I am trying to think if I was there in 2013...I skipped a year in there somewhere, but you are right, it is a crap shoot when it comes to what kind of weather you will get. I was there in the late 80's when it was near triple digits, camped for 6 nights and it SUCKED! The last night we were there, a cold front moved through and cooled things off, but all I recall from that year was stadning in lines to refill my water bottle, and looking for shade.
I have weathered a few thunderstorms while over there, and last year my buddy and I rode in 7 hours of HEAVY rain ALL the way over there. We recovered by drinking beer and other adult beverages until way too late....made Sunday a tough way to walk around and look at airplanes