How much does temp. affect running / workout time?

for sure...it's been 90 here all week and our workouts have suffered slightly

It affects people differently. I know that I would probably be 5-10 seconds faster at least on that workout going from 90 to 50. even if you are a good hot weather runner I would guess that with cooler temps you are in the 3:10 range.

here's a performance estimate based on temperature (runworks running calculator,

http://www.runworks.com/calculator.html

). probably not the most accurate thing ever but it gives a pretty good range. all i know is i've been training based on heart rate this summer, and when we had a "cold front" roll through (from 100 or so down to low 80's) I dropped 40 seconds / mile off my training pace, at the same heart rate. training in the heat sucks, but it sure does feel good when the temperatures finally drop.

60F/16C or below 3:07.9 3:07.9 5:02.5

65F/18C 3:09.1 3:09.1 5:04.4

70F/21C 3:10.5 3:10.5 5:06.5

75F/24C 3:11.9 3:11.9 5:08.9

80F/27C 3:13.5 3:13.5 5:11.4

85F/29C 3:15.2 3:15.2 5:14.1

90F/32C 3:17.0 3:17.0 5:17.0

Thanks, guys, for the info. I really appreciate it.

I am currently in marathon base training with a lot of mileage (to me) and not sure if the slowness was caused by the mileage or the heat and was really hope it was cause by the heat - since I am doing about 70 mi/wk, which is not very much, but I was doing only 50 before.

Glad to know that I have not lost much speed if any - I still do 1 speed workout each week and 1 form drill session per week and hoping to keep my speed. I have a 10K coming up in 3 weeks and hope I will do OK with that 6x1K time (my vVo2max pace).

I recently ran a race when it was 100 hot. How accurate do you guys think that runworks calculator is? 10-15 seconds for a mile?

Heat can cost me 20-30 seconds per mile. I live in a fairly hot, humid area though, and am a terrible heat runner.