It's hard to believe that a fluffy cumulus cloud, looking as light as cotton candy, actually weighs as much as 100 elephants. Here's how scientists calculate a cloud's real weight, and how something that heavy can float in the sky.
NCAR researcher Margaret (Peggy) LeMone estimated the density of water droplets in a cloud at about 0.5 grams per cubic meter. Based on this, calculating the volume of a typical cumulus cloud about 1km on each side gives a total water weight of roughly 500 tons. Converted to 6-ton elephants, that's about 100 of them. A cloud may not look large, but adding up the water spread throughout its entire volume produces this much weight.
The secret is the size of each individual droplet. The water droplets that make up a cloud are extremely small — only tens of micrometers in diameter — and extremely light. An updraft of air warmed at the surface is enough to hold up a droplet this small. In other words, the cloud's weight isn't absent; it's spread across tens of billions of tiny droplets, each light enough to be easily supported by the updraft.
Tiny droplets in a cloud collide and merge, growing larger over time. As a droplet grows, its weight increases, and once it becomes too heavy for the updraft to support, it finally overcomes gravity and falls to the ground — that's rain. It's not that the cloud's total weight suddenly spikes; it's a matter of individual droplets growing heavy enough.
A cloud's type and how developed it is are directly tied to how likely rain is. Checking sky condition alongside rain probability in sanCheck lets you prepare before a fluffy cumulus cloud grows into a rain-producing storm cloud.