By Ian Simpson
WASHINGTON (Reuters) - A major winter storm set to hit the East Coast on Tuesday and Wednesday is threatening to snarl millions of Thanksgiving travelers' holiday plans, forecasters said on Monday.
The same storm that lashed New Mexico and the southern Plains with snow and ice over the weekend will spread heavy rain across the South before moving into the U.S. Northeast ahead of the Thursday holiday, the National Weather Service said.
The Appalachian Mountains, West Virginia, western Pennsylvania and northern New York could get 6 to 12 inches of snow on Wednesday before the storm moves into western Maine on Thursday, weather service meteorologist Dan Petersen said.
East of the snow front, the I-95 highway corridor from Boston to New York could receive 2 to 3-1/2 inches of rain, he said.
"The storm is going to occur from (Monday night) through Wednesday, and it will be pretty much out of the area" by Thursday, he said.
"Thanksgiving will be just blustery and chilly and windy across the (Great) Lakes and Northeast."
Some 39 million people are expected to travel by road from Wednesday to Sunday, centering around Thanksgiving Day, travel group AAA said last week.
High winds could ground the giant character balloons in the Macy's Inc Thanksgiving Day Parade in New York. City rules bar the huge balloons from flying when sustained winds top 23 miles per hour (37 km per hour), and gusts exceed 34 mph.
Freezing rain and bad weather from the Plains storm contributed to the cancellation of 378 airline flights in the United States on Monday, most of them at Dallas-Fort Worth International Airport, according to FlightAware.com, which tracks delays and cancellations.
The storm is combining with a cold front that dropped temperatures to minus 3 Fahrenheit (minus 19.4C) at Saranac Lake, New York, the coldest spot in the contiguous United States on Monday morning.
New Hampshire's Supreme Court was briefly forced to close on Monday because it had lost heat and electricity.
At least 13 people were killed in storm-related accidents over the weekend in Oklahoma, Texas, California, New Mexico and Arizona, according to NBCNews.com.
(Reporting by Ian Simpson, Scott Malone and Curtis Skinner; Editing by Scott Malone, Lisa Von Ahn and Maureen Bavdek)