Lenticular clouds are unique clouds which typically form around hills and mountains, as a result of the way that the air moves. These clouds look quite distinctive, like giant flying saucers or something like lopsided stacks of pancakes. Many famous mountains around the world are often photographed with a cap of these clouds, including Mount Shasta and Mount Fuji.
You may also hear these clouds called altocumular standing lenticularis. They form when a current of moist air is forced upwards as it travels over a mountain, causing the moisture to condense and form a cloud. Sometimes the air is forced into a wave pattern, generating what is known as a wave cloud. Wave clouds can look like strings of discs spreading out from the leeward side of the mountain. They can also form miniature waves which sometimes look exactly like a choppy sea.
One interesting thing about lenticular clouds is that they look like they are perfectly stationary and frozen in time. This is not, in fact, the case. These clouds appear stationary because the flow of moist air continually resupplies the cloud from the windward side even as water evaporates and vanishes from the leeward side. These clouds can look like they are hovering for hours or days, until the wind or weather changes and the cloud disperses.
Observing and identifying lenticular clouds is generally fairly easy, because the clouds are so distinctive. If you ever see a cloud which looks like a flying saucer, a lens, or a giant beret, you're looking at a lenticular cloud. If you look around the cloud, you may see a geographical feature which is creating the conditions which lead to the formation of these clouds. If you don't see a mountain or hill, there is probably a current of air running in the opposite direction to create a wave cloud.
Many people enjoy photographing lenticular clouds because they look unusual and they can be quite stunning. If you happen to live near a mountain which is often wrapped with a lenticular cloud, you may find it interesting to photograph it every day, looking at the way the cloud moves and changes with the weather. After a few years, you may find yourself able to make weather predictions based on the presence, position, and shape of the cloud.