The weather will be great in December! It is just about perfect now. It was 45 degrees on my way in to work this morning, and should be about 70-75 degrees on the way home. December will be a little cooler, but not by much. The normal high for December is the high 60s I believe. I have ridden in January when it was 72, so it varies. Also, mostly clear skies, and the wind is pretty calm this time of year. Perfect for riding!

I would recommend "Fair Wheel Bicycles" to set up your bike. They have a couple of great mechanics.