Formation of strange undulations within the mid-level cloud cover being in actual fact a true hybrid between undulatus and mammatus. The weather sounding on the first thumbnail clearly showed the ideal conditions for such cloud formation being composed of ice crystals and with wind shear rolling the clouds into parallel rolls. However, this altocumulus undulatus also had the mammatus feautures underneath it. The latter features gave a fuzzy apperance to the whole cloud cover and the sac-like feautures might have formed due to rain falling from underneath these clouds (in which case only a few drops of rain reached the ground). The clouds themselves were formed by a desert low moving across the Southern Mediterranean as per second and third thumbnails.