textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- Scattered showers and gusty winds (choppy lake conditions) this afternoon/evening - Minor travel impacts over mountain passes Sunday night/Monday due to snowfall

Satellite imagery this afternoon indicates a fast-moving disturbance moving north to south near the Canadian border, as well as a well-formed low pressure circulation off the coast of Alaska. In the near term, the Canadian disturbance will bring gusty winds and chances for precipitation this afternoon. Precipitation will move from north to south with the shortwave. Expect winds of about 30 mph across the higher terrain and some valleys of western Montana. Gusts to 40 mph will grace the Continental Divide. Boaters on Flathead Lake should be prepared for strong winds and choppy seas. Showers will be most frequent over the higher terrain but may occasionally move across valleys, locally enhancing wind gusts. Snow levels will stay above 5000 feet, with only minor accumulations expected in the high backcountry.

A short-lived ridge of high pressure will build on Saturday as the Alaskan circulation moves south and east towards the Pacific Northwest. After a day of mostly fair weather on Saturday, that circulation will arrive in Washington state on Sunday. The pattern turns active as a cold front associated with this system enters the Northern Rockies. Expect widespread showers and gusty winds on Sunday morning through the afternoon, once again producing choppy lake conditions.

Snow levels will begin near 7000 feet on Sunday but will drop sharply to 4500 feet by Sunday night. The main concern will be accumulating snow over mountain passes late Sunday into Monday morning, enhanced by lingering showery, upslope flow. Current ensemble means suggest 2-4 inches of snow for Lolo, Lookout, Lost Trail, and Marias Passes, with 4-8 inches in the higher terrain. These conditions will create cold, snowy, and potentially hazardous travel for backcountry users. While some valley locations may see rain mixed with snow by Monday morning, snow accumulation will be minimal at best.

Looking ahead, much of next week appears mild, with seasonable to above- normal temperatures and occasional light showers. However, ensemble trends hint at the potential for a more significant atmospheric river event around October 25-27 with a moderate risk of heavy mountain snow. Stay tuned for updates as details become clearer.

AVIATION

A cold front will move through the region today, bringing widespread west winds. Gusts up to about 25 knots will develop across most terminals by 17/1900Z. There remains a low (~20%) probability for gusts reaching or exceeding 35 knots, particularly in association with stronger showers or storm outflows. Scattered showers and an isolated thunderstorm are possible through about 18/0600Z under west-northwesterly flow. These could briefly reduce visibility and lower ceilings, leading to a temporary deterioration in flight conditions.

Clearing and drying are expected tonight into Saturday, with the potential for patchy morning valley fog or low stratus to redevelop.

MSO WATCHES/WARNINGS/ADVISORIES

MT...Lake Wind Advisory until 7 PM MDT this evening for Flathead/Mission Valleys.

ID...None.