textproduct: Western and Central Wyoming

KEY MESSAGES

- Increasing monsoonal moisture brings an increase in coverage of showers and thunderstorms today, especially in western Wyoming. Locally heavy rain and local flooding is possible with any shower or storm.

- The most active day looks to be Wednesday, with a possibly record moist atmosphere along the best chance of showers and thunderstorms, as well as the highest chance of flooding.

- A good chance of thunderstorms lingers into Thursday, although likely fewer than on Wednesday. Things finally dry out somewhat Friday with a return of above normal temperatures.

DISCUSSION

Issued at 158 AM MDT Tue Jul 21 2026

After a lull for the past couple of days, the monsoon is coming back with a vengeance. Showers and embedded thunder have broken out across much of western Wyoming as I write this shortly after midnight. Most of these should continue until around 3 am before tapering to just a few stragglers for the rest of the overnight like last night.

Things ramp up considerably today, as much deeper monsoonal moisture moves over the area. Precipitable waters, which right now are running around 150 percent of normal, are now expected to climb as high as 1.3 inches at out office and as high as 1.5 inches in other locations. This is more than 200 percent of normal for many areas. The Weather Prediction Center has also increased the slight risk of excessive rainfall over southwestern Wyoming, with a marginal risk across all but the northeastern portion of our forecast area. As a result, with some rainfall rates that could be over 2 inches an hour, we will hoist a flash flood watch starting at noon today for all areas across our county warning area. The best chance today would be West of the Divide, but the models, both the synoptic and high resolution, have been doing a terrible job in showing the placement of the convection. Case and point, showers popped up in Washakie and Johnson County and no models had it there. It does look like the progression will start in western Wyoming and spread east through the day. And like the past few nights, most convection should end by midnight, but some showers and a few storms should linger through into Wednesday morning. As for temperatures, with more cloud cover, temperatures will still be cooler than yesterday. Still quite warm, but generally 3 to 8 degrees cooler than Monday.

The main event still looks to be on Wednesday. Precipitable water values will reach a zenith on this day, topping out at around 1.5 inches at our office (around 250 percent of normal). If this comes to fruition, this would be a new record high for the office (the old record is 1.42 inches). The main difference will be a shortwave that will tracking across the area during peak heating of the day, adding some additional lift. With the combination of the possibly record moist atmosphere and the passing shortwave, this looks to be most likely day with flooding problems. The Weather Prediction Center also agrees and has expanded the slight risk of excessive rainfall to cover most of the County Warning Area. As a result, we will continue the flood watch through this day as well. Another difference here is that a lot of the convection will linger through the evening and possibly even into the night time hours, much for than the previous couple of nights. And with this, the flood watch was run though Wednesday night.

We should begin a downward trend starting on Thursday. Most guidance shows the main plume starting to moving to the east and south with precipitable water values dropping, especially West of the Divide. All in all, values look to drop between 20 and 30 percent. However, this is still close to 200 percent of normal, especially across areas East of the Divide. However, coverage should be less with somewhat less moisture and the lack of a trigger like Wednesday's shortwave. There is still the risk of flooding on this day given the remaining moisture and possible saturated ground from the previous days convection, although it should be somewhat less than Tuesday and especially Wednesday. We will let future shifts make the decision whether or not to extend it through Thursday.

Friday is when it finally looks like the main area of moisture will retreat out of the area and chances of convection finally go back to normal, giving the people of Wyoming and meteorologists a break (including me, I HATE the monsoon!). There could be another secondary surge over the weekend, but it should not be anything like it has been during the middle of this week. In addition, the ridge will still be present over the area through the period. So, after a few days of cooler weather with more cloud cover. Well above normal temperatures look likely to return with triple digit high temperatures possible in eastern Big Horn Basin possibly on both Saturday and Sunday.

AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/

Issued at 439 AM MDT Tue Jul 21 2026

Monsoonal moisture will continue to move over the area over the next few days. There will be a few showers around in the morning, but most will hold off until the afternoon. The earliest main impacts are expected to start around 21Z. With a lot of moisture around, any shower or thunderstorm will be able to produce heavy rain, with MVFR to IFR conditions possible around any shower or thunderstorm. We have elected to continue the PROB30 groups since the exact placement and timing of any showers or storms remains uncertain. Most storms should end by midnight tonight, but a couple of showers and storms will likely linger until 12Z Wednesday. Wind across the area will be largely light except in and around any shower or thunderstorm.

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

Flood Watch from noon MDT today through late Wednesday night for WYZ001>020-022>030.