As water molecules in the atmosphere cool water molecules are rejoined (hydrogen bonding) and water droplets form. This is called:

Cohesion forces

Explanation:

The ability of water to hold all molecules tightly together, through hydrogen bonds, forming water droplets, is called the cohesive force. This force can be defined as, literally, forces of attraction between the cmoleculas of this liquid, causing them to be strongly united, forming the drops of water that we know.