Motivation? Don’t look for motivation. Just do it! If you’ve decided to be a rain-or-shine kind of cyclist, then you find yourself actually looking forward to “epic” winter rides. Make sure you’ve got a separate rain/utility bike, with wider tires (it’s not about speed, it’s about not slipping on paint stripes or getting flats) and possibly a bit more relaxed riding position (because if you’re heavily bundled up you might not feel comfortable in your normal riding position).
It’s quite the challenge for my group, because our Tuesday/Thursday-morning training ride includes 3300ft of climbing and, of course, 3300ft of descending. What you learn is that it’s very important to keep up a consistent pace because if you relax the cold and wet will get to you very quickly. Dress in a way that you’ll remain warm even if soaking, because there’s no truly waterproof cycling stuff out there. The high-tech stuff (including GoreTex) won’t keep up with a cyclist at high output… you end up as soaked on the inside as things are on the outside.
You could, of course, just set up a trainer in front of a TV and watch your favorite races, but there’s a small number of us who would rather ride through a hurricane than sit on a trainer. Mental defect of some sort. Or just a refusal to believe that anything can stop you and your bicycle. Do keep in mind that I’m in Northern California so the worst winter will throw at me are a few 40 degree days with driving rain, or upper-20s but dry, or once in a while, snow at the higher parts of our ride. We also rarely see ice, because it’s typically dry when it’s that cold. –Mike–