Why is the weather in Beijing always bad this year? It still snows in spring? !

As we all know, clouds are composed of many small water droplets and small ice crystals, and raindrops and snowflakes are composed of these small water droplets and small ice crystals. So, how is snow formed?

In the water cloud, all water droplets are small water droplets. They grow into raindrops mainly through continuous condensation and collision.

Ice cloud is made up of tiny ice crystals. When these small ice crystals collide with each other, the surface of the ice crystals will heat up and melt, and they will stick together and freeze again. Repeat this for many times, and ice crystals will increase. In addition, there is water vapor in the cloud, so ice crystals can continue to grow through condensation. However, where the ice cloud is generally high but not thick, and there is not much water vapor, the condensation growth is slow, and there are not many opportunities to collide with each other, so it cannot grow to a great extent to form precipitation. Even if it causes precipitation, it often evaporates on the way down and rarely falls to the ground.

The most favorable cloud droplet growth is the mixed cloud. The mixed cloud consists of small ice crystals and supercooled water droplets. When a mass of air is saturated with ice crystals, it is unsaturated with water droplets. At this time, the water vapor in the cloud condenses on the surface of ice crystals, while the supercooled water droplets are evaporating, which produces the phenomenon that ice crystals "adsorb" water vapor from supercooled water droplets. In this case, ice crystals will grow rapidly. Besides, supercooled water is very unstable. If you touch it, it will freeze. Therefore, when supercooled water droplets collide with ice crystals in mixed clouds, they will freeze and adhere to the surface of ice crystals, making them grow rapidly. When small ice crystals grow up, they overcome the resistance and buoyancy of air and fall to the ground. This is snow.

In early spring and late autumn, the air near the ground is above 0℃, but this layer of air is not thick and the temperature is not very high, which will make the snow fall to the ground and melt completely. This is the so-called "wet snow", or "both rain and snow". This phenomenon is called "sleet" in meteorology

Similarly, the size of snow is also classified according to precipitation. Snow can be divided into three categories: light snow, medium snow and heavy snow.

So snow has nothing to do with seasons. As long as there is a cold wave and the weather is cold enough, snow will form.

Chun Xue not only exists now, but also existed in the past, as evidenced by poetry.

Spring snow

Han Yu

There is no youth in the New Year.

The grass bud was surprised at the beginning of February.

Snow is too late for spring,

Therefore, the tree is a flying flower.