Why is there a rainy Huangmei day?

Every June and July, warm and humid air in the south and cold air in the north meet in the Jianghuai area. Because warm air is lighter than cold air, it slides northward along cold air, and a large amount of water vapor brought by warm air condenses into clouds in the process of sliding up, forming a long rain belt, but this rain belt is relatively narrow, generally only two or three hundred kilometers wide.

During my stay in Huangmei, it is still impossible to tell who wins and who loses. They tend to be stronger at one time and stronger at another. If the cold air in the north is strengthened, the rain belt will be pressed to the south, and it will rain in the south; If the warm air is stronger, push the rain belt to the north, and it will rain in the north. In short, the two armies confronted each other and were evenly matched. Therefore, the rain belt has been swinging from north to south in the Jianghuai basin, making the weather in this area wet and rainy.