These are indeed Kelvin-Helmholtz waves. What is happening is that the nocturnal near-surface layers (lowest 50-100m) of the atmosphere are much more stable than the layers above it in the mornings. Until the ground heats up due to daytime heating, the surface layers stay more stable than the air over it. Kelvin-Helmholtz waves occur when the wind shear between the layers destabilizes the topmost portion of that stable layer, and entrains the air into the unstable layer. What you see is stable air being lifted, cooled, and condensed so that this process becomes visible, though this commonly happens many places without being visible. 

Photos posted at Reddit by alison bee, taken near Birmingham, Alabama.

Explanation by zensunnioracle

Read more about and see more photos of the Kelvin-Helmholtz waves over at TYWKIWDBI!

(via suicidegeeks)