Formation of dense altocumulus due to convection within the unstable mid-level air as a small upper-level trough (2nd thumbnail) passed over the Maltese Islands. This cloud produced some isolated rain. Some undulations within the cloud layer could be clearly observed from this photo. This was confirmed through the weather sounding that showed wind speed shear at mid-levels. The temperature within the cloud layer at an altitude of around 3.5km was only slightly below freezing hence composed of water droplets or supercooled droplets rather than ice crystrals.