textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- Wintry Mix Today: A pulse of moisture moving from south to north will create slick travel conditions today. Expect a messy transition of snow and freezing rain in the valleys through the afternoon.

- Christmas Arctic Wedge: Forecasters are closely watching for a shallow push of Arctic air into Northwest Montana on Christmas Eve. This could lead to a sharp temperature drop and localized heavy snow near the Divide.

- Cold Front Friday: A robust cold front remains on track for Friday, which will bring a definitive changeover from rain to snow for all valley floors and gusty winds.

A complex and active weather pattern continues as moist Pacific air overrides stubborn cool air trapped in our mountain valleys. This setup remains the primary challenge for the early part of the week, with a broader shift toward a colder, more wintry regime arriving just in time for the holiday weekend.

Today through Wednesday: The next wave of precipitation is advancing into the region this morning. We are seeing thermal profiles that favor snow and freezing rain rather than a clean switch to rain this morning. Winter Weather Advisories are in effect for parts of Lemhi County, the Clearwater Mountains, the Bitterroot/Sapphire range, and Missoula/Bitterroot Valleys through midday for low elevation mixed precipitation and mountain pass level snow. Elsewhere, isolated slick spots are expected with a wintry mix. The difference between wet and icy road surfaces will be narrow.

By tonight, precipitation becomes focused to northwest Montana. While most valleys may see a brief period of rain or a rain/snow mix as the airmass modifies, the far northern tier near Marias Pass and Essex needs to be monitored. There is a persistent signal that a "wedge" of Arctic air could spill over the Continental Divide, which would lead to much colder temperatures with either increase potential for snow or freezing rain for those specific areas while the rest of the region remains relatively mild.

Thursday through Sunday: The weather remains unsettled through Christmas Day with scattered mountain snow and valley rain/snow showers. Hopes for a white Christmas are slim for the valleys, with only a 5% chance for a half-inch of snow. This would mark a rare third snow-free Christmas on record for locations like Kalispell and Missoula.

Changes occurs on Friday. A strong Pacific cold front is forecast to sweep through the Northern Rockies. This will:

Crash snow levels to the valley floors, ending the rain/snow mix and transitioning everything to snow.

Increase winds, with gusty conditions likely along the front.

Cooldown: Temperatures will trend back toward seasonal normals for the weekend.

Looking ahead toward the New Year, ensemble guidance is already hinting at a potential Atmospheric River event. This could bring another round of significant moisture and windier conditions to end the year, though details on the exact track remain uncertain.

AVIATION

Brief showers is north-central Idaho into west-central Montana will continue to lower ceilings and reduce visibility at times through around sunrise. The next system arrives from the south this morning. Expect conditions to deteriorate to MVFR/IFR this morning as precipitation overspreads the region, and mountain obscuration will be widespread. The primary concern for terminals like KMSO, KHRF, and KSMN will be a wintry mix of snow and freezing rain through 18Z. This area of precipitation will shift northwards during the day and generally be over northwest Montana by evening.

MSO WATCHES/WARNINGS/ADVISORIES

MT...Winter Weather Advisory from 5 AM early this morning to noon MST today for Bitterroot/Sapphire Mountains... Missoula/Bitterroot Valleys.

ID...Winter Weather Advisory from 4 AM to 11 AM PST this morning for Southern Clearwater Mountains.

Winter Weather Advisory until noon MST today for Eastern Lemhi County...Western Lemhi County.