Non-Tornadic Funnel Clouds
Horseshoe vortices seem to occur rather frequently in areas just east of the Blue Ridge Mountains. My location is about 25 miles east of the highest ridges of the Blue Ridge Mountains. When westerly flow exists, with little or no directional shear, but strong vertical speed shear, horseshoe vortices can occur. There needs to be enough low level moisture for clouds to form. From personal observations and sounding analysis it looks like the vortices start as horizontal rolls in clear air. If the rotation intensifies the pressure drop is large enough to support saturation of the roll and a cloud forms. The next piece of the puzzle is still questionable, but I think the roll needs to intersect an updraft, which pushes up on the roll and creates the horseshoe shape to the cloud. Some of the vortices seem to break away from the tops of cumulus clouds, which is another indication of strong shear.
Horseshoe Vortex over Opal, VA (May 02)
First Horseshoe Vortex over Opal, VA (Jul 06)
Second Horseshoe Vortex at Mature Stage (Jul 06)
Close-up of second Mature Vortex
Close-up view as second Vortex is weakening
Norman, OK (2/28/07)
Opal, VA (4/30/07)
Opal, VA (4/04/07) - This was sort of a hybrid in that the small rotating cumulus cloud began to arch into a horseshoe shape, but then stopped with only a small helical funnel developing along the left side of the cloud. This lasted for several minutes before it dissipated.