As we all know, it is hot in summer and cold in winter, but why does it snow in winter and hail in summer?

First of all, it is not said that there is more hail and snow than temperature. Their difference as precipitation lies only in the size and structure of ice.

Then the real question.

The answer is: hot in summer and cold in winter means near the ground, and has nothing to do with the high-altitude temperature!

The main source of atmospheric temperature is ground radiation, so it is heated more by ground radiation near the ground. Therefore, the degree of warming of the earth by the sun in winter and summer is different, and the heat radiated by the ground is also different. This is why it is hot in summer and cold in winter.

This is not the case at high altitudes. Air is a poor conductor of heat. Because the air at high altitude is thin under the action of gravity, it is quite cold at high altitude (until the stratosphere of 10km, of course, why the stratosphere suddenly becomes hot is another problem).

Most clouds are distributed at a height of several thousand to 10km. Obviously, the temperature at this height has nothing to do with the ground. Even in summer, there is a certain height, above which the temperature will be lower than 0 degrees.

Most of the precipitation forms we usually see, such as rain, snow and hail, are born at high altitudes (only a few, such as dew and frost, are at low altitudes). The temperature here is low enough, so water exists in the form of small ice crystals.

Then in winter, the temperature near the ground is very low, below 0 degrees. At this time, the small ice crystals in the sky will grow to a certain size, because gravity will fall directly and will not melt when it reaches the ground. Strictly speaking, some visible crystals will be called snow. Some of them will lose their crystal shape (graupel) due to the heat generated by friction during falling, and of course some of them have an inversion layer in the middle. It was snow at first, but halfway down, it froze again near the ground (Song, also called freezing rain). The ground temperature is high enough, so it is ordinary rain.

Then say winter, and you will understand what happened in summer.

The ground temperature is very high in summer, and the air will rise when heated. When the rising force is strong enough, the small snow flowers that were originally condensed and ready to fall will liquefy into spherical water droplets in the middle, which may be directly pushed back to the sky by the rising airflow, so they will be refreezed in the air (forming a ball), and new snowballs will fall outside. If the updraft is strong enough, the second falling snowball will return to the sky. ...

Repeatedly, the snowball rolled bigger and bigger. Finally, the updraft didn't stop him from falling. At this time, he will hit the ground with a bigger ball and form hail.

Obviously, hail does not appear in the form of snow ice crystals, but is wrapped in layers of ice hockey shells. The melting of the outer spherical shell will absorb heat, indirectly ensuring that the inside of the spherical shell is still 0 degrees. Because there is no temperature transfer, the inner spherical shell is often complete.

It can be seen that the conditions needed for the occurrence of hail are not the low temperature near the ground at all, but the strong updraft. Therefore, the rain that originally fell smoothly can be pushed back into the sky and then condensed and wrapped in the outer layer. The stronger the updraft, the more layers the package can have. The high temperature near the ground in summer is beneficial to the formation of updraft. Therefore, hail will only appear in summer and strong convective weather. But once again, there is no saying that hail and snow are colder than temperature!