By Gary England, NEWS 9 Director of Meteorology

This screenshot was taken when there was a one quarter-mile wide multiple vortex tornado on the ground under the four mile wide radar indicated mesocyclone. 

A mesocyclone is a low pressure area inside the thunderstorm that sometimes helps to cause a tornado.  Visual evidence of a mesocylone is sometimes displayed as a wall cloud.  A wall cloud is a lowering in a rainfree (usually) area that is rotating.

At least ten tornadoes (and probably several more) touched down from this storm over a 3 plus hour event.  Movement was slowly east along an east-west boundary (miniature cold front that became stationary).  I call such a storm, a boundary crawler.

The storm and its numerous tornadoes were captured on video by SkyNEWS 9 and six StormTracker units - truly compelling video of a very unusual and prolific tornadic supercell thunderstorm.  If this storm had been over the metro instead of 40 to 50 miles north, we would have suffered a major hit.