not sure what St. Louis is like in July, but if it's anything like Tulsa, you'll be loving life on AC in May. I was there this May for my first time, and loved it. This is a guess, but I don't think temps got above 85-90 while I was there, and the evenings cooled off pretty well. Of course it was very humid, but with the breezes off the ocean, it was really very nice. I'm sure you'll enjoy it.