Central Park, NYC - Running on the snow covered bridle path is more than possible, it's fantastic. You don't even need those grippy things to attach to your shoe, just the lowered expectation that you can't get in a quality training session. It does take extra leg strength to get around though, so if you run long enough, you may expect some soreness in parts of the leg you don't normally get. Traction is better than the half-paved road too.