In a weird way, running in an Indiana summer is a lot like running in an Indiana winter. Stay with me here for a moment.
In both seasons, we are hit with very extreme weather; July and August, January and February. It is so hot/humid, cold/windy; both will nearly take your breath away. Both certainly tax one's motivation to go out the door. Both diminish running speed.
And both demand a shift in attitude; rather than speed, you just get in the miles. That's it...just get in the miles. You can't predict much from your training times. BUT, and it's a big but, you CAN count those miles. And by counting the miles, you are far better off for the spring and fall races that count.
Persevere. Whatever the season.