Thousands Of US Flights Cancelled As Snow Hits Northeast

More than 30% of flights into and out of both Philadelphia International and Reagan National Airport in Washington, D.C., have been cancelled.

Boston Logan and LaGuardia and JFK Airports in New York are also reporting high cancellation rates, according to FlightAware.com.

AirTrain service to JFK has been suspended and replaced with free shuttle buses, the Port Authority of New York and New Jersey said.

Several airlines have already waived fees for passengers who want to change their reservations. JetBlue's COO warned on Twitter that the airline, which runs most of its flights through New York or Boston, is preparing to scale down its operations for today and tomorrow:

JetBlue was criticized earlier this month when it left passengers stranded for days in the Caribbean without flights home. It has cancelled nearly 30% of its flights for today, and 21% of its flights for Wednesday.

FlightAware's Misery Map shows how delays and cancellations ripple through the U.S. aviation network. Here's how it looked just after 9:30 a.m.: