textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- Hot, dry, and smoky conditions continue through this week.

- Isolated thunderstorms remain a threat for southwest Montana including Butte. Potentially expanding northward late this week.

- Even hotter, drier, and windier conditions by Saturday. Elevated fire weather conditions.

- Cool down to near average temperatures Sunday, though it remains dry.

The Northern Rockies will remain along the western periphery of a broad ridge of high pressure. Toward the end of the work week, the ridge will amplify as a deep, stationary Pacific trough moves east into British Columbia. Beginning as early as Friday, embedded shortwave energy ejecting off the trough could interact with the ridge. Current guidance targets late Saturday into early Sunday morning for the ridge breakdown.

Hot, dry, and smoky conditions will be common this week. Depending on the thickness of wildfire smoke, daytime temperatures could be attenuated several degrees from the current forecast. Degraded air quality and reduced visibility remain the primary impacts. Sensitive groups should limit outdoor exertion.

The only hint at precipitation for the first part of the week is isolated thunderstorm chances in Lemhi County and southwest Montana (mainly afternoons/evenings) as limited monsoonal moisture interacts with daytime heating. Beginning Wednesday and lasting through Friday, models show potential disturbances that could expand thunderstorm coverage further north into west-central Montana and north-central Idaho. If thunderstorms do develop, they would be mostly dry with gusty outflow potential. There is a concern for nocturnal storms, particularly on Thursday night but overall confidence is low at this point.

There is a growing consensus that a ridge breakdown will occur later Saturday into Sunday based on the latest ensemble clusters. This transition period is significant given increased wind potential and elevated fire weather concerns.

AVIATION

Wildfire smoke will continue to be the primary concern through mid week, as terminals will occasionally drop to MVFR visibilities. Otherwise, ridging will dominate with hot and dry conditions. There is only a slight probability (less than 20 percent) for thunderstorm development across Lemhi County into southwest Montana each afternoon. Expect afternoon gusts to 20 kts diminishing around sunset for terminal sites.