"1929 didn't shoot, walked on the ice in 3949, watched willows along the river in 5969, opened geese on the river in 79, and added 19 in 99 to plow cattle everywhere." This proverb can best explain the winter temperature changes in Hebei and northern China.
The "nine" above is commonly known as the number nine. Starting from the solstice in winter, this number represents the first nine days. Therefore, it should take at least one and a half months from the beginning of freezing to thawing in Hebei.