Ac cumulonimbogenitus

Formation of altocumulus clouds from the spreading out of a very large cumulonimbus cloud which was also visible in the satellite image. The prefix ‘genitus’ denotes that the photographed cloud was actually the extension of a very slow-moving autumnal thunderstorm cloud known as cumulonimbus capillatus incus of which only the anvil or incus part had passed over the land areas with the main cloud feature remaining out at sea on the western side in the direction towards the photo was taken.

This extension was actually the beginning of an internal transformation of the cumulonimbus cloud towards high-level and mid-level clouds genera as the thunderstorm had reached maturity and was clearly in a weakening phase as noticed by the weakening rainfall pulses with only about an average of 8mm of rain falling in land areas. In a case of large or complete transformation of the cloud the prefix ‘mutatus’ would have been used but this was definitely not the case for this photographed cloud and when this stage did take place later in the day, the thunderstorm cloud had long left our Islands. The non-severe thunderstorm itself had occured due to a line of bad weather that developed over the western side of Malta which corresponded to the visible satellite image (fourth thumbnail) taken at 10AM CET.

The cloud was photographed at around 0720 CET but unfortunately a visible satellite image was unavailable in view that it was only about 30 minutes past sunrise. The first thumbnail is another panormaic view of the cloud but with cumulus clouds underneath it which was completely seperate from the main cloud and in fact was moving in the opposite direction due to differing wind with altitude. The second thumbnail is a weather sounding showing wind shear but limited instability creating a non-severe and very slow-moving thunderstorm that produced lots of rain just offshore our Islands as per fifth thumbnail.

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