Formation of a mature single cell cumulonimbus capillatus incus praecipitatio given away by the rainbow on the right hand side of the photo. The first thumbnail shows the same cloud, some time earlier having a clear low topped cirriform anvil hence the ‘capillatus’ and ‘incus’ as the air was not particularly unstable as indicated by the weather sounding on the fourth thumbnail. In fact, it’s quite easy to explain how this cloud had formed. As indicated by the upper-level chart and freezing level on the second and third thumbnails respectively, a cold pool of air was present above the Maltese Islands. Combined with a warmer surface, moderate westerly winds and strong sunshine, this created a steep lapse rate from the bottom to the top of the atmosphere leading to the photographed cloud formation towards the west of Malta. Due to lack of instability, the cloud structure quickly decayed as it moved eastwards producing only quick showers and no thunderstorms.