Cumulonimbus calvus (Cb cal) - CEN 1926
(Section 2.3.10.2.1)
Cumulonimbus where the sproutings of the upper parts are indistinct and flattened and have the appearance of a whitish mass without sharp outlines. No fibrous or striated parts are visible. Cumulonimbus calvus usually produces precipitation; when it reaches the ground, it is in the form of showers.