"The amount of water suspended in the air in the form of cloud is enormous. A small cumulus cloud, 'like a man's hand,' may hold anything from a hundred to a thousand tons of water in suspension. A large cumulus cloud is a mountain of water drops and ice crystals, weighing perhaps a hundred thousand tons, and no meaningful figure can be given for the weight of the deep layer-cloud systems that accompany the depressions of the temperate latitudes."
O.G. Sutton, Understanding Weather.