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.

Winter weather advisories for all 21 counties are in effect with ice and up to 3 inches of snow possible in spots.

Nearly half of the United States from the Midwest to Northeast will see snow or a freezing rain mix before the weekend arrives, weather forecasters say.