A winter storm blowing through the northwest was being called the “Pineapple Express” and consisted of Pacific moisture moving across the area. This moisture teamed up with a very cold Arctic air mass which developed across the Continental Divide according to National Weather Service reports.
The two distinctly different air masses were reported to have a crippling effect on the area especially north of Interstate 90. The warmer coastal air caused light to moderate snowfall which changed to freezing rain in some areas.
By Saturday, temperatures were reported to reach 32 degrees, causing the snow to be heavy and wet, with the West Central Montana Avalanche Center cautioning backcountry sportsmen to use extreme care as there was an increasing danger for avalanches. Wind will cause layers of snow to be deposited on ridgelines accompanied by heavy snow causing unstable layers in the backcountry. The Forest Service Idaho Panhandle Avalanche Center also reported an avalanche warning for the St. Regis Basin area with travel in the area not recommended as of Friday, Dec. 29.
On Friday drivers were warned of near white-out conditions in the Flathead and Mission valleys with between 8 and 14 inches of snow. It was expected that the mountain areas could expect one to two feet of snow, making travel conditions dangerous especially at Lookout, Marias, Lolo and Lost Trail passes. Lookout Pass was predicted to have snow accumulations of 19 to 23 inches with 33 inches possible in some areas. Winds were also reported to be as high as 30 mph in places causing blowing and drifting snow.
It was reported that the Missoula Division of the Montana Department of Transportation has approximately 70 plow trucks on the road between Missoula, Lolo, Drummond and Lookout Pass, dumping about 168,859 cubic yards of sand and 8.4 million gallons of liquid deicer to keep roads clear.