About Horseshoe vortex
What a subtle little wisp of cloud the horseshoe vortex is! It is easily missed by anyone other than the most keen-eyed CloudSpotter, intent on adding it to their collection. The rare and fleeting horseshoe vortex cloud appears for just a minute or so before evaporating. Anyone lucky enough to spot one must take a photo if they want to be believed by their cloud-collecting friends.
This cloud forms in a region of rotating air, or vortex. While the familiar orientation for a vortex is vertical (see the tuba cloud), they can occasionally develop on a horizontal axis. This is when the gently rotating crescent of the horseshoe vortex cloud can form. The movement of air seems to result from thermal that is sent into a spin as it reaches stiff horizontal winds above. Only rarely are conditions right for cloud to appear as the low pressure within this horizontal vortex causes the air to cool slightly. When they are, the twisting ribbon of cloud that forms is soon lifted upwards at its centre by the rising thermal, and distorts into a crescent shape.
This rare and beautiful little cloud won’t lead to any precipitation, but it will rain down luck upon anyone fortunate enough to spot it – as well as five CloudSpotter stars.
Image: Spotted over Salo Corner, Saint Louis County, Minnesota, United States by Suzanne Winckler.