Most of the United States is being assailed with extreme winter weather this week as Arctic air blasts south from Canada, snow tracks up the Northeast coast and a potentially crippling winter storm takes aim at the South.

It's been a while since it last snowed in Mobile, but snow is in the forecast for the city on Tuesday, and a winter storm watch is in effect. The photo above is from the Mobile office of the National Weather Service from a rare south Alabama snow in December of 1996. Joe Maniscalco/National Weather Service

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.