Posted: Oct 22, 2012 9:11 AM by Meteorologist Mike Heard
Updated: Oct 22, 2012 9:45 AM
Over the next 72 hours a strong Pacific storm system will push through the western U.S., Pacific NW and Northern Rockies. A deep trough forms and this system will travel from Northern California lifting NE up into Montana and finally spinning up into central Canada over the next 3 days.
Right now there are Winter Storm Warnings up for western Montana's mountains and up along the front range. These warnings begin at 6pm tonight and continue into the afternoon hours Tuesday. Snow accumulations of 4" to 10" above 4,000' and as low as 3,000 in NW Montana. For the Northern front range a winter storm warning above 4,500' and a winter weather advisory below 4,500'. Snow accumulations in this region: 3"-6" for the lower elevations with up to 20" for the higher mountain peaks. Strong NW winds 10 to 20 mph will cause areas of drifting snow and reduced visibilities especially in Choteau, Browning and Marias pass.
Mountain passes to see the most snow overnight will be Lookout, Lolo, Lost Trail with several inches of snow and possibly icing conditions. MacDonald and Homestake passes may see a couple of inches of snow along with Monida, Raynolds, Bozeman pass and Boulder Hill.
Warm air advection in a SW flow should keep temperatures above freezing for SW Montana thus there is a low probability of valley snow for our region and snow levels should stay around 6,000' today. Forecast lows tonight will be around freezing or a few degrees below freezing so we could see minor snow accumulations in the valley floors, however, mountain snow of 4" to 5" is possible for the higher peaks, 2" to 3" are possible for most mountain passes. There is a better chance for light valley snow behind this system as colder air digs into the state.
As the colder air digs in behind the storm starting Wednesday and periodic weak shortwaves of moisture push into the state there is a continued chance for off and on scattered snow showers with minor accumulations for the mountains and valleys for the latter half of the week. Forecast lows will drop temperatures down into the teens and single digits Thursday and Friday.