textproduct: Western and Central Wyoming

KEY MESSAGES

- A weather system will bring some showers and thunderstorms to northern Wyoming today. Some storms could be strong to severe with large hail and strong wind, with the highest chance in Johnson County.

- Low humidity and a gusty wind will bring elevated fire weather to much of central and southern Wyoming this afternoon.

- Chances of showers and thunderstorms continue through much of the week, with another possibility of strong to possible severe thunderstorms on Wednesday.

DISCUSSION

Issued at 243 AM MDT Mon Jun 22 2026

It is now June 22nd, and it is a sad day for summer lovers like myself. It is now when days begin getting shorter. But enough of this, we do have things to talk about today, as we will continue to have the chance of convection, and possibly a few stronger ones.

We have been talking about today for a couple of days now, and we continue to have some uncertainty. The main uncertainty is how far west will the threat of stronger storms move. The slight risk area has moved little at this point, covering mainly far eastern Johnson County. The Marginal Risk as shifted a bit further west, right now mainly covering an area East of a Powell to Greybull to Kaycee to Casper line. This makes sense. A cold front will be moving through the area, and areas further west will likely see more stable and air move in behind it. The other factor will be moisture. Precipitable water values will drop behind the front, leading to little to no convection across the western and southern two thirds of the area. Instability parameters look impressive across northern areas East of the Divide though, with CAPE values as high as 1500 J/Kg and lifted indices to minus 4. The uncertainty is that some of the models, both of the synoptic and high resolution varieties, have little coverage in our area. In addition, the jet core, which was previously predicted to be over the Wyoming-Montana border, has shifted further north. For now, we have elected to largely go with the Storm Prediction Outlook, putting convection in this afternoon across the Bighorn Basin to northern Natrona County and northward. We have kept chances generally less than 1 out of 4 in any particular location though given the uncertainty. Further south and west, the atmosphere may be too dry. A high based shower storm or virga shower can't be ruled out, but with a chance of less than 1 out of 8 we kept them out of the forecast for now.

Now for the threats. For areas further to the east, the main threat looks to be large hail. Lapse rates remain rather impressive, approaching 9 C/Km in the late morning and early afternoon. Shear values of over 50 knots over the 0-6 km layer are sufficient for this as well. The main threat for this would be over Johnson County, where deeper moisture will be present and low level upslope southeasterly flow should aid in convective initiation, with diminishing chances further west and south as you move into the drier air. As for strong wind gusts, this is possible with any shower or thunderstorm. This includes areas further west and south. Many model soundings further east show inverted Vs with steep lapse rates. Any convection here would be higher based with little rain. Dew point depressions do approach 50 degrees in places like Riverton so in the unlikely chance that convection can form, there could be a downburst when the clouds collapse. And, as for tornadoes, this is by far the least likely. There is a 2 percent area in Eastern Johnson County where cloud bases are lowest and shear is the highest. Chances are not zero, but very small. And there is one more thing. Further south, humidity will fall into the teens and with a gusty wind elevated fire weather is likely. This will be in areas where fuels are not critical, so no Red Flag Warnings. However, any fire starts could spread rapidly.

Most strong convection should end by sunset, but like tonight, a few showers and storms will likely linger through the night. Tuesday at this point looks like a cooler day behind the cold front. There will still be a few showers and storms around, but coverage will be less as shortwave ridging and some upper level convergence moves over the Cowboy State. Chances of convection then increase again as another shortwave passes over the area. This time, a jet streak will be passing by and this could increase the chance of strong to severe thunderstorms again. The Storm Prediction Center already has a Marginal Risk over Natrona County, where northeasterly upslope flow is predicted and where the maximum instability and moisture is present. This is another day we are going to have to watch closely. The active pattern looks to continue into next weekend with more chances for convection, although timing of the individual shortwaves remains uncertain. With the area near the top of a ridge, temperatures should average close to normal with no heat waves expected through next weekend.

AVIATION /12Z TAFS THROUGH 12Z TUESDAY/

Issued at 444 AM MDT Mon Jun 22 2026

Largely VFR conditions will continue through most of the TAF period. Drier air should spread into most of the area today, and keep convection more limited. Most convection will be restricted to along and north of a KCOD to KGEY to Kaycee line, we have added a PROB30 group to KCOD as a result. A cold front will move across the area through the day, reaching the Continental Divide by this evening. A stray shower may occur in vicinity of KJAC until around 13Z this morning. A stray afternoon shower can't be ruled out in other terminals East of the Continental Divide, but with the chance less than 15 percent we left it out of the forecast for now. Breezy conditions will develop at all terminals. Northeast flow behind the front has a greater than 50 percent chance of lower clouds in vicinity of KCPR after 09Z Tuesday, bringing MVFR ceilings.

RIW WATCHES/WARNINGS/ADVISORIES

None.