As of Wednesday morning, airlines have cancelled over 200 flights in anticipation of a Noreaster that will hit the New York area and surrounding territory starting Wednesday afternoon. About half the cancellations involve New York Laguardia and Newark Liberty. The cancellations are generally to avoid having planes trapped in places where they won't be able to fly back out.
Most airlines are waiving change fees for travelers in areas that are or might be affected. Pointless to give details here; the situation is fast-moving. Again: Check with your airline! More DETAILS here from USA Today.