If your airline is concerned about the flight being on time due to weather, they will cancel it 3-4 days before it is scheduled to leave. You'll then scramble to find an alternative way to get there.
In 2011, my wife and I were scheduled to arrive in early February at the Poly. 12" of Snow was forecast for Philadelphia the Friday we were to leave. On Monday, 4 days before the flight, US Air texted me that my Friday afternoon flight was cancelled. I called, and they gave me a Saturday afternoon Flight. I called Disney, and got the reservation moved 1 day. I was paying, not using points, so they were accommodating. The next day, Tuesday, US Air cancelled my Saturday flight and put me on Sunday morning. I called Disney, and moved it back another day. On Friday, US Air texted me again. Sunday flight cancelled. I re-scheduled for Monday morning. I called Disney. The CM thanked me for calling to cancel, and moved my reservation again.
It started to snow Friday late afternoon (hours after my initial flight was to be), and it continued snowing until Sunday afternoon. 20+ inches of snow. The airport opened at 11pm Sunday night. I flew out at 7am Monday morning.
When we arrived at the Poly, the lobby was full of guests. Apparently, for the last few days, people had been extending their vacations because there were no flights on the east coast. Now that the planes were again flying, everyone was leaving. We were told that the only empty room the previous night was a suite in the Contemporary that was $3k a night.
We watched the forecast for the return flight, and fortunately didn't have an issue getting home. Had we been stuck due to planes not flying, we had a backup plan to stay with my brother in Tampa until we could fly home.
I'd advise anyone being in a similar circumstance to strongly consider driving out a day early instead of being at the mercy of the airlines. Had my wife and I not had understanding employers, our 10 day trip would have been a 6 day trip or cancelled. Had we driven south on Thursday or even Friday morning, we could have flown out of anywhere south of Washington without any issue whatsoever or just driven the whole distance (Ford Expedition 4WD, goes through anything).