What kind of clouds mean it's going to rain?

1. Hook-shaped cloud

Hook-shaped cloud is also called "Gou-shaped cloud" among the people. It is like bunches of silk floating in the sky. The cloud threads point upward and have a small hook at one end (as shown in the picture). The cloud color is milky white and translucent. Generally appears before the influence of northern cold air or high-altitude low pressure. This kind of cloud appears and it will rain soon. Therefore, there is a saying that "the clouds are hooked and the rain is pouring".

2. Cirrocumulus clouds

Cirrocumulus clouds, people call them "fish-scale sky". It usually appears in blue skies. The small white clouds are arranged neatly and closely, like the fine scales of a fish, or like ripples of microwaves, which is very beautiful.

After formation, the duration is short, usually only a few minutes, up to about an hour. Its appearance indicates that a low-pressure trough is approaching over the local area and is a sign of a change from sunny to cloudy and rainy days. There is a saying that "the sky is fish-scale, and even if it doesn't rain, it will be windy".

3. Flocculent Altocumulus

Flocculent Altocumulus, commonly known as "cotton clouds". They often appear in the clear sky in summer, like clusters of scattered and broken cotton wool, or like bursts of exploding cotton. Cloud bodies vary in size and height. It is formed under extremely unstable conditions in the moist air, so the clouds are fragmented, which is also a symbol of rain. A farmer's proverb says, "There are cotton clouds in the sky, and soon there will be thunder and rain."

Extended information

Atmospheric science research points out that the cloud droplets or ice crystals formed during the cloud formation process are very small, with a diameter of about 10 microns. It is impossible to fall to the ground in the atmosphere.

To make the cloud droplets in the cloud grow into raindrops (with a diameter of at least 200 microns, or even 1 mm), two processes are required. One is the condensation growth process, but because the efficiency of this process varies with the cloud droplets The diameter increases lower and lower.

For cloud droplets with a diameter greater than 10 microns, it is difficult to achieve volume growth through condensation; the other is the collision and growth process, if the sizes of particles in the cloud are different. Then the falling speed of the large particle will be greater than that of the small particle, so it will catch up with the small particle and collide and merge with it (referred to as "collision and merger").

Make the small particles along the way of the big particle fall merge into the big particle, thereby rapidly growing in size, and the larger the particle, the higher the efficiency of its collision and growth. Natural precipitation particles, whether liquid raindrops or solid snowflakes, graupel, and hail, are mainly formed through this process.

Baidu Encyclopedia - Cirrocumulus Clouds

Baidu Encyclopedia - Cirrocumulus Clouds

Baidu Encyclopedia - Flocculus Altocumulus