Washington - Snow blanketed much of the northeastern United States on Tuesday, grounding thousands of flights and causing chaos on the roads as forecasters warned that a brutal cold spell was on its way.
Downtown Washington fell eerily silent after the federal government, seeing the swift-moving storm approaching, closed its doors and told civil servants, who already had the day off on Monday for the Martin Luther King holiday to stay home.
Many offices and schools followed suit, as 32km/h winds whipped through the US capital's unusually quiet streets.
Washington's metro public transit system reported half as many riders as on a typical weekday, and business was so slow that many restaurants used Twitter to woo customers with bargain-priced drinks while others offered customers 2-for-1 deals.
The "storm system will strengthen overnight in the Atlantic waters off the East Coast, spreading heavy snow and strong wind into coastal sections of New England and the Northeast", the National Weather Service said.
"Blizzard conditions are possible in eastern Massachusetts", it added.
Meanwhile, temperatures across the eastern part of the country will be 10 to 25°C below average, amid "bitter wind chills", it warned.
FlightAware, a website that monitors air traffic in real time, said nearly 3 000 flights into, out of or within the United States had been cancelled on Tuesday.
The lion's share of affected flights involved busy airports in the New York, Philadelphia and Washington areas.
18cm of snow had fallen at Washington's Dulles International Airport while some 27cm were reported at the Philadelphia International Airport, according to AccuWeather, a private forecasting service.
Accumulations of 15 to 30cm of snow are expected over the mid-Atlantic to southeastern New England, it said.
National rail company Amtrak said it would operate "a modified schedule" on Wednesday on its Northeast Corridor line between Washington and Boston, as well as on two other routes in the hard-hit region.
In New York, a storm alert remained in effect until 06:00 on Wednesday with as much as 30cm of snow forecast for the metropolitan region.
A State of emergency was declared there, as well as in New Jersey and Delaware, according to CNN.
More than 1 700 ploughs were to be mobilised in New York on Tuesday night to clear up to 25cm of snow, it reported.
"For your safety and the safety of emergency responders, motorists are strongly urged to avoid unnecessary travel at this time", the New York state department of transportation said.