How is Huangmeitian formed?

In May and June, in the middle and lower reaches of the Yangtze River, the warm and humid air flow from the ocean was not strong enough, and the high pressure from Siberia in the north had not receded. In this way, the high cliffs have been "carrying" the warm and humid airflow in the middle and lower reaches of the Yangtze River, which has brought a lot of rainfall. Because it happens that plums are ripe, it is called rainy day.