(CNN) -- A powerful winter storm left thousands of travelers stranded Thursday, particularly in the Northeast, as scores of flights were canceled or delayed.
More than 400 flights within, into or out of the United States were canceled early Thursday, according to the tracking website flightaware.com.
Some flights arriving at New York's LaGuardia Airport were delayed an average of an hour Thursday morning, the Federal Aviation Administration said.
Sixty flights were canceled Thursday at Philadelphia International Airport, after 300 flights were grounded the day before, airport spokeswoman Victoria Lupica said.
Some smaller airports were also hit hard. Syracuse Hancock International Airport in upstate New York was open, but only about half the flights were getting off the ground, officials told CNN.
Many roads throughout the Northeast were treacherous.
In Massachusetts, more than 1,000 crews were clearing streets, where pavement temperatures were below freezing, the state's Department of Transportation said. Vermont authorities warned of difficult driving conditions.
In Maine, the National Weather Service warned of "very hazardous traveling conditions" because of heavy snow and powerful winds. State offices were closed.
Authorities in New York and New Jersey reported train delays and local traffic accidents.
The Federal Emergency Management Agency called on people to update their vehicles' emergency kits for cold weather. The kits should include blankets, gloves, first aid materials, a shovel and a battery-powered radio, the agency said on Twitter.
The mix of snow, rain, and winds left many people holed up at home this week as the storm worked its way eastward. Among the most frustrated are those stuck at airports -- and not just passengers.
Comments by an American Airlines pilot have given the weather a new twist. On Tuesday evening, his plane sat for nearly seven hours at Dallas/Fort Worth International Airport.
"I have no words to tell you to how sorry I am. This is way, way above our heads, by people who obviously -- in my humble opinion -- don't have a clue what they're doing," the pilot told passengers after they sat for hours without taking off for Las Vegas, CNN affiliate WFAA reported.
The station happened to be interviewing a frustrated passenger on the plane by phone when the pilot made the announcement.
American Airlines has said it was focused on deicing the plane and ensuring everyone's safety.
The airline added that "Tuesday was obviously a very challenging day at DFW."
"We had a significant number of delays and cancellations due to winter weather and icy conditions in the North Texas area. We apologize to our customers for the inconvenience," an airline statement said.
The pilot is not expected to be punished, airline spokesman Matt Miller said.
The company's website says that for domestic flights, passengers can deplane before a ground delay exceeds three hours. It was not immediately known whether all the procedures were followed.
Winter storm advisories are in place from central Pennsylvania to Maine, with snow accumulations of up to a foot expected by Friday morning, CNN meteorologist Bonnie Schneider said.
CNN's Jesse Solomon, Rande Iaboni and Todd Sperry contributed to this report.