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.

Preparations are underway from Houston to Atlanta as a rare winter storm sets its sights on the southern U.S., where it's expected to bring a messy mix of heavy snow, sleet and freezing rain that could have a major impact on travel and daily life.