James Hill of Shamokin, Pa., rides his bike in Coal Township, Pa. The storm… (Larry Deklinski, The News…)
A massive storm system upended post-Christmas travel plans Wednesday as it marched toward the Northeast after dumping snow and sleet on the middle of the country and producing tornadoes through the South on Christmas Day.
The storm stretched from Michigan to Florida and had been blamed for seven deaths so far.
The nation's airlines had canceled more than 1,800 flights and delayed more than 9,000 by at least 15 minutes, mostly into and out of Dallas, Philadelphia, Cleveland, Chicago, Indianapolis and New York, according to the airline monitoring website Flightstats.com.
PHOTOS: Northeast braces for winter storm
Los Angeles International Airport, the nation's fifth-busiest, has been largely spared the impact of the storm, with only a handful of delays and cancellations Wednesday, to airports including New York's John F. Kennedy International and Chicago's O'Hare International.
The storm could dump 12 to 18 inches of snow from the lower Great Lakes to northern New England, the National Weather Service said.
A tornado watch had been in effect for part of the day in eastern North Carolina and northeastern South Carolina.
"It is a significant storm in terms of its size and its range of impacts from severe weather to winter weather," said Chris Vaccaro, spokesman for the weather service.
The storm was expected to clear most of the mid-Atlantic states Wednesday night, the service said, and northern New England could expect steady snow starting Thursday morning.
On Christmas Day alone, the weather service received 34 reports of tornadoes in eastern Texas, Alabama, Louisiana and Mississippi, Vaccaro said.
A twister touched down in Mobile, Ala., on Tuesday, blowing roofs off homes and knocking down trees and power lines. Several mobile homes north of the city were toppled, but no serious injuries were reported.
"Right now it's cleanup and damage assessment," said Donald Leeth, plans and operations officer with the Mobile County Emergency Management Agency.
The storm caused tens of thousands of customers to lose power across Alabama, but most had it back by Wednesday.
Snow and ice hit Arkansas hard, with about 200,000 customers losing power. Gov. Mike Beebe declared a statewide disaster Wednesday. The Arkansas Department of Emergency Management said two counties had opened shelters for those without heat.
The department received a report that a man died when a tree fell on his house in Saline County. Two children died on Christmas when the car they were in crossed the center line of an icy Arkansas highway and struck an SUV.
In Oklahoma, two people were killed in separate crashes Tuesday.
On Christmas, the storm's winds were blamed for toppling a tree onto a pickup in Texas, killing the driver, and for knocking another tree onto a house in Louisiana, killing a man there, the Associated Press reported.
Mississippi Gov. Phil Bryant declared a state of emergency for several counties after the storm injured more than 25 people.
The New York City Office of Emergency Management issued a travel advisory for Wednesday evening through Thursday morning, citing forecasts of "snow with sleet and freezing rain." The area was also under a high wind warning, with gusts of up to 60 mph possible, Vaccaro said.
The worst of the weather should be gone by Friday, he said. "Come Friday morning, it will largely be a sunny day across the eastern third of the country."
Times staff writer Hugo Martin contributed to this report.