textproduct: Western and Central Wyoming

KEY MESSAGES

- Low humidity (10 to 20 percent) and breezy winds (gusts of 20 to 30 mph) will contribute to near-critical fire weather conditions through sunset.

- An approaching system will return showers and thunderstorms to the area today, starting mid-afternoon across southwestern Wyoming. This activity will move northward through tonight. Western Wyoming will have the best rain chances (50-70% chance of at least 0.25").

- Cooler and windy on Monday with widespread gusts of 30 to 50 mph during the afternoon.

- Wind and low humidity will lead to continued fire weather concerns through the week. A late week system may bring cooler and wetter conditions though uncertainty remains high at this time.

UPDATE

Issued at 1244 PM MDT Sun Sep 6 2026

Fire weather concerns continue this afternoon, with near-critical conditions for much of the area given a gusty southwest wind and humidity near or below 20 percent. Showers and thunderstorms with the incoming system are expected to start across southwestern Wyoming between 3 PM and 6 PM, which is a little later than forecast yesterday. By sunset this activity will become more widespread across western and southern Wyoming. Chances then increase through tonight farther north, though especially across western Wyoming. One thing to note, even after sunset, is the potential for outflow wind gusts of 30 to 40 mph. Convection-allowing models are showing this most widespread east of the Divide this evening as showers move in there, also aided by a deepening surface low across northern Wyoming.

DISCUSSION

Issued at 105 AM MDT Sun Sep 6 2026

I was thinking back to where I was 18 years ago tonight. I had just finished my last shift at my previous job for a private company in Pennsylvania, and begin a 5000 mile drive to start my career in the National Weather Service, in Alaska. At this time I was sound asleep in a motel room in Sparta, Wisconsin. I was quite tired after driving 800 miles after working a midnight shift and having to endure the Chicago rush hour traffic. And this ties into the weather pattern coming up the next week, mainly with transitions and changes. As temperatures changed from the warm late summer temperatures in the lower 48 states then cooling as I drove northward, especially when I reached the Yukon, Northwest Territories and Alaska. This reminds me of the pattern over the next week, when we will see a little bit of everything. This includes some continued warm late summer temperatures, gusty to strong wind, elevated to potentially critical fire weather and maybe, just maybe, the first real taste of fall for next weekend.

Today will be another very warm day across the area as ridging holds for another day, with the warmest spots likely seeing highs around 90. We have a couple of concerns over the next 24 hours. The first is, once again, fire weather. The set up looks similar to yesterday. Some areas will be see relative humidity under 15 percent, especially East of the Divide. Others will see a gusty afternoon wind, especially in southern Wyoming and West of the Divide. Most of these areas are not together though. With this, along with increasing cloud cover and dew points ticking higher later in the day, we will not issue any Red Flag Warnings. Elevated fire weather still looks likely though. The other concern, especially late today and especially tonight, will be the chance of showers and possible thunderstorms. Deeper moisture will moving into southwestern Wyoming later this afternoon, spreading across the area tonight. At this same time, an upper level low will be lifting northward in Idaho. This will drag a Pacific Cold Front and negatively tilted trough across the area. This will be a typical monsoon set up though, in that all areas will have a chance of showers, but not everyone will see one. Models have come into decent agreement in keeping the most numerous showers in western Wyoming, with lessening chances further east. We still have a marginal risk of excessive rainfall across this area as well. Precipitable water values will rise close to an inch in some locations, which is over 175 percent of normal. However, there is plenty of steering flow, with some 500 millibar winds approaching 50 knots. So, the main threat of from training storms. With the strong wind level wind as possible mixing from the frontal passage, there could be some strong wind gusts as well. The deepest moisture will be through the area by Monday morning, but a few showers will be possible into Monday with wrap-around moisture, mainly in the northern and western Wyoming.

Monday will be a cooler day behind the front. The main concern here shifts to wind. We will have a fairly pressure gradient between the low to the northwest and the ridge to the south and east. That means a gusty to potentially strong wind across much of the area. Much of the area, especially East of the Divide, has at least a 1 in 2 chance of wind gusts past 35 mph. With 700 millibar winds approaching 40 knots at times, there could be some gusts to around 50 mph, especially in the higher elevations and in some wind prone areas like the south side of Casper. As for fire weather, the wind will be there but there should be enough residual humidity to keep conditions above critical. It will be another day of elevated fire weather though. The real day of fire weather concern will be Tuesday, when dew points really crater and a gusty wind continues. As of now, there is at least a 2 out of 3 chance of seeing some Fire Weather Watches issued for this time period. Dry zonal flow will dominate through Friday with dry conditions, warm temperatures and a continued gusty breeze. Further fire weather highlights may be needed on these days bit wind may be borderline in some locations.

And now to the potential change I was talking about. The main word of this sentence is POTENTIAL, since this is a week out a lot can change between now and then. Both the European model and the GFS show a decent system coming out of Canada for the weekend. There are differences in timing and details, as would be expected this far out. In addition, the GFS has more of a front / open wave while the European has a closed low. I won't even try to hash out the details at this point. However, the potential for the coolest temperatures we have seen since last spring are possible. Both models show below zero temperatures at 700 millibars at some point next weekend, with some showing as low as minus 5. And with some moisture, this could also mean some snow for the mountains. Again, this is still a long way out so uncertainty is still very high. However, this could be the first taste of fall and some relief for people who are sick of the long and hot summer we have had.

AVIATION /18Z TAFS THROUGH 18Z MONDAY/

Issued at 1057 AM MDT Sun Sep 6 2026

VFR conditions prevail through this afternoon. Widespread southwest gusts 15 to 30 knots are expected across the area ahead of an incoming cold front. High clouds begin to move in from the southwest through the afternoon. Tonight, a cold front brings increasing clouds and a shot for rain. Chances begin to increase around KBPI, KJAC, and KRKS around 01z, spreading northeastwards overnight. Most sites have a prevailing rain group overnight as the front passes through. A gusty wind is also possible with frontal passage. Clouds look to quickly clear into Monday morning. Monday afternoon will be windy across the area, with winds beginning to pick up late Monday morning (15z-18z).

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 105 AM MDT Sun Sep 6 2026

Today will be similar to yesterday. Humidity will fall into the teen at times this afternoon, especially East of the Divide with gusty breeze developing, especially in southern Wyoming. Although critical fire weather is not expected, elevated to near critical fire weather conditions will be fairly widespread this afternoon. Elevated to critical fire weather will be possible much of next week, with low humidity and breezy to windy conditions continuing. At this point, Tuesday looks like the day of greatest concern.

RIW WATCHES/WARNINGS/ADVISORIES

None.