According to the National Weather Service, temperatures in New York's iconic Central Park peaked at 72 degrees Fahrenheit (22 Celsius), the warmest Christmas Eve since records began in 1871.
In the capital Washington, tourists and last minute shoppers wore T-shirts and sat outside at sidewalk cafes as federal workers left their offices dressed for holiday parties.
High temperatures were reported as far north as Saint Anicet in the Canadian province of Quebec, which hit 70 degrees Fahrenheit, and the NWS reported that the port of Norfolk in Virginia broke its all time December record of 82 degrees (28 C).
The New York Times cooking blog broke away from its coverage of traditional Yuletide fare to offer "Recipes for a 70-Degree Christmas" -- leading off with roast salmon and a soft herb salad.
At Maryland's only ski station just one of 35 trails was open, thanks to artificial snow-making machines. Last year the Wisp Resort's runs opened on December 13, NBC Washington reported.
But the abnormally balmy temperatures had tragic consequences in weather further south, where more than a dozen tornadoes were reported in six states.
At least 11 people were killed as the storms, feeding on the unseasonable warm air, left a trail of destruction from Illinois to Alabama.
Heavy damage was inflicted in the south, causing seven deaths in Mississippi alone, according to the state's Emergency Management Agency.
A seven-year-old boy was found dead after the storm picked up and tossed the car he was traveling in, fire chief Kenny Holbrook told reporters in the town of Holly Springs, where some 5,000 customers were still believed to be without power.
- Violent tornado -
At least 40 people were injured in the state, Governor Phil Bryant said, as he issued a state of emergency that will allow local governments to request aid for recovery.
"Most of these storms caused a lot of damage in north Mississippi but our teams are out assessing the damage, trying to put a quantity on how many homes and how many businesses have been damaged," the emergency agency's Brett Carr said.
The Tennessee Emergency Management Agency said three people were killed in the state, while media reported one fatality in the state of Arkansas.
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