A Cumulonimbus cloud produces precipitation which may reach the surface or not. In the WMO classification of clouds this is given in the supplementary features. When precipitation reaches the Earth surface this is called "praecipitatio", when not "virga". At a certain horizontal distance of the cloud this is sometimes very hard to distinguish. Some additional info can be obtained by the presence of a rainbow: when this optical phenomena reaches the surface, the cloud falls unquestionable in the category of "praecipitatio" as supplementary feature.       

Taken in the opposite direction of a setting sun, this Cumulonimbus cloud has two supplementary features: besides the presence of praecipitatio, on the upper left part "mamma" is distinguished as as well.