Kelvin Helmholtz clouds are the result of a particular type of wind shear. Wind shear occurs when one layer of air slides across another layer while moving in a different direction or a different speed (or both). This results in vertical eddies that produce a regular pattern of air waves.
In the case of Kelvin Helmholtz clouds, the eddies must be strong enough to carry the cloud over the peak and down the other side. This results in the appearance ocean waves breaking as they approach the shore.
Since these cloud formations last only a few minutes after forming, they are rarely observed.