Lenticular clouds are a distinctive cloud formation resembling lenses and are thought to be an explanation for some supposed UFO sightings.
Height of base: 6,500 - 16,500 ft
These orographic wave clouds form when the air is stable and winds blow from the same or similar direction at many levels of the troposphere. As the wind blows across hilly or mountainous regions, the air undulates in a downstream train of waves. If there is enough moisture in the air, these waves will condense to form the unique appearance of lenticular clouds. The clouds can be seen as far as 60 miles downwind of the hills or mountains that led to their formation and they are believed to be one of the most common explanations for UFO sightings across the world.
More cloud information
For more information on cloud spotting and pictures of different types of clouds, view our Cloud types for observers guide.