PHILADELPHIA — A powerful storm that slowly moved across the country dumped a mix of snow, sleet, and freezing rain on the Mid-Atlantic region Sunday and headed northeast, threatening to bring as much as a foot of snow to sections of Delaware and New Jersey.
The storm covered the fields of the Philadelphia Eagles and Pittsburgh Steelers with white and forced the cancellation of thousands of flights across the United States.
The tracking website Flightaware.com estimated that more than 2,000 flights were canceled nationwide Sunday and more than 6,000 flights were delayed. That followed two days of similarly difficult air travel conditions.
The storm slowed traffic on roads and led to a number of accidents, including a fatal crash on the Pennsylvania Turnpike near Morgantown that led to a series of crashes involving 50 cars.
The National Weather Service says snow accumulation in some sections of Delaware and southern New Jersey could reach 9 to 11 inches.
Earlier Sunday, the storm prompted officials in Virginia, parts of Maryland, and other states to urge residents to stay off the roads. In Wisconsin, there were several vehicle pileups due to snow and dangerous road conditions, with one fatal interstate rollover.
The Weather Service said the high pressure system from North Carolina north to New England was fed by disturbances from the Southwest and moist air off the Atlantic.
‘‘This is not one big storm but a couple storms lined up side-by-side,’’ meteorologist Kevin Witt said. ‘‘That’s just a recipe for winter precipitation.’’
Virginia, parts of West Virginia, and the metropolitan Washington, D.C., area coped with power failures under steady freezing rain, wet snow, and sleet.
In North Texas, bitter cold settled in Sunday after sleet, snow, and ice had pelted the region. About 400 departures from Dallas-Fort Worth International Airport were canceled Sunday. On Interstate 35 north of Dallas, graders with blades to break up thick ice were brought in.
To ease the pain of travel delays, the Dallas-Forth Worth airport has been giving away free coffee and sandwiches. It also has brought in entertainment to the terminals, including musicians, comedians, and balloon artists.
‘‘We are trying to keep the mood light and do everything we can to make sure that our passengers have as good an experience as possible given the situation,’’ airport spokesman David Magana said.
American Airlines, which has its main hub in Dallas-Fort Worth, said it had 1,100 cancellations across its system Sunday. It expects 550 cancellations for Monday, the bulk of which are at Dallas-Fort Worth.
The airline has updated its travel policy due to the tough weather, allowing passengers who have trips planned through affected areas to change their flights at no charge to avoid some of the complications.
Icy conditions were reported over the weekend from Texas to Ohio to Tennessee.
Laura Southard, spokeswoman for the Virginia emergency management department, said Sunday that the storm had the potential to be a ‘‘historic ice event’’ in Virginia.
Southard said many people had heeded warnings to stay at home, and that was still the message. ‘‘We’re not out of this thing yet,’’ she said.
Dominion Virginia Power, the state’s largest utility, said the storm could knock down tree limbs and power lines and it had company trucks ‘‘stocked and fueled’’ and crews ready to respond. Several hundred outages were reported Sunday.
Forecasters said the storm caused freezing rain and icy conditions in parts of Tennessee as it surged across that state late Saturday and early Sunday.
Bob Nations Jr., director of the emergency operations command center for the Memphis area, said early Sunday that ice coating roads, bridges, and overpasses caused several multivehicle crashes.
He issued a statement urging drivers to use extreme caution, particularly on bridges and overpasses.
‘‘It looks like we’re going to be stuck with this for one, two, maybe three days,’’ said Memphis attorney Sam Chafetz, who tried to get off the roads before the worst of the storm hit. ‘‘I'm not afraid of the ice and snow. I'm afraid of the other drivers who don’t know how to drive in it.’’
In Kentucky, a winter weather advisory remained in effect for most of the state until late afternoon.