textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- Minor snow impacts possible tonight on Lolo, Lookout and Marias Passes

- Anticipate cooler temperatures and periods of valley rain and mountain snow through the weekend.

A low pressure system digging into the Pacific northwest coastline will continue to push a fetch of moisture into western Montana and north central Idaho this afternoon into tomorrow morning. The main plume of moisture will generally focus north of Interstate 90 tonight, with areas sough of Interstate 90 largely seeing precipitation come to an end by this evening. Snow levels will continue to hover between 4000 and 5000 feet this afternoon, lowering to around 3500 feet overnight tonight. Passes such as Lolo, Lookout and Marias will likely see a couple inches of accumulation, making for a period of slick road surfaces over night. Valley locations near the Continental Divide, such as West Glacier, will likely see a brief period of snow as well, though surface temperatures will make it difficult to accumulate.

As the low pressure system digs slightly to the south Thursday into Friday, a warmer southwesterly flow sets up over the region. Forecast models generally show drier conditions by Thursday afternoon into Friday, though cloud cover will linger. Seasonably cool temperatures will continue into the weekend.

Later Saturday into Sunday, forecast models are beginning to show the nearly stationary low pressure system along the west coast finally giving way and moving eastwards into central Idaho and southwest Montana. Another push of moisture will bring a focus of precipitation into the region, generally along and south of Highway 12. There is still a wide spread in potential snow levels (between 5000 to 7000 feet is the most likely range) but there is relatively high confidence that mountains and high mountain passes (Lost Trail, Homestake, MacDonald, Bannock) will see accumulating snow and periods of slick conditions by Sunday morning.

AVIATION

Regional radar imagery this afternoon shows numerous showers moving eastward along the ID/MT border in northwest Montana associated with a elongated trough of low pressure. These showers will focus across north-central Idaho and northwest Montana through this evening, with activity becoming scattered overnight. Snow levels this afternoon range from 4,500-5,000 feet and will drop to near 3,500 feet overnight into Thursday morning. Substantial snow impacts are not experienced across terminal sites, with an outside chance (less than 20% chance) for brief visibility impacts at KGPI associated with snow showers from 29/0600-1500Z. Ceilings will trend lower overnight across northwest Montana, with probabilities for 3,000 feet or less ceilings increasing above 50% after 29/1200Z, including KGPI. Flight impacts associated with ceilings and showers will become less common, especially south of the I-90 corridor this evening into Thursday morning.

MSO WATCHES/WARNINGS/ADVISORIES

MT...None. ID...None.