(Adds Washington federal offices closed, updates flights, adds weather service quote)
By David Beasley
ATLANTA, Feb 12 (Reuters) - A deadly winter storm gripped the southeastern United States on Wednesday, crippling travel, grounding flights, knocking out power to 363,000 customers and encasing magnolia and palmetto trees in ice.
The weather was blamed for at least 13 deaths in the region, including three people killed when an ambulance transporting a patient skidded off an icy road in Carlsbad, Texas.
Winter storm warnings and advisories were in place from Arkansas east to much of the Atlantic coast, the National Weather Service said. The storm is expected to sock the northeastern United States in the next two days with up to 15 inches (38 cm) of snow.
"We definitely consider this to be a high-impact event, and we're definitely telling everyone to stay off the roads and stay inside as much as possible," said Carl Barnes, a weather service forecaster in Sterling, Virginia.
Snow and freezing rain that pummeled South Carolina and North Carolina created a dangerous commute for drivers in a hurry to get home as the snowfall got heavier and the ice thickened.
A possibly historic accumulation of ice as well as heavy snow was expected to add up to nearly 8 inches (20 cm) of frozen precipitation for Charlotte, North Carolina, and 9 inches (23 cm) were forecast for Spartanburg, South Carolina, meteorologists said.
More than an inch (2.5 cm) of ice was possible from central Georgia into South Carolina by Thursday morning, according to forecasters.
Traffic on interstate highways ground to a halt, and at least one snow plow went off a North Carolina highway into a ditch.
Todd Pekks, a chef at Duke University, was just half a mile (800 meters) into his drive home to Raleigh when he began to skid so badly he gave up, his wife Sherri Pekks said.
He made his way back to work on foot, and returned to the kitchen, she said.
"He's definitely gone for the night. I wonder if he'll be able to make it back tomorrow," Pekks said.
Fatal road accidents were reported in Mississippi and South Carolina. In Georgia, a man died of exposure near his home in Butts County, south of Atlanta, and North Carolina Governor Pat McCrory told CNN two people had died in weather-related incidents.
STATES OF EMERGENCY
Governors declared states of emergencies from Louisiana to New Jersey, and hundreds of schools, colleges and offices throughout the region shut down. The basketball game between archrivals Duke University and the University of North Carolina was called off.
About 6,700 U.S. flights were canceled or delayed on Wednesday, and another 3,700 were scrubbed for Thursday, according to flight-tracking website FlightAware.com. About half of the Thursday flights to and from Washington and New York were called off.
The U.S. Department of Energy reported that 363,000 power customers were without electricity as of mid-afternoon. More than a third of them were in Georgia, where some residents may have to wait up to a week for power to be restored, said Georgia Power spokeswoman Amy Fink.
About 5,000 people were without power in Birmingham, Alabama, with more than 6 inches (15 cm) of snow expected. Roads were closed across the northern part of the state, authorities said.
In the path of the storm, the White House delayed a Thursday event to mark the launch of My Brother's Keeper, a campaign to help young black men. Federal offices in Washington were closed.
Washington city officials authorized a $15 snow surcharge for taxi rides to encourage cabbies to stay on the road. In New York, the MTA Metro-North train system was to operate on a reduced schedule on Thursday.
Most motorists in Georgia, where thousands were stranded in their vehicles during the last weather front, stayed off the roads after a state of emergency was declared, Governor Nathan Deal said.
Vehicles that did venture out were soon coated with ice, their radio antennas looking like ice skewers, television images showed.
Shelters were opened in Georgia, Alabama and North Carolina to help those stranded by the storm. (Additional reporting by Harriet McLeod, Jon Herskovitz, Karen Jacobs, Scott DiSavino, Dave Warner, Verna Gates and Marti Maguire.; Writing by Colleen Jenkins, Ian Simpson and Barbara Goldberg; Editing by Bernadette Baum, Gunna Dickson and Ken Wills)