textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- October weather has arrived! Seasonal temperatures mean cool afternoons and cooler mornings.

- Confidence is increasing for potential winter driving conditions at mountain pass level Tuesday night into Wednesday. Precipitation will continue this afternoon ending from northwest to southeast late afternoon into early evening. Observations from around the region also demonstrate snow levels are slowly lowering. Precipitation may linger in southwest MT as snow levels lower to or below mountain passes, 6000 feet or lower. Winter weather advisories remain in effect for this evenings rush hour to highlight the potential for slick driving conditions over Homestake and MacDonald Passes.

A northeasterly gradient continues over night as a cold Canadian air mass settles into central MT. If the gradient relaxes and clouds clear, efficient radiational cooling will allow for patchy to areas of valley fog or low stratus clouds to develop.

Saturday through Monday will feel like October with seasonable temperatures, cool afternoons and cold mornings. Sunday and Monday valley fog and low stratus chances will contract back to more typical valleys.

The models are coalescing around a solution that brings another weather system on Tuesday. Another round of valley rain and mountain snow is expected. Snow levels are forecast to lower below mountain passes overnight Tuesday and winter driving conditions may be present at most regional passes Wednesday morning while only Lost Trail Pass has the potential to receive snow for Tuesday mornings commute. Also Wednesday morning, along the Continental Divide the change over to snow in valleys may allow for minor accumulations on vegetation.

AVIATION

Widespread precipitation is producing varying categories for visibility and ceilings at all terminals through 23/2100z. The precipitation type is expected to transition over to snow at KBTM this afternoon, at times visibility will be reduced to a mile or less. Low level moisture, weakening easterly gradient, and radiational cooling Saturday morning could produce patchy fog or low level stratus at any terminal. Any terminal that does develop fog or stratus may be slow to lift, with conditions remaining through 24/1800z.

MSO WATCHES/WARNINGS/ADVISORIES

MT...Winter Weather Advisory from 3 PM this afternoon to midnight MDT tonight for Butte/Blackfoot Region.

ID...None.