textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- A potentially impactful band of heavy, wet snow could disrupt the Thursday and Friday morning commutes across western Montana valleys, mostly in the form of downed trees/ power outages.

- Cold overnight lows on Friday and Saturday mornings could impact sensitive vegetation.

Widespread precipitation will continue into Friday as the Montana low moves east and another disturbance moves over the Northern Rockies from the north. Colder air associated with this system will bring snow levels down to mountain passes and some valleys. Expect wet, heavy snow over passes and higher valleys for Thursday morning. Motorists should expect winter driving conditions over Homestake, MacDonald, Lolo, Marias, and Lookout passes.

Valley impacts are less certain than mountain passes. Rain showers are expected to change over to or mix with wet snow. A wave is forecast to drop south into the Northern Rockies in the next few hours (Thursday morning). This boundary will allow for a period of enhanced precipitation and heavy wet snow could accumulate on tree branches this morning in northwest MT and overnight into Friday morning for west-central and southwest MT. The biggest concern would be breaking branches under the weight of snow, producing isolated power outages. Higher valleys of southwest MT and Seeley/ Swan Valleys could also have a trace to 3 inches of wet, slushy accumulations on sidewalks and roads Friday morning.

Friday and Saturday mornings, depending on clearing clouds, temperatures are forecast to drop into the upper teens and lower 20s. Please protect sensitive vegetation, that may have already been planted or sprouted.

Cooler and showery conditions will continue through late Sunday, with the potential of a weak wave producing more organized showers on Sunday.

AVIATION

Showers are coming to an end along and west of US-93, IE KGPI, KMSO, KSMN, and KHRF. However, the atmosphere is saturated in these locations and lower ceilings are expected to persist throughout the morning hours. Through 23/1000z, periods of light snow are expected at KBTM, producing 1SM or less visibility and ceilings down to 1000 feet or less.

The Northern Rockies airspace will remain in northwest flow throughout the afternoon with rain and snow showers at all terminals potentially producing temporary IFR conditions in showers. A more organized band of showers is possible along I-90 overnight into Friday morning from KMSO to KBTM.

MSO WATCHES/WARNINGS/ADVISORIES

MT...Winter Weather Advisory until noon MDT Friday for Bitterroot/Sapphire Mountains...Butte/Blackfoot Region... Potomac/Seeley Lake Region.

Winter Weather Advisory until 6 PM MDT Thursday for West Glacier Region.

ID...Winter Weather Advisory until noon MDT /11 AM PDT/ Friday for Eastern Lemhi County...Southern Clearwater Mountains... Western Lemhi County.