Project Vortex-99. An occluded mesocyclone tornado rated an F3 by an NWS damage survey. Occluded means old circulation on a storm; this tornado was forming while the new circulation was beginning to form the tornadoes which preceeded the F5 Oklahoma City tornado. Photo #1 of sequence. Oklahoma 10 miles south of Anadarko. May 3, 1999.
Credit: OAR/ERL/National Severe Storms Laboratory (NSSL).