Stacy Nicholson & Skip Wood, visiting Colorado from Moorhead, Minnesota, wrote saying they’ve never seen anything like it.
These clouds are known as Kelvin-Helmholtz instability clouds, named for Lord Kelvin and Hermann von Helmholtz, and they are formed due to wind shear in the atmosphere.
Wind shear is a change in either speed, direction, or both over a short distance.
The wind shear creates waves in the flow of air and when there is enough moisture present to make a cloud, the result is little rolling eddies seen along the top of the cloud.
These eddies are usually evenly spaced and easily identifiable and often don’t last too long.
Kelvin-Helmholtz instability clouds are most commonly seen in mountainous areas and they indicate extreme turbulence for aircraft.