Yes weather does affect these things bigtime, running meth limits the effect. There were Friday nights last year, I couldn't break into the 12's on the V10 91 tune, then other Friday nights it would. I've had nights were it was sooo humid that the car slowed down each round. Also track prep affects too. Also don't forget track location too. Close to sea level has an effect too. I hope to prove that here in Oct when bunch of us plan on going to Cecil County. Talking with the racers at BSD that have gone to Cecil County, they run .2 to .3 tenths quicker.