textproduct: Western and Central Wyoming

KEY MESSAGES

- An active day today as a weather system brings some showers and thunderstorms, most numerous in northern Wyoming. Some storms could be strong to severe.

- The chance of showers and storms continues Sunday and Monday, with the best chance once again across northern Wyoming.

- Elevated to near critical fire weather remains likely through Monday, with today and Monday the days of the most concern.

DISCUSSION

Issued at 233 AM MDT Sat Jun 20 2026

It is always rather interesting when coming back from a vacation to see what you walk into. There are some things to talk about this morning, as we look to have an active few days across western and central Wyoming.

Even at the early morning hour this morning, a subtle shortwave is moving into western Wyoming and bringing a few showers and even an isolated lightning strike or two. There have been a few wind gusts with this, but the maximum has been around 40 mph or so. A few showers will continue this morning, but the main event still looks to be this afternoon. Most guidance continues to favor the areas East of the Divide as well as western Wyoming, where the deeper moisture will be found, with a maximum chance of around 3 out of 5 across the northern border as well as Johnson and Natrona Counties, with tapering chances further south as you move southward into the drier air. The highest chance will be during peak heating, with a gradual decrease through the evening. However, a few showers will linger through the night. As for the chance of any stronger storms, most of the area is under a Marginal Risk of severe thunderstorms. There will be decent forcing and dynamics as a shortwave will approach the area and there will be a but of upper level support from the left front quadrant of a jet streak moving into southern Wyoming this afternoon. The limiting factor, as it usually is in this part of the country, is moisture. We have several threats, we will tackle each one of them individually.

Severe wind gusts...Not surprisingly, this is the main threat from the storms, as it usually is in western and central Wyoming. Model soundings show well defined inverted V soundings across much of the the area, with an emphasis on the southwestern half of the area. There are steep lapse rates as well, approaching 9 degrees celsius per kilometer in some locations. In addition, shower and thunderstorm bases look to remain fairly high, generally more than a mile above the surface. Dew point depressions are not the highest I have seen, but are still decent. The largest are in southwestern Wyoming, where some approach 60 degrees. Depressions drop to around 40 degrees in central Wyoming and to around 30 degrees in northern Wyoming where the deepest moisture will be found. However, any shower or thunderstorm could have a strong wind gust, even any cumulus cloud that could collapse. The dreaded "Little Green Blobs" are definitely possible this afternoon, especially in the southern half of our area.

Hail...There is a very small area of a marginal risk of large hail, largely along an east of a Glenrock to Midwest into eastern Johnson County. This does make sense since moisture will be deepest in this area, along with the lowest cloud bases. This is also the location of the best instability, with CAPE values approaching 1000 J/Kg and lifted indices as low as minus 4. Johnson County looks to have the best chance, as most guidance shows some weak upslope flow into the Bighorns this afternoon, which should aid in convective initiation. The best chance of large hail remains across eastern Wyoming, but there is around a 1 in 10 chance of some in our area, mainly along and east of Interstate 25.

Flooding...The chance of this is low but not zero, and mainly in the northern half of the state. As for climatology, the predicted precipitable water value of 0.63 at 00Z this afternoon puts moisture in the top 20 percent of historical values for this value and around 125 percent of the daily mean (0.50 inches). The most likely locations will be, again across Johnson County, where some areas have over an inch or precipitable water, as well as the Big Horn Basin. However, there will be some steering flow today, so most of the storms will have some movement, mitigating the threat somewhat. In addition, it has been dry, so the soil does have a decent amount of capacity. The Weather Prediction Center does have eastern Johnson County under a marginal risk of excessive rainfall, and this looks reasonable given the pattern.

Dry Lightning and Fire Weather...This will largely be a threat across the southern half of the area, where cloud bases will be higher. This will obviously bring a threat of some fire starts, given the continuing drought conditions across the area. Elevated to near critical fire weather is likely across southern Wyoming where winds gusting over 30 mph and humidity falling to around 15 percent may bring erratic fire behavior if any fires can start.

And one bonus I will throw in, tornadoes. The threat is very low, less than 2 percent across the entire area as the best instability and shear will be across eastern Wyoming. Like many of the other threats, the main area of concern is Johnson County, where the most shear will be found and deeper moisture will allow for lower cloud bases and allow for the possibility of any rotation to reach the ground. This threat is by far the lowest of all the threats though.

Looking further out, things look to stay active over the next couple of days. Another shortwave will move across the area Sunday with another chance of convection. Instability values are around 25 percent less with this wave and there is much less jet support. So, the threat of strong to severe thunderstorms will likely be less. And like today, the main threat will be East of the Continental Divide.

Monday has the potential to be a bit more interesting. Another shortwave will be crossing the area. The main difference here is that there will be more jet support, with an 100 knot jet streak moving along the Wyoming / Montana border. The limiting factor here is moisture, with precipitable water values falling to as low as 0.20 inches across western Wyoming. If the dry air wins out, the main threat would be fire weather with a gusty wind and lower humidity with the jet close by. However, if moisture could linger, we could have a situation with storms firing along a pseudo dry line. There is still a lot of uncertainty but we will have to watch this.

More settled conditions should move in for Tuesday as a building ridge brings upper level convergence. Uncertainty increases from midweek on as some guidance has ridging over the area and only isolated convection while others have the area near the top of the ridge with shortwaves topping the ridge and bringing a few chances of convection. Temperatures look to remain close to normal, with the biggest temperature anomalies across southern Wyoming where drier air and less cloud cover should allow for warmer temperatures.

AVIATION /12Z TAFS THROUGH 12Z SUNDAY/

Issued at 405 AM MDT Sat Jun 20 2026

Aviation impacts will continue through today, maximizing between 18Z Saturday and 02Z on Sunday. A few light showers will move through through around 15Z but most precipitation should not reach the ground. An approaching weather system will bring a decent chance of showers and thunderstorms today. The greatest chance will be along and north of a KJAC to KWRL line, and in these TAF sites TEMPO groups were maintained with at least a 50 percent chance of a thunderstorm this afternoon. Further south, in vicinity of KCPR, KRIW, KLND, KPNA and KBPI, chances are generally between 25 and 35 percent, so PROB30 groups were maintained here. We can't rule out a shower or thunderstorm in vicinity of KRKS but with the chance less than 20 percent we elected to leave out of the TAF for now. A few showers will linger across northern Wyoming through the night, so we kept VCSH in the northern terminals after 06Z.

RIW WATCHES/WARNINGS/ADVISORIES

None.