Ah, the Midwest in July. It's definitely not the funnest time to get into a hot racecar and I have no plans to do so in 2013. Given I am renting this year and I can pick and choose; I pretty much planned to opt-out of the dreadful summer months.
When it's 90-105 degrees with a heat index ranging from 95-115, and you're in out in the sun all day, on even hotter blacktop, in a 2 or 3-layer fire suit, driving a car with insanely hot operating temps, and many times running the vent or heater toward warm to help out the engine... etc... It sucks. And that's the good scenario when you're not laying underneath the car sweating and trying to hastily fix something!
Oh, there's people with crew members, in-car helmet blowers, fancy cool suits with icewater circulating through them and rigs with A/C to cooldown between sessions - but I've never been that special!
Btw; never been worse than the July weekend in 2009 I spent at VIR for the UTCC where I was getting dizzy in the TT grid (not even 100% full firesafety setup).
I did try a little to find a seat in the 4.5 hr NASA MW Enduro at Autobahn mid-month that goes into the night. I did not try real hard though, as we had some tentative plans throughout July. I had another 2 'feeler' offers that timing simply did not line up for. All-in-all this looks to be an 'off' month.