I was surprised to see how many people mentioned the HUMIDITY there! We live just a few hours from you, in southern Ontario, so we have the very same weather you do. We're accustomed to the 90 degree days and the extremely high humidity but, last year in Tulsa, it was over 100 pretty much every day, I think. However, the air was soooo dry (at least compared to home), that the sweat would evaporate right away. You have to be super careful to drink enough water. It cooled down nicely at night, though, to about 80 or so. We don't have air conditioning in our trailer, but didn't really need it at night anyway. It's a very different climate than what we're used to, IMO.
Be prepared to be awestruck! I think Nationals is the most amazing show in the world!!