Formation of dense patches of high-level clouds known as cirrus spissatus. Notice that vertebratus seemed to have been spreading out of the thick cirrus clouds whilst there were virga-like feautures in the background which was zoomed into as per second thumbnail photo for further details. It could have also been upper-level altocumulus floccus cloud with virga. The first thumbnail is exactly the same photo taken at a different position for better illustration.

The meteorological explanation behind this cloud formation was an upper-level frontal system that passed over the Maltese Islands from the NW as confirmed by both the satellite and surface pressure on the fourth and fifth thumbnails respectively. The third thumbnail is the weather sounding showing a totally overcast sky from 500mb upwards which are good conditions for such type of cirrus to form in.