Mountain waves

A Lancair aircraft is pictured in the foreground with a lenticular cloud in the background. I have been getting many questions asking about this weather effect. These clouds are caused by mountain waves, which is when stable smooth air crosses a mountain barrier and the air flowing up the windward side is relatively very smooth. Wind flow across the barrier is a laminar (smooth) air flow, that is it tends to flow in layers. The barrier may set up waves in these layers much as waves develop in disturbed water. The lenticular cloud remains nearly stationary over the same spot in relation to the ground. That is where we get standing or mountain wave or lenticular clouds.

From the "Aviation Weather Services Handbook" published by the Federal Aviation Administration and the National Weather Service: "From my experience flying sailplanes in a mountain wave was the leading up wind edge is very smooth with lots of upward movement of air. Very safe to fly sailplanes in this location and many high altitude sailplane flights use this effect to climb to 50,000 feet and above. The trailing edge is very turbulent with lots of downward movement of air. Not where you want to be flying any kind of aircraft."