The reason for the rain in Tomb-Sweeping Day

The reason for the rain in Qingming period is the weakening of cold air, more low pressure in spring and more water vapor in the atmosphere.

1. Cold air weakening: During the Qingming period, cold air gradually weakened and warm and humid air currents on the ocean gradually became active. As the winter weather subsides, the cold air in the northern area begins to weaken, while the warm and humid air flow in the southern sea area gradually increases. This warm and humid airflow will encounter cold air rising to form convection, resulting in precipitation. Therefore, Tomb-Sweeping Day is often the beginning of the rainy season in southern China.

2. More low pressure in spring: more low pressure in spring. Spring is one of the seasons with the most drastic changes in atmospheric circulation, and various weather systems are very active. In China, some low-voltage systems often appear around Tomb-Sweeping Day, which will cause rainy weather and thunderstorm weather, and bring a lot of inconvenience to people's life and travel.

3. There is more water vapor in the atmosphere: there is more water vapor in the atmosphere before and after Qingming, and the temperature difference between day and night is large. Although the temperature in Tomb-Sweeping Day is high during the day, it is relatively low at night. This atmospheric temperature difference will lead to water vapor condensation and precipitation. In addition, because plants begin to germinate in spring, the water vapor content in the atmosphere also increases, which also provides conditions for the formation of rain.

Tomb-Sweeping Day originated in the Spring and Autumn Period, and people would worship their ancestors and heroes in spring to pray for a bumper harvest and ancestors' blessings. Later, with the rise of the Zhou Dynasty, Tomb-Sweeping Day became an official sacrificial festival to commemorate the dignitaries of loyalty and honor. In the Tang Dynasty, the scale and significance of Tomb-Sweeping Day were further expanded, and it was designated as a national public holiday for five days.