Of course it's like 60 and beautiful outside today as I write this, but yesterday it was kind of like this old photo above of Craig Virgin leading Alberto Salazar in presumably a 10K track race. That said, I always feel satisfied when I brave the elements and run a good workout. You can't control the weather on race day, so why take days off or reschedule a workout if Mother Nature isn't cooperating? I hadn't done mile repeats in a while and I realized that I missed them. I think they're the best workout you can do for races 5K - marathon. Just adjust the rest breaks accordingly, depending on what you're trying to accomplish. As I'm training for 5K/10K I gave myself about 2-minutes recovery (400 meter jog on the track) when I did 5 of them yesterday. If you're trying to get closer to the 3K/5K zone, I'd recommend more like an 800 meter recovery. If you're training for a half-marathon or longer I'd slow down the effort and give yourself maybe one-minute recoveries. I like long repeats better than tempo runs because it's easier to stay in the appropriate zone and not turn the workout into a time trial. If the rest breaks are pretty minimal you get the same benefit too.