Under the right atmospheric conditions, clouds can form in a distinctive but short-lived breaking wave pattern known as a Kelvin-Helmholtz cloud. The animation above shows the formation and breakdown of such a cloud over the course of 9 minutes early one morning in Colorado’s Front Range region. Kelvin-Helmholtz instabilities occur when fluid layers with different velocities and/or densities move past one another. Friction between the two layers moving past creates shear and causes the curling rolls seen above.
In the background, you can also see a foehn wall cloud low to the horizon. This type of cloud forms downwind of the Rocky Mountains after warm, moist Chinook winds are forced up over the mountains, cool, and then condense and sink in the mountains’ wake. (Image credit and submission: J. Straccia, more info)