Two Winters
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Did you know that there's more than one winter?

Hi, this is Bryan Yeaton and this is The Weather Notebook.

What we most commonly refer to as winter is what is known as astronomical winter. This starts on December 21 at the winter solstice and ends at the vernal equinox around the 21st of March. For some of us , though, despite the calendar, we've already seen winter weather this year and it seems as though winter has started. Maybe it has.

That's just another kind of winter called meteorological winter and the farther north you live, the earlier it starts, sometimes way before December 21st. Meteorological winter is based on weather; astronomical winter is based on the earth's position in its orbit around the sun. While the start of astronomical winter is the same everywhere, the beginning of meteorological winter can change from town to town.

Ecologists and climatologists have tried to nail down, on average, where meteorological winter happens. They say that meteorological winter happens only where the temperature on average, stays below 30 degrees for three months in a row, and where the snow depth averages ten inches or more for the same three-month period. This excludes a lot of the planet from meteorological winter in spite of what the calendar says. According to this demarcation, true winter occurs in less than a third of the country, north of a line that runs west roughly from Boston to Salt Lake City to Anchorage. South of this line there are certainly abbreviated attempts by the atmosphere to put on a winter performance, but it's only a one-act play.

To find out when meteorological winter starts of if it starts at all where you live, check our link to meteorological winter at our web site www.mountwashington.org. Our show is a production of the Mount Washington observatory, with support from the National Science Foundation. Have a question or comment? Call us at 888-RAIN-001.