The hottest I've experienced in direct heat is in the low 40s C. But if you include Head Index readings, then I experienced about 52 C in Chicago's 1995 heat wave. It was absolutely miserable, even though the actual temp peaked at about 41C, the Heat Index reading of about 51C really did more accurately the way it felt. I worked in the Sears Tower at the time, and both in the morning and coming back from lunch I'd feel sweat just pouring off me just from being outside, but the A/C in the Tower is so kick-ass that I'd walk into the lobby and felt instantly refreshed and I'd be dry and comfortable within minutes even on the hottest days.
The previous summer, in 1994, I worked construction in Boise, Idaho, and we had a long string of 32+ C days, peaking at about the same 41C, but with a heat index of only about 38 C because of the much lower humity. I actually liked the Idaho weather for the most part, because it was dry enough that as long as I drank enough water and salts I was fine (my blue workshirts were often white with salt by the end of the day).
There's a definite difference between dry and humid air at high temps.
I looked up the record for heat indexes:
In Dhahran, Saudi Arabia on July 8, 2003, the dewpoint was 95 °F while the temperature was 108 °F. The heat index at that time was 172 °F (78°C).
Last edited by emathias; Mar 24, 2009 at 2:24 AM.
Reason: Adding record info