Which nine days are the coldest? When is it coldest?

1, the coldest in 39 days and 49 days.

2. Nine is the lowest temperature in the whole year. According to previous years' experience, the temperature is usually not particularly cold in September and September, but the accumulated cold air reaches the maximum value in March and April, and the temperature reaches the lowest value in the whole year. There is a proverb: 1929, don't shoot, walk on the ice in March and September, see the willows by the river in May and September, open the river in July and September, and come in September.