Known as the UFO cloud, its formal name is “Altocumulus Lenticularis Clouds” and they are named for their smooth, round, lens-like shape, commonly known as a lenticular cloud (lenticular means lens or lentil-like). These alien clouds form when winds blow across a mountain range, to form air waves on the lee side.
This process, known as the mountain wave effect, is usually invisible, but when moisture is present at the top of these waves, lenticular clouds form where the wind rises and dissipate where it falls.
If alternate layers of moist and dry air are present above the mountains, the clouds may pile up on top of each other like stacks of plates. It is these distinctive stack formations that have, on occasion, been mistaken for UFOs.
Their formation relies upon mountains and valleys, the places that you can see them at their best are very limited. A well formed altocumulus lenticularis cloud is remarkable and ensure you have your camera.
If you want to see these altocumulus-lenticularis clouds you should head for the mountains, the best place to see these clouds are:
The Rockies in North America, sometimes in the Bow Valley during a Chinook.
The Alps in either Italy, France or Austria or Germany
The top four photos were taken in the Bow Valley while the Chinook winds were howling near Canmore. The bottom photo snapped on the west side of Cochrane, at sunset.
Just another Rocky Mountain moment!