Ever seen clouds like those? A bunch were seen (and You Tube’d) around Birmingham Alabama Friday. They look like waves breaking. They are called Kelvin-Helmholtz clouds, and are the result of shearing winds up at cloud level. A particular type of turbulence can develop in a layer of cirrus cloud, which happens to form below an inversion between air currents of differing speeds and/or directions. The wind speed at the top of the cloud layer is faster than that at the bottom, which rolls the cloud into wave shapes.
Sea waves break as their bases are slowed down upon reaching shallow water and their crests surge ahead. Cloud waves break in the same way: when their crests are pushed ahead of their troughs by the difference in air currents.