Kelvin-Helmholtz clouds form when pressure differences amplify disturbances at the interface between two air layers, lifting wave crests toward the faster flow and pressing troughs downward until they develop into characteristic billows. After wind is forced up and over a barrier such as a mountain, the air continues in a wavelike pattern through the atmosphere. Complex evaporation and condensation processes create the capped tops and cloudless troughs of these waves. These clouds occur when there is a difference in wind speed or direction between two atmospheric layers.

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