This enormous storm cloud, which is often in the shape of a blacksmith’s anvil, can form individually or co-ordinate with neighbours to form ‘multicell’ and ‘supercell’ storms. The capillatus species, shown here, is the most mature stage of the storm cloud, when the ice-crystal canopy (known as the incus) has the appearance of Cirrus-like fibres or striations. Capillatus means ‘hairy’ in Latin, while the name of the less mature species, calvus, means ‘bald’.