What exactly does the beginning of winter mean? The answer is more complicated than you might think. First, you can have what some refer to as astronomical winter. Others, primarily meteorologists, often define winter in the northern hemisphere as the months of December, January, and February. So, the definition is somewhat illusive in that it varies depending on who you are talking to and the context of the discussion.
Let's start with the astronomical definition of winter. In other words, the date you can go to a calendar and read the words "First Day of Winter." The Earth, as many of you know, tilts on its axis at approximately 23.5 degrees. This axial tilt produces what we call seasons on Earth. The key to understanding the importance of the tilted axis begins with the realization that how direct the sun's incoming solar radiation impacts Earth is more important than the distance between the two. As a matter of fact, we are only a couple of weeks away from the perihelion, the point at which Earth is closest to the sun.
Wait just a minute. Am I suggesting to you that Earth is actually closer to the sun during the winter in the United States? This is exactly what I am telling you. However, the northern hemisphere is tilted away from the sun at the furthest most point it will be during the entire year, which also results in the shortest day of the year. Aren't you glad the day will be slightly longer on December 23rd than it will be on December 22nd? No? If not you obviously understand that despite the shortest day occurring on the winter solstice, temperature averages colder in January. The best way to think of this is that there is still more heat leaving than arriving after the winter solstice, which is kind of like your bank account. Never mind, I'm sure your bank account if more like the summer solstice.
Meteorologists often think of seasons in this way: winter as December through February, spring as March through May, summer as June through August, and fall as September through November. This is based primarily on the most common type of weather we experience in those rather than a specific date on a calendar. However, I will admit that this doesn't always work either because several of Oklahoma's biggest snow storms have occurred in the month of March. So, technically there is no "official" beginning or ending to any season. The reality is that the way you define a season is more or less a matter of opinion. Let it snow, let it snow, let it snow…as long as it isn't a repeat of the Christmas Eve blizzard of 2009.