So true! My riding in 117F didn't happen out of the blue. I had been riding (training) throughout, so when temperatures started rising, it wasn't a big deal. My body was coping to those constantly hot temperatures. If you live in a place where temperatures are normally cool and one day it hits 100 or higher, it's not safe to go for a ride or practice any other outdoor activity. You simply haven't given your body enough time to get used to (adapt or cope) to those kind of hot temperatures.

Living in Phoenix, AZ you see how many tourists suffer from heatstroke on hikes near the city because their bodies are not used to that kind of heat and/or they underestimated the amount of water they needed. In the hot desert, at least a gallon of water per hour is the rule for cycling... again if you've given your body several days or weeks to cope with the temperatures.