Why are there frequent attacks this year, and a few cold, rainy and snowy weather are rare in a large scale? It snows in the south of China.

First, you need to know how clouds are formed, then how rain is formed, and then you will understand how snow is formed.

Then I began to explain your question,

Global warming leads to the increase of water vapor evaporation on land.

Environmental pollution leads to the increase of impurities in the air. It is easier to form rain and snow.

Large-scale reclamation and urbanization. With the increase of population, the obstruction of cold air becomes less. It's easier to go south, so the smog in the north is very serious this year. At low pressure, there is less water and more impurities. Sandstorms in Inner Mongolia can easily blow to Beijing, Hebei and other places.

This is the El Nino phenomenon this year.

There are many secondary factors. I won't list them one by one.