Sometimes it may happen that there are several cirrus layers above a building thunderstorm cloud. Only when the cumulus cloud has grown to a high level breaking through these cirrus layers, its top casts a shadow upon the cirrus layer.
If there are several cirrus layers, this multiple projection is caused by the perspective effect.
Also this photograph is rather old, it is still very impressive.
Camera: Nikon D40x; focus lenght: 55mm; exposure-time: 1/500 sec.; aperture: F/11; Date: 05.09.2009
Author: Michael Großmann, Kämpfelbach, Germany