(CNN)A tornado watch has been issued for parts of the Northeast Corridor, including the New York City metro area, the Storm Prediction Center said, and the forecast has affected air travel ahead of the holiday weekend.
Tornado watch issued for New York metro area
The watch includes parts of Connecticut, Massachusetts, New Jersey, New York state, Pennsylvania and Vermont.
Along with the threat of a couple of tornadoes, residents face the possibility of wind gusts up to 70 mph and large hail, the center said.
The watch stretches through the evening to 10 p.m.
The Federal Aviation Administration initiated ground stops that prevent many flights bound for New York's three main airports from taking off. Other airports across the Northeast were subject to delay programs, with takeoffs held for more than one hour.
As of 5:30 p.m. ET, the flight tracking site FlightAware.com reported 456 cancellations across the United States.
Newark Liberty International Airport led the list with about 9% of its flights canceled. And 15% of the flights headed there were delayed, according to FlightAware.
Also, 20% of the flights bound for New York's LaGuardia Aiport were delayed, along with 18% of those headed to John F. Kennedy International Airport.
In total, more than 251 flights into or out of New York City were canceled, as of 5 p.m.
"The storm is being triggered by a cold front that moves offshore overnight tonight, CNN meteorologist Taylor Ward said.
"Summer thunderstorms are popping up and there's enough energy for them to be severe," Ward said. "That cold front moves offshore overnight tonight and that sets the stage for a nice weekend."
He said storms are possible in Philadelphia and/or Washington on Monday.