Airlines reported storm-caused delays, with some flight cancellations in the Northeast.
Delays were building in Baltimore, Philadelphia and Newark, New Jersey, said Southwest Airlines spokesman Dan Landson. Delta Air Lines cancelled 35 flights on its regional carriers due to inclement weather at New York's LaGuardia Airport, spokesman Morgan Durrant said.
Travel conditions were expected to worsen later in the day, with a combination of precipitation and rapidly falling temperatures resulting in slick roads, said AccuWeather.com meteorologist Bill Deger.
"Travel around some of the big cities by road could be a little tricky if people wait until tonight," Deger said.
Boston, New York and Philadelphia "still have a lot more rain to go as we head through the rest of the day," he added.
Rain was moderate to heavy in the Southeast, mid-Atlantic and Northeast regions on Wednesday, with light to moderate snowfall from the Southern Appalachians to western New York, the National Weather Service said.
The National Weather Service said western Pennsylvania, western New York and Vermont could get more than 1 foot (30.5 cm) of snow before skies cleared on Thursday.
Flood watches were in effect for eastern portions of the Northeast United States.
The Thanksgiving holiday is one of the nation's busiest travel times, with 43 million Americans expected to make trips this weekend, travel group AAA said.
Thirty-seven percent of travellers will be leaving on Wednesday, making it the year's busiest single day of holiday travel, AAA said. That travel forecast was expected to hold true despite the stormy conditions, AAA spokeswoman Heather Hunter said.
"With the storm we expect some people may have shifted their dates, leaving earlier to get ahead of it," she 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 prohibit flying the huge balloons when sustained winds top 23 miles per hour (37 km per hour), and gusts exceed 34 mph (55 kph).
The National Weather Service on Wednesday predicted that New York City would be sunny and breezy on Thursday, with winds up to 24 mph (38 kph) and gusts as high as 40 mph (64 kph).
Gusting winds toppled a tractor-trailer on Interstate-77 in Virginia on Wednesday, slowing traffic that otherwise had been flowing briskly, said an employee at the welcome center in Lambsburg by the Virginia-North Carolina state line.
Travelers were in good spirits and eager to arrive at their destinations, said Tonja Koger, the center's tourism relations manager.
"They're ready to get to grandma's Thanksgiving," she said.
