Airlines cancelled thousands of flights into and out of East Coast airports as a major snowstorm packing up to three feet of snow barrels down on the region.
JetBlue, whose flights are largely in the Northeast, has already cancelled about a third of its entire schedule.
Airlines cancelled 2,194 flights Monday, according to the flight tracking site FlightAware. More than 2,000 additional flights have been scrapped for Tuesday.
Problems in the Northeast are rippling outward, however.
In West Palm Beach, Florida, where temperatures are expected to be in the 70s Monday, about 30 percent of all flights have been cancelled. Fort Lauderdale and Orlando are also reporting major cancellations.
Most major airlines are allowing customers whose flights are canceled in the next few days to book new flights without paying a penalty. Customers ticketed on flights to dozens of Eastern airports are generally eligible for the allowance, though specific terms vary by airline.
The Monday morning commute was normal for much of the Northeast as officials continued to urge residents to prepare for a "crippling and potentially historic" storm that could bury communities from northern New Jersey to southern Maine in up to 2 feet of snow starting later in the day.
The National Weather Service said the nor'easter would bring heavy snow, powerful winds and widespread coastal flooding through Tuesday. A blizzard warning was issued for a 250-mile stretch of the Northeast, including New York and Boston.
Officials cautioned residents to not be misled by a relatively smooth morning commute. They warned that getting home could be difficult and asked residents to avoid any unnecessary travel.
The morning commute was delayed Monday for drivers on a section of Interstate 81 near Harrisburg, Pennsylvania. A tractor-trailer jack knifed, and a truck hauling beer crashed into the median. No injuries were reported.
Some schools were planning to close early or not open at all Monday in Pennsylvania, New Jersey, New York and Connecticut.
Government officials began to activate emergency centers on Sunday as professional sports teams, schools and utilities hastily revised their schedules and made preparations.
"This could be a storm the likes of which we have never seen before," New York City Mayor Bill de Blasio told a news conference in a Manhattan sanitation garage where workers were preparing plows and salt for the massive cleanup on about 6,000 miles of city roadways.
In Massachusetts, Gov. Charlie Baker warned residents to prepare for roads that are "very hard, if not impossible, to navigate," power outages and possibly even a lack of public transportation.
Boston is expected to get 18 to 24 inches of snow, with up to 2 feet or more west of the city, and Philadelphia could see up to a foot, the weather service said.
The Washington area expected only a couple of inches, with steadily increasing amounts as the storm heads north.
"We do anticipate very heavy snowfall totals," said Bob Oravec, lead forecaster with the weather service in College Park, Maryland. "In addition to heavy snow, with blizzard warnings, there's a big threat of high, damaging winds, and that will be increasing Monday into Tuesday. A lot of blowing, drifting and such."
President Barack Obama, who is traveling in India, has been briefed on the storm, spokesman Josh Earnest said Monday. White House officials also have been in touch with officials from states "up and down the Eastern seaboard" that are in the storm's path, Earnest said.
Wind gusts of 75 mph or more are possible for coastal areas of Massachusetts, and up to 50 mph further inland, Oravec said.