Formation of wave-like cloud formation due to lots of wind shear as clearly indicated by the weather sounding on the second thumbnail which showed very strong southeasterly winds on the surface combined with lighter SSW wind higher up in the atmosphere. Such difference in wind causes the cloud system to rotate. The surface pressure on the third thumbnail showed a low pressure system over Southern Tunisia moving northeastwards along with a warm front that was moving towards the Maltese Islands which correspond exactly with the cloud cover and thunderstorm activity via satellite images on the fourth and fifth thumbnails respectively. It is not completely understood the reason behind the altocumulus undulatus cloud formation instead of nimbostratus as is more typical in a warm front but perhaps this was the effect of an occluded front following immediately on the heels of the warm front. The user could argue about it by sending me an email. The first thumbnail shows a wide-angle view of the cloud cover present over Zurrieq in Malta. The passage of this system was preceded by high-level clouds, cirrus radiatus, photographed several hours earlier here.