textproduct: Western and Central Wyoming

KEY MESSAGES

- The heat wave continues today, with the hottest temperatures today. Some all time record high temperatures are likely to broken this afternoon.

- Elevated to critical fire weather is likely this afternoon across most of the area with humidity falling as low as 4 percent and a gusty southerly breeze developing.

- Well above normal temperatures continue through Tuesday. Following that, it won't be as hot with an increasing chance of showers and thunderstorms.

DISCUSSION

Issued at 136 AM MDT Sun Jul 12 2026

A ridge of 5990 meters at 700 millibars is now centered over Wyoming. And, no surprise, it is brought a very hot day yesterday, with numerous records set. If we were to compare the heat this to an internal combustion engine in a car, we would be running at around 4000 to 5000 rpms, with the engine working hard but not really hard. Today will be the day we push the engine up to the red line, and could be one of the hottest days we have seen in many years, especially in certain portions of the area. It is even warm right now. As I write this, it is still 80 degrees at our office at 1 am this morning.

Guidance shows 700 millibar temperatures climbing an average of 2 degrees higher than yesterday, topping out at around 23 degrees celsius. This translates into temperatures an average of 3 to 5 degrees higher than yesterday. Ensemble guidance is giving a nearly 10 percent chance of high temperatures over 100 degrees below 6000 feet with locations below 7500 feet having a nearly 100 percent chance of over 90 degrees. Most locations below around 4800 feet have at least a 4 out of 5 chance of high temperatures of 105 degrees or higher, especially the eastern half of the Big Horn Basin, which has a greater than 9 out of 10 chance. When we bump it up to 110, most of the stretch from Thermopolis to Lovell has at least a 1 in 3 chance, with the highest chance from Basin to east of Lovell in the lower elevations, as high as 2 out 3 of 110 degrees of higher. I have posted some facts about the temperatures and potential for all time record highs in the climate section of the discussion as well as on social media. The other thing to talk about is critical fire weather, we have two slam dunk ingredients the third may be more questionable in spots. Dry fuels are one of the slam dunks. The other is low humidity, which will fall to as low as 4 percent in some locations. The one question is wind. Almost all guidance is showing the strongest wind across northern portions of the Red Flag Warning area, with gusts as high as 35 mph. The southern zones, especially Zone 283, are a bit borderline on this. However, given the low humidity and record heat, we will keep it up. Otherwise, it will be almost completely dry. Some guidance does how a bit more mid level moisture in western Wyoming and some possible cumulus buildup in that vicinity. Given the very dry low levels, anything that falls out of the clouds would only be virga. We did add some 10 percent POPs though, mainly for spot purposes.

The center of the ridge will move eastward somewhat on Monday. And it may be just far enough to allow a bit of return flow moisture to move up the backside of the ridge for some isolated convection in the western mountains. This is isolated with a capital I though, with at most a 1 out of 6 chance with most locations seeing nothing. Slight smaller thickness and 700 millibar temperatures cooling to around Saturday's levels will allow for slightly cooler temperatures, but still well above normal with still a greater than 4 out of 5 chance of high temperatures above 1000 degrees below 5400 feet. All time record highs are not expected on this day, but the Big Horn Basin from Worland through east of Lovell will again have at least a 2 out of 5 chance of highs of 105 or greater. There will be less wind on this day, so at least Fire Weather Concerns will be decreased.

Tuesday will be another very hot day. A majority of guidance is showing the ridge building back west this day, so temperatures could end up being a degree or two warmer, with again a greater than 1 in 2 chance of highs over 105 in the Bighorn Basin and most locations below 5500 feet seeing highs over 100 degrees, many for a fourth day in a row. There will be more moisture in the air though, with precipitable waters climbing back toward normals levels. This could lead to an increased coverage of convection. However, continued very warm air aloft may cap most of the activity. For now, we have confined it to the northern mountains but uncertainty is high here.

The ridge will finally begin to weaken somewhat as we head into Wednesday. It will still be rather hot, but not like this weekend. And next, to quote Monty Python, now for something completely different. That is the potential, emphasis on potential, for some heavy rain from thunderstorms. We will have low level east to southeasterly flow to bring upslope conditions. Precipitable water values will also be rather highs, climbing to over 150 percent of normal in some locations by Wednesday afternoon. There could also be a subtle shortwave topping the ridge to provide some lift, although these are difficult to time this far out. The WPC does have the area under a marginal risk of excessive rainfall as well. This is not a certainty but we will watch it. Following this it looks like we will be on the northern edge of the ridge with the potential of shortwaves running over the ridge, bringing chances of convection each day. Temperatures will remain above normal through next weekend, though not as hot as this weekend.

AVIATION /12Z TAFS THROUGH 12Z MONDAY/

Issued at 409 AM MDT Sun Jul 12 2026

VFR conditions are expected through 12Z. There will be more cumulus buildup in the western mountains. A couple of virga showers are possible but the chance is less than 15 percent. The only impacted terminal would be KJAC but here the chance is only around 10 percent. Wind gusts over 15 knots are possible at all terminals with gusts over 20 knots possible at all the terminals East of the Continental Divide after 19Z and before 06Z Monday.

Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for the latest information on smoke, icing and turbulence forecasts.

FIRE WEATHER

Issued at 136 AM MDT Sun Jul 12 2026

A combination of record high temperatures, humidity falling as low as 4 percent and a gusty southerly breeze will bring elevated fire weather to much of the area. Critical fire weather is likely this afternoon with the areas of most concern bring Park, Big Horn, Washakie, Hot Springs and Johnson Counties. Humidity will remain below 15 percent on Monday but with lighter wind fire conditions should improve somewhat.

CLIMATE

Issued at 136 AM MDT Sun Jul 12 2026

We have the potential for a record setting day today as far as all time record high station high temperatures. This is especially so at locations with a shorter period of record, like the Greybull and Riverton airports, where the stations between a 70 and 80 percent chance of breaking their all time record highs (108 F at Greybull and 102 F at Riverton). Some longer term stations also have a good chance with the Worland airport (all time record of 107 F) having a 70 percent chance. Most impressive, Lander has a 60 percent chance of breaking the all time record high temperature of 102 F, and records here date back to 1891.

RIW WATCHES/WARNINGS/ADVISORIES

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

Red Flag Warning from 11 AM this morning to 10 PM MDT this evening for WYZ275-276-280>283.