textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- Northeast winds Friday night through Saturday will create choppy conditions on area lakes.

- A cutoff low pressure system brings widespread rain, with snow above 6,000 feet Saturday night through Monday morning.

A fast-moving trough will drop south out of Canada today, bringing upper-level energy with it this evening and overnight. This will push a band of showers and isolated thunderstorms through western Montana and north-central Idaho by early Friday morning. Expect breezy westerly winds gusting 15 to 25 mph, along with brief, light to moderate rainfall of 0.10 to 0.40 inches by sunrise Friday morning.

Behind this trough, a cold front will move south out of Alberta, Canada, bringing breezy east to northeast winds Friday evening. These winds will remain over the area through the day on Saturday. Temperatures Friday and Saturday will run 5 to 10 degrees below normal for this time of year. It will feel even cooler Saturday afternoon with east winds gusting around 20 mph. The east winds will increase after sunset Saturday evening, with gusts up to 30 mph in the favored east-west gaps and canyons.

We continue to track a cutoff low pressure system that is forecast to move onshore of the Pacific Northwest on Saturday, passing over the Northern Rockies Saturday evening and Sunday. This system will bring widespread rain and high mountain snow and much cooler temperatures that will make it feel more like fall than late summer. The challenging part of the forecast has been the exact track of the low, which will play a huge role in where the heaviest rain and snow will fall. The track has been trending slightly north the past 24 hours, with the center of the low now moving over northwest Montana. In this scenario, the most widespread and persistent rain will be north of I-90, bringing snow levels down to around 6,000 feet in Glacier National Park and along the Continental Divide. Wherever the track of the low ends up being, wet, cool, and breezy conditions will be present throughout the Northern Rockies, increasing the hypothermia risk in the backcountry of western Montana and north-central Idaho. As it stands now, we expect anywhere from 0.50 to 1.25 inches of rain to fall across most of the region through Monday morning, with southwest Montana being on the drier end of the system, where only about 0.25 inches are expected. There is a 10 to 20 percent probability this northerly trend in the track will continue. In that case, rain and snow amounts could be considerably less. Stay tuned.

Temperatures will begin to moderate by mid-week next week, with afternoon temperatures warming back closer to normal for this time of year, along with a mix of clouds and sunshine.

AVIATION

Breezy southwest winds will continue throughout the Northern Rockies, bringing gusts around 20 to 25 knots to all area aviation sites in western Montana and north-central Idaho. An increasing mid-level cloud deck will begin to move south and east over the Northern Rockies late this afternoon and evening as an upper-level trough moves south out of British Columbia. This trough will bring an increasing chance of rain showers throughout the region overnight, along with a 20 percent probability of lightning between 11/0600Z and 11/1200Z for KGPI, KMSO, and KHRF tonight and early Friday.

MSO WATCHES/WARNINGS/ADVISORIES

MT...Red Flag Warning until 9 PM MDT this evening for East Beaverhead.

ID...None.