Mount RainierNational Park, Rainier pictured with Lenticular Clouds (altocumulus standing lenticularis)
Lenticular Clouds are formed when damp wind moves over the crests of obstacles [mountains, rugged terrain] said obstacles form the wind into waves, the lenticulars sometimes materialize at the crests of these waves...
Wikipedia explains it better : en.wikipedia.org/wiki/Lenticular_cloud
...except they use the word 'moist' (eeeeeeeeeeuuwwwwww) and I've been unable to discover why they're round, unless I'm missing something obvious.
These shots have been around a while, they were taken in 2003 but...