Surf's Up?

Looking like a large wave about to break onto shore, this shelf cloud moves relentlessly forward toward Noelridge Christian Church (right) in NE Cedar Rapids, Iowa at 9:00 PM, Friday, July 22, 2011. This view looks due north. Until about this moment the leading edge of this gust front was silent in its steady and swift advance from the northwest, but winds soon began to pick up. The front was gobbling up all the hot and muggy air in front of it. This is a 3-second exposure at f/5.6, 200 ISO and 18mm focal length.