textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- Slow moving thunderstorms with heavy rain will cause a flash flood threat through this evening, especially in the Sapphire mountains and southwest Montana.

- Thunderstorms will be a near daily occurrence for Lemhi County, ID and southwest Montana.

- Gradual warming and drying trend through the weekend.

A trough over the region today combined with all the recent moisture is a good set up for thunderstorms. A lack of strong wind shear or really any strong winds aloft at all means storms will move slowly at 12-20 mph towards the northeast. This slower motion and ample moisture supply means the biggest threat from these storms will be heavy rain. The HREF shows the potential for up to 0.80 inches of rain in under an hour this afternoon. Rain amounts this high would only occur in limited areas directly under the core of the strongest storms, and would not be a widespread event. Still, this is a concern for potential flash flooding, especially considering how moist the soils are with the recent rain. Current forecasts have these stronger storms focused in the Bitterroot Valley and areas eastward and south of Highway 12, including the Sapphire mountains.

The trough pattern with southwest flow into the region will continue into early next week, and as a result, thunderstorms remain in the forecast through next week. The affected region will remain fairly consistent as well with a focus in the Bitterroot and eastward south of Highway 12. The flash flood risk is expected to diminish each day as a little more moisture gets worked out of the system.

Even with the trough over the region for the next week, we expect a gradual warming and drying trend. That is because the trough will trend weaker with time. By this weekend much of the region will see relative humidity drop into the low 20 percent range with the southwestern portions of Idaho County, ID dropping into the teens again.

AVIATION

A broad trough over the region combined with a very moist air mass is already causing convection this afternoon. Terminal KMSO will be on the northwestern edge of the convection, with KGPI the least likely to be affected by storms. Terminals KHRF, KSMN, and KBTM are under threat of thunderstorms through 02/06Z with heavy rain and small hail as the main threats.

MSO WATCHES/WARNINGS/ADVISORIES

MT...Flood Watch through this evening for Bitterroot/Sapphire Mountains...Butte/Blackfoot Region...Missoula/Bitterroot Valleys.

ID...None.