Often seen above mountains or hills, lenticular clouds are extraordinary clouds that, due to their smooth saucer-like shape, are often mistaken for UFOs. Lenticular clouds are formed when a current of moist air is forced upwards as it travels over a mountain, causing the moisture to condense and form a cloud. They can appear as if they're sitting stationary, hovering above our planet in an unusual fashion for hours or even days. That's because the flow of moist air continually resupplies the cloud from the windward side even as water evaporates and vanishes from the leeward side. Lenticular clouds are considered a rare sight, especially in areas where there are no mountains. When the sun sets, viewers are often treated with a spectacular display as the clouds are lit with brilliant colors, almost as if someone had painted the sky. As Adamus said about the photo above, “Surreal, otherworldly, foreboding...perhaps a once in a lifetime combination of colors, shapes and textures. This awesome lenticular cloud formation occurred at sunset over Oregon's Alvord Desert in late December, ahead of an impending storm."