What is "mildew weather"?

Plum rain

Plum rain refers to the continuous rainy weather that often occurs in the Jianghuai River Basin to southern Japan in late spring and early summer. This is the plum season in the south of the Yangtze River, and it is also a time when clothes are prone to mildew, so it is called plum rain, commonly known as mildew rain. The plum rain begins in mid-June every year, and ends in early July, which is called the plum rain. It lasts about 20 days. However, the rainy season starts and ends at different times every year, and the duration varies from more than a month to only a few days. In a few years, there is no plum rain, so it is called empty plum rain. There are obvious changes in the weather before and after the plum rain. Before the rainy season, it will be sunny. During the Meiyu period, there is abundant rainfall, high relative humidity, short sunshine hours, and generally continuous rain, but sometimes there are heavy rains and heavy rains. After the rainy season, the weather becomes sunny and dry, and the temperature rises sharply, entering midsummer. Meiyu is caused by the stalemate between warm and cold air in the middle and lower reaches of the Yangtze River in late spring and early summer, forming a quasi-stationary front. Every year from spring to early summer, the cold high pressure in the north gradually weakens, but the cold air still often moves southward to the middle and lower reaches of the Yangtze River. At the same time, the western Pacific subtropical high pressure strengthens and moves northward, bringing warm and humid air. When the subtropical high pressure ridge moves north to 20° north latitude and stops between 20° and 25° north latitude, the cold and warm air stalemate in this area to form a quasi-stationary front. Therefore, the intensity of the western Pacific subtropical high and the seasonal changes in the ridge position determine the morning and evening of the plum season, the duration of the plum rain, and the amount of plum rain each year. It directly affects summer droughts and floods in the Yangtze-Huaihe River Basin and North China.