Mongolians traditionally classify the winter season into nine sets of nine days in order to interpret forecasts from ancient times.

Today nine sets of nine days starts according to the Mongolian lunar calendar, on December 22nd. Even before the founding of the National Agency for Meteorology, Hydrology and Environment Monitoring in Mongolia, Mongolians used the physics of the freezing point to measure winter cold, which lasts for 81 days, or nine sets of nine days of winter.

Each set of nine days has its own behavior of weather conditions progressing from the winter solstice (around December 22) through to the Lunar New Year and the first days of spring. The description for each set of the nine days are much talked about among Mongolians.

The day when the first set of nine days is marked begins with the shortest day and longest night of the year. However, the nine sets of nine days begins today, with a  temperature high of -6 C and low of -20 C.

Nine sets of nine days:

What happens during the first set of nine days ?  12/22-12/30
Homemade Mongolian milk vodka freezes

What happens during the second set of nine days ? 12/31-I/8
Vodka freezes

What happens during the third set of nine days ? I/9-I/17
Horns of three-year-old oxen freeze

What happens during the fourth set of nine days ? I/18-I/26
Horns of four-year-old oxen freeze

What happens during the fifth  set of nine days ? I/27-2/4
Rice will not congeal

What happens during the sixth set of nine days ? 2/5-2/13
Road gets black under the snow

What happens during the seventh set of nine days 2/14-2/22
Hilltops blacken

What happens during the eighth set of nine days ? 2/23-3/2
Ground becomes muddy

What happens during the ninth set of nine days ? 3/3-3/12
Warm days come in