So I live in Iowa.  It is sooo humid here in Iowa during the summer months.  I hate humidity. Sigh..... The other day I ran in blazing sun but the humidity was in the 50's... so I completed a long run with no problem.  Today the humidity is above the 70's but no sun, total cloud cover... and I made it 2 miles before I said NO MORE!  Thank the lord the bigger races in this area all fall during the nice cool fall months.