Formation of altocumulus mammatus due to very moist air in the upper atmosphere. The clouds themselves had formed due to a very strong jet stream (third thumbnail) over the Maltese Islands caused by a large and deep upper-level trough (fourth thumbnail) which in the following days, became an upper-level trough centred around the Maltese Islands and sicily. The beautiful breast-like features of the altocumulus in the setting sun is due to the air reaching the end level of free convection at 10,016 metres. This process was perhaps aided by precipitation not reaching the ground (virga) falling underneath these clouds as sometimes I witnessed the formation of such clouds during such instance. The cloud base could have well been at an altitude of 6.6km due to thicker troposphere as it was Summer in the area. The first thumbnail shows sunset taken at the same time clearly indicating the presence of clouds that became altocumulus mammatus. The second thumbnail is the weather sounding of that day at 2000 CEST which is explained in the description and combined with the upper level trough.