Tied my personal record for coldest bike commute this morning, 17 F. Forecasters were calling for a low in the mid-teens, and I was wavering about riding, but it was "only" 21 F when I got up, so I decided to ride. Apparently some high clouds kept a lid on the temperatures, but then it must have cleared off again because the temperature dropped another 4 degrees during my ride to work. I was very comfortable, and I think wearing a wind vest over my soft-shell jacket did the trick. Ironically, my previous coldest ride also occurred on January 4, in 2008.