Another picture shows a view from the ground of a cumulonimbus with a base at around 3,000 feet and vertical development upward to around 30,000 feet - small compared to most thunderstorms which are associated with really severe weather. They indicate that the atmosphere is quite unstable and can also be an indicator of impending severe weather. The picture of mammatus clouds, shown here, was taken by Mark Gibbas, a PSC meteorology alumnus, at Acadia National Park. Orographic clouds, as the name implies, are produced by the flow of air interacting with mountainous terrain. The spectacular picture was provided by Michael Nahmias and shows the cap cloud shrouded summit of Mt. Ranier.
Lenticular clouds are lens-shaped clouds that can result from strong wind flow over rugged terrain.
At the time of this photo, the winds were blowing around 30-40 mph from right to left, forming several lenticular clouds. Sometimes they stack up like pancakes in multiple layers as are several depicted in this first photo. The strong flow produces a distinct up and down wavelike pattern on the lee side of the mountain or large hill and the lenticular clouds tend to form at the peaks of these waves. They sometimes are very round and the edges are so well defined that they resemble flying saucers. This close up sequence shows a large lenticular cloud at various stages of illumination as the sun moved lower on the horizon and lit the cloud from below.