A wave of canceled flights is moving north to New York and Boston as the first major winter storm of 2018 threatens to paralyze cities and airports over the next couple of days. Airlines have scrapped more than 2,100 Thursday flights so far on top of 558 Wednesday, according to FlightAware, an online tracking service. The winter blast is expected to bring snow, ice and freezing temperatures from Florida to Nova Scotia. “It’s going to be a very challenging day tomorrow in the Northeast due to heavy snows in some areas and strong winds,” said Ross Feinstein, a spokesman for American Airlines Group Inc. “We’re making some proactive cancellations today because we know we’ll be forced to cancel some flights tomorrow.” American Airlines has grounded all departures from Boston’s Logan International Airport on Thursday, along with all flights by its regional airline partners at New York’s LaGuardia Airport. That includes its LaGuardia shuttle operations to Boston and Ronald Reagan Washington National. Delta, JetBlue Delta Air Lines Inc. scrubbed more than 400 flights Wednesday night and Thursday, as did JetBlue Airways Corp., including 260 at Boston on Thursday. United Continental Holdings Inc. is grounding some flights at its hub in Newark, New Jersey, and also in Boston. Southwest Airlines Co. canceled 30 flights Wednesday night and nearly 300 Thursday. Smaller cities to the south also are affected, with Delta suspending daytime flights Wednesday at Myrtle Beach and Charleston, South Carolina, and until midday Thursday at Savannah and Brunswick, Georgia. American has nixed all flights from Bradley International near Hartford, Connecticut, on Thursday. Airlines often cancel flights ahead of massive winter storms or hurricanes to prevent passengers, crew members and aircraft from being stranded at airports. The Federal Aviation Administration also may delay or shut down flights at airports if the weather gets bad enough.