But late Sunday, conditions began to ease. Tempe-based US Airways went from trying to find seats for 100,000 passengers systemwide, to 30- to 45-minute lines in Philadelphia and Charlotte, N.C., by the end of the day.
"The lines are down to what is normal for a holiday weekend," said US Airways spokeswoman Andrea Rader.
The company hoped to be back to normal operations Monday, she said.
From Friday to Saturday morning, more than 3,600 commuter and mainline flights were canceled nationwide because of the effects of the storm. JetBlue, US Airways, Delta Air Lines and American Airlines all reported cancellations.
The storm stranded hundreds of passengers at New York's Kennedy International Airport, including hundreds stuck on planes Friday night as aircraft were unable to take off or find space at gates.
By Sunday, there were scattered delays of up to two hours at New York's Kennedy and LaGuardia airports, with some delays of up five hours at Newark Liberty, said Alan Hicks, spokesman for the Port Authority of New York and New Jersey.
Many US Airways customers were diverted to Charlotte on Friday when the late winter storm dumped snow, sleet, ice and freezing rain on Philadelphia, New York and other Northeast cities, the airline said.
Computer problems, airline staffing rules and other problems slowed US Airways' attempts to clear the backlog. Meanwhile, 275,000 passengers were already booked on US Airways flights on Sunday that were nearly sold out from the start.
Airline officials were trying to round up spare planes and crews to work on added flights. Four extra flights departed Charlotte, spokesman Andrew Christie said early Sunday.
There were also long lines at US Airways ticket counters in Pittsburgh early Sunday due to cancellations and delays at other airports over the weekend, said JoAnn Jenny, spokeswoman for the Allegheny County Airport Authority.
Other airlines did not have similar backups at Pittsburgh International Airport because they do not have the same volume of flights as US Airways does, Jenny said.
Passengers in Philadelphia reported waiting three hours or more to rebook a ticket or reach a reservation agent by phone over the weekend. Automated US Airways kiosks at the airport were also down at times, they said.
US Airways operates two-thirds of the approximately 1,200 daily flights in Philadelphia.
Airport staff handed out disposable silver blankets and pillows to the several hundred people stranded at the airport overnight Saturday - down from an estimated 1,000 or more people the night before, a spokeswoman said.
"Once the passengers were rebooked and going through security, they were moving them (through) pretty quickly," airport spokeswoman Phyllis VanIstendal said Sunday. "But in a situation like this, where you have thousands of people, I guess there are limits to everything."
Dan Stacey, 34, of Philadelphia, was at the airport Sunday trying to find his luggage. An Irish fiddler, Stacy had tried to fly on Friday to Phoenix, where he was slated to perform in four St. Patrick's Day concerts over the weekend.
Instead, he said he sat in a US Airways plane on the Philadelphia tarmac for eight hours. He then went back home - but found out Sunday that his luggage went to Phoenix anyway.
"I lamented the fact that I was the only Irish musician in America not working on St. Patty's day," Stacey said.