Meiyu season is a warm and humid air flow in the Pacific Ocean brought by the southeast monsoon in June and July every year, which passes through the middle and lower reaches of the Yangtze River in China, Taiwan Province Province in China, south-central Japan and south Korea. Because it is the mature period of plums in Jiangnan, it is called "Meiyu", and this period is called Meiyu season.

Every year from late April to early May, cold air from the north and warm air from the south meet in South China, forming a quasi-static front in South China. By the end of May, the influence of warm air was strengthened, and the quasi-static front moved northward to the Jianghuai area, forming the Jianghuai quasi-static front (also known as Meiyu front). Because the warm air from the south carries a lot of water vapor, when it meets the cold air mass, it will produce a lot of convection activities. Because of the equal influence of cold and warm air during this period, the front stays in Jianghuai area. Typical plum rains generally "enter plum blossoms" in the middle and late June, and bloom in early to mid-July. Meiyu refers to the rainy weather before entering plum blossom, which generally starts in mid-April and lasts for about half a month. Meiyu mainly occurs in the middle and lower reaches of the Yangtze River in China, Taiwan Province Province in China, Liaodong Peninsula, the southernmost tip of the Korean Peninsula and the subtropical monsoon climate zone in south-central Japan. There is no plum rain in other parts of the world at the same latitude. There is no obvious plum rain in South China.