(CNN) -- If you're heading to the Northeast for Thanksgiving, you might want to get an early start.

A nor'easter is expected to pour heavy rain or snow on that part of the United States late Tuesday and cause problems on Wednesday, traditionally the busiest travel day of the year, CNN meteorologists say.

"All of the major metro areas in the Northeast will be impacted by either heavy rain or heavy snow, along with high winds," said CNN senior meteorologist Dave Hennen.

He said it's too early to predict which metro areas will be hit hardest, but airport delays are predicted Wednesday in New York City, Philadelphia, Boston and Washington, D.C.

"The I-95 corridor may end up being the dividing line between heavy snow and heavy rain," Hennen said. "Either way travel in the Northeast will become dangerous, especially interior sections of the Northeast with heavy snow."

American Airlines is waiving rebooking charges for holiday travelers using 18 airports in the Northeast. In a press release, the airline said:

"Customers ticketed on American Airlines, American Eagle or US Airways or US Airways Express flights on November 26 to, from, or through (the 18 airports) may change flights without penalty, have the ticket-reissue charge waived for one ticket change, and begin travel as early as November 25 or as late as November 27 under American's current travel waiver."

AAA is expecting 46 million Americans to travel 50 miles or more from home during the Thanksgiving weekend. That would be the most travelers since 2007, AAA said in a press release.

On the bright side, people traveling by car will probably pay lower gas prices than in recent years, AAA says.

The current average price of gasoline in the United States is $2.85 per gallon, 43 cents per gallon lower than the average price for Thanksgiving in 2013.

CNN meteorologist Chad Myers said a European computer model calls for a foot of snow in Connecticut and Massachusetts, whereas an American computer model doesn't predict as much snow.

"This is going to be a rainmaker more than a snowmaker," he said. "It isn't quite cold enough to make that big snow event. You'll see snow in the Poconos and the Alleghenies and in Vermont, but along the I-95 corridor (expect) rain-snow mix."

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