textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- A strong cold front sweeps through this afternoon and evening, bringing rapidly plunging snow levels and a burst of heavy precipitation.

- Sudden, intense snow squalls are a significant threat for southwest Montana this evening, which could rapidly drop visibility and create hazardous travel conditions.

- Lingering snow showers on Thursday and Friday will give way to a brief, pleasant warm-up this weekend.

A plume of Pacific moisture will continue to fuel precipitation over north-central Idaho and northwest Montana this afternoon. The main event, a robust cold front, will sweep from west to east across the region late this afternoon and through the evening. As this front passes, expect a sharp drop in temperatures and an intense burst of precipitation. Snow levels will rapidly crash from around 4,000-6,000 feet all the way to the valley floors. The most critical impact tonight will be the potential for sudden snow squalls, particularly across southwest Montana. These fast- moving bands of intense snow and wind can cause near-zero visibility and instantly coat roads in ice and slush. If you are traveling this evening, especially over mountain passes or along the I-90 corridor in southwest Montana, be prepared for rapidly deteriorating and hazardous conditions.

Behind the front, a cooler and unsettled pattern takes hold. Expect snow showers to persist across the Northern Rockies through at least Thursday. There is a renewed chance that a secondary push of cold air (a backdoor front) moving into northwest Montana Thursday morning could bring 1 to 3 inches of snow to lower- elevation spots like the Flathead Valley. High- resolution models suggest that the front will move through the rest of the region during Thursday afternoon and evening with winter-like travel conditions possible again over MacDonald and Homestake Passes.

Showers will continue into Friday but will gradually taper off by Friday evening as the main storm system exits to our east.

We will see a break in the active weather this weekend. A ridge of high pressure will build over the region, clearing the skies and bringing a return to warmer, drier, and more seasonable conditions. Long-range models suggest another weather disturbance will arrive early next week, bringing a return to cooler and wetter conditions.

AVIATION

Moisture will continue streaming into the Northern Rockies this afternoon, bringing periods of precipitation and lowering ceilings. Breezy southwest winds will increase ahead of an approaching cold front, with gusts of 20-30 kts at terminal sites. This strong cold front is timed to reach KMSO by 15/2300Z, and KBTM by 16/0200Z. Expect a window of heavy precipitation and a sharp shift to northwest winds gusting 30-40 kts during the frontal passage. Snow levels ahead of the front will range from 4,000 feet in northwest Montana to 6,000 feet near Lemhi County. Behind the front, snow levels will crash to all valley floors. Snow showers and mountain obscurations will continue through Thursday.

MSO WATCHES/WARNINGS/ADVISORIES

MT...Winter Weather Advisory from 6 PM this evening to 9 AM MDT Thursday for Butte/Blackfoot Region...Potomac/Seeley Lake Region.

Winter Weather Advisory until 9 AM MDT Thursday for Lower Clark Fork Region...West Glacier Region.

Winter Weather Advisory from 3 PM this afternoon to 9 AM MDT Thursday for Bitterroot/Sapphire Mountains.

ID...Winter Weather Advisory from 6 PM MDT /5 PM PDT/ this evening to 9 AM MDT /8 AM PDT/ Thursday for Eastern Lemhi County... Northern Clearwater Mountains...Southern Clearwater Mountains...Western Lemhi County.