This arcus cloud under the species of cumulonimbus have formed approximately 20 minutes after observing typical cumuluonimbus praecipitatio clouds which are explained in the next photo. A very important element to identify such specific Cumulonimbus (Cb) cloud from the rest of Cbs is the sudden increase of wind. In fact, this was felt and recorded by the Luqa weather station which within just 45 minutes, average wind speed increased from 9.3 kmh to 22.2kmh and then back to 9.3 kmh within just 15 minutes but always maintaining a Westerly direction. It is certain that this cloud was the result of wind gusts from earlier Cbs ejecting a downdraft of cold air below it which then spreads outwards. This prevents further rising air from being pulled into the cloud`s updraft. The rolling effect of the photographed clouds is due to buffeting from the wind as the updraft and downdraft compete with each other. The first thumbnail shows the start stages of this specific cloud species as the downdraft from the thunderstorm is colliding with the background airmass as it fully spreads out. The second thumbnail shows the Cb arcus cloud in its full glory at its advanced stage. The third thumbnail is the rain radar image showing a line of rain over the NW Malta. Offshore areas of the SW later experienced heavy thunderstorm rain though this might be unrelated to the arcus cloud formation event.