Looking like enormous waves breaking on the shore, this type of cloud is rare and fleeting – lasting no more than a minute or two. The distinctive breaking-wave shape is caused by wind shear.

Lenticularis stack, caused by a north westerly over Mount Ruapehu in the North Island of New Zealand.

'Spotlights' taken off the west coast of Levkas, Greece.

Shark Bay, Western Australia.

Mount Rainier, Washington, US.

The "tentacles", which you can see hanging down, are called "virga". They are essentially rain, or snow, that evaporates away before ever reaching the ground.

Nacreous clouds over Lillehammer Norway.

Storm Clouds at Sunset, Cochrane, Alberta. Canada. Some faces in there also.

Sky above Virginia Beach, Virginia US.

Taken early evening from MV Paros SG, off the coast of South Georgia Island in the South Atlantic.

Lions Head Cape Town, wearing its cloud hat.

Early morning, riverside, Exeter. UK.

Over Matching Tye , Essex, UK

Fair weather at Castlerigg Stone circle in Cumbria U.K.