I don't think I have the proper data to answer that question. In the winter, my average commute is around 35 degrees. In the summer, it's probably closer to 75. For the year, who knows? Temperature range is probably the relevant question.

For me, I haven't found a day that's been cold enough to keep me from commuting by itself, but it hasn't been below 27 this year. Below freezing and raining will keep me off the road, because that doesn't happen often enough to justify the equipment necessary to handle it.

Above 90, my wife starts telling me I should ride. Above 100 I started acquiescing.