable water levels return to levels similar to much of late last week, generally about 175 to 200 percent of normal. The one thing that is missing is some kind of a forcing mechanism, like a jet streak or a shortwave. So, these storms look like more of the random pop up variety. There will be a better chance of flooding with the higher precipitable water content and expected slow movement. If there is one good thing, it that much of the area has been largely dry the past 48 hours or so, so the soil won't be as saturated. Nevertheless, the marginal risk of Excessive Rainfall looks justified at this time. The most numerous storms will be in western Wyoming on this day, with less coverage north and east. And with more cloud cover, temperatures will finally cool off somewhat, an average of about 5 degrees when compared to Monday. Showers and storms should decrease after sunset, although some will linger through the night.

The main event still looks to be on Wednesday. The deepest moisture moves over the area during the afternoon and evening. The models continue to show a possible record breaking precipitable water value, over 1.50 inches, breaking the old record of 1.42 inches. In addition, a shortwave will be passing through the area, bringing additional lift and an increased coverage of thunderstorms. If there is one thing working against flooding, it is that with the shortwave, there should be more steering flow and this may mean more movement with the thunderstorms. However, the threat of flooding is there. The Excessive Rainfall Outlook continues to show a slight risk across much of the area, which has basically not moved since yesterday. And, with the shortwave, showers and storms may continue well into the evening and even the overnight hours. We will likely need a flood watch, possibly as early as Tuesday afternoon but we will let future shifts make this decision.

Thursday also looks like a rather active day as high precipitable waters remain, although about 10 to 20 percent less than Wednesday. Nevertheless, this is still 200 percent of average for many locations. So, expect another of fairly widespread showers and thunderstorms across the area. Following that, somewhat drier air will begin to push into the area from the north and west, bringing an end to the widespread showers and thunderstorms. There will be some around each day into next weekend, but more scattered and more limited to the favored locations like the mountains. However, above normal precipitable waters will linger into the weekend, although more on the 125 to 150 percent of normal. And with less cloud cover, temperatures should return to above normal levels Friday and continue into next weekend, with some triple digit highs possible once again in the warmer spots.

AVIATION /18Z TAFS THROUGH 18Z TUESDAY/

Issued at 1125 AM MDT Mon Jul 20 2026

Upper-level high pressure centered over NW CO continues to dominate the weather pattern over western and central WY today into Tuesday. Moisture will be limited today with fewer showers and thunderstorms expected. Southern WY will have the best chances for showers and thunderstorms late this afternoon into the evening hours, though mid level clouds will increase from mid-afternoon into the evening. Thus, VFR conditions are generally expected at all TAF sites, though KRKS could see MVFR conditions with thunderstorms from 20/23-21/04Z. KLND has an outside chance of a thunderstorm or two, but the probability is less than 10%, so have not mentioned it in the TAF. Winds are relatively light today, through showers and thunderstorms could produce gusts 25-40 kts. In addition, a boundary will be moving from MT into northern and central WY this afternoon and evening, bringing gusty NNE winds to sites east of the divide starting at 20Z at KCOD, pushing into KLND/KRIW/KCPR between 00-01Z. The gusty NE winds will push into KRKS around 04Z and influence wind dir at KBPI/KPNA as well.

Mid-level clouds are expected to remain overnight and a few isolated mountain showers are possible. Moisture increases Tuesday, with showers and thunderstorms initiating between 18-20Z across western and southwest WY. Scattered showers and thunderstorms will increase Tuesday afternoon and evening, impacting all TAF sites except KWRL and KCOD. Gusty winds of 30-40 kts and brief heavy rain could bring MVFR conditions.

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.