High Quality Content by WIKIPEDIA articles! A wall cloud, or pedestal cloud, is a cloud formation associated with thunderstorms. It is a marked lowering typically beneath the rain-free base (RFB) portion of a deep cumulus cloud (normally cumulonimbus but on rare occasion cumulus congestus), and indicates the area of primary and strongest updraft which condenses into cloud at altitudes lower than that of the ambient cloud base. Most strong tornadoes form from wall clouds.