CHICAGO (REUTERS) - A massive winter storm walloped the central United States with heavy snow, freezing rain and gusty winds on Wednesday (Feb 2), threatening to make travel virtually impossible and possibly knocking out power for millions of Americans.

Winter and ice storm warnings and watches were in effect for a wide swathe of the United States that reached from Texas and Colorado up through the Midwest and into Northern New York until Friday morning, the National Weather Service (NWS) said.

Much of the northern part of the region could get 30cm of snow while southern spots may see a mixture of snow and freezing rain that will rapidly deteriorate travel conditions on Wednesday, the NWS said. Winds gusts as high as 64kmh were also forecast.

"Expect power outages and tree damage due to the ice. Travel could be impossible. The hazardous conditions could impact the morning or evening commute," the service said in its advisory for Memphis.

More than 100 million people are under winter weather alerts that stretch from the Rockies to New England, CNN reported.

Some 2,400 flights were cancelled in the United States as of Wednesday morning, according to Flightaware.com. More than 400 flights alone were cancelled to and from the two major airports in Chicago, where as much as 30cm of snow was in the forecast for parts of the metro area.

The storm also forced dozens of school districts in the region to cancel classes for at least Wednesday.

Extremely cold air caused by Arctic high pressure that is forecast to descend over the Plains on Wednesday will send temperatures plummeting 15 to 25 degrees below average in some areas, the NWS added.

The storm threat comes days after fierce winter weather engulfed the northeastern part of the United States, dropping more than 60cm of snow on some areas and packing high winds, prompting thousands of flight cancellations and curtailing access to the roads in some states.