Winter Storm in Southern Lewis and Clark, Montana

Severe driving conditions reported on highway 12 from MacDonald Pass to Helena due to snow and winds. Relayed by twitter.

On November 7th, deep troughing over the western US kept Montana in an area of large scale ascent and upper level divergence, allowing H700 mb and surface low pressure systems to deepen over Eastern Idaho and move northeastward through Eastern Montana and the Dakotas. This is a favorable track to bring cold temperatures, gusty winds, and sufficient moisture for accumulating snow to Central/North-central Montana. The snowfall was enhanced by northerly upslope flow over the plains onto the higher terrain in addition to the moisture wrapping around the northwest side of the low pressure system. Snow and gusty northerly winds initially developed over the Northern Rocky Mountain Front early Saturday November 7th, before expanding south and eastward through the remainder of the region Saturday night into Sunday. At the height of the storm, winds gusted into the 40 to 60 mph range, resulting in blizzard conditions over much of Central and North-central Montana.