What kind of clouds mean rain?

Hook cloud is also called "hook cloud" among the people. It floats in the sky like bundles of silk, the clouds are upward, and there is a small hook at one end (pictured). Clouds are milky white and translucent. Generally, it 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 "clouds hook raindrops".

2. cirrocumulus

Cirsium japonicum, people call it "Fish Scale Day". It usually appears in the blue sky. Small white clouds, arranged neatly and closely, rippling like fish scales, are very beautiful.

The duration after formation 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 that sunny days turn cloudy and rainy days. There is a saying that "it's a fish-scale day, it's windy and it doesn't rain."

3. flocculent cumulus clouds

Flocculent cumulus, commonly known as "cotton cloud". It often appears in the clear sky in summer, like clusters of scattered and broken cotton wool, and like a burst of cotton. Clouds vary in size and height. It is formed under the condition of extremely unstable humid air, so the cloud is fragmented and a symbol of rain. The farmer's proverb says, "There is a cotton cloud in the sky, and it will rain thunderstorm soon."

Extended data

The research of atmospheric science points out that the cloud droplets or ice crystals formed in the process of cloud formation are very small, with a diameter of about 10 micron, and it is impossible for such particles to fall to the ground in the atmosphere with updraft.

It takes two processes for cloud droplets to grow into raindrops (at least 200 microns in diameter or even 1 mm). One is the condensation growth process, but the efficiency of this process is getting lower and lower with the increase of cloud droplet diameter.

For cloud droplets with a diameter greater than 10 micron, it is difficult to achieve volume growth through condensation; The other is the process of collision and growth, if the particles in the cloud are different in size. Then the big particles will fall faster than the small particles, so they will catch up with the small particles and collide with them (referred to as "collision and merger").

Make the big particles merge all the way down into this big particle, thus becoming bigger rapidly. The bigger the particle, the higher its collision and growth efficiency. Precipitation particles in nature, whether liquid raindrops or solid snowflakes, graupel and hail, are mainly formed through this process.

Baidu Encyclopedia-Hooked Cirrus Cloud

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