textproduct: Western and Central Wyoming

KEY MESSAGES

- Western and central WY will see another warm day (near to slightly above normal temperatures) with isolated afternoon and evening showers and thunderstorms (generally less than a 1 in 4 chance). Any shower or storm could have strong wind gusts. The main area for storms will be from Star Valley east to Pinedale and the Wind Rivers and into the Wind River Basin. Southern Sweetwater County will also see some storms off the Uintas, and northwest WY will see showers and storms during the evening hours. A couple of strong storms are possible in far eastern Johnson County too.

- Independence Day will be dry and warm (80s to low 90s) with afternoon breezy winds in places. The evening will be quite nice across the area with essentially no precipitation or storms expected.

- Low humidity will bring elevated fire weather each afternoon, but wind is expected to remain light to moderate and below critical thresholds, except for around showers and thunderstorms.

- Temperatures climb a few more degrees on Sunday with some late day showers and thunderstorms across northwest WY. Monday through Wednesday will remain warm with isolated afternoon showers and thunderstorms, then hot and dry conditions develop for the rest of the week.

UPDATE

Issued at 100 PM MDT Fri Jul 3 2026

Instability for isolated showers and thunderstorms continues this afternoon across western and central Wyoming, with some CAPE between 500-1000 J/kg, lifted indices between -1 and -2, and lapse rates around 9 C/km. A very weak disturbance appears to be moving west to east today across the MT/WY border aiding the convective development, which is just starting after 1200 PM. Convective Allowing Models (CAMs) are indicating initial development and activity this afternoon north and northeast of the Uintas in SW WY. Shortly after, initiation started over west-central WY and moves eastward through the afternoon and early evening. As with the past two days, these showers and thunderstorms combined with a relatively dry boundary layer and large surface dew point depressions will lead primarily to gusty outflow winds over 40 mph, with local 50+ mph wind gusts. While virga showers are most likely, under the core of the thunderstorms could see brief heavy rain (Thursday say a few places get between 0.25" and 0.75" of rain. Showers and isolated thunderstorms will continue through about sunset across parts of western and central WY. Models are also indicating some showers impacting the northern parts of YNP and the Absarokas into the northern Bighorn Basin during the early evening hours. Breezy southwest-west winds today will again be dominated by gusty outflow winds during the late afternoon and evening hours.

SPC has extended the marginal risk of severe thunderstorms to about the northeast half of Johnson County, including Buffalo. Storms across the MT/WY border and Sheridan county could impact northern Johnson County with brief heavy rain and outflow winds over 50 mph. The most likely time for these storms appears to be between 6 and 9 PM this evening.

Overall conditions will be mild overnight, with the Fourth of July seeing warming temperatures by a few degrees, mostly clear skies in the morning with some partly cloudy skies in the afternoon and evening. At this time, no showers or thunderstorms are expected, though breezy west-southwest are likely in the afternoon, but should decrease by sunset.

DISCUSSION

Issued at 221 AM MDT Fri Jul 3 2026

Things turned out pretty close to what was expected yesterday, with scattered showers and thunderstorms along with some strong wind gusts (we had 56 mph at the Riverton Airport), as well as 54 mph at Buffalo and 49 mph at Worland. Things are fairly quiet right now though.

It is often said that a lot of things in the physical and mathematical sciences are governed by sine waves, and meteorology is one of them. The most prominent being Rossby waves (look it up if you are curious). And that is how the chances of convection will be over the next several days. We reached the peak of the wave the past couple of days. We are now on the way down with chances.

There will still be a few storms around today. However, parameters are not the most impressive. CAPE tops out at only 500 J/kg and Lifted Indices only fall to minus 2. Precipitable water values are also generally near to somewhat below normal. However, we continue to have very steep lapse rates (approaching 9C/km). In addition, a subtle (emphasis on subtle) shortwave will be moving through the area. Many areas will have a chance, mainly in western and northern Wyoming where the most instability will be found. Most places won't see a shower/storm though, so chances for a vast majority of the area are less than 1 out of 5. We continue to have high based storms with inverted-V model soundings and large dewpoint depressions (greater than 50 degrees in many locations). That means the most likely threat from any shower or thunderstorm would be strong wind gusts. This includes the dreaded "Little Green Blobs", innocent showers that produce strong wind gusts when they collapse. This looks to be an earlier show, with almost all convection over by sunset. The other risk is fire weather. Some locations will see relative humidity fall below 15 percent. However, wind is not expected to reach critical levels. Elevated fire weather is likely in many locations though. Temperatures should be within a few degrees of normal.

We will reach the trough of the sine wave on Independence Day. Shortwave ridging will be in place across the area, providing some subsidence. Dry air will be in place across the area, with precipitable water values below normal for all areas. This means a very small chance of convection. The one spot that could see a stray storm is southern Sweetwater County, where models are showing some meager CAPE values (around 200 J/kg). I can't rule out a storm here, but the chance is less than 1 out of 10. And this would mainly be south of Interstate 80 and near the Unitas, where there is little population. Temperatures also move up a few ticks this day, on average around 5 degrees above normal for most of the area, which means near or above 90 for many locations east of the Divide. So quite warm, but not as hot as a firecracker.

On Sunday we begin to climb the sine wave again, as chances for storms begin to increase. However, they are fairly small on this day. This will be mainly across the north, but chances here are only 1 out of 5. The big story this day will be the heat. This could be the day one of major climate sites could reach triple digits. GFS MOS shows 100 for a high at Greybull and 99 at Worland. The NBM ensemble gives around a 2 out of 5 chance for this. Nevertheless, this will be a day of widespread 80s in the lower elevations west of the Divide and 90s east of the Divide. Humidity will remain very low on this day as well (10 percent or below east of Divide). But once again, wind should remain light to moderate so fire weather conditions will remain elevated.

Chances increase for storms early in the week, probably reaching the peak of the sine wave on Tuesday as another deeper trough moves across the area. There are still some different solutions with this, with some guidance keeping most of the storms north and others bringing it further south. Nevertheless, Tuesday looks like the best chance for showers and storms for most of the area. Chances then begin to descend toward the trough (of the sine wave) as ridging builds across the western United States. There are indications of a possible heat wave the end of next week, but still some uncertainty. So, this the story as we ride the rollercoaster of the sine wave of mid summer weather in western and central Wyoming.

AVIATION /18Z TAFS THROUGH 18Z SATURDAY/

Issued at 1041 AM MDT Fri Jul 3 2026

VFR conditions will be in place through the TAF period. A weak weather system will move through the area this afternoon and bring isolated showers and thunderstorms (a 15 to 20 percent chance) roughly along and south of a Alpine-to-Worland line. Terminals KBPI, KPNA, KRIW, KLND and KWRL will be most impacted by this convection between 20Z and 02Z. Confidence remains too low to include a PROB30 at KRKS, but there could be convection within 20NM of the terminal. The main threat from any shower or storm will be erratic wind gusts over 35kt from associated outflows. Otherwise, gusts up to 20kt are expected at most terminals through the afternoon and subsiding around 02Z. Skies will clear overnight, becoming SKC across the area by 13Z.

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.