Such cloud is formed when moisture rises in the atmosphere and become attached with condensation nuclei. It is identifiable by the various holes that are formed in them and look pretty much like a honey-comb. These holes are formed due to sinking pockets of air within the cloud itself whereby the cooler air sinks down through the warmer air because the former is denser than the latter. It may also indicate stormy weather ahead which in fact did occur mainly because the Maltese Islands were situated on the SE side of an upper trough whereby the worst weather is found (click on the last thumbnail showing the storm on the satellite image). The precipitable water chart indicates high humidity at all levels of the atmosphere.