Day 336: Definitions of “Winter”

Posted by pmarshwx on 2 Dec 2010 | 3 comments

Yesterday (1 December 2010) began what most meteorologists refer to as “meteorological winter“, which lasts until the end of Februrary. This differs from the astronomical definition of winter, which begins on the winter solstice, which occurs each year on either the 21st or 22nd of December, and lasts until the Vernal, or Spring, Equinox.

This morning, I saw yet another definition of winter offered by the Iowa Environmental Mesonet (IEM). This definition is a slightly different take on meteorological winter; in this new definition, winter is defined as the 91-day period in which the coldest mean temperature is observed. The 91-day period is used because this is almost exactly 1/4 of a calendar year. The image above was produced by IEM and depicts the start of this modified meteorological winter. It’s fascinating to see that the onset of winter is generally later the farther east one goes.

For those who tire of my daily dose of meteorology, the IEM offers their own daily dose, although it is typically Iowa centric. You can check out the IEM Daily Feature at this top of IEM website homepage.