textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- Dry weather will continue through early next week (January 20). Expect persistent valley fog, freezing fog, and low clouds, which may cause icy spots on roads and low visibility.

- A 60 percent chance of a shift to colder and wetter conditions is expected mid-to-late next week (January 2123).

Today through Tuesday: High pressure remains over the region. Expect a mix of sunshine and valley fog/low clouds, primarily across northwest Montana and north-central Idaho today. Areas with clear skies will enjoy mild temperatures in the 40s and 50s, while fog-covered valleys will be stuck in the low to mid 30s. This pattern of valley fog and trapped cold air (inversions) will be the main challenge through early next week as the atmosphere remains stable. Visibility will slightly improve in northwest Montana later this afternoon, before diminishing once again overnight tonight.

Air Quality: Air Stagnation Advisories remain in effect through 4:00 PM PST Tuesday for north-central Idaho. Stable conditions will keep pollutants trapped near the valley floors, likely leading to poor air quality over time.

Next Week's Pattern Change: There remains at least a 60 percent probability that the weather will turn more active next week, though the exact timing is uncertain. Most data suggests the change will occur around January 2223, when a blast of arctic air may cross the mountains into northwest Montana. Some scenarios bring this air in as early as Wednesday the 21st. While specific details on snow amounts and the exact reach of the cold air are still unclear, a transition toward much colder and potentially snowy conditions is likely. Stay tuned for updates.

AVIATION

Valley fog and low stratus will once again be the main impacts for area aviation terminals today. KGPI and other locations across northwest Montana will continue to see widespread fog and low stratus lowering ceilings and visibility. There is a decent chance the visibility and low ceilings will slightly improve this afternoon, after 16/2100Z. Locations further south along the I-90 corridor, including KMSO will see more patchy fog and low stratus, which will periodically impact the terminal, without being a persistent impact. KSMN, will see persistent fog and low stratus throughout the day as well.

MSO WATCHES/WARNINGS/ADVISORIES

MT...ID...Air Stagnation Advisory until 4 PM PST Tuesday for Northern Clearwater Mountains...Orofino/Grangeville Region... Southern Clearwater Mountains.