A storm expected to blast the East Coast with rain and snow through Thursday morning is threatening to snarl traffic for millions and impede air travel ahead of the Thanksgiving holiday.

The nor'easter that formed over the Gulf of Mexico and is sweeping the northeast will bring rain to major cities, including New York and Boston, while higher elevations of New England will see as much as a foot of snow, said National Weather Service meteorologist Andrew Orrison.

"Either way, travel is not going to be in a good state," Orrison said. Both rain and snow, which can cause slick roads, air turbulence and low visibility, would likely slow travel, he said.

More than 800 flights into and around the United States were canceled on Wednesday, while more than 1,000 were delayed, according to tracking website FlightAware.com.

"I'm very anxious," Amber Fernandez, 19, said at LaGuardia Airport, where she waited to board a flight Detroit that had been delayed more than two hours. "I just hope I can get on the plane."

The Thanksgiving holiday is one of the nation's busiest travel times with more than 46 million Americans expected to make trips between Wednesday and Sunday, travel group AAA said. More than 89 percent of travelers will travel by car, the group said.

In New York, which was pummeled with a snow storm last week that killed at least 13 people, Governor Andrew Cuomo urged travelers to drive with caution.

The state has reserved snow plows to respond to emergencies, employed some 1,800 plow operators and had more than 130,000 tons of road salt to use between New York City and Albany.

The Port Authority of New York and New Jersey said it would beef up staffing at its airports and toll collection booths at its tunnels and bridges to accommodate an uptick in holiday travelers.

A region spanning from Florida to Maine will be hit by the rain from the storm, while snowfall is anticipated from the central Appalachians to the inland Northeast, with the most snow falling in New England, the National Weather Service said.

Cold weather will continue for much of the rest of the United States, including the Midwest, while southwestern states will largely remain clear and dry, the service said.

Eastern states, which will dry out on Thursday, are expected to see temperatures below average for Thanksgiving, Orrison said.

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