Why does it always rain?

Rain is a natural phenomenon. When the clouds reach a certain thickness, the water droplets that make up the clouds naturally fall to form rain.

Rainwater is the water on the earth that is irradiated by sunlight and forms water vapor, which evaporates and rises into the air, and condenses into water droplets when it meets cold air in the air. Condensation releases heat and heats the temperature, so the warm air will continue to rise, and when it is cold again, the water vapor will continue to condense, and so on, and the updraft can extend from low altitude to 1, meters.

At a higher altitude, when the temperature is lower than ℃, ice crystals appear, and small water droplets and ice crystals form cumulonimbus clouds. When the cumulonimbus cloud reaches the tropopause, the upward movement stops.

when the ice crystals in the cloud collide and merge with each other, and some water vapor directly condenses and adheres to the surface of the ice crystals, the small ice crystals will grow up. When the updraft can't support it, it will fall under the action of gravity, forming various forms of precipitation (rain, snow, hail, etc.). During the descent, the low-altitude temperature rises and the ice crystals melt, which becomes rainfall. When some small ice crystals become larger ice crystals, they will fall directly to form hail.

Extended information:

Several precursor clouds before rain

First, the hook cloud

People call it "hook cloud". It floats horizontally in the sky like strands of silk, with upward clouds and a small hook at one end. The color of the clouds is milky white and bright. It usually appears before the influence of cold air in the north or low pressure at high altitude. This cloud has appeared, and it will rain soon. Therefore, there is a saying that "the cloud is hooked and the rain is dripping".

Second, cirrocumulus

People call it "Fish Scale Day". It usually appears in the blue sky. Small white clouds, arranged neatly and tightly, are like fish scales and ripples. After formation, the duration is short, usually only a few minutes, and more than an hour. Its appearance shows that there is a trough of low pressure approaching over the local area, which is a sign of the change from sunny to rainy days. Therefore, there is a saying that "it's a fish scale day, and it's windy without rain."

Third, flocculent cumulus clouds

People call them "cotton clouds". It also often appears in the clear sky in summer, like clusters of scattered and broken cotton wool, and also like a burst of cotton. Clouds vary in size and height. It is formed under the condition that the humid air is extremely unstable, so the clouds are fragmented and it is also a symbol that it will rain. Therefore, the agricultural proverb says, "There is a cotton cloud in the sky, and soon there will be a thunderstorm."

Baidu Encyclopedia-Rain

China Weather Network-Several Precursor Clouds Before Rain in Summer