WASHINGTON (Reuters) - A winter storm that dropped roughly two feet of snow (61 cm) on parts of the eastern United States is expected to move out to sea on Friday but the cold will remain.

The National Weather Service warned of flooding and told commuters from the lower Mississippi valley to the mid-Atlantic to be wary of dangerous road conditions created by the snow, ice and slush. 
             
While forecasters predicted only pockets of scattered snow at most in the east, they said temperatures were expected to be 10 to 30 degrees below average across the region. 
             
"Arctic air settling in behind the boundary will make for a chilly end to the work week," the National Weather Service said.
             
In Kentucky, where cities were buried under as many as 23 inches (58 cm) of snow, Governor Steve Beshear declared a state of emergency on Thursday as traffic halted on interstate highways and motorists were left stranded.
             
A Delta Air Lines plane arriving in heavy snow at New York's LaGuardia Airport from Atlanta on Thursday slid off the runway and came to rest just feet from the frigid waters of Flushing Bay. No serious injuries were reported.
             
Just shy of 600 U.S. flights had been canceled as of early Friday morning, according to FlightAware.com, as compared to the 4,957 cancellations tallied on Thursday.
             
Parts of Massachusetts got up to 12 inches (19 cm) of snow, but Boston only received trace amounts, leaving intact its annual snowfall record at nearly 108 inches (274 cm), NWS meteorologist Bob Oravec said. Two inches (5 cm) would break the city's record, which was set in 1995-96.
              
(Reporting by Ian Simpson and Curtis Skinner; Editing by Gareth Jones)