Nokian studs, front and rear. 140 bucks in tires is way cheeper than medical bills or going down in traffic on a dark winter road surrounded by grumpy sleepy drivers. The studs don't help at all in snow as far as I can tell. We don't usually get warm enough up here (Anchorage, Alaska) to need a rain bike in the winter. Even if it does rain, the streets are still frozen, and it immediately turns to ice. Be careful when you put your foot down.
I've so far resisted getting a fat bike for snow days, but think I might put one together for this year as it can be a !@#@ to get in when it snows, and I'm tired of carrying my bike through deeper sections, and can't find a good route to ski in from where I am living now (whine, whine, whine).
