Formation of Cumulonimbus cloud with a somewhat low-level anvil as the airmass was becoming more stable. The previous day saw heavy rain showers over the Maltese Islands due to a cold drop. The trigger for this cloud formation was an isolated cut-off low in the upper levels to the south of Malta generating instability as cold air at upper levels contrasted with warmer and more humid low-level airmass. The third thumbnail shows this cut-off low while the first thumbnail shows another cloud formation (cumulus congestus) with a rain shower. The second thumbnail shows the air profile over Malta clearly showing a thermal over the area due to the contrast in the vertical air profile created by this upper low. On the surface pressure chart (4th thumbnail) this upper-level trough was shown as a solid black line to the south of Malta and combined with a weak low pressure of 1026mb (of course in relation with the surroundings). The fifth thumbnail shows high moisture content at low levels. This is also a very important component when expecting heavy rainfall because the higher up that moisture level extends to higher altitudes, the more likely heavy rain is. That was the case on the previous day whereby some locations in southern Malta registered over 70mm of rainfall (aided by very little wind).