A persistent winter storm that moved into the northeastern United States Wednesday has forced the delay of hundreds of airline flights, frustrating travelers still trying to return home after the Christmas holiday.

The storm spawned high winds, snow and sleet across several states all the way up to Maine. The system also created hazardous driving conditions.

Up to 30 centimeters of snow fell on parts of the northeast, with the heaviest accumulation across northern New York and into New England.

The northeastern United States is still under a winter storm warning.

While the East Coast's largest cities — Boston, New York, Philadelphia and Washington, DC — got mostly high winds and cold rain, other areas experienced a messy mix of rain and snow that caused many accidents on the highways.

At least a dozen people have been reported killed in storm-related incidents.

Earlier in the week, nearly three dozen tornadoes were reported in the southern U.S. states of Texas, Louisiana, Alabama and Mississippi. Tens of thousands of people were left without power by the massive storm system.