I think all of us here would have found Dhahran, Saudi Arabia on July 8, 2003 too hot to ride, even for a short distance.

I've done up to 30min rides in a heat index of ~135F plus full unfiltered sun and would not ride for longer time periods at similar levels.

Note that heat index assumes full shade and sun exposure can add up to 15F in apparent heat index. Places with low humidity tend to have the least cloud cover or haze to filter the sun.