Mountain Wave

Mountain Wave is a form of atmospheric wave generated when stable air flows over a mountain range. The air oscillates vertically downwind of the mountains, creating areas of severe turbulence, strong updrafts and downdrafts, and potentially dangerous rotor zones near the surface.

Lenticular (lens-shaped) clouds indicate mountain wave activity
Rotor zones below the wave crests can produce extreme turbulence
Cap clouds on mountain summits suggest strong wave activity
Can produce sustained updrafts exceeding 3,000 ft/min — exploited by glider pilots
Mountain Wave Turbulence can extend well above the tropopause