A nor'easter headed up the East Coast could cause havoc for millions of Thanksgiving travelers.
A coastal storm is forecast to dump rain along the coast and snow inland. That could cause delays along busy Northeast highways and possibly upset travel plans at airports throughout the region.
Precipitation is forecast to sweep in from the south Tuesday night into Wednesday morning and exit the region Thursday morning.
Jeff Masters is chief meteorologist for Weather Underground. He says a small deviation in the track could change things dramatically.
The highest amount of snow is expected to fall in northeastern Pennsylvania, the Catskills of upstate New York and into Connecticut, Massachusetts, New Hampshire and Maine. Up to 10 inches is possible in some places.
"I would pack your patience," said Robert Sinclair of AAA New York. "Unfortunately, the storm is scheduled to hit right in the middle of getaway day."
Masters said coastal cities are likely to mostly receive rain, although meteorologists were keeping a close eye on the rain/snow line. As of Monday, the highest amount of snow was expected to fall in northeastern Pennsylvania, the Catskills of upstate New York and into Connecticut, Massachusetts, New Hampshire and Maine. Up to 10 inches was possible in some places, forecasters said.
Read MoreCost of Thanksgiving rises slightly
Officials at the three major airports in the New York City area — Kennedy, LaGuardia and Newark Liberty — were "monitoring weather forecasts carefully," and were ready to take action if needed, said Steve Coleman, a spokesman for the Port Authority of New York and New Jersey, which operates the airports.
All the major U.S. airlines were closely monitoring the situation but have not yet canceled flights or made any other changes.
American Airlines was allowing passengers flying to some Northeast cities on Wednesday to move their flight, for free, to Tuesday or Thursday. Delta Air Lines had a similar waiver for Wednesday flights to the region, but it was letting passengers only reschedule for flights on Thursday or Friday, which might be too late for many travelers.
Read MoreMore weather news
Sinclair noted that an estimated 41.3 million travelers were expected to hit the nation's highways for the holiday weekend. That's a 4.3 percent increase over last year.
He suggested travelers consider traveling on Tuesday or Thursday, instead of Wednesday, if they can.