Northwest Montana Regional Forecast

Includes Lincoln and Sanders Counties ( Libby, Troy, Eureka, Yaak, Bull Lake, Noxon, Heron, Trout Creek, Thompson Falls, and The Cabinet Mountains)

Issued Sunday September 22, 2019 - 7:45 p.m.

Sunday night…Mostly cloudy with scattered showers, most numerous along and west of the Cabinet Mountains. Snow level near 7000 feet. Lows in the lower 40s to lower 50s with upper 30s around 5000 feet. Light wind except ridge top winds southwest 15 to 25 mph.

Monday…Mostly cloudy, breezy and cooler with a chance of showers, greatest chances near the Idaho and Canadian borders. Highs in the upper 50s to mid 60s with mid 40s around 5000 feet. Southwest winds 10 to 15 mph with gusts to 20 mph in the afternoon. Ridge top winds west 15 to 30 mph with gusts to 40 mph.

Monday night…Mostly cloudy in the evening with a slight chance of showers near the Canadian border then partial clearing overnight with patchy valley fog and low clouds developing. Lows in the mid 30s to mid 40s with upper 30s around 5000 feet. Evening southwest winds 5 to 15 mph decreasing overnight. Ridge top winds west 15 to 25 mph.

Tuesday…Considerable cloudiness and locally breezy with a slight chance of showers, mainly over the higher elevations. Highs in the 60s with mid 40s around 5000 feet. Southwest winds 10 to 15 mph with ridge top winds west 15 to 30 mph.

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Extended Outlook (Wednesday through Sunday)

Wednesday…Dry and locally breezy. Lows in the upper 20s to near 40 with mid 30s around 5000 feet. Highs in the 60s with mid 40s around 5000 feet.

Thursday…Locally breezy and turning colder with valley rain and mountain snow likely. Lows in the 40s with lower 30s around 5000 feet. Highs in the 50s with upper 30s around 5000 feet.

Friday through Sunday…Unseasonably cold and unsettled with a chance of rain and snow showers in the valleys and snow showers in the mountains. Lows in the mid 20s to mid 30s with mid 20s around 5000 feet. Highs in the 40s with upper 20s to near 30 around 5000 feet.

In-Depth Weather Discussion for Northwest Montana/Rockies

Issued 09/22/2019 8:00 p.m.

Short term (Sunday night through Tuesday):

Another nice day across the region for the most part on Sunday with areas of valley fog and low clouds clearing to a warm day with plenty of fair weather cumulus clouds around. A few showers did develop by late in the afternoon as the next system begins to push its way inland as of this writing. Expect showers to increase through the evening hours especially across western portions of Lincoln and Sanders Counties with some shadowing likely for locations east of Lake Koocanusa and the Fisher River. Some locations in the far southeast part of Sanders County such as Hot Springs and Paradise may not see any showers at all. A strong and fast moving zonal (west to east) jet will set up across the International border on Monday with a surface low developing and deepening across Alberta in the afternoon. This will create some breezy conditions across valley locations with much stronger winds across higher elevations. A couple of showers will still be possible especially in the orographically favored locations to westerly flow so areas along and west of the Cabinets stand the best chance of rainfall on Monday. The weak disturbance that generates these showers on Monday will rapidly exit to the east Monday night leaving behind still a strong and fast moving zonal flow but without the added lift from a shortwave mainly clouds are expected Monday evening. Tuesday will feature similar conditions to Monday with breezy conditions in valley locations and windy conditions across higher elevations. It looks to be a brighter and dry day on Tuesday as flat upper ridging builds across the region. Major changes are still in store for the rest of the week.

Long term (Tuesday night through Sunday):

* Major change to MUCH COLDER conditions to end the month of September *

A quiet and chilly night is expected Tuesday night into Wednesday morning as a very strong upper level low and trough begins to descend southeast along the British Columbia coastline during the day on Wednesday. Clouds will be on the increase by Wednesday afternoon along with some breezes beginning to pick up. Lift and dynamics dramatically increase overnight Wednesday into Thursday with rain developing overnight and lasting through much of Thursday. Colder air will begin pouring into the region late Wednesday night into Thursday with rapidly falling snow levels to near 3500 feet by Thursday afternoon as the rain begins to wind down. This looks to be a good soaker for all of Lincoln and Sanders Counties, even the typically dry areas south and east of Plains will likely see a good rainfall. Snow amounts in the higher elevations above 5000 feet look significant with a preliminary guess of 3 to 6 inches of snow above 5000 feet by Thursday evening with more to follow. A deep upper level trough will continue to press into our region Friday and lasting through the weekend with further lowering of snow levels, possibly down to all valley floors. Valley snow accumulations remain highly uncertain at this time but are unlikely during daylight hours but will be possible during the night and morning hours. High temperatures will run a good 20 to 25 degrees below late September average highs not likely hitting 50 degrees while overnight lows will drop well below freezing if winds remain calm and skies clear. Higher elevations will drop well down into the 20s and likely not rise above freezing by Friday and remain below freezing through the weekend. Anyone planning on hunting or taking a last season hike into the mountains should pay close attention to the forecasts over the next several days and be prepared for winter-like conditions in the backcountry. Best to drain the hose pipes and blow out the sprinkler systems as cold weather looks to stick around for a while even beyond this weekend as the cold upper trough will be in no rush to move out as a strong blocking upper ridge will remain anchored across the Midwest and Eastern US through the weekend.