A winter storm that brought snow, sleet and freezing rain to a large swath of the Midwest swept into the mid-Atlantic and Northeast on Thursday, causing treacherous travel conditions, prompting school delays and closures and potential power outages for millions of Americans.

Of all the precipitation types, freezing rain is by most measures the worst because it can weigh heavily on trees and power lines.

The National Weather Service says a mix of snow, sleet and freezing rain will continue to fall until Thursday evening.