switch to velocity image

This radar image shows two supercell thunderstorms, and we are focusing on the northern one (the southern one was about to produce a tornado in Adams County when this image was taken).  Notice the tail on the southwest side of the storm.  This feature is referred to as a hook echo, and is evident in the photograph as an area of heavy rain on the left-hand side of the picture.  The wall cloud is located in the weak echo region of the storm, at the base of the storm's updraft..