textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- High Pressure to bring prolonged dry pattern through early next week (January 20)

- Areas of valley fog and stratus through Friday.

- Trend toward a major pattern shift to colder and wetter starting Jan 21-22.

Low clouds and freezing fog developed last night and this morning across portions of the region. The satellite imagery early this afternoon depicts that the low clouds persist from Missoula west to northwest Montana, and in Idaho, the Dworshak Reservoir and portions of US-12 had fog and/or low clouds. Where it is sunny, temperatures have warmed into the 40s...but mid- slopes are well into the 50s! The Philipsburg, Montana RAWS weather station is depicting a temperature of 58 degrees with light winds...gorgeous! The previous record high from the USFS Ranger Station in Philipsburg was 53 degrees, set back in 1996.

If the fog is able to thin out in places, temperatures may be able to warm up this afternoon. If not, then they may struggle to get out of the 30s.

More fog and low clouds are expected to develop tonight, particularly near river systems and large bodies of water. This stable pattern is expected to last through early next week. The stagnant conditions will result in degrading air quality with initial concern for lower elevations of north- central Idaho thus Air Stagnation Advisories remain in effect. Additional air stagnation advisories may be required in the coming days across western Montana but the pattern is less favorable at least initially for immediate concerns.

Increasing confidence, 70% chance, in an active pattern developing by mid- week next week (January 22-24). This could be favorable for both mountains and valleys. Details still vary on how far west colder air will reach and the amount of moisture available for precipitation production. Stay tuned as this would be a major shift from the mild and dry weather through early next week.

AVIATION

Valley fog and stratus will be the primary concern over the coming days as high pressure ridging remains along the West Coast. A weak disturbance will slide down from the northwest on Thursday morning but with limited cloud cover and lack of significant flow, valley inversions should continue to strengthen. This strengthening will allow for an expansion and further persistence to fog and stratus development, especially along and north of Highway 12.

MSO WATCHES/WARNINGS/ADVISORIES

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