Horseshoe cloud
A horseshoe cloud is a relatively uncommon meteorological phenomenon which manifests as a cloud in the shape of a horseshoe or inverted letter "U".
They occur when a horseshoe vortex deforms a cumulus cloud. The clouds are relatively short-lived. Horseshoe vortex clouds are a form of "fair-weather" funnel cloud and are similar to the shear funnel type of funnel cloud.
A March 2018 instance was explained by the United States' National Weather Service:
