textproduct: Western and Central Wyoming

KEY MESSAGES

- The hottest temperatures of this heat wave, some of which may exceed all-time record highs, are likely Sunday. Readings of 104 to 108 degrees have already been recorded as of late Sunday afternoon.

- The unseasonably hot temperatures, relative humidity of 3 to 6 percent, and southeasterly wind gusting 25 to 35 mph combine Sunday to create critical to near-critical fire weather conditions until late evening.

- Temperatures continue to run 10 to 15 degrees above seasonal normals through Tuesday. Therefore, the Extreme Heat Warning was extended and is now in effect until 9 PM Tuesday.

- Slightly cooler temperatures occur over the latter-half of the work week. At least a few showers develop over the far west Tuesday afternoon, with an increased chance Wednesday onward.

UPDATE

Issued at 1200 PM MDT Sun Jul 12 2026

IR shows mainly clear skies and nothing on radar to note for the day extending through Tuesday. The only forecast change is in reference to the excessive heat warning being extended through Tuesday evening. Temperatures have trended a bit up for Tuesday afternoon to similar conditions as Saturday and Monday has and will be. Therefore, it made sense to include Tuesday as well. Otherwise, not as hot Wednesday and beyond as storm chances start to creep back in through the weekend each afternoon and early evening with the monsoonal trough fetch of moisture from the south to southwest.

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 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 /00Z TAFS THROUGH 00Z TUESDAY/

Issued at 351 PM MDT Sun Jul 12 2026

VFR conditions through the period. Gusty afternoon winds decrease this evening. Winds increase a little for Monday following diurnal trends, but aren't as windy as today was. A mostly clear sky through the period, though some afternoon clouds and virga showers develop around the western Wyoming mountains Monday afternoon.

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

FIRE WEATHER

Issued at 1200 PM MDT Sun Jul 12 2026

Record high temperatures, minimum relative humidity falling as low as 5 percent and a southeasterly breeze will bring near critical to critical fire weather to much of the area. Elevated to near critical for Monday and Tuesday with minimum relative humidity values below critical thresholds, but wind will remain relatively light.

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 Tuesday for WYZ003>006-010- 011-013-016>020-023-025>030.

Red Flag Warning until 10 PM MDT Sunday evening for WYZ275-276- 280>283.