In my experience, your biggest problem is the combination of weather and time of year. Yes, the airports in the NE are used to snow, and can usually cope. But you've seen this winter how even the best-prepared can get caught out. I

If they DO have to start cancelling flights, Xmas is such a busy time that the usually-easy process of rebooking you on the next available flight becomes a real problem...the 'next available flight' could well be 2 or 3 days later. We travelled via Philly in the run up to Christmas 2008, and we missed our connection. This was due to technical problems on the first leg, nothing to do with weather. But despite that it still took us 2 days to get to Orlando, as half the USA seems to be travelling at that time and every flight (to anywhere) was full.