In winter, Zurich is often covered by a thick layer of high-altitude fog. That doesn't sound very pleasant, but in fact fog is way better than clouds in Switzerland as all you have to do in this case to get some sun is to climb a nearby mountain. Or even better: ski it. There are many resorts so close to Zurich that it's worth going to one just for the day. These resorts listed here open as soon as there is enough snow, usually by the end of November or mid-December. Always check the conditions before you leave. The Swiss Federal Railways SBB offer combined tickets (including train and bus travel and the lift pass) to many of these resorts.