Rain is made when water vapor in the air condenses, and the water droplets become too heavy and fall rain drops. When a mass of air cools to saturation point, it leads to condensation of the water vapor, which forms clusters of water droplets and frozen water crystals.
The air is always filled with tiny drops of water vapor. However, warm air contains more vapor than cool air, and that is why the air is more humid during warmer months. When warm air rises, the water droplets rise. Mountains also cause water droplets to rise, which is the reason why rain occurs frequently in mountainous areas. Clouds form once the air holds plenty of water droplets.
Water droplets and crystals form cluster clouds. After some time, more water is added to the droplets and crystals. When these water droplets become heavy enough, they fall down as raindrops due to gravity. At times, cold air causes ice crystals to retain their frozen form and grow larger to fall as hail, sleet or snow.
Typically, rain occurs as a shower or a drizzle. A shower happens when fast, heavy rain falls for a short period, while a drizzle happens when slow, light rain falls for hours. Raindrops generally fall at a speed of 7 to 18 mph. Aside from water, rain also contains dust, dirt, grass, insects and even chemicals.