Not to pile on here (and not sure this point has been made) but another cynical reason for going with AS or winter tires in the cold is the potential that your insurance company would deny covering damage sustained when driving in the winter on summer tires.
As I understand it, a big issue using summer tires is that the rubber compound provides great grip in warm weather conditions but will harden in sub 45 degree temperatures. This will cause traction to decrease significantly and can cause your tires to crack - rendering them useless.