It depends on how much snow you get. Normal tires are fine on snow once you get used to it. So if you have icy conditions just for a few weeks, it's probably not worth the hassle to switch. (I've been riding a road bike throughout all winter for more than a decade now. Riding on snow is fine. The only dangerous situation in winter is actually on warmer days without snow, where one doesn't expect anything, but when the road has frozen over invisibly in some dark corner.)