textproduct: Western and Central Wyoming

KEY MESSAGES

- A hot today with isolated thunderstorms mainly in and near the mountains.

- Very hot and likely record breaking temperatures arrive on Saturday and continue into Monday and possibly Tuesday. The hottest temperatures are expected on Sunday.

- A combination of very hot temperatures, very low humidity and breezy conditions may bring critical fire weather Sunday and Monday afternoons.

DISCUSSION

Issued at 245 AM MDT Fri Jul 10 2026

We are now transitioning from thunderstorms being the emphasis to heat being to emphasis. The radar is quiet right now, and should be through most of the morning. However, there is just enough instability and mid level moisture for some isolated convection this afternoon, mainly in and near the western mountains. These would be very isolated, with chances generally less than 1 out of 5 at any given location. And given the dry low levels, the main threat from any shower or storm would be those strong wind gusts that are ubiquitous with July convection in Wyoming. Any storms would end fairly quickly this evening. Temperatures will also be warming today. It will be hot, but the type of hot we see every July in western and central Wyoming.

The heat will really ramp up on Saturday as the death ridge over the desert southwest moves northward toward the northern Rockies. The 500 millibar heights will climb as high as 5970 meters on Saturday afternoon, bringing a very hot today. Most locations below 5500 feet have at least a 1 in 2 chance of high temperatures of 100 degrees or higher, with elevations below 7000 feet having a nearly 100 percent chance of highs over 90 degrees. Humidity will be low on this day as well, with widespread relative humidity falling into the single digits in the lower elevations. However, the peak of the heat is still looking to be on Sunday. The center of the heat dome should be centered over Wyoming on this day, with 500 millibar heights rising as high as 6000 meters. At the same time, 700 millibar temperatures climb as high as 23 degrees celsius. At this is a recipe for very hot temperatures, with some monthly and all time high temperatures possibly being set during this afternoon. Locations below 6000 feet have at least a 9 out of 10 chance of high temperatures over 100 on Sunday afternoon. Even places like Rock Springs, Farson and even Jackson have a 1 in 2 chance of breaking 100 degrees. The center of the heat continues to look to be Big Horn Basin where locations from Thermopolis to Lovell have at least a 9 of 10 chance of high temperatures at least 105, and the hottest locations like Basin and Greybull have a 3 out of 5 chance of high temperatures of 110. The heat continues into Monday, although with center of the ridge moving into the northern plains, it may be a few degrees cooler. However, it will still be similar to Saturday, with widespread 100 degree temperatures below 5500 feet and 90s below 7000 feet. Temperatures remain very hot into Tuesday as well, although a few degrees cooler than on Monday.

Now about the extreme heat warning. We realize that the heat index will be lower than the temperatures, due to the humidity being very low (below 5 percent at times). However, due to possibly historic nature of the high temperatures, we decided not to split hairs and just upgrade everything. It will be unhealthy for a lot of people and impacts are more important the raw criteria.

As for other things, we also have to talk about fire weather. Humidity will be very low through Monday, with many locations seeing values below 10 percent. However, wind is expected to remain below critical levels both today and tomorrow. The main day of concern would be Sunday, when a decent southwesterly breeze will develop. The strongest wind would be in northern portions of the area, especially the Bighorn Basin where some areas have at least a 4 out of 5 chance of wind gusts over 25 mph. This could bring critical fire weather to these locations with the extremely low humidity and dry fuels. Guidance is still a little split on this though. We we hold off on any fire weather highlights for now but will watch it closely. Concerns could linger into Monday and possibly even Tuesday.

As for convection, the warm temperatures aloft capping the atmosphere and lack of moisture should keep the area dry through the weekend. The chance rises a bit on Monday as guidance does show some weak easterly flow as the core of the ridge moving eastward providing some upslope. Moisture is still lacking though. The main chance would be in the northwestern mountains but the chance is less than 1 out of 10 at this point. The chance does increase a bit on Tuesday as moisture increases a bit but even here the current forecast is probably too wet given the still warm temperatures aloft capping the atmosphere. Chances should increase for the middle of the week as the ridge slowly weakens and increasing moisture brings a better chance of mainly diurnal convection into the end of the week. Temperatures should cool off some for the middle of the week but will remain above normal for much of next week.

AVIATION /12Z TAFS THROUGH 12Z SATURDAY/

Issued at 415 AM MDT Fri Jul 10 2026

VFR conditions are expected through the TAF period. All locations should start of dry, but isolated afternoon showers and thunderstorms this afternoon (10 to 20 percent) will be possible in the western mountains. The most impacted location would be KJAC where we maintained the PROB30 group for this afternoon. We also maintained the VCSH for KCOD. There is around a 10 percent chance for a shower or storm in vicinity of KCPR but not enough confidence to include at this time. The other possibility is for outflows but we can't pinpoint these at this time. Wind gusts to 18 to 20 knots are possible this afternoon in vicinity of KBPI, KPNA and KRKS, otherwise wind should be 11 knots or less except in and around showers and thunderstorms. Any convection should end around sunset with dry conditions after around 03Z Saturday.

FIRE WEATHER

Issued at 245 AM MDT Fri Jul 10 2026

Elevated fire weather is likely today and Saturday for much of the area with hot temperatures and low humidity. However, wind should remain light to moderate for the most part. The main day of concern will be Sunday as a south to southwesterly breeze develops with gusts to 30 mph possible. With record high temperatures and very low humidity, critical fire weather will be possible Sunday afternoon.

RIW WATCHES/WARNINGS/ADVISORIES

Extreme Heat Warning from noon Saturday to 9 PM MDT Monday for WYZ003>006-010-011-013-016>020-023-025>030.