textproduct: Western and Central Wyoming

KEY MESSAGES

- Hot today and Friday with Friday being the warmest day with some locations seeing highs in the upper 90s. There will be isolated afternoon showers and thunderstorm in western Wyoming, but the chance of an spot seeing one is less than 1 out of 4.

- Deeper monsoonal moisture returns to the area on Saturday with an increased chance of showers and thunderstorms, with heavy rain possible with any storm.

- The daily chance of mainly afternoon showers and thunderstorms continues Sunday into early next week.

DISCUSSION

Issued at 110 AM MDT Thu Aug 20 2026

Yesterday was one of those late summer days that make me happy to live in Wyoming. Warm temperatures, low humidity, no precipitation and lots of sunshine. However, that will be the last one of these days we will see for a while. Portions of the area may see one from time to time, but not all at once.

All is quiet right now across Wyoming and the humble Riverton weather abode. However, things will begin to turn more active again starting today. However, it will be a gradually ramp up rather than flipping a switch. And, we will start the day off dry today. However, monsoonal moisture, which was suppressed to the south yesterday, will begin to come back into the area today. However, as is the usual trend, it will start at the mid levels and mainly in western Wyoming. The result will be a scattering of late day and evening showers and storms across this region. However, most locations will not see one. The chance at any one spot is no more than 1 out of 4, with the highest chance in places like southern Lincoln and western Sweetwater County having the highest chance. Mainly dry conditions should continue East of the Divide. I can't completely rule out a stray shower to cross the mountains, but the chance is small, less than 1 in 10. And, these storms would likely produce more wind than rain. Many locations will have a greater than 50 degree dew point depression with the dry lower levels of the atmosphere. This, plus the tell tale inverted V soundings, show a good possibility of strong wind gusts with any shower or storm. This does have a good chance to be one those "little green blob" days. Most activity should be diurnal and end shortly after sunset. And, with the ridge expanding northward and 700 millibar temperatures rising, it will be hot day across much of the area. Most locations below around 5500 feet will see highs over 90.

Friday at this point looks fairly similar, with most convection confined to the western mountains, and chances remaining small at any particular location, generally less than 1 out of 4 once again. The bigger story on this day will be the heat. The 700 millibar temperatures peak on this day, rising as high as 20 celsius. Most locations below 6000 feet have at least a 1 in 2 chance of high temperatures over 95. There is even an outside chance of a few of the warmer spots, like Greybull and Worland, touching 100.

Chances of showers and storms begin ramping up Saturday. However, the latest guidance does show a somewhat slower arrival of the deeper moisture. As a result, POPS were cut back late Friday night with most locations likely remaining dry through sunrise on Saturday. A shortwave should be tracking across the area in the afternoon and will help to enhance shower or thunderstorm activity across the area. Precipitable water values do rise considerably, to as much as an inch in portions of the area East of the Divide. As for area of greatest coverage, most guidance favors area West of the Divide. However, not only there. This will be a situation where all areas will have a chance of a shower or storm, but not everyone will see one. Much of the area is also under a marginal risk of excessive rainfall, so heavy rain and possibly local flooding is not out of the question. And this far out, it is impossible to pinpoint. Most guidance shows most activity weakening and ending after midnight. The models lately, both the synoptic and convective, have been absolutely terrible in handing nighttime convection with the monsoon. So may confidence on a dry Saturday night is rock bottom at this point. Temperatures will cool somewhat with more cloud cover, but remain well above normal, with highs in the 90s East of the Divide.

Near to above normal precipitable water is expected to hang around through Sunday and into next week. It will not be as deep as on Saturday. The result will be a daily chance of mainly diurnal showers and thunderstorms, although it is difficult to nail down a more active area or day this far out. With ridging remaining over the area, above normal temperatures are likely to continue although record high temperatures are not expected.

AVIATION /12Z TAFS THROUGH 12Z FRIDAY/

Issued at 404 AM MDT Thu Aug 20 2026

VFR conditions will dominate through 12Z Friday. Isolated showers and thunderstorms will develop across southwestern Wyoming after 19Z, impacting mainly KBPI, KPNA and KRKS, but the chance of a shower or storm at each of these sites is only around 20 percent. The main threat will be wind gusts up to 45 knots with most precipitation evaporating before it hits the ground. A shower or storm can't be ruled out in vicinity of KRIW, KLND or KJAC, but the chance is 10 percent or less so we did not include it in the TAF forecast. Wind gusts to 12 to 20 knots will be possible at terminals west of the Divide as well as KCPR, with lighter wind expected elsewhere.

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.