textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- High pressure will bring a long period of dry weather through early next week (January 20).

- Expect areas of valley fog and low clouds through Friday.

- A major weather shift to colder and wetter conditions is likely starting around January 22nd.

Widespread freezing fog has returned overnight, creating low visibility in several areas. High moisture near the ground may create slick spots on roads for the morning commute. Due to the widespread low visibility, a Dense Fog Advisory may need to be issued for the morning commute. Allow for extra travel time as you head out to work and school today. Satellite imagery shows low clouds and fog stretching from Missoula into northwest Montana. In Idaho, the Dworshak Reservoir and parts of US-12 are also seeing fog. Like yesterday, areas that see plenty of sunshine will warm into the mid-40s to low 50s. Valleys where the fog remains trapped (Missoula, Flathead, and Kootenai) will likely stay in the 30s.

More fog and low clouds are expected to form tonight, especially near rivers and lakes. This stable weather pattern will likely last through early next week. The stagnant air will cause air quality to worsen, with the first concerns appearing in lower elevations of north-central Idaho where Air Stagnation Advisories are in effect. Additional advisories may be needed for western Montana in the coming days, though the air quality there is less of a concern for now.

Confidence is increasing (80% chance) that an active, stormy pattern will develop by the middle of next week (January 22-24). This shift could bring needed snow to both the mountains and valleys. Details are still being determined regarding how far west the cold air will reach and how much moisture will be available for snow. This would be a major change from the mild, dry weather we are seeing through early next week.

AVIATION

Valley fog and low clouds will be the main concern for aviation terminals today and over the next few days as high pressure remains over the West Coast. A weak weather disturbance moving south from Canada helped clear some fog in the Flathead Valley earlier, but fog and low clouds are expected to return and persist through much of the day due to light winds. The Bitterroot Valley (from Stevensville to Hamilton) and areas near Orofino and Grangeville may see some afternoon clearing. However, the Missoula and Kalispell airports will likely keep low clouds and fog through at least 15/1700Z. Any fog that clears this afternoon will likely return tonight.

MSO WATCHES/WARNINGS/ADVISORIES

MT...ID...Air Stagnation Advisory until 10 AM PST Friday for Northern Clearwater Mountains...Orofino/Grangeville Region... Southern Clearwater Mountains.