These clouds are called lenticular clouds, due to its lens-shaped appearance.
These clouds are formed by so-called mountain waves of air created by strong winds forced over high mountain.

Huge clud watches us! It's very scary. 2003.11.25 Photo by NAMIKAWA,Kazuhito／SUBARU Telescope

2003.11.25 Photo by NAMIKAWA,Kazuhito／SUBARU Telescope

SUBARU and Lenticular Cloud 2003.11.25 Photo by NAMIKAWA,Kazuhito／SUBARU Telescope

L>R CFHT, Gemini North, UH88, UKIRT 2003.11.25 Photo by NAMIKAWA,Kazuhito／SUBARU Telescope

Photo by NAMIKAWA,Kazuhito／SUBARU Telescope