Meiyu refers to the natural climate phenomenon of continuous overcast and rainy days from mid and late June to the first half of July in the middle and lower reaches of the Yangtze River in China, Taiwan, South Central Japan and South Korea. Because the period of plum rain is the mature period of plums in the south of the Yangtze River, the Chinese call this climate phenomenon "plum rain", which is also called "plum rain season".
In the plum rain season, the air humidity is high, the temperature is high, and clothes are easy to get moldy. Therefore, some people call plum rain the homonym "moldy rain". After the plum rain season, the weather in Central China, South China and Taiwan began to be dominated by the Pacific subtropical high and officially entered the hot summer.
From late April to early May every year, the cold air from the north and the warm air from the south to the North converge in South China to form a quasi quiet and stop front in South China. In late May, the warm air force increased, and the quasi static front moved north to the Jianghuai area, becoming the Jianghuai quasi static front (also known as Meiyu front). Due to the large amount of water vapor entrained by the warm air from the south, a large amount of convective activity will occur when encountering a colder air mass. During this period of time, the cold and warm air forces were quite strong, so that the front stayed in the Jianghuai area.
Typical plum rain is generally "plum in" from mid June to late June, and plum out from early July to mid July. Welcoming plum rain refers to the overcast rain before entering the plum, which generally starts in mid April and lasts for about half a month.