textproduct: Western and Central Wyoming

KEY MESSAGES

- A hot day today with isolated afternoon and evening virga showers and dry thunderstorms occurring along and north of a Afton-to-Worland line (a 1 in 5 chance). Any shower or storm could have strong wind gusts up to 60 mph.

- An increased chance of showers and thunderstorms Monday through Wednesday, with the most numerous storms expected on Tuesday. Locally heavy rain will become possible with the stronger storms Monday and Tuesday.

- The hottest temperatures of the year are likely Friday through Sunday with record high temperatures possible.

UPDATE

Issued at 1120 AM MDT Sun Jul 5 2026

Not much change in the forecast for this afternoon. CU clouds are beginning to form off the east slopes of the Absaroka and Wind River Mountains and the Salt River/Wyoming Ranges as of 11AM. Buffalo, Thermopolis and Cody are already 90F. Virga showers/dry thunderstorms are expected to be developing over the western mountains by 2PM, moving to the northeast through the rest of the afternoon into the evening. Most of this activity will occur along and north of a Afton-to-Worland line, ending around midnight. Wind gusts up to 60 mph will be the main threat, due to the large dewpoint depressions/inverted-V sounding profile in place today. Needless to say, fire weather conditions will be elevated this afternoon due to the hot temperatures and critically low RH values. The good news will be winds will be relatively light, generally staying 20 mph or less, apart from any strong outflow winds that could occur.

DISCUSSION

Issued at 136 AM MDT Sun Jul 5 2026

We have now reached the end of the holiday weekend. All in all, the Fourth of July was pretty nice, with warm temperatures, no convection and lots of sunshine. All that except for a new fire start southeast of Lander. But, we don't want to talk about the past, let's talk about the future, this is a forecast after all.

There will be two changes. The first will be warmer temperatures today as flow turns southwest ahead of a weak cold front. Temperatures should average around 5 degrees warmer than yesterday, making this the hottest day for quite a while, possibly the hottest so far this year. This is looking like the day when we will see the first 100 degree high temperatures of the year, with much of the eastern and southern Bighorn Basin having around a 1 in 2 chance of seeing highs at or over the century mark. Just about all locations east of the Divide in the lower elevations will see highs in the 90s, with some 80s to low 90s west of the Divide. The second change is the chance for convection returns. The atmosphere remains rather dry (precipitable water values are below normal). However, there is enough mid level moisture for some isolated showers and thunderstorms across northwestern Wyoming, largely west and north of a Frannie to Alpine line. The only hazard would be strong wind gusts. There are very steep low level lapse rates (greater than 9C/km) along with very large dewpoint depressions (up to 60 degrees). All this adds up to the threat of microbursts, even from small showers (the infamous "Little Green Blobs)." Coverage will be small, generally less than 1 out of 5 in the impacted area. Most of these showers should end shortly after sunset with dry conditions through Monday morning. Elsewhere, elevated fire weather is likely with humidity falling into the single digits at times. Largely light wind should keep conditions from becoming critical.

A cold front (or a reasonable facsimile of one) then slips into northern Wyoming, getting close to the Continental Divide by Monday morning. This should knock high temperatures down around 5 to 10 degrees compared to today. The other difference will be an increase in moisture as low pressure passes to the southeast of Wyoming and turns low level flow to the south and southeast. Precipitable water values rise to around 125 to 150 percent of normal by 00Z Tuesday. This means an increase in convection across the area, and maybe some needed rain. Most guidance favors northern Wyoming, where greatest instability will be found (up to around 500 J/kg of CAPE). Most soundings show a decent cap initially, so this is favored to be a later show, mainly in the evening with some convection lingering into the overnight hours. Guidance is fairly consistent in having the highest chance (up to a 1 out of 2 chance) across northern Wyoming, with decreasing PoPs further south, with little chance in southeastern Sweetwater County. Most storms should not reach severe limits, but there could be a few.

Storm coverage should peak on Tuesday. A more defined shortwave will be moving through the area. Precipitable water values also reach a maximum on this day, with many locations seeing greater than 150 percent of normal and some locations reaching values over an inch. The atmosphere is also the most unstable on this day, with negative lifted indices across the entire area. As for stronger storms, again the most favored location would be across the north where the greatest CAPE (>1000 J/kg) and lifted indices (down to minus 4) will be found. There will be some movement with the storms and with the recent dry weather there is room in the soil, but locally heavy rain cannot be ruled out due to the moist atmosphere. Most of these storms should end after sunset. More cloud cover should also keep temperatures cooler on this day, with the current forecasted highs being a bit too warm and may trend a bit cooler.

Starting on Wednesday, we will have what is called an inverse relationship. A very strong ridge will begin building across the Desert Southwest and will be expanding northward late next week and especially into next weekend. The inverse relationship will be temperatures going up, and chances of convection going down. On Wednesday, there will still be enough lingering moisture for a decent coverage of storms, but more scattered. Drier air really surges into the area starting Thursday, any storms would be restricted to eastern portions of the area on this day. Temperatures really begin climbing on Friday and especially into the weekend. Many runs of the ensembles center the ridge on or very close to Wyoming, with 500 millibar heights as high as 6000 meters. This is the classic definition of a death ridge, bringing very hot temperatures and little to no chance of rain. Ensemble forecasts start giving at least a 2 out of 5 chance of highs over 100 once again in the typically warm locations by Friday. But the weekend is where the heat may really hit. On both Saturday and Sunday, the NBM ensemble gives a greater than 3 out of 5 chance of triple digit highs both days for areas eat of the Divide below 5500 feet. Some of the typically warmer spots, like Greybull and Worland have a 2 out of 5 chance of highs over 105. A word of caution, this is still a week out and things can change. However, we do have the chance of one of the more notable heatwaves we have seen in a while.

AVIATION /18Z TAFS THROUGH 18Z MONDAY/

Issued at 1105 AM MDT Sun Jul 5 2026

VFR conditions prevail through the period. Clouds increase from the west through this afternoon and evening. A few showers and thunderstorms are possible, mainly across the western mountains, with PROB30 groups at KCOD and KJAC. A few showers could be as south as KBPI and KPNA this afternoon. A weak cold front moves in from the north after 00Z, bring a northerly wind shift to sites east of the Divide. A few hours of gusty winds are possible with the frontal passage.

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.