Probably cumulus radiatus clouds from an approaching thunderstorm. Due to high-level and mid-level clouds, the approaching thunderstorm cloud`s edges were not clear but it does not look like a shelf cloud. This produced isolated heavy rain showers on some areas as can be seen in the background. The formation of such line of cloud could have been due to a divergence zone towards the western side of Malta whereby a light SW wind could be easily seen interacting with the prevailing SE wind in the surface wind map of the second image. The third image shows the visible satellite image at the time indicating a clear zone in the area where such divergence was occurring and the fourth thumbnail of the water vapour satellite image clearly shows a dry air intrusion over our area. Such dry air intrusions in a low pressure system could make storms even more intense which to some extent it did with some 30mm of rain falling over Gozo in an otherwise very limited instability. In fact, the weather sounding on the first thumbnail indicated lots of upper-level moisture but only some 400J per kg of CAPE meaning that severe thunderstorm did not occur due to generally limited instability. The surface pressure chart (fifth thumbnail) indicated a line of bad weather in the vicinity of the Maltese Islands.