What is Winter 99?

Winter 99 is an ancient folk method to calculate cold weather. The number nine, also known as winter nine nine, is an ancient folk method to calculate cold weather. Counting nine starts from the twenty-four solar terms "to the winter" and counts as a "nine" every nine days. Count nine cold days, that is, count nine every nine days from the winter solstice to the eighty-first day, and the weather will warm up.