textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- Today: Pass level snow, potential minor travel impacts.

- A potent cold front drops snow levels to the valley floors tonight and Thursday, bringing the potential for sudden snow squalls in southwest Montana and travel impacts over mountain passes.

- A brief warm up with drier weather is expected for the upcoming weekend before active weather returns.

Today through Thursday:

Moisture continues to stream overhead this morning, with the heaviest precipitation focused across north-central Idaho and northwest Montana. Snow levels currently range from 4,000 feet in northwest Montana to 6,000 feet in Lemhi County; consequently, impacts will remain primarily confined to the higher terrain. There is a high probability (60-80%) that Lookout, Marias, and Lolo passes will receive several inches of new snow. Slick and slushy roadways will remain near the to of the passes this morning, as areas just below pass levels are expected to remain mostly wet.

A strong cold front will sweep across the region this afternoon and evening, bringing sustained pass-level snow and scattered valley showers. This front will trigger a burst of heavy precipitation and rapidly plunging snow levels, eventually reaching valley floors.

- Localized High Impact Potential: Be prepared for sudden snow squalls as the front moves through southwest Montana this evening. These squalls can cause near-zero visibility and rapidly changing road conditions. Expect moderate travel impacts on all mountain passes through Thursday morning.

Uncertainty Details:

Significant uncertainty remains regarding valley snow accumulations. Current model guidance shows the deepest moisture arriving concurrently with the cold front, a setup that typically limits accumulation in the valleys; however, heavy localized bursts remain possible. Also, models have trended toward a weak backdoor front in Northwest Montana Thursday morning with an outside chance (20%) of 1-2 inches of snow for lower valley locations such as the Flathead Valley.

Friday through Next Week:

Showery conditions will persist through Friday as the trough exits the region, gradually tapering off late Friday. A ridge of high pressure will build this weekend, providing a brief but welcome return to warmer, drier weather. This break will be short- lived, however, as the next weather disturbance is projected to arrive by early next week.

AVIATION

Moisture continues to stream into the Northern Rockies today, bringing periods of precipitation. While downsloping will limit intensity for western Montana valleys, light rain is expected at times. Breezy southwest winds will increase ahead of the front, with gusts of 20-30 kts.

A strong cold front is timed to reach north-central Idaho by 15/1900Z, Missoula by 15/2300Z, and Butte by 16/0200Z. Expect a window of heavy precipitation and a sharp shift to northwest winds gusting 30-40 kts during passage. Snow levels ahead of the front will range from 4000 feet in northwest Montana to 6000 feet in Lemhi County, behind the front, snow levels will drop to all valley floors. Though post-frontal moisture is limited, scattered snow showers will continue across the Northern Rockies 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.