Heavy snow is expected to blanket large portions of the Eastern U.S. while much of the country will endure dangerously cold temperatures in the coming days.

The updated forecast on timing and track of the storm calls for the snow to end from southwest to northeast as midnight approaches. “The heaviest precipitation looks to occur between roughly 4 and 9 p.m. during which time snowfall rates could reach or exceed 1 inch per hour,” the National Weather Service said.

A polar vortex is slated to sweep most of the continental US bringing winter storm warnings and a hazardous freeze to millions.