"It's going to be a shock to the system," said National Weather Service meteorologist Ryan Leach in a press briefing Friday morning. "It seems that winter decided to show up in January this year."
The Weather Service projects snow throughout western Montana and parts of Idaho to last from Friday afternoon through Monday. with most of it falling in two phases. The first, from midday Friday through early Saturday morning, will bring heavy snow to the Idaho panhandle and the mountains of Montana. Lolo Pass is projected to receive between 9 and 14 inches, but Missoula and the Mission, Flathead and Bitterroot valleys should get 4 inches or less.
The second phase should come Sunday night and early Monday morning, when meteorologists say blizzard conditions are possible in a band extending from Eureka south to Ovando and across to Ovando and then across the Continental Divide. It's projected to bring 8 to 12 inches Sunday and early Monday in Kalispell and other areas north of Flathead Lake, while Missoula will receive 3 to 4 inches, and the Mission and Bitterroot Valleys 4 to 6 inches. It's not clear where the Arctic air front driving this system will hit directly — and bring the heaviest snow — but Leach said that "we're pretty confident right now that it's not going to reach Missoula on Monday."
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Temperatures are nonetheless expected to plunge across the region, after several weeks of mild weather. Noting temperatures more than 50 below zero in Alaska and Canada's Yukon Territory, Leach said that "this is the cold air that's about to get unleashed on us."
While he expects the core of the air mass to miss northwest Montana, instead sliding east of the Continental Divide, "we're looking at a very sudden change from above-normal to below-normal conditions," Leach said. In Missoula, meteorologists expect temperatures to reach highs in the 20s and 30s through Monday, but then range between the single digits and teens through Thursday. Temperatures could reach as low as -9 in Kalispell on Wednesday. The cold will be accompanied by wind, especially north of Flathead Lake. "We're going to have blowing snow and dangerous travel conditions," Leach told reporters. The Weather Service advises motorists to be prepared for possibly impassable roads Monday.
The West Central Montana Avalanche Center warned of a "considerable danger" of avalanches on area slopes Thursday morning, while the Flathead Avalanche Center warned of "moderate" avalanche danger in the Whitefish, Swan and Flathead ranges. "I expect to see new snow instabilities developing, but the new snow is also going to be stressing a medley of weak layers that we have buried around 2 to 4 feet deep right now," said Zach Guy, director of the Flathead Avalanche Center. "The combination of new snow instabilities and then stressing these weak layers means that we expect dangerous avalanche conditions to develop." He recommended that backcountry travelers stay on gentle slopes under 30 degrees.