Most of us see clouds every day, but only very occasionally will you be lucky enough to spot one of these 7 particularly rare types - some of which can only be seen in very specific circumstances or locations.

Noctilucent clouds
One of the rarest and most beautiful of all cloud types. They are found at very high altitudes – up to around 250,000 feet Visible on clear, summers nights between 45 °N and 80°N latitude ,they appear illuminated by a blue or occasionally red or green light. We still do not know much about how they are formed, but they are thought to be made up of ice crystals.

Kelvin-Helmholtz clouds
They can sometimes be seen as far as 60 miles downwind of the mountains that formed them. An extremely rare phenomenon, where clouds form as a billowing wave pattern Occurs when there is a strong vertical shear between two air streams. This causes some winds to blow faster at the upper level, than at the lower level.

Mammatus clouds
Bulge or pouch shaped, they’re usually seen emerging from the anvil at the top of cumulonimbus clouds. Formed by turbulence, they are one of the few clouds that come from sinking, rather than rising air.

Lenticular clouds
Usually formed behind hills or mountains, where the air is stable and winds are blowing from a similar direction. These tall geographic features interrupt the wind, the airflow undulates and condenses into these disc shaped clouds.

Funnel clouds
Cone shaped clouds which extend from the cloud base, but never actually touch the ground. Formed in the same way as a tornado around a small area of intensely low pressure. If a funnel cloud reaches the land it becomes a fully fledged tornado and if the funnel cloud reaches the surface of a body of water, it becomes a waterspout.

Fallstreak Hole clouds
Also known as a hole punch cloud - they form when part of the cloud layer turns to ice crystals which are large enough to fall. Water droplets in the cloud, cooled below 0°C but not yet frozen, will freeze if they find a particle to freeze on to or are cooled to below -40°C. Aircraft can cause this to happen by making the air expand & cool as it passes through the cloud

Arcus cloud
Formed when warm air within a storm cloud is pushed up from the ground by the cold air exiting downwards. Unattached to the storm cloud they are known as roll clouds, but when attached they are called shelf clouds.

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Credits
Intro: FREEMEDIABANK -    • Sky with clouds. Relaxing background.   Noctilucent clouds Kevin Lewis -    • Timelapse of Noctilucent Clouds over ...   Timow2s -    • Noctilucent Clouds   Kelvin-Helmholtz clouds Benjamin Brown-Steiner -    • Kelvin-Helmholtz Cloud Time Lapse   Diana Armendariz -    • WAVE CLOUDS seen over Phoenix, AZ (Ke...   keidashs -    • Kelvin-Helmholtz Wave Clouds   Mammatus clouds GenePoolChlorine -    • Video   Ronan O Keeffe -    • Lenticular clouds   Bazmo75 -    • Lenticular Clouds - Dublin   Funnel clouds xxRosalynLxx -    • Funnel Cloud (Small Tornado) South We...   Steven Harman -    • St. George Island - Funnel Cloud   Fallstreak Hole clouds Barry Morwood -    • Weird cloud formation over Oshawa, On...   Mad Astronomer -    • Video   Arcus clouds piratefux -    • Shelf Cloud über Karlsruhe, 21.06.2012   Marcelo Albuquerque -    • Roll Cloud   Music: We Remain by Cocolixe