What are the odds?

Recently, we purchased a new couch. Gavin arranged for a friend to help him pick it up and for Salvation Army to come and pick up the old ones. However, that could not all be done on the same day. The new couch was picked up and the old couches were moved outside into the backyard until a few days later. We live in Las Vegas, where the weather is sunny 99.9 percent of the time. So the thought of rain never crossed our minds. What are the odds that on the night that we put couches outside it would down pour!?!?