A wave of Arctic air is poised to descend from Canada, ushering in an extended period of dangerously cold conditions across the Eastern United States. Nearly 100 million Americans are projected to experience sub-zero wind chills as a disrupted polar vortex traps frigid air in place through late January. Temperatures will struggle to rise across the Midwest and Northeast, with some cities potentially recording their coldest temperatures of the season. The biting winds will amplify the risk of frostbite, and the deep freeze is expected to linger into early February.