Typically the heaviest snows come in late January, and Feb. Some of our storms at that time can dump FEET of snow in a short time. This is usually on top of several feet of snow already on the ground, and the avalanche areas run BIG.
BTW, running a rotary plow into the slides was frowned upon, as the slides often contained large logs, trees and really big boulders embedded into the snow. As mighty as the plows were, a 24" log by 15 feet reeks havoc on the blades.