I live right outside of Philly and to be honest, you don't NEED snow tires for the amount of snow we have gotten over the last few years. I seem to recall only one big storm last year. But you have to be careful in the snow with the stock contis. They aren't great in the snow and if the car is a manual and this is your first rwd car, it can take some time to get used to the car in snow. Also, if your all season don't have much tread left, they will be all but useless.

Having said all of that, once the stock contis wear out on my car, I'll probably try to get some more aggressive winter rubber for the stock wheels and buy a set of wheels/tires for the summer. I will tell you one thing that if you get snows for the rear, don't cheap out and keep the all seasons on the front. Brake is more important than acceleration, especially in the snow, so why give the car enough traction in the snow to get yourself into trouble without having the proper traction in the front? Think about it.