Cold and snowy weather has gripped much of the northern tier of the United States since Thanksgiving, but a pattern change will torch the chance of white Christmas for many.

Thanksgiving is a week away and the weather has the potential to disrupt travel for the tens of millions visiting family and friends.

An arctic air mass has descended into the US, and a disrupted polar vortex will keep the nation in the freezer at times deeper into December. More than 200 million people will wake up to freezing ...