With a big snowstorm forecast to hit the Northeastern Seaboard, airlines began canceling flights scheduled for early this week before snowflakes began to fall.

But deciding how and when to cancel such flights can be tricky. 

If airlines cancel too early, they may find themselves stuck on the ground while competitors continue to fly, says Darryl Jenkins, chairman of the American Aviation Institute. But if companies wait too long, they may have to divert planes, stranding passengers, crew and equipment in random cities, says Bob Mann, president of airline consulting firm R.W. Mann & Company.

Diversions can be costly for airlines because it can take longer for an airline to return to its regular schedule than it would if flights were canceled and passengers were re-booked on later flights.