MISSOULA — A potent push of Pacific moisture will move in late Saturday night into early Monday. At the same time, a very cold airmass will spill southward out of Canada & interact with that moisture (along with wind) causing our first significant system of the season!
Here are the specifics:
The primary period of concern for winter travel impacts over mountain passes begins Saturday evening along the Divide (Marias Pass) and spreads westwards Sunday through Monday morning. Valleys in northwest Montana could face a dual threat: slick conditions during the initial rain-to-snow transition Sunday morning, followed by accumulating snow and icy conditions for the Monday morning commute. By Monday morning, accumulating snow and difficult travel are expected to become more widespread, including the Butte/Blackfoot, Potomac/Seeley Lake & Kootenai/Cabinet Regions. Monday will be the coldest day, with morning wind chills in the teens and 20s combining with gusty winds to create areas of blowing and drifting snow, especially near mountain passes.
Winter Weather Highlights have been issued from 6pm Saturday until noon Monday and are as follows:
Winter Weather Advisories for Potomac/Seeley Lake Region (4,000'+), Lower Clark Fork Region (4,500'+), Butte/Blackfoot Region (5,000'+) & Bitterroot/Sapphire Mountains (5,500’+).
Winter Storm Warning for the West Glacier & Kootenai/Cabinet Regions (all elevations).
It’s also looking more likely now that a period of high-impact, potentially damaging winds will impact northwest Montana from Sunday night into Monday. Northeasterly wind gust of 40-55mph are expected especially through channeled terrain in the eastern Flathead valley, southeastern portions of Flathead Lake and through the mountainous terrain where a High Wind Watch is in place.
According to the NWS, The primary threat is ramped up by several unique factors. Heavy, wet snow above 3,000’ on Sunday/Sunday night will accumulate on trees that have not yet lost their leaves, increasing the potential for significant branch and tree failure. This is compounded by wet, unfrozen ground, which makes trees more susceptible to the seasonally abnormal northeasterly wind direction. Key impacts include the potential for widespread power outages, falling trees, and dock damage along the southern shores of Flathead Lake.
Bottom line: if you’re traveling or plan on being in the backcountry, prepare for winter-like conditions beginning Saturday night into Sunday morning. Winter weather impacts will escalate Sunday night into Monday as colder air arrives, setting the stage for windy & snowy conditions, especially along the divide and in northwest Montana.
Although temperatures begin to moderate some on Tuesday, an overall active and cool weather pattern is anticipated for much of next week.
