MISSOULA — Another moist Pacific weather system is going to hit western Montana starting Sunday afternoon along the Montana/Idaho border, and impact the entire area through Monday morning.
As this upper level low moves in from the west, a very cold, arctic airmass will slide over the Divide and into northwest Montana. The cold air mass is expected to be relatively shallow. The importance of this is that moisture riding over a shallow air mass is the ideal recipe for accumulating snowfall.
Because of this, all of northwest Montana, including the Flathead and Mission valleys have an opportunity for a very good snowfall between late Sunday afternoon through noon on Monday. It would not be a surprise to see anywhere from 6"-to10" of snow over that stretch of time in the Flathead Valley. For the Mission Valley, 3"-to-6" of snow is expected. The surrounding higher elevations, including pass levels in the West Glacier Region, Lower Clark Fork Region, and Kootenai Cabinet Region are expected to receive 6"-to-15" of additional snow.
For the Bitterroot and Sapphire mountains a Winter Weather Advisory is in effect. Snow in the range of 6"-to-15" is also expected. The difference is the lack of strong winds found in the locations where a warning is in effect. For the Bitterroot and Missoula valleys, about 1"-to-4" is expected from late Sunday through Monday morning.
The focus on Monday will turn to blowing snow and sub-zero windchills for the Flathead Valley and the higher elevations of northwest Montana. Windchill values in the neighborhood of -15 to -25 are expected Monday into Tuesday.
For the rest of western Montana, the air will not be as cold, and winds won’t be quite as strong. The cold, shallow air discussed earlier will lose much of it’s punch as it moves into the Missoula Valley and areas south.
For the rest of the week, look for below average temperatures with periodic snow showers under a mostly cloudy sky.