textproduct: Western and Central Wyoming

KEY MESSAGES

- A weather system will cross the area today and tonight with showers and thunderstorms. Some thunderstorms could be severe with large hail, strong wind and heavy rain.

- Additional strong thunderstorms are possible Thursday afternoon, with areas East of the Divide having the highest likelihood.

- Turning cooler this weekend. An approaching weather system may bring some snow to the mountains Saturday night and Sunday.

DISCUSSION

Issued at 212 AM MDT Wed Jun 24 2026

Things are still shaping up to be rather active across the area over the next several days. And in true Wyoming fashion, we may pass through a few seasons over the next few days.

The main concern today will be thunderstorms as a shortwave moves across the area, and some of them have the potential to be severe. There will be some storms around in the afternoon, but a bulk of the activity may end up being in the evening and even overnight hours. The risk of stronger storms would likely be before sunset though, when instability will be the greatest. Our partners at the Storm Prediction Center have largely kept the Marginal Risk status quo, running largely east of the Worland to Hiland line, and covering Johnson, Natrona and eastern Washakie Counties. The area of most concern is Natrona County, where a slight risk is in effect. This makes sense given CAPE is maximized here (as high as 1500 J/Kg) as well as lifted indices (as low as minus 4). The strongest storms at this point should remain East of the the area over Eastern Wyoming, but it is a bit too close for comfort. And there is another area of concern, this one across southwestern Wyoming, although the main and probably only threat here would be strong wind gusts. We will not discuss the individual threats with the storms: large hail, strong wind, tornadoes and heavy rain.

Large Hail...The main threat of this looks to be in our eastern counties, mainly Johnson and Natrona Counties. This chance maximizes in southern Johnson and Natrona Counties though. Conditions are good for this as model Skew Ts show as much as 50 knots of 0 to 6 kilometer shear with large lapse rates of almost 9C / Km. There will be a cap on the atmosphere initially though, so this looks like a later show, with most worst possibly in the evening. This area also has a Conditional Instability Group Level 1, meaning hail up to golf ball size or higher. However, there is Conditional Instability Group 2 just to the east of the Casper, which means the chance of baseball sized hail. Chances of large hail do drop further west, but almost any storm to the East of the Divide could have small hail. The greatest threat of this should end around midnight as the we lose the heating of the day and instability.

Strong Wind Gusts...As usual, this will be a threat with just about any shower or thunderstorm, this is Wyoming after all. There are two main areas of concern. The first is in the area similar to the large hail threat, and this area has the most instability. There is another area of concern though. And this is across southwestern Wyoming. This is more of a little green blob scenario as the shortwave approaches this evening, with soundings showing very well defined inverted V soundings resulting in some high based showers and thunderstorms. Lapse rates are very steep (as much as 9C/km) with dew point depressions over 50 degrees in some locations. The result will likely be some wind gusts over 55 mph at times in any thunderstorm, shower or even cumulus cloud when it collapses. The main threat of this will be in the afternoon and evening, then decreasing later in the evening as the atmosphere cools.

Tornadoes...This again is by far the least threat, but it is not zero. There are things going for it, mainly the deep directional and speed shear. In addition, cloud bases will be lowering into the evening as the moisture increases. The main factor against it is that with slow 700 millibar flow, there may be more storm interactions and not as many stand alone supercells. The best chance of this would be in eastern Natrona County, but even here the chance is only 2 percent, with chances decreasing further west.

Heavy Rain...Most storms, but especially the ones East of the Divide will have the potential of this. Precipitable water values rise two over an inch in some locations Wednesday evening, and this gets my attention as this is 200 percent of our climatological value. Dew points will also get fairly high for these parts, rising into the 50s in our eastern counties. Flow will also be easterly up to around 700 millibars, bringing in additional moisture. One mitigating factor is that there will be decent flow at 500 millibars, anywhere from 20 to 30 knots, so the storms should have some movement. It is also been very dry across most of the area, so there is room in the soil to soak up some moisture. There will still be the chance for some localized flooding, but it should not be widespread. The best chance would be East of the Divide, where upslope flow and the greatest moisture will be found.

More strong storms will be possible on Thursday. However, there will be more uncertainty here. Another shortwave will be moving across the area. The limiting factor may be cloud cover and showers that will linger across the area during the morning hours. This may limit surface heating and instability somewhat and decrease the chance of stronger storms. There will still be a decent amount of shear present though. So, if there can be some clearing, we could see another round of strong to severe storms. This will again be in areas similar to today, largely East of a Greybull to Worland to Hiland line. But the chance of stronger storms looks less than today at this time.

Looking further out, Friday should be a lull with shortwave ridging over the area and less storms. Attention then turns to an upper level low that will be moving onshore in the Pacific Northwest Friday night and moving into the northern Rockies this weekend. Recent model trends have weakened the system a bit and also shifted to low a bit further to the west. This has decreased the QPF across the area. The system has also trended a bit warmer, so potential snowfall amounts in the west look less. The 700 millibar temperatures now look to bottom out around minus 1 or so, which would put snow levels around 8000 feet later Saturday night and Sunday. Nevertheless, locations above 9000 feet will likely see a light accumulation of snow during this time. This includes anyone going over Togwotee Pass as well, although most snow would melt on roads. So, the active weather pattern will continue across western and central Wyoming for the next several days.

AVIATION /12Z TAFS THROUGH 12Z THURSDAY/

Issued at 358 AM MDT Wed Jun 24 2026

Mainly VFR conditions are expected through 00Z today. One exception are some low clouds in vicinity of KCPR through 15Z. A few showers moving through northern and western Wyoming may bring some local low VFR conditions through around 15Z. An initial round of thunderstorms develops this afternoon, but look isolated. The only location with greater than a 25 percent chance is KCPR so we maintained the PROB30 group there. We removed it in vicinity of KRIW and KLND with the main area of showers and thunderstorms expected after 00Z Thursday.

After 00Z on Thursday, the main push of showers and thunderstorms moves in from the south, with impacts at KRKS, KBPI/KPNA, KLND/KRIW and KCPR between 00Z and 06Z/25. Confidence remains low on exact timing, so we maintained PROB30 groups for now. KJAC may be on the drier side of this system, so have a small chance for showers in the evening, with bkn midlevel clouds after 00Z. Showers will move north into the rest of the state around 06Z/25, moving into vicinity of KWRL and KCOD after 06Z.

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.