textproduct: Western and Central Wyoming

KEY MESSAGES

- A bit cooler today with an increased coverage of showers and thunderstorms. Some thunderstorms could contain heavy rain.

- Chances of showers and storms drop through the rest of the week into the weekend, with a near zero chance Saturday into early next week.

- Very hot temperatures return for the weekend, with some all time monthly record high temperatures possible on Sunday, especially in central and southern Wyoming.

- A gusty wind and low humidity may bring critical fire weather from Sunday into early next week.

DISCUSSION

Issued at 129 AM MDT Wed Jul 29 2026

Sometimes when forecasting the weather, you feel like you are trapped in a time warp, with the same concerns day after day. For much of may last string of shifts, the concern was the monsoon and hot temperatures. And as I arrive back on shift tonight, the concern once again is the monsoon and hot temperatures. However, one will be of somewhat less concern than last week.

And that one thing will be the monsoon. We will have another surge of monsoonal moisture moving northward across the area today with a shortwave crossing the area. Radar shows some showers moving toward the southern border, and these will move northward through the day. Precipitable water values are rather high today, over an inch in some locations. This would put portions of the area over 150 percent of normal (average this time of year is around 0.60 inches). However, it is less than the 200 to 250 percent of last week. Steering flow is not the strongest though. A few parts of the area are under a marginal risk of excessive rainfall, mainly far southern and eastern portions of the area. So there is some risk of local flooding, but the risk looks low. Most convection should end after sunset, although a few showers may linger after midnight. As for temperatures, with more cloud cover spreading over the area, temperatures should be cooler than yesterday. We did lower temperatures a few degrees, with many locations staying in the 80s for highs today, mainly in the southern half of the County Warning Area.

Then, starting on Thursday, we will begin to move into what is known as an inverse relationship, where one thing goes up and another goes down. And in this case, temperatures will be the thing on the way up, and the chance of convection as well as humidity will be on the way down. On Thursday, precipitable water values drop around 20 to 30 percent across the area. They will still be somewhat above normal but only about 120 percent of normal versus over 150 percent. There will still be some convection around but less then Wednesday, with most concentrated in and near the mountains. But even here, the chance is generally 1 out of 3 or less. Temperatures will also begin to rise again, to generally about 5 degrees above normal which would put highs in the 90s across most locations below 5500 feet once again. Precipitable water values continue to drop on Friday as the core of the moisture continues to get pushed to the east. Any storms on this day would likely be restricted to the eastern portions of the County Warning Area. Temperatures should run similar to Thursday, very warm but not unusual for the latter part of July.

The main concern then shifts to heat, possibly record breaking heat, for the first weekend of August. Another heat dome will continue to build northward, bringing 500 millibar heights as high as 5980 meters and 700 millibar temperatures as high as 23 degrees celsius. This will lead to another very hot weekend. Saturday looks hot, with at least a 1 in 2 chance of high temperatures of 100 or greater across elevations under 5500 feet. However, the warmest day looks to Sunday, when a tightening pressure gradient ahead of an advancing cold front will bring a gusty, southwesterly downsloping breeze. At this time, there is at least a 9 in 10 chance of high temperatures over 100 in locations under 5500 feet, with around an 1 in 2 chance of temperatures 105 or warmer below 4800 feet. Some locations have already set new monthly record highs 3 times this year (March, May and July); and this could occur again for August. For example, it has never been 100 degrees at the Riverton airport in August, and it is highly likely this will occur on Sunday afternoon. And, this will raise another concern, possible critical fire weather. Humidity will be very low on this day, with most areas East of the Divide seeing humidity in the single digits. With the gusty wind, we may need some fire weather highlights for Sunday afternoon as the front approaches. In addition, this looks like a dry frontal passage with any convection likely remaining over Montana.

We may finally have some relief from the heat on Monday after the frontal passage, especially East of the Divide. The 700 millibar temperatures fall as much as 6 to 7 degrees celsius, which could drop temperatures back into the 80s for most locations. The front may be slow to move West of the Divide so there could be one more very warm day there before cooler air moves in for Tuesday. The concern for fire weather may continue here is as well, with humidity remaining low and a gusty breeze continuing. Ridging may then begin building northward again, bringing more above normals temperatures for the latter half of next week.

AVIATION /12Z TAFS THROUGH 12Z THURSDAY/

Issued at 408 AM MDT Wed Jul 29 2026

Largely VFR conditions are expected through 12Z Thursday. Clouds will increase from southwest to northeast as monsoonal moisture moves in from the southwest. A few showers will be possible around sunrise in vicinity of KJAC but should hold off until around 15Z in most of the remaining terminals West of the Divide (KRKS, KPNA and KBPI) and largely after 20Z East of the Divide. All TAF locations continue to have PROB30 groups and not prevailing due to the difficulty in timing individual showers and storms. Most should end by sunset, although a few may linger until after 06Z tonight, especially in vicinity of KJAC and KCOD. Wind should remain 14 knots or less except in and around any shower or thunderstorm where wind gusts to 35 knots are possible. Brief MVFR conditions are possible around any shower or storm, mainly for visibility. Occasional mountain obscurations are possible around any convection.

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

RIW WATCHES/WARNINGS/ADVISORIES

None.