To end our review of the different types of clouds We address what is possibly the most striking and interesting cloud, we refer to the Cumulonimbus, the second type of vertically developed clouds, although in reality it is the result of a cluster with a greater development.
According to the WMO it is described as a thick and dense cloud, with a considerable vertical development, in the form of a mountain or huge towers. Part, at least of its top, is normally smooth, fibrous or striated, and almost always flattened; this part is often extended in the form of an anvil or a vast plume. Below the very dark base, there are low ragged clouds and precipitation or showers.
As we said, Cumulonimbus is the next development step, on the ascending scale of convection, to Cumulus Congestus, therefore, they are clouds of great vertical development (the tops are usually between 8 and 14 km high). In our latitudes they originate mainly in spring and summer in unstable situations.
They are made up of water droplets and ice crystals on the top or anvil. Inside they also contain large raindrops, snowflakes, granulated ice, hail and in cases of extreme instability hail of considerable size.
They almost always produce storm, that is, precipitation in the form of showers, rain or hail, generally, although also snow in winter, accompanied by gusty winds and electric discharges that occur between clouds or between cloud and ground (lightning).
The Cumulonimbus are the kings of the clouds, the most photographed and the most spectacular. They lend themselves to being portrayed in any situation and it is interesting to be able to photograph them in a complete sequence of a storm. Not to be confused with Cumulus congestus since the Cumulonimbus are taller, they present fibrous structure in the tops.
They have two species (Calvus and Capillatus) and there are no varieties.
Source - AEMET
More information - The Cumulus