textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- Widespread rain develops today, followed by much cooler temperatures and a return to winter driving conditions over mountain passes by Thursday.

- A potentially impactful band of heavy, wet snow could disrupt the Thursday and Friday morning commutes across western Montana valleys.

The ridge of high pressure that brought summer-like conditions has moved out as a strong low pressure system moves onshore across the Pacific Northwest. Scattered rain showers will spread from south to north across the Northern Rockies through the day today.

A cold front associated with this system will move across the region this morning, bringing brief moderate to heavy rain and gusty west winds between sunrise and mid-morning. Wind gusts of 25 to 35 mph are expected as the front passes.

Widespread precipitation will continue through Thursday night. The highest moisture amountswith some areas seeing over an inch of rain and melted snoware expected along the Clearwater Mountains and the Continental Divide. Behind the front, temperatures will plummet 30 to 40 degrees compared to Tuesdays highs.

As cold air settles over the region, snow levels will drop rapidly tonight into Thursday. By Thursday morning, snow levels will fall to between 3,000 and 4,000 feet. This will bring wet, accumulating snow to higher valleys and mountain passes, including Lookout, Lolo, Homestake, and MacDonald passes. Travelers should prepare for slushy roads and winter driving conditions along the Continental Divide. Winter Weather Advisories are in effect from 9 PM this evening through noon Friday.

We continue to track a potential narrow band of heavy precipitation that could impact the Thursday morning commute across Northwest Montana. If this band develops over the valleys, heavy wet snow will cause low visibility, slushy roads, snapped tree branches, and isolated power outages. A second band of snow may develop over West-Central Montana Thursday night, impacting the Friday morning commute. Detailed weather models continue to show these bands, leading to higher confidence in these impacts.

The cool and showery pattern will persist through the weekend as a broad area of low pressure remains over the western United States.

AVIATION

A cold front will move across the region this morning and afternoon, bringing brief moderate to heavy rain and gusty west winds between sunrise and mid-morning. Wind gusts of 25 to 30 kts are expected as the front passes. The front will move through the region between 22/1800Z and 22/2100Z. Expect mountain obscurations throughout western Montana and north-central Idaho today. Snow-levels will lower to valley floors across northwest Montana tomorrow morning, potentially bring moderate to heavy snow, impacting KGPI with accumulating snowfall and low visibility. Another narrow band of moderate to heavy precipitation may bring snow and low visibility to KMSO and KHRF Friday morning.

MSO WATCHES/WARNINGS/ADVISORIES

MT...Winter Weather Advisory from 6 PM this evening to noon MDT Friday for Bitterroot/Sapphire Mountains...Butte/Blackfoot Region...Potomac/Seeley Lake Region.

Winter Weather Advisory from 6 PM this evening to 6 PM MDT Thursday for West Glacier Region.

ID...Winter Weather Advisory from 6 PM MDT /5 PM PDT/ this evening to noon MDT /11 AM PDT/ Friday for Eastern Lemhi County... Southern Clearwater Mountains...Western Lemhi County.