textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- Flooding threat continues in far northwest Montana.

- Precipitation continues into Friday but in diminished quantities compared to Wednesday/early today.

- Snow returns to the Glacier Region on early Friday.

Hydrology and Precipitation: The atmospheric river plume has shifted south out of northwest Montana into north-central Idaho and west-central Montana. While considerable flooding continues in parts of Lincoln and Sanders counties due to earlier rain and snowmelt, the break in precipitation across the northern half of northwest Montana will persist through this evening. The moisture plume is expected to shift back northward late tonight, stalling over northwest Montana on Friday. Precipitation amounts on Friday will be lighter than the Wednesday event, with valleys likely seeing another 0.15-0.30 inches and mountains receiving 0.50-1.00 inches. Snow levels will drop to 4000-5000 feet tonight in the impacted areas before rebounding to 6000 feet on Friday. Flooding remains a concern in previously affected areas, though significant expansion into new areas is not anticipated.

Winter Weather: A wintry component will develop by this evening as Arctic air banks against the Continental Divide. This cold air will filter down the US-2 corridor, though uncertainty remains regarding how far west it will progress. Snow is expected at Marias Pass, occasionally reaching down to Essex. A secondary concern is the potential for light freezing rain if the shallow cold air reaches West Glacier. Given the potential for hazardous travel, a Winter Weather Advisory has been issued for the Glacier Region from Friday into early Saturday.

Extended Forecast: Upper-level ridging builds over the weekend, maintaining mild temperatures but increasing the threat of fog and low stratus development. Another atmospheric river arrives late Monday into Tuesday with snow levels initially near 7000 feet. Most models indicate a strong Pacific cold front passing late Tuesday or Wednesday, which will likely produce strong winds and crash snow levels to valley floors. This signals a regime change, with widespread winter weather impacts including valley snow becoming more likely by the middle of next week. Stay tuned for this expected return to winter!

AVIATION

The atmospheric river has sagged southward into north-central Idaho and into west-central Montana with lowered ceilings and reduced visibility this afternoon. The stream of moisture will work northward again tonight/Friday impacting northwest Montana. Gusty winds and significant wind shear will continue to diminish this afternoon/evening. There is an outside chance (10-15%) of light freezing rain at KGPI early Friday as a shallow intrusion of Arctic air works down US-2.

MSO WATCHES/WARNINGS/ADVISORIES

MT...Flood Watch until 5 PM MST this afternoon for Flathead/Mission Valleys...Kootenai/Cabinet Region...Lower Clark Fork Region...Potomac/Seeley Lake Region...West Glacier Region.

Winter Weather Advisory from midnight tonight to 5 AM MST Saturday for West Glacier Region.

Wind Advisory until 7 PM MST this evening for Butte/Blackfoot Region.

ID...Flood Watch until 4 PM PST this afternoon for Northern Clearwater Mountains...Orofino/Grangeville Region.