I agree with the ladies above- you need layers and special clothing. This is the first winter season I've gone out, thanks to my husband who got me into winter riding (he's been doing it for years). You do have to buy a couple items- AmFib tights by Pearl Izumi are the best- expensive but worth it. You only need 1 pr and just wash them, 2 if you ride every day. Also purchase a good tight fitting cycling jacket made for the cold weather. You want it tight because the wind is your biggest enermy out there- loose stuff just flutters and makes it harder to ride. But since you'll be wearing at least one or two layers under the jacket, make sure the jacket is sized right to fit with those other layers. Lots of them out there- I have Sugoi Inverter (can't remember what my DH has). Also essential is neoprene booties and windproof gloves and overmitts. I prefer the Goretex gloves, but any windstopping fabric will probably work. Colder than 40 and I' also wear a goretex overmitt- very thin so as not to compromise on hand movement. The rest you might already have as part of cold weather gear anyway, like a thin balaclava, polypro shirts, cycling shorts, polypro tights, polypro thick socks, etc. A helmet cover is optional. I like it a lot b/c I don't have to put anything else on my head besides the balaclava. Otherwise, you'd have to put on a hood or hat of some sort- really too bulky for most helmets.

I ride my bike with smooth tires on most days. Only use the knobby bike when there is obvious snow or ice on the roads or road margins. One thing you will definitely have to accept is road grit all over you. Be sure to wear glasses regardless or you'll get an eyeful of sand!

Otherwise I am a total winter bike convert! I used to absolutely HATE the thought of riding in the winter and hung up the bike, but now I'm out there whenever it is above freezing (and thank God we've been blessed in NY the last two weeks!!!)