Formation of small, inactive cumulonimbus as seen above the Mosta church (highly controversial) due to a rising air thermal meeting a stable layer which is marked by stratocumulus clouds in this case. The weather sounding shown in the second thumbnail marks end of instability at an altitude of only 4.4km. Another pic shows the formation of a towering cumulus cloud in the same area but on a patch of clear sky devoid from stratocumulus. It might have been possible that the higher level cloud marked the atmospheric level at which instability ended but I cannot confirm this theory.