How to explain the rain on May 9th?

Ensure a bumper harvest of grain in the coming year.

On May 9, the weather began to get warmer, and the willows along the river began to show their buds. However, on the first day of May 9, according to the weather forecast, there will be a new round of rain and snow in the central and eastern regions, and even heavy snow will appear in some areas. "May 9th" is the fifth day of the ninth grade. The number nine is generally calculated by taking the arrival of the winter solstice as 1 day, and the 9th day of 1 is called "Yijiu", the second 9th day is called "Erjiu" and the third 9th day is called "Sanjiu". This is the season of spring ploughing. This proverb means that it snowed or was hit by snow on the first day or two of May 9th. Farmers don't have to worry anymore, which means that the weather is very cold, and the thick snow has solved the problem of winter drought and ensured the bumper harvest of grain in the coming year.