Tsunami Wave Clouds Over Birmingham, Alabama!

"The breaking waveforms of 'Kelv-Helmz' (as they
aren't known) are the result of shearing winds up
at cloud level. A particular type of turbulence
can develop in a layer of Cirrus cloud, which
happens to form below an inversion* between air
currents of differing speeds and/or directions.
Sea waves break as their bases are slowed down
upon reaching shallow water and their crests surge
ahead. Cloud waves break in the same way: when
their crests are pushed ahead of their troughs by
the difference in air currents.""