This photograph of Kelvin-Helmholtz clouds was taken in the foothills of the Rocky Mountains. Click on image for full size (38 Kb) Courtesy of Benjamin Foster/UCAR

Kelvin-Helmholtz clouds look like breaking waves in the ocean. After wind blows up and over a barrier, like a mountain, the air continues flowing through the atmosphere in a pattern that looks like a wave.

These clouds form when there is a difference in the wind speed or direction between two wind currents in the atmosphere.