textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- Rounds of showers and thunderstorms with locally heavy rain, the potential for debris flows, and gusty winds (mainly western Montana) through today.

- Temporary relief from smoke with easterly winds.

- Gradual warming and drying trend this weekend, daily thunderstorm threat continues.

Scattered rain showers and isolated thunderstorms continued to redevelop and move over western Montana and north-central Idaho during the overnight hours into early this morning. Brief heavy rainfall and occasional lightning occurred with these storms. Lingering showers will continue to stream over western Montana through mid-morning.

This afternoon, several rounds of showers and thunderstorms will impact the Northern Rockies and will likely bring isolated activity through the overnight once again. The main threat with these thunderstorms will be brief heavy rainfall. Yesterday afternoon, thunderstorms produced up to 0.40 inches per hour, which can be expected with the thunderstorms today. The strongest storms are expected between 3 PM and 9 PM, bringing a threat for debris flows and excessive runoff to flood-prone areas of northern Lemhi County and burn scars in the southern Bitterroot Valley. A Flash Flood Watch may be needed to highlight areas at most risk for impacts this afternoon and evening. Gusty and erratic winds between 30-40 mph will also be a threat, that could blow around unsecured objects and bring minor tree damage.

A ridge of high pressure will rebuild over the Northern Rockies this weekend into early next week. Persistent southwest winds aloft will continue to bring moisture into the region, keeping atmospheric moisture high. This pattern will sustain daily chances for afternoon showers and thunderstorms through next week, preventing a full return to dry conditions. Wildfire smoke will remain an ongoing challenge, with air quality expected to degrade slowly this weekend as southwest winds transport smoke plumes from source fires in eastern Washington and Oregon.

AVIATION

Scattered rain showers and isolated thunderstorms will continue to stream over western Montana and north-central Idaho through 14/1500Z this morning. Shower and thunderstorm activity will redevelop this afternoon and evening, bringing a threat for frequent lightning, brief heavy rainfall, and gusty, erratic winds up to 35 kts to all aviation sites across the Northern Rockies. However, KMSO, KHRF, KBTM, and KSMN will have the highest chance for the strongest storms between 14/2000Z and 15/0200Z this evening.

Persistent easterly winds have limited the impacts due to smoke from regional and local wildfires, but this is likely to change this weekend and early next week, when a southwest wind pattern returns to the Northern Rockies.