It's definitely the humidity. I was able to bike my 8 mile commute to/from work while in Portland, OR in the middle of a 100+ F heat wave a couple of years ago.

It's definitely the humidity. I was able to bike my 8 mile commute to/from work while in Portland, OR in the middle of a 100+ F heat wave a couple of years ago. On the other hand, I'm currently dying in this Toronto heat wave that's 90F's during the day and 80F's at night. For me the real difference is the humidity. Portland, is super dry during the summer, and wet during the fall, winter, and spring.