September is the coldest weather.

Nine cold days refer to the coldest days in winter, usually during March 9 and April 9. In March 1949, dogs in Jilin froze to death, while in Jiangsu, it was "the old man who picked up dung ran all over the street in March 1949", which shows that the temperature has changed greatly. This is mainly because the total heat budget deficit on the ground only reaches the maximum in April and September, and the earth's heat storage is the least in a year, so it is the coldest. In addition, the cold air mass in Siberia has also developed to a very strong stage during this period, and the frequent invasion of strong cold air is also one of the reasons for the low temperature.

The "Jiujiu Song" in the middle and lower reaches of the Yellow River is: 1929 without a gun; Walking on the ice in 3949; 5969 see willows along the river; Seven or nine talks, eight or nine geese come; 1999 and 1999, cattle are being farmed everywhere.

Jiangnan's "Jiujiu Song" is: 1929, meeting a husband; On March 27th, cymbals (an ancient musical instrument, meaning the fence crackled with cold wind) were played at the fence head. 4936, the night is like a heron (the night is cold like a crane); In 5945, the sun opened the door, and in 6954, poor children fought for spirit; In 7963, cloth sleeves were worn on the head; In 8972, the cat looked for the sun; Plow and rake go out together.

Jiangsu, Zhejiang, Shanghai and other southern regions say: "The ninth day is warm, the ninth day is cold, the third day is nine frozen birds, the fourth day is nine wax hearts, the wax insect essence freezes to death, the fifth day is five nine four five, the knife is not buried, the sixth day is six nine five four, the second day is cold and stuffy, the clothes and hats are ambiguous, the eighth day is eight nine seven two, cats and dogs seek shade, the first day is nine nine eight one, and a hundred herbs report green leaves."