A wide cumulonimbus anvil with pouch-like clouds resembling female breasts. This is the end stage of a thunderstorm cell. These clouds are causing by sinking air after the hot air bubble reaches the upper troposphere. This sinking air motion of the airmass is sometimes also referred to as anti-CAPE because the stronger its ascent, the stronger is its downward momentum transfer of the raised air. Because of the strong instability and moisture, these mammatus clouds were especially beautiful. The photographed cloud was taken at St Thomas Bay. The first thumbnail shows part of the cumulonimbus anvil underwhich these mammatus were formed. Further weather explanation is available here.