textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- Snow Impacts Travel: Friday through Saturday, definitely on passes but valleys become problematic beginning Friday evening.

- High Wind/Outage Risk (Friday): Southwesterly gusts of 30-45 mph (valleys) and 60+ mph (mountains) arrive Friday afternoon. Saturated soils will make trees more prone to falling, increasing the risk of power outages.

- Saturday Arctic Push: Flash freeze potential as bitterly cold air moves west of the Divide Saturday morning. Strong northeast winds will develop in prone canyons and gap areas (e.g., Bad Rock Canyon).

Today through Friday Morning: Transition Period

Fog and low stratus will gradually lift today, though elevated instability maintains scattered showers, primarily across NW Montana. A weak cold front arriving late this evening will lower snow levels to 4,000 feet by Friday morning.

-Mountain Passes: Minor impacts likely Friday morning due to slushy accumulations.

-Lemhi County: Cold air trapped in valleys may support a brief wintry mix (snow/freezing rain) Friday morning.

-Wind: Southwest winds increase Friday morning. A Wind Advisory is in effect for southwest Montana, including the Bitterroot Valley and Butte/Blackfoot region, for gusts up to 55 mph.

Friday Afternoon through Saturday: Potent Cold Front

A robust Pacific front arrives Friday afternoon, bringing a high-impact combination of wind and snow.

-Snow/Squalls: Widespread pass-level snow begins Friday afternoon. Transition to convective snow showers with a few snow squalls is expected Friday night into Saturday morning, impacting both mountains and valleys. Snow squalls will primarily occur along the Continental Divide, SW Montana, and Lemhi County, however most all locations will receive snow by Saturday morning. A rapid transition from wet, to slushy/icy surfaces is anticipated.

-Wind: Valley gusts of 30 to 45 mph (convective gusts 50+ mph) are expected with the frontal passage. Ridges will see 50 to 65+ mph. Given saturated soils and recent stress, expect a higher- than- normal risk for downed trees and power outages.

Saturday: Arctic Intrusion (Marias Pass & Flathead Valley)

Arctic air will spill south along the Divide and bleed westward through gaps (e.g., Marias Pass) into NW Montana on Saturday.

-Winds: Sharp shift to N/NE winds, accelerating through canyons. Bad Rock Canyon and the northern Flathead Valley will see the strongest gusts.

-Flash Freeze: Temperatures dropping into the teens and low 20s will freeze wet/slushy roads.

-Uncertainty: The southward and westward extent of the arctic boundary remains the primary forecast challenge; further refinements are likely.

Sunday through Mid-Week: Building Ridge

High pressure builds over the Pacific Northwest, leading to drier conditions. However, northwest flow aloft may allow minor disturbances to clip the region, keeping low-end chance for precipitation and fog/stratus in the forecast. Confidence decreases by late week as models hint at a potential Atmospheric River event.

AVIATION

Valley fog and low stratus continue to linger at some terminals this afternoon, though slow improvement is expected into the later afternoon. Attention is quickly shifting toward a potent incoming storm system arriving late tonight into Friday. Strong southwesterly flow increases overnight creating widespread low level wind shear and mechanical turbulence, notably including 45 knots of shear at terminals such as KBTM by 26/0700z. While surface gusts begin to increase elsewhere Friday morning, valley decoupling will help to enhance those shear profiles especially at KSMN, KMSO, and KHRF for a a couple hours overnight and into the morning before those gusts mix down to the surface. Snow and freezing levels begin to fall through the day on Friday toward valley floors. Anticipate lowering ceilings, widespread mountain obscurations, and reduced visibility through Saturday morning across much of the region.

MSO WATCHES/WARNINGS/ADVISORIES

MT...Winter Weather Advisory from 8 AM Friday to 2 PM MST Saturday for Lower Clark Fork Region.

Winter Weather Advisory from 5 AM Friday to 8 PM MST Saturday for Bitterroot/Sapphire Mountains.

Winter Weather Advisory from noon Friday to 5 PM MST Saturday for Kootenai/Cabinet Region.

Winter Weather Advisory from 8 AM Friday to 5 PM MST Saturday for West Glacier Region.

Winter Weather Advisory from 8 PM Friday to 8 PM MST Saturday for Flathead/Mission Valleys.

Wind Advisory from 5 AM to 5 PM MST Friday for Missoula/Bitterroot Valleys.

Winter Weather Advisory from 2 AM to 5 PM MST Saturday for Missoula/Bitterroot Valleys.

Wind Advisory from 6 AM Friday to 5 AM MST Saturday for Butte/Blackfoot Region.

Winter Weather Advisory from 5 AM to 8 PM MST Saturday for Butte/Blackfoot Region.

Wind Advisory from 8 AM Friday to midnight MST Friday night for Potomac/Seeley Lake Region.

Winter Weather Advisory from 11 AM Friday to 8 PM MST Saturday for Potomac/Seeley Lake Region.

ID...Winter Weather Advisory from 7 AM Friday to 1 PM PST Saturday for Northern Clearwater Mountains.

Winter Weather Advisory from 4 AM Friday to 7 PM PST Saturday for Southern Clearwater Mountains.

Winter Weather Advisory from 4 PM Friday to 10 AM PST Saturday for Orofino/Grangeville Region.

Winter Weather Advisory from 2 AM Friday to 8 PM MST Saturday for Eastern Lemhi County...Western Lemhi County.