They occur when a
horseshoe vortex deforms a
cumulus cloud.[2] The clouds are relatively short-lived[2] and is the last stage before one dissipates.[3] Horseshoe vortex clouds are a form of "fair-weather"
funnel cloud and are similar to the shear funnel type of funnel cloud.[citation needed]
As the
updraft pushes flattish cumulus clouds up & a horizontal vortex develops from differential updraft speeds... As the
vortex climbs, it's caught in the faster horizontal
winds aloft, & the middle part of the vortex catches the faster
speeds with the ends being slower.
These clouds do not occur often because all the needed conditions rarely occur together.[3]