textproduct: Western and Central Wyoming

KEY MESSAGES

- Elevated to critical fire weather conditions are expected through 9PM tonight, with high confidence in critical conditions (very low humidity and gusty winds) East of the Continental Divide.

- Widespread warm and mostly dry weather through midday Sunday. Shower and thunderstorm chances increase across the entire area Sunday afternoon through Monday.

- Anticipate high temperatures in the 70s and low 80s west of the Continental Divide and highs in the mid 80s and low 90s east of the Continental Divide Friday and Saturday afternoons.

DISCUSSION

Issued at 1254 AM MDT Fri Sep 4 2026

For the first time in several days, the radar is clear across western and central Wyoming as well much of the surrounding states as much drier air has moved over the Cowboy state. This drier will stick around for a couple of days, but this leads to other concerns.

We had critical fire weather across the area yesterday with the low humidity and gusty afternoon wind. And, it looks like we will have another bout of critical fire weather today. There will be roughly the same set up as yesterday. We continue to be between an upper level low over the Pacific Northwest and a ridge across the southeastern United States. We continue to have 20 to 30 knots of wind at 700 millibars along with a decent height and pressure gradient across the area. The NBM ensemble has at least a 3 out of 5 chance of wind gusts over 25 mph across a good portion of the area this afternoon. The limiting factor today will be humidity. Somewhat higher humidity will move into southern Wyoming, and this should keep most of that area from reaching the 3 hours of critical fire weather to justify a Red Flag Warning. With a greater than 3 out of 4 chance of relative humidity falling under 15 percent this afternoon across areas East of the Divide, we will keep the Red Flag Warning as is this morning. The wind may not be quite as strong in northern areas, but will be close enough the justify keeping the warning. It will be a warm day as we head into Labor Day weekend as well. Much of the Bighorn Basin, Wind River Basin and areas along and east of Interstate 25 have at least a 1 in 2 chance of reaching or exceeding 90 degrees today.

The ridge will retrograde over the weekend, pushing into the southern Plains states during the three day weekend. Temperatures will remain well above normal on Saturday and Sunday, with the heat peaking on Saturday. Most locations below 5000 feet in elevation will have at least a 1 in 2 chance of high temperatures of 90 or higher. As for fire weather, concerns should begin to ease somewhat. Humidity will begin to climb as another surge of monsoonal moisture slowly makes it's way toward the area. The core of it should remain east of the area on Saturday, so almost all areas should see no rain (the highest chance of a shower or storm is only 1 out of 10). There will also be less wind. Elevated fire weather conditions are still possible but the chance of critical fire weather looks smaller than today. So, we will not extend the Red Flag Warning at this time.

The monsoonal plume will move over the area on Sunday, as the ridge continues to drift westward. Wyoming looks to be in a decent spot for the moisture, with a moist conveyor belt between the ridge and the upper level low that continues to spin over Oregon. A bit of added moisture will also be coming in from Tropical Storm Marie. Precipitable water values look to peak on Sunday evening, with some models rising to over an inch, which is close to 200 percent of normal. The models do sometimes overcook this though, so reality is probably around 20 percent less. Nevertheless, it is high for early September. There could be a good coverage of showers and storms though. The moisture will be moving in ahead of an approaching Pacific Cold Front and negatively tilted trough associated with the upper level low that will be lifting northward over Idaho. As for the potential of heavy rain, there is some. A mitigating factor to possible flooding will be that there will be steering flow, which will keep the storms moving. This still looks like the best chance for rain. It will be one more very warm day on Sunday, although more cloud cover could keep high temperatures a couple of degrees cooler.

The end of the holiday weekend on Labor Day will be a cooler day with temperatures close to seasonal averages. Drier air will likely be moving into the area. However, there will may be enough moisture wrapping around the low as it moves into Canada to bring a few showers and storms (a 1 in 5 to a 1 in 2 chance), mainly to northern and western Wyoming. With a decent pressure gradient across the area, it also looks like a rather breezy day, but cooler temperatures should keep any fire weather concerns below critical.

There is good model agreement in drier air moving over the area for Tuesday and Wednesday, bring a couple of nice late summer / early autumn days (depending on they are astronomical or meteorological seasons) with comfortably warm temperatures. Monsoonal moisture should then return for later in the week, although there are differences in model guidance in regards to exact timing to when it will arrive. So, it looks like a hot start to the holiday weekend, with a return to more seasonably weather for early next week. And, has been the case over the past couple of months, the everlasting monsoon will make a couple more appearances.

AVIATION /12Z TAFS THROUGH 12Z SATURDAY/

Issued at 418 AM MDT Fri Sep 4 2026

VFR conditions will continue through 12Z Friday. The main concern today will be wind which will begin increasing after 16Z. All terminals could see gusts of at least 20 knots with strongest wind in vicinity of KCPR where gusts over 30 mph are possible. Wind should again decrease after sunset as the atmosphere decouples. Only passing areas of mid to high level clouds are expected through Friday night.

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 1254 AM MDT Fri Sep 4 2026

A combination of relative humidity falling under 15 percent, a gusty southwest wind and dry fuels will bring critical fire weather to most locations East of the Continental Divide this afternoon. Elsewhere, elevated fire weather is likely but humidity should remain above 15 percent for the most part. Elevated fire weather is likely Saturday before increasing moisture on Sunday brings an improvement to fire weather conditions.

RIW WATCHES/WARNINGS/ADVISORIES

Red Flag Warning until 9 PM MDT this evening for WYZ275-276- 280>283-285>287-289.