Quite a rare form of altocumulus undulatus because the cloud’s shape seemed more like that of an arcus clouds to the eye. Even though both Cb and Ac clouds were being observed at the time, the photographed cloud was labelled as altocumulus because of rapidly rising air motion and the fact that no thunderstorms were associated with it which is a required ingredient for Cb arcus clouds classification. The first thumbnail shows how mundane this cloud feature was and according to the weather sounding on the second thumbnail, this cloud had formed due to light winds at all levels of the atmosphere and wind shear, the latter which is a required ingredient for cloud undulations. The bad weather on this day was caused by a very small low-pressure system to the north of the Maltese Islands generating cumuiform clouds. The same ingredients also caused a reported small waterspout over Xrobb l-Ghagin area from cumulonimbus clouds.