Cb altocumulogenitus

The photographed cloud is classified as “Cumulonimbus altocumulonimbogenitus with virga“ according to the newly issued cloud atlas. This cloud is actually altocumulus castellanus with a great extent giving it the looks of a cumulonimbus due to its dark base and clear smooth outline at the top. The first thumbnail is the weather sounding from which the height of the cloud base was estimated at 3.6km which is very high and above that level, plenty of moisture and instability were available for such cloud formation whose base is normally in the lower atmosphere. Furthermore, it outlined a dry lower atmosphere meaning that the photographed virga was the result of evaporation of falling precipitation at that level. The second thumbnail is the surface pressure chart indicating a trough line (solid black line) moving across the Maltese Islands at the time. This trough line corresponds exactly with the clouds seen in the visible satellite imagery on the third thumbnail. Strikingly similar to a cold front, it was noticed that following the passage of the trough line the cloud was clean cut and the weather eventually cleared and became cooler and windier with a NW Force 6 wind.

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