A winter storm is snarling travel across the East Coast on Wednesday, causing trouble on the nation's roadways and delays of up to six hours at airports in the Northeast on one of the busiest travel days of the year.
About 30 million people from the mountains of North Carolina to Maine could be affected by the holiday storm.
"The storm in the Northeast continues to develop and is causing long delays and numerous cancellations at D.C., New York city and Philadelphia airports, along with trouble on the roadways, as snow increases in coverage," CNN senior meteorologist Dave Hennen said. "Most delays and cancellations will occur from late morning through Wednesday evening."
The silver lining for Thursday morning fliers? "By Thanksgiving, the storm will be exiting, and conditions should return to normal," he said.
CNN's Chad Myers has the latest on the wintry weather hitting the Northeast and what to expect this weekend.
Rain, snow and a mix of both is covering the Northeast. CNN's Rosa Flores reports from New England.
Rain and snow
Travelers are already seeing significant snow accumulations as rain and snow target the Washington, New York and Boston metro areas.
"Roughly 30 miles west of Washington, Philadelphia, New York and Boston will see heavy snow while the cities themselves receive only light amounts," Hennen said.
Up to 18 inches of snow has fallen in parts of West Virginia as of 2 pm ET, and parts of New England could see up to 20 inches of snow. Thundersnow has been reported around Baltimore, parts of New Jersey and the Hudson Valley in New York.
Mike Todd, a spokesman for the New Hampshire Department of Safety, said power outages are a major concern.
"This is New England; this is just another winter storm here, and the complication is just that it's the holiday weekend," he said. "We caution individuals to drive carefully and slowly. Consider staying put if you're concerned. Safety first, as always."
Pennsylvania said it'll have state police and the National Guard in the state emergency operations center. State officials urged residents to avoid the roads if they can.
"The bottom line is, the less cars the better, the less traffic the better," said Cory Angell of the Pennsylvania Emergency Management Agency. "If you don't have to go, you don't need to go. You don't want to be stuck in a queue for hours and then run out of gas and whatnot. It's important people realize there are hazards involved with travel, and more often than not, they don't."
Airlines had canceled 735 flights and had 4,647 delays "within, into, or out of the United States" as of 9 p.m. ET Wednesday, and that number is expected to increase, according to FlightAware.com. (That website does not distinguish whether flights are canceled or delayed for mechanical, weather or other reasons.)
"This is not a huge number of cancellations, but due to the holiday, flights will be more full, and there will be fewer available seats to accommodate displaced passengers from canceled flights," FlightAware.com's Daniel Baker wrote in an email.
"We expect thousands of delays that will cause moderate disruption to Thanksgiving travelers," he said. "The delays will begin accumulating early afternoon as the worst of the weather impacts the Northeast and will continue to cascade through the evening."
The Port Authority of New York and New Jersey, which operates major airports in both states, estimates that 1% of flights will be canceled at New York's LaGuardia Airport today, 8% at New Jersey's Newark Liberty International Airport and hardly any cancellations at New York's John F. Kennedy International Airport.
Fliers should try to rebook their flights for Thursday, Baker said.
"Customers ticketed on American Airlines, American Eagle or US Airways or US Airways Express flights on November 26 to, from, or through (18 affected 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," according to an airline release.
Midwest affected, too
The Northeast isn't the only region where bad weather is predicted. Light snow is forecast until Thursday in Minneapolis, Chicago and other parts of the upper Midwest. The Northwest is expecting rain, with snow in the mountains. Denver is expecting wind gusts of up to 30 mph on Tuesday and 15 mph on Wednesday.
Drivers should check weather forecasts before setting out on the road, and travelers should also check tire pressure, car batteries and windshield wipers.
On the bright side, people traveling by car will probably pay less for gas 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 at the same time last year.