Cloud waves over the Machars

 If you look at this view from Sands of Luce, it looks as though there are 4 evenly spaced cloud covered hills in the distance. The view below was taken a day later: there are not 4 evenly spaced hills. The original pattern looked suspiciously like a stationary wave at ground level with a fixed wavelength that must have been some miles long. The day in question was one of much visible evaporation at ground level on the beach. The air over the Machars must have been saturated with water vapour.

I have not been able to find any identical pictures but I did find this: https://communitycloudatlas.wordpress.com/category/kelvin-helmholtz-waves/ If you scroll down to the diagram of how the waves form, it looks like the picture for "small disturbances". I can make a case that there was a lower layer more dense because it was laden with water vapour and moving more slowly because of proximity to the ground. A layer of faster moving air above would lead to a wave pattern forming. I think it now helps me to understand the ribbed patterns in high clouds as well.