Given the many variables of our atmosphere, you might imagine that not all clouds could fit in standard categories.
You would be right. There are probably infinite shapes, densities, temperatures, and colors of clouds. Many varieties may occur without anyone ever even noticing them! Some unusual clouds, including banners, caps, and lenticular altocumulus, result from air passing over peculiar land forms.
Banners, caps, and lenticular altocumulus all form as a result of mountains affecting air currents. The names banners and caps describe two shapes of clouds that are caused by dry, high-pressure air hitting humid, low-pressure air sitting on top of a mountain peak.
Lenticular altocumulus means a high cumulus cloud in the shape of a lens, or two contact lenses cupped together and filled with cloud.
These bizarre clouds form at the crest of a breaking wave of air over a mountain peak or ridge. From there, they can sail off into the sky, keeping their otherworldly shape.
Lenticular altocumulus clouds look remarkably like UFOs we’ve seen in the movies.