By Ian Simpson
WASHINGTON, Nov 26 (Reuters) - A powerful storm dumped heavy rain and snow over much of the eastern United States on Tuesday, threatening to snarl travel plans for millions of people over the busy Thanksgiving holiday, forecasters said.
The Atlantic coast into New England will be drenched with 2 to 4 inches (5 to 10 cm) of rain by late Wednesday, the day before Thanksgiving, as the storm moves northeast out of the South, said the National Weather Service.
The windswept rain will pound the Atlantic corridor from Richmond, Virginia, as far north as Portland, Maine, likely causing poor visibility, flight delays and urban flooding, said online forecasters Accuweather.com.
The Thanksgiving holiday is one of the nation's busiest travel times. Some 39 million travelers are expected on the roads between Wednesday and Sunday, centering on Thanksgiving Day, travel group AAA has said.
"The timing of the storm could not come at a worst time," said Alex Sosnowski, Accuweather.com senior meteorologist.
Snow on the flanks of the rainstorm is likely to cause travel delays in Boston, Columbus, Ohio, Pittsburgh and Buffalo, New York, while the storm's wind-driven rain will slow travel from Atlanta to New York, Accuweather.com said.
Late on Tuesday, flight delays were reported in Charlotte, North Carolina, Philadelphia, Memphis and Baltimore, Maryland.
Where the start of the holiday travel period was smooth, travelers were bracing for trouble.
At New York's LaGuardia Airport, Terry Colley, 59, an operations manager for a company in Memphis, said he and his wife came to the airport four hours early in case of delays, although their fears were as yet unfounded.
"So far, so good," he said.
At Hartsfield-Jackson Atlanta International Airport, the world's busiest, Michelle Duncan, a 26-year-old graduate student from Chicago, arrived to spend Thanksgiving with a friend. She expressed surprise that her trip had been relatively hassle-free.
"I'm sure tomorrow it's going to be chaos," she said.
Forecasters added that freezing rain was expected to coat the Appalachian Mountains in Virginia and West Virginia.
More than a foot (30.5 cm) of snow could fall in western Pennsylvania, western New York and Vermont before skies clear on Thursday, they said.
But those clear skies will bring winds of 15 to 25 miles per hour (24 to 40 km), gusting higher, and temperatures below freezing in the northeastern United States, said Bruce Terry, lead forecaster with the National Weather Service.
"We've got everything with this - real heavy rains, (at) the lower elevations a band of freezing rain, heavy snows and then behind it, wind," he said.
The giant character balloons in the Macy's Thanksgiving Day Parade in New York may be grounded if the winds are too strong. City regulations bar the huge balloons from flying when sustained winds top 23 miles per hour (37 km per hour), and gusts exceed 34 mph (55 kph).
New York Governor Andrew Cuomo issued a winter weather warning and urged motorists to use extreme caution.