As of this writing, the forecast models are in pretty good agreement that there will be a storm. Many are indicating at least the possibility of big snows, but it's simply too early to determine how much or where. This appears to be a classic winter storm setup in the VA-DC-PHL-NYC area where temps will be near freezing, which means that a difference in storm track 100 miles to the west or east could be the difference between a foot of snow and next to nothing in the cities in this region. Further inland and at higher elevations, all snow is always more likely, but for coastal storms, they have to toss moisture further inland as well, which is how the big cities can get a big snowfall if they're cold enough while places such as Pittsburgh may be colder but get far less.
Two main factors will affect whether NYC gets more snow: where the rain/snow line sets up and how far away the storm passes. Some models are indicating the maximum precip will be over the Virginia area with decreasing snowfall amounts as you go north, even if it happens to be an all-snow event. But it's really, really hard to forecast snowfall amounts on Tuesday evening for an event that is mainly a Friday PM/Saturday storm.
Living in PHL and seeing this many times, personally, I wouldn't do anything to reservations before Wednesday night or Thursday morning, and I would think AA may issue travel waivers in that rough timeframe assuming we're still trending towards a larger snow event. If the forecast models trend towards a big snow and are in general agreement, I would consider changing plans only at that point. Often the forecasts are decent, but sometimes they've been complete busts, and 3-4 days out they're more likely to be a bust than within 36 hours of the start.