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Snow covered the northeastern United States on last day of meteorological winter, 2014. Climatologists and meteorologists break seasons down into three-month groups, based on annual temperature and our calendar. This method is helpful for weather observing and forecasting, and for planning consistent agricultural dates, such as expected first frosts or best planting date. Meteorological winter – the season where temperatures are, on average, coldest and when snow is most likely to fall – runs from December 1 to February 28 in the United States and Canada. Winter can also be defined by the ast…