Why does the Dragon Boat Festival rain frequently every year?

Around the Dragon Boat Festival, the weather in South China is the most complicated period. The first is that the cold air in the north is "reluctant" to South China. Although after May every year, the forces of warm and humid air flow from the tropical ocean have been continuously strengthened, and the temperature in the area south of Nanling Mountains has gradually increased, and the weather has turned hot, but the cold air will never be willing to "retreat northward". In some years, the stronger cold air in the north will break through the layers of resistance and carry the wind and rain all the way south, making the weather in Guangdong cool again. Therefore, there is a folk saying that "the dumplings in May have not been eaten, and the cold clothes have not been put into the cage". "Dragon Boat Water" is available almost every year. May and June are also the months with the most precipitation and the most frequent rainstorm in South China. Strictly speaking, the formation mechanism of rainstorm is quite complicated, but there are two important macro conditions: first, there must be rich sources of water vapor; Second, there must be a strong updraft and a favorable atmospheric circulation situation to make the intensity of precipitation large enough and last long enough. Coincidentally, before and after the Dragon Boat Festival every year, when South China is affected by the low trough of the front, these two conditions are easy to meet, so heavy rain and "dragon boat water" are in an outbreak state.