When warm air rises, it expands and cools. Cool air can't hold as much water vapor as warm air, so some of the vapor condenses onto tiny pieces of dust that are floating in the air and forms a tiny droplet around each dust particle. When billions of these droplets come together they become a visible cloud.
Artificial rain is caused by spraying salt over clouds. As we know rainfall occurswhen oppositely charged clouds meet, since, clouds are colloidal in nature and carry charge. Spray of silver iodide, an electrolyte, leads to artificial rain. Sometimes electrified sand is also used for this purpose
