'Sky' surf is up in Alabama

Not that Birmingham would be considered a haven for surfers but check out the gnarly waves in the sky spotted there on Saturday.

The phenomenon are called "Kelvin-Helmholtz" waves and just like how waves work on the ocean, it's somewhat similar to what's happening in the sky in this instance.

In the ocean, as the wave nears shore and reaches shallower water, the water near the ground slows down due to friction as the water above speeds past, creating the waves we know and love along the beaches.

In the air, these waves are caused when you have a stable layer of clouds -- usually around here it's a thin fog layer over Puget Sound. But if you have a layer of varying wind speeds blowing through the layer, it can create these waves.

Here are some videos taken from the scene, courtesy of ABC 33/40-TV (Birmingham)'s weather blog,

You can see some more photos on as well.

It must be the season for them. Simiar K-H clouds were spotted in the Puget Sound region on Dec. 9. UW Atmos. Sci. professor Cliff Mass has a photo in his weather blog and a brief explanation of how they occur.