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.

An arctic air mass sprawling across the eastern, central and parts of the western U.S. on Monday will channel temperatures 20-30 degrees below already historically cold January averages and was poised to slam parts of the South with a disruptive winter storm.