I was at Sturgis last year. It was really hot a few days but not unbearable. Just be sure to stay well hydrated during your legs. Drink plenty to start out and carry water with you. Drink often and then drink some more.
On the other hand the weather in that region of the North can be really freaky. You could wake up one morning to some really LOW temps as well.
the possibilty of high plains thunderstorms always exists as well.
