What is the reason for the formation of Meiyu in the middle and lower reaches of the Yangtze River?

Meiyu in the middle and lower reaches of the Yangtze River belongs to "quasi-static front" in common weather systems.

When the cold and warm air masses meet, an interface will be formed between them, which is called the front. Because of the low density, the warm air mass will climb up along the front, the height will increase, the temperature will decrease, and the water vapor will condense into clouds. It may eventually lead to precipitation. According to the relationship between cold and warm on both sides of the front, the front system can be divided into cold front, warm front and quasi-static front. Quasi-static front refers to the weather system in which the cold and warm air masses are equal in strength, which leads to the front and precipitation wandering in this area for a long time.

The formation of quasi-static front needs a specific time and place to ensure that the cold and warm air masses are equally strong.

Every March and April, the subtropical high in the northwest Pacific begins to form, and the warm and humid air in the Pacific affects China from north to south. In June, warm and humid air and northern cold air meet in the middle and lower reaches of the Yangtze River. Form a quasi-static front.

This specific time-June (neither too hot nor too cold) and the specific location-the middle and lower reaches of the Yangtze River (neither south nor north) just contributed to the equal influence of cold and warm air masses, forming the precipitation weather in this area for nearly 1 month.