Formation of towering mid-level clouds produced by an unstable warm desert airmass. In fact, the weather sounding on the first thumbnail showed quite a steep lapse rate at mid-levels. These clouds could also be seen in the visible satellite image on the southwest side of Malta from where this photo was taken. A dark base was also noted on the horizon and it means that this cloud was actually raining over the sea area. The same desert airmass that produced such clouds also brought with it some desert sand haze as rising air over the Sahara desert picks up sand particles which also aid the cloud formation, in this case altocumulus.