textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- Unsettled, cool, and showery conditions persist into the weekend.

- Mountain snow this weekend will create difficult conditions for backcountry recreation, especially along the Continental Divide.

- Widespread frost and freezing temperatures are highly likely Sunday through Tuesday mornings.

Showery conditions have developed this afternoon under modest instability and moisture ahead of an approaching trough. Showers will mainly favor the higher terrain across northwest Montana. Snow levels will continue to hover around 5,000-6,000 feet, so light snow accumulations will remain confined to the higher terrain.

A more organized low pressure system will begin to drop into western Montana and north central Idaho this weekend, bringing increased chances for precipitation area wide. The system has anomalously cold air associated with it, and will drop snow levels as low as 4000 feet by Sunday morning. Accumulating snow is anticipated for the higher elevations, bringing difficult conditions for backcountry recreation due to slushy snow accumulations on unpaved roadways. Cold, wet and breezy conditions will increase the hypothermia risk for any recreationalists. The precipitation looks to intensify along the Continental Divide on Sunday as northeasterly flow enhances lift along the Continental Divide. Accumulating slushy snow even into the higher elevation valleys in southwest Montana (Butte) is possible. Winter weather advisories have been issued for the higher terrain and may need to be expanded westwards on future shifts.

Unseasonably cold temperatures will be in place Sunday through early next week, bringing the threat for a frost/freeze across many valleys of western Montana and north central Idaho. Those with sensitive vegetation or early season plantings may want to take protective measures, especially on Monday morning when frost has the potential to be most widespread due to decreased cloud cover.

A general warming trend is anticipated next week, though generally returning to normal for this time of year. A period of brief drying is possible but may not be long lasting.

AVIATION

West winds of about 10 to 20 knots will be widespread this afternoon ahead of a trough of low pressure approaching from the west. Scattered showers at KMSO and KGPI may bring brief, localized reductions in visibility into this evening. More widespread showers will arrive overnight tonight or early Saturday morning, favoring KGPI, KMSO, and KHRF. Expect widespread lowered ceilings down to about 2500 feet by Saturday morning, as well as continued precipitation through about midday transitioning to scattered showers and thunderstorms in the afternoon. Precipitation will obscure terrain throughout the Northern Rockies airspace.

MSO WATCHES/WARNINGS/ADVISORIES

MT...Winter Weather Advisory from midnight Saturday night to midnight MDT Sunday night for Bitterroot/Sapphire Mountains... Butte/Blackfoot Region...Potomac/Seeley Lake Region...West Glacier Region.

ID...None.