Why does the weather change a lot in spring?

First of all, since June 5438+0, the atmospheric circulation in the middle and high latitudes in Europe and Asia has been high in the west and low in the east. This abnormal circulation pattern has lasted for 19 days (the average climate in June of 5438+0 is 6 days), which is more than three times of the climatic conditions for many years and the longest circulation pattern since 5438+095 1 year, which is beneficial to the self-circulation of cold air.

Secondly, the subtropical high in the northwest Pacific is stronger to the north, and the position of the strong subtropical high is stably maintained over the ocean on the southeast side of China, and it extends to the west many times, so that the main area where cold and warm air meet is located in the middle and lower reaches of the Yangtze River and its adjacent areas to the south.

Thirdly, the south branch trough of the southern margin of the Qinghai-Tibet Plateau is active, which is rare in recent ten years, prompting the southwest warm and humid air to be transported to China along the Yunnan-Guizhou Plateau.

Fourthly, due to the intersection of cold and warm air, warm and humid air is above the ground, forming a stable inversion layer in the middle and lower troposphere, which is the main reason for the occurrence of large-scale freezing rain.

The above-mentioned abnormal situation combination of atmospheric circulation has lasted for nearly 20 days since mid-June 65438+1early October, resulting in a rare large-scale continuous low-temperature rain, snow and freezing weather in eastern China.