I commute in inland Northern CA no matter what. Plus 100 around here isn't altogether uncommon.
My commute is only 8 miles, so it's never that bad. But I rode the Davis Double Century in 100+ weather. I'd rather do that then ride in the ice or snow like the amazing people here who live in teh east and are dedicated commuters.
As long as you are moving and have water, it's survivable.