What phenomenon involves the joining of small cloud droplets into larger ones?

The joining of small cloud droplets into larger ones is a key process that leads to precipitation. This phenomenon occurs through a process called coalescence, where tiny droplets collide and merge as they move through the cloud, ultimately forming larger droplets. When these droplets become heavy enough, they overcome the forces keeping them suspended in the cloud and fall to the ground as rain, snow, sleet, or other forms of precipitation.

Cumulonimbus formation refers specifically to a type of cloud associated with thunderstorms and severe weather, but it does not explicitly describe the process of droplets coming together. Humidity is a measure of the amount of moisture in the air, while fog development pertains to the formation of clouds at ground level, which does not involve the specific merging of droplets into larger ones as seen in the precipitation process.