Detroit Lions head coach Jim Schwartz walks the sidelines as snow falls during the first half of an NFL football game against the Philadelphia Eagles, Sunday, Dec. 8, 2013, in Philadelphia. Ice forms on holly leaves as sleet falls in Richmond, Va., Sunday, Dec. 8, 2013. A powerful storm system that spread hazardous snow, sleet and freezing rain widely across the nation's midsection rumbled toward the densely populated Eastern seaboard on Sunday. AP Photo/Steve Helber Philadelphia Eagles' Nick Foles warms up as snow falls before an NFL football game against the Detroit Lions, Sunday, Dec. 8, 2013, in Philadelphia. A light snow falls over visitors to the White House in Washington, Sunday, Dec. 8, 2013, as snow followed by freezing rain and sleet is expected in the Washington region. PHILADELPHIA (AP) - A powerful storm that crept across the country dumped a mix of snow, freezing rain and sleet on the Mid-Atlantic region and headed northeast Sunday, turning NFL playing fields in Pennsylvania into winter wonderlands, threatening as much as a foot of snow in Delaware and New Jersey and raising concerns about a messy morning commute. The storm forced the cancellation of thousands of flights across the U.S. and slowed traffic on roads, leading to a number of accidents, including a fatal crash on the Pennsylvania Turnpike near Morgantown that led to a series of fender-benders involving 50 cars. What was forecast in the Philadelphia area to be a tame storm system with about an inch of snow followed by rain mushroomed into a full-blown snowstorm that snarled traffic along Interstate 95 in Pennsylvania from the Delaware to New Jersey state lines. Paul Jones, 24, a youth hockey coach from Warminster in the Philadelphia suburbs, was on his way to a game in Lancaster when he got stuck - along with his fiancee, another coach and three players - in a major backup on the turnpike. The roadway was "snow-covered, slick," Jones said in an interview from the car, where he was a passenger and had been at a standstill for more than an hour. "People are in and out" of their vehicles, he said. Kids are having a snowball fight on the side of the road, making snow angels, people are walking their dogs. The National Weather Service said the low pressure system from North Carolina north to New England was being fed by disturbances from the southwest and moist air off the Atlantic. The forecast called for the wintry mix to continue through Sunday, turning to rain early Monday. Total snow accumulation in some sections of southeastern Pennsylvania, Delaware and southern New Jersey could reach 9 to 11 inches, while other areas could see as little as an inch or 2, said Valerie Meola, meteorologist with the National Weather Service in Mount Holly, N.J. The snow fell so heavily in Philadelphia on Sunday that yard markers at Lincoln Financial Field - where the Eagles beat the Detroit Lions - were completely obscured. It was almost as bad in Pittsburgh, where the snow intensified after opening kickoff. Philadelphia fan Dave Hamilton, of Ivyland, layered up for the game, wearing an Eagles shirt topped with an Eagles sweatshirt and Eagles winter coat. "Twenty-seven years I've been a season-ticket holder, I've never seen snow at the game like this," he said. It just kept coming down. But we are all having fun out there. Philadelphia International Airport had a temporary ground stop Sunday afternoon with snow totals around 4 to 6 inches. Spokeswoman Stacey Jackson said a number of passengers were expected to remain in the airport overnight since area hotels had been full for several days. She said staff would hand out pillows and blankets to travelers to make them "feel at home even though they are not." Air passengers in the Washington-area experienced increasing delays as the season's first real snowstorm set in. The Metropolitan Washington Airports Authority said many flights had been delayed at Dulles International and Ronald Reagan Washington National airports. Virginia, parts of West Virginia and the metropolitan Washington, D.C., area braced for blackouts under steady freezing rain, wet snow and sleet. Parts of northwest and southwest Virginia and southern West Virginia were getting snow, while sleet and freezing rain prevailed west and north of Richmond. In Maryland, a chain-reaction accident on Interstate 81 in Washington County involving more than 20 vehicles delayed snow removal efforts for hours. The highway was closed for more than three hours after a tractor-trailer ran into the median to avoid cars that had spun out. It was hit by another tractor-trailer that overturned and spilled its load. Several other tractor-trailers ran off the road and jackknifed as their drivers tried to avoid the crash. North Texas started to thaw out slightly Sunday after two days of a near standstill with icy roads and low temperatures. It will likely be a couple of days before the ice that's coated the region melts completely. The snowstorm raised fears about a potentially dangerous Monday morning commute, with snow-laden cars and perilous, icy roads. New Jersey's new U.S. senator, Cory Booker, tweeted a promise to a Mount Holly resident to help him shovel out his car if he still needed the help in the morning. But the heavy snow wasn't limited to the East Coast. A snowstorm that hit along the Utah-Arizona border left hundreds of travelers stranded on Interstate 15 overnight into Sunday. The Arizona Highway Patrol said passengers in about 300 vehicles became stranded after up to 10 inches of snow and slick road conditions prompted the closure of part of the highway. There were no immediate reports of serious injuries. Rubinkam reported from Pennsylvania. Associated Press writers Steve Szkotak in Richmond, Va., Ben Nuckols in Washington, D.C., Jamie Stengle in Dallas, and Samantha Henry in Newark, N.J., contributed to this report.