Nearly 400,000 customers in North Texas were without power on Tuesday morning as a powerful storm with strong winds swept across the region.

The storm, part of a system that stretched from Iowa to Texas, was expected to strengthen as it moved east. Warnings were in place for blizzards in the Plains and severe storms across the South, with damaging gusts, hail and possible tornadoes forecast from eastern Oklahoma to Alabama and in western parts of Florida. The system is expected to affect much of the East Coast on Wednesday.

Flights into Dallas-Fort Worth International Airport were briefly halted, and 12 percent of both departing and incoming flights at the airport were canceled as of Tuesday morning, according to FlightAware, which tracks flight data. More than a quarter of incoming flights were delayed.

Severe storms were expected to affect the Fort Worth area through Tuesday morning, according to the National Weather Service. The storm ripped part of the roof off a high school in Plano, Texas, according to WFAA, a television station in Dallas.

In southern Oklahoma, about 25,000 customers were without power, according to the tracking site poweroutage.us. A mobile home in Ada, Okla., was destroyed after a possible tornado hit, according to KOCO-TV, a television station in Oklahoma City.