Why is there rainy weather?

As rivers, lakes and oceans are exposed to sunlight, water becomes steam. Water vapor rises into small water droplets and finally becomes clouds. The water droplets or ice crystals that make up the cloud are supported by the airflow below, and the rising airflow continuously transports the water vapor below to the cloud. Small water droplets and small ice crystals in the cloud collide with each other in motion, and the volume will increase. The water droplets in the lower layer of the cloud gradually get bigger. After the volume of ice crystals in the upper layer of the cloud increases, they will fall between the water droplets in the lower part of the cloud, and the water droplets will become bigger and bigger. When these water droplets are too big for the updraft to contain them, it will rain.