In meteorology for the Northern hemisphere, winter begins on December 01, 2017. It is also called the beginning of meteorological winter. The meteorological seasons are divided according to the calendar months. Winter is often defined by meteorologists to be the three calendar months with the lowest average temperatures. This corresponds to the months of December, January and February in the Northern Hemisphere.
The coldest average temperatures of the season are typically experienced in January in the Northern hemisphere. Nighttime predominates the winter season, and in some regions it has the highest rate of precipitation as well as prolonged dampness because of permanent snow cover or high precipitation rates coupled with low temperatures, precluding evaporation. Blizzards often develop and cause many transportation delays.
Accumulations of snow and ice are commonly associated with winter in the Northern Hemisphere, due to the large land masses there. At the winter solstice, the days are shortest and the nights are longest, with days lengthening as the season progresses after the solstice. (With material from: Wikipedia)