Airlines are continuing to cancel large numbers of flights today at snowbound airports in New York, Philadelphia, Washington, D.C. and Boston. Yesterday, more than 3,000 departures and arrivals were scrubbed at the three New York airports, at Philadelphia and at Dulles, Washington Reagan and Baltimore-Washington. As of 11 a.m. Eastern time this morning, nearly 2,000 additional flights had been canceled at those airports. That’s a whole lot of flights (some flying between affected airports are obviously counted twice, as both departures and arrivals) — each one presumably booked full with passengers, that did not occur in a two-day period (so far). At the start of the Christmas travel season, most of those passengers are now trying to re-book seats into a system that is already fully booked — because airplanes have been flying almost full…