+1,000

I always find myself starting out feeling a little chilly, but then once I get going, my core is fine. Typically I'll wear a normal sleeveless base + jersey with arm warmers and either a wind vest or winter vest - that helps to fix the issue with the cold on descents. I guess I'm wondering why riding isn't keeping your core warm? I'll bet it's the wrong sorts of fabrics, as mentioned above. Believe it or not, I normally keep my Craft summer base layer in the winters here (I'll ride with it into the high 30's, before I switch to something else. With the right layers you shouldn't have a problem.

One thing that can make a BIG difference is whether you where anything under your helmet to keep your head warm. You can lose a lot of heat through your head, if I don't wear a cap or equivalent, I really chill down quickly.