Joining the CAS Community

To view the CAS Community pages, you will need to confirm you accept our Terms and Conditions. If you do not accept them please click Back in your browser.

To participate in Cloudspotter Groups and to view other Cloud Appreciation Society members, you will need to complete your own Community Profile by uploading profile and header images and confirming details about yourself.

Filter Photos:

You have selected:

Main Cloud Types

Other Clouds

Optical Effects


May 2016

May 2016

The Golden Horseshoe

One of the rarest cloud formations, and quite possibly the most difficult one to spot, is the ‘horseshoe vortex cloud’. This example, gilded by the rays of the setting sun, was spotted by Mark Evans (Member 8,452) over Cwmdare, in the Cynon Valley, South Wales, UK. Mark tells us it only lasted some 15 minutes before the distinctive curve of cloud dissipated away.

Conditions need to be just right for this short-lived cloud to form. A rising air current, often a thermal lifting off the sun-warmed ground, needs to take on a twisting motion as it ascends. This air current also needs to encounter a crosswind overhead and a ‘temperature inversion’, which when the way that the air temperature changes with altitude acts as an invisible lid on the rising thermal. And the moisture and temperature conditions need to be just right too, so that a ribbon of cloud can form as the temperature drops within the spinning vortex of the rising air. Upon reaching the invisible ceiling, this ribbon of cloud tumbles back downwards. The result is an upside-down curve of twisting cloud that resembles a horseshoe before it disappears.

Many congratulations to Mark for the May Cloud of the Month. Not only did he manage to capture a horseshoe vortex cloud, he got a golden one!

Photograph © Mark Evans

  • Kevan Hubbard avatar


    May 7, 2016at9:41 pm

    Almost a Madonna look to it.could deceive the god fearing folk?or a UFO. Or a bit like the hand of creation nebula from the Hubble space telescopes shot of much larger clouds in space.

  • Michael Davies avatar

    Michael Davies

    August 20, 2016at12:56 pm

    congrats Mark a great image

Post a Comment

This site uses Akismet to reduce spam. Learn how your comment data is processed.