We're sitting under a heat advisory right now. I'm pretty sure that for my purposes, this is better than being in DC, where there's an air quality advisory, but if the buildings in which I spend much of my time weren't air conditioned, I might fel differently.
Tomorrow's projected high temperature is 38 C /100 F — and that's not accounting for the heat index.
The temperature right now is sitting at 34 C / 94 F (down 1 degree Fahrenheit from the high, btw) with a heat index of 39 C / 103 F. The humidity is probably the biggest problem — a dry heat can even be pleasant, if you stay hydrated, but high temperatures coupled with high humidity make for brutal weather.
Basically, what I'm trying to say is: if you live in the Louisville area, now would be a good time to restrict any hard efforts — or, really, any efforts — to the early morning hours (late evening might also be okay). If you happen to have access to an air-conditioned airplane hangar, that might work, too (or you could just ride rollers in you basement, or something — if I had a set, I totally would).
Likewise, I'm pretty sure that if you plan to leave the house at all — even if it's just to walk five or six meters or so to the garage and check on your bikes — you should probably bring an entire Camelbak filled with icewater.
Good luck out there, everyone.