The National Weather Service warned of whiteout conditions and possible blizzard conditions that could make travel impossible in some areas.

More than 3,000 flights were canceled or delayed across the United States on Sunday after a winter storm packing ice and snow slammed the Midwest and Great Lakes regions during the busy travel period between Christmas and New Year's.

NWS warns of a severe winter storm with blizzard conditions across six states, threatening post-holiday travel.

A powerful storm system continues to disrupt travel, placing 52 million people under winter weather alerts from the northern Plains to New England. Over 6,000 flights were delayed and more than 500 were canceled into or out of the United States by midday Sunday.

“Across the Midwest and Great Lakes between Sunday and Monday, a powerful storm will take shape,” said AccuWeather Meteorologist Brandon Buckingham. “The storm will bring risks for heavy snow, ice, severe thunderstorms, powerful wind gusts and heavy rain.”

High pressure will continue to promote dry weather across the Southeast. There will be at least some sunshine and it will be quite warm. Temperatures will be 10 to 20 degrees above average for this time of year.

A Winter Storm Warning is in effect for New York City and areas to the north and east through late morning and midday hours on Saturday.