How is the mildew weather caused?

Meiyu weather occurs in June or July in early summer every year. There is a period of continuous rainy weather in the Jianghuai River Basin east of Yichang, Hubei, my country. This is the ripening season for plums in the south of the Yangtze River, so it is called "Meiyu". Because of the long time and high air humidity, everything is susceptible to moisture and mildew, so it is also called "mold rain". The beginning of the plum rain is called entering the plum season, and the end of the plum rain is called the emerging plum season. The time for plum blossoms to come in and out is different in different places. The plum blossom season is generally from the end of May to the beginning of June in southern Jiangxi and Zhejiang, mid-June along the Yangtze River, and the end of June in Huainan. The plum blossom season ends from the south to the north from the end of June to mid-July. The duration of plum rain is generally about one month, and it is about 20 days in Huainan. The main reason for the formation of Meiyu is that the Pacific warm air mass moves northward between the Yangtze River and Nanling Mountains in May and June, and reaches both sides of the Yangtze River around mid-June. At this time, the cold air mass controlling the Yangtze-Huaihe River Basin is still relatively strong and cannot easily move northward quickly. retreat. Therefore, warm and cold air masses encounter each other in the lower reaches of the Yangtze River, resulting in continuous rainy weather. The amount of plum rain, the time of onset and emergence of plum rain, and the length of the plum rain period vary greatly from year to year. In some years, there is no obvious plum rain period, resulting in "empty plum rain". In some years, the plum rain period arrives earlier, which is called "early plum rain." In some years, the plum rain period arrives later, which is called "late plum rain season." Empty plum blossoms, early plum blossoms and late plum blossoms will bring disadvantages to agricultural production. Early plum blossoms will affect the summer harvest and cause wheat to become moldy, and empty or late plum blossoms will have a negative impact on summer planting.