Out on this morning's drive, I spotted a row of wave-shaped clouds. By time I could pull over safely, the sharpness of the wave crests had softened. I knew it was a rare phenomenon but had to google to find the name (I'm not that smart!) Kelvin-Helmholtz clouds!

Camera is a Canon 5D Mkiii with a 70-200mm lens, shot in manual mode:
Shutter speed 1/500, F stop 16, 100 ISO

Processed in Lightroom