If you stepped outside this evening, you may have seen some "waves" in the sky. They were very translucent, but were very distinct. We don't see these that often, but I believe they are cirrostratus undulatus clouds. What was so cool about these were that they covered a HUGE chunk of the sky! Here's another picture from one of my Twitter friends: http://twitpic.com/905nq
I thought you might find these interesting. Have a great night!