textproduct: Western and Central Wyoming

KEY MESSAGES

- Widespread showers and thunderstorms today, most numerous across northern Wyoming. Strong gusty wind over 50 mph is the main hazard with any storm, but some small hail is also possible, most likely around Johnson and Natrona Counties.

- Shower and thunderstorm chances continue for Monday and Tuesday, mainly across northern Wyoming.

- Elevated fire weather conditions remain into next week, given the low humidities, breezy winds, and lack of rain chances.

UPDATE

Issued at 1037 AM MDT Sat Jun 20 2026

Not seeing any notable changes regarding the storm potential for today compared to the discussion below. The latest HRRR runs in particular continues to have a widespread push of 50 to 70 mph associated with storms this afternoon, from the Wind River Basin eastwards to Natrona and southern Johnson Counties. The HRRR can sometimes overdo these types of events, so caution is taken. The timing of this is between 2pm and 7pm (moving west to east in that time). Other storms will also have the capability to bring isolated gusts of similar magnitude. The HRRR also brings another push of storms and strong winds to Lincoln County and the Green River Basin between 6pm and 9pm, so another area to watch. This is all far from certain, but gives an idea of potential wind hazards today.

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 /18Z TAFS THROUGH 18Z SUNDAY/

Issued at 1150 AM MDT Sat Jun 20 2026

Numerous thunderstorms will move across the area this afternoon and evening, brining brief heavy rain, lightning, and sudden strong wind gusts to many locations. The erratic wind gusts near any thunderstorm will be be quite strong given the atmosphere is supportive of high winds today. Weather models shows numerous regions where 45 to 60 kt outflow winds push ahead of thunderstorm complexes. Brief MVFR conditions could occur near storms, and expect nearby mountains to be obscured at times by heavy rain showers.

A passing weather system will support showers and isolated thunderstorms after sunset into the overnight, so do not expect storms to fully dissipate around sunset (often they do in the mountains of Wyoming, but today will be an exception to this general pattern). This weather system exits the region after sunrise Sunday, decreasing overall precipitation and storm chances, but isolated thunderstorms are again possible (10 to 20% chance) Sunday afternoon in the buoyant air mass left in wake of this system.

RIW WATCHES/WARNINGS/ADVISORIES

None.