Well, it was only a drizzle, but that song is fun to sing. I did 5 miles in 57 minutes, including some long walking breaks. I ran one mile at 10 minutes and then slowed down to my 10:30 resting pace.
The temperature was 50 (F), and I enjoyed the rain. By the completion of the first mile, I was starting to sweat, and I had no problems with being cold.