The northeastern United States braced Monday for what meteorologists predict could be the worst winter storm of the season, with blizzards feared to dump knee-high snow on New York.
The National Weather Service issued a blizzard warning from midnight Monday (0400 GMT) Tuesday to midnight Tuesday in the New York region, extending south in New Jersey and north into Connecticut.
Hundreds of flights have been cancelled ahead of the storm, according to the tracking service FlightAware.
Dubbed Winter Storm Stella and forming near the coast, the collision of two low pressure systems is expected to dump snow on a wide area home to millions of Americans from the central Appalachians to New England.
The weather service said whiteout conditions in New York are expected to make travel "extremely dangerous." Winter storm warnings have been issued from southern Maine to Virginia, south of Washington.
The treacherous conditions are expected to wreak havoc on the Tuesday morning commute. In New York, America's largest city, home to 8.4 million people, residents were warned to expect closures, delays and cancellations.
The heaviest snow is expected to wallop the coast north of Philadelphia up to New England, with one to two feet (30-60 centimeters) feared in New York, National Weather Service meteorologist Melissa Di Spigna told AFP.
"This is a very impressive system," she said. "We're expecting it to be the worst snow of the season," she added. Winter has so far been relatively mild in the northeast with temperatures "well above normal."
The blizzard warning in effect for New York is likely to see winds of 25-35 miles per hour (40 to 56 kilometers per hour) and could see gusts as high as 55 miles per hour, which could hamper visibility, Di Spigna said.
The National Weather Service (NWS) cautioned that the storm could bring record-low temperatures, as well as "difficult travel and power outages" in places.
Mayor Bill de Blasio warned New Yorkers to avoid unnecessary travel on Tuesday and keep roads clear for sanitation crews and emergency responders.
Light snow is expected to begin late Monday and intensify overnight into Tuesday with the heaviest snowfall expected through Tuesday afternoon with rates as much as two to four inches (five to 10 centimeters) per hour.
Temperatures on Monday were already icy, with afternoon highs expected to be around 15 to 30 degrees Fahrenheit (9 to 1 degrees Celsius) below normal from the northern Plains to the Mid-Atlantic region, with the possibility of some record lows.
Closer to the coast, from southern New Jersey to the Carolinas, rain is expected while the southwestern United States will remain warm.
"Only travel in an emergency. If you must travel, keep an extra flashlight, food and water in your vehicle in case of an emergency," the NWS said.
More than 1,160 flights within, into or out of the United States have been cancelled for Tuesday, the bulk at airports in Baltimore, Maryland; Washington, New York's LaGuardia airport and Philadelphia, according to FlightAware.
Southwest Airlines warned of cancellations, delays and diversions through Wednesday. Delta Air Lines told travelers they could book alternative flights without fees.