today was the opposite experience on my commute to work. I met up with a couple guys to climb up Old San Marcos Road up to Hwy 154. http://www.toughascent.com/blog/?p=127
At the bottom of the hill, it was 37 degrees. We climbed up 1150 feet in 3 miles, and at that point the temperature was a balmy 55 degrees. I have experienced this before where there is a double digit temperature difference between the bottom of the hill and climbing up to Hwy 154. Temp does not go up much after that point in the climb. Of course we were all shedding layers on the ride up, and I was in shorts and a tee shirt at the top.

Anyway, on the ride down it was like riding into a meat locker. Dropped the same 20 degrees, plus much less exertion and much higher speeds. Fortunately we all geared back up before the ride down.