Why "Yun Zheyue on August 15th, the fifteenth day of the first month"?

"On August 15th, Yun Zheyue, it snows and lights on the 15th day of the first month" is an agricultural proverb circulating in China. It is the weather forecast experience summarized by the working people in our country in the long-term production practice, which reflects the echo relationship between holiday weather. It means that on the Mid-Autumn Festival on the 15th day of the eighth lunar month, if the sky is covered by clouds (cloudy or rainy) and the full moon cannot be seen, then the 15th day of the first month of next year will be a cloudy or snowy day.

According to the data, on the day of the Mid-Autumn Festival in 2006, Beijing and other areas turned cloudy and cloudy, and the Mid-Autumn Festival began in Yun Zheyue in the evening, and then it turned cloudy and sunny. There was a heavy snow in the early morning of the Lantern Festival on the fifteenth day of the first month of 2006, and it stopped gradually after noon, but it was still cloudy to cloudy and the cold wind roared, which just verified the accuracy of this agricultural proverb again.

On the surface, "Yun Zheyue" and "Snow Lantern" are the echo phenomena of clouds and snow, but in essence they are the echo relationship of two cold air activities. In other words, if there is cold air activity around the Mid-Autumn Festival, it will cause the "Yun Zheyue" phenomenon. Then around the Lantern Festival, cold air will invade again, forming a situation of "snow hits the lights".

Therefore, the proverb "It snows and lights on August 15th and January 15th in Yun Zheyue" is a reflection of the rhythmic activity of the cold air invading China for about five months. According to this proverb, many meteorological stations have studied the rhythm relationship of cold air activity for about five months, and applied it to long-term weather forecast, and achieved good results; The weather on other days also has this rhythm relationship, but it is not generally noticed.