Surf's up -- in the skies over Mukilteo

But these clouds aren't directly temperature related -- they're caused by when you have wind shear -- that is, layers of air moving in different directions. As those layers interact with clouds, you can get turbulence that causes these impressive wave-like formations to occur.

Or amore detailed explanation from the University of Illinois, Champaign website: "Billow clouds are created in the upward branch of each of the eddies if the air within this branch has a high enough relative humidity that, upon lifting, the air parcel reaches saturation. Individual billow clouds generally have life times of a few minutes. The presence of billow clouds provides a visible signal to aviation interests of potentially dangerous turbulence."

OR... how about just some compelling video evidence that demonstrates this quite clearly?

Here is time lapse video captured from atop the University of Washington Atmospheric Sciences Building from 2010. You can see how two cloud layers are moving in almost exactly the opposite direction. As the day gets into evening about 50 seconds into the video, you can see some of the tube-type clouds form, and then just before sunset, watch in the bottom left corner and you'll see the "breaking-wave" cloud formations:

And here is perhaps the most dramatic version of KH clouds I've ever seen (this was in Alabama in 2011):