Anecdotal, but I've ridden a bike in winter only once. There was a lot of melted snow "slush". I almost slipped twice. One of those two times, I was right in front of a car when my back wheel slid off to the side, and I caught myself from falling just in time. I've never done it again, it seems suicidal to me. It was a mountain-style bike, and I would have assumed the tires had enough grip. I'm sure you can pick up tricks and get better at this with experience, but it seems at least an order of magnitude more dangerous than summer time biking.