textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- Hot, dry, and smoky conditions continue with the persistent weather pattern through Friday.

- Isolated dry thunderstorm potential: This afternoon Lemhi County/SW Montana, expanding into west-central Montana on Thursday afternoon.

- Elevated winds and fire weather concerns: This weekend, region- wide.

This afternoon through Friday: Variable air quality remains the primary short-term impact across the region as a dry, hot southwesterly flow persists over the Northern Rockies. This pattern will hold through Friday before a Pacific trough moves onshore Saturday, breaking down the dominant upper-level ridge of high pressure. Historically, synoptic ridge breakdowns following an extended period of hot, dry weather significantly elevate fire weather concerns.

There will be just enough monsoonal moisture for isolated thunderstorms this afternoon and evening from Lemhi County into Southwest Montana. This moisture pushes northward on Thursday to include areas east of US 93 and south Highway 200. Gusty outflow winds of 40-50 mph will be common near any thunderstorms with a marginal chance (5%) of severe gusts over 60 mph. Dry lightning ignitions will be an additional hazard.

Saturday through early next week: Winds will increase on Saturday as the main Pacific trough advances eastward. The strongest winds will accompany and follow a dry cold-frontal passage Saturday afternoon into Sunday, with widespread westerly winds sustained at 10 to 25 mph and gusts reaching 25 to 40 mph across the region. The combination of gusty winds, persistent low relative humidity, and dry fuels will create critical fire weather conditions, accordingly fire weather watches have been issued. Additionally, winds will produce hazardous, choppy water on area lakes and rivers.

This system will remain predominantly dry with no significant precipitation expected. However, post-frontal cold air advection will drop temperatures 10 to 20 degrees for Sunday and Monday, returning high temperatures to slightly below seasonal averages.

AVIATION

High density altitudes and widespread visibility reductions due to wildfire smoke will persist across regional terminals through Saturday.

A high-based convective threat develops this afternoon/evening mainly south of a line from Butte to Salmon. High cloud bases (10,000-12,000 ft AGL) will keep precipitation minimal at the surface, but inverted-V soundings will promote isolated dry thunderstorms capable of producing strong, erratic outflow gusts up to 35-45 kt. A similar threat exists on Thursday afternoon/evening but the coverage area will expand northward generally east of US 93 and south of Highway 200.

Note: AMD NOT SKED for KGPI due to missing METARs during runway maintenance.

MSO WATCHES/WARNINGS/ADVISORIES

MT...Fire Weather Watch from Saturday afternoon through Saturday evening for Bitterroot...East Lolo...Flathead Reservation... Flathead/Glacier Park...Kootenai...West Lolo.

Fire Weather Watch from Saturday afternoon through Sunday evening for Deerlodge/West Beaverhead...East Beaverhead.

ID...Fire Weather Watch from Saturday morning through Saturday evening for Clearwater/Nez Perce...Palouse/Hells Canyon.