A winter storm is set to hit the northwestern US and parts of the Northern Plains, bringing heavy snowfall and plunging temperatures. The storm, which is the first significant snowfall of the season, is expected to leave high elevation areas buried in more than a foot of fresh snow. The cold air and deep moisture will spread from Washington and Oregon through much of Montana on Tuesday before the storm drops into the Northwest on Tuesday night. Snowfall is expected to start on Monday night or Tuesday morning in the Cascades in Washington, with higher elevations experiencing more snow and potentially disruptive travel conditions. The storm will continue to move east, covering portions of Idaho and Montana, as well as the Cascades in Oregon. Temperatures will plummet, forcing high-elevation locations to fall well below freezing, with some areas dropping into the single digits. By Tuesday night, heavy snowfall is expected, with pass levels in the Cascades potentially seeing six inches or more of snow. The storm will continue to bring snow and wind to the Northwest and northern Rockies, with some low elevation spots also experiencing wintry weather.