overseeding in Ohio

[harrydog]

I'm in southwestern Ohio (clay soil) and last Fall I used a slitter/seeder to overseed my lawn with Crossfire II seed. It filled in very nicely and this Spring it looked great. But it's turned brown during the heat of the summer and looks bad.
I'm thinking of overseeding again. What is the best grass seed for my area? I need something that is very drought tolerant.
Thanks.