Calendars across the Northern Hemisphere say winter will begin on Dec. 21, but for meteorologists, the start of the season will happen three weeks earlier.
The reason behind the discrepancy is that weather experts follow what’s called meteorological seasons, while others use the astronomical calendar to signify the change.
Meteorologists and climatologists break down the seasons based on when temperatures typically change, not the status of Earth’s rotation.
Under the meteorological season scheme, the four seasons are each allotted three months, making it easier to calculate statistics and compare weather conditions to previous years.
The rotation of Earth around the sun and the planet’s tilt make the basis for the astronomical calendar.
The astronomical changing of the seasons are marked by either a solstice or an equinox.
The summer and winter solstices occur when the Northern Hemisphere is at its maximum tilt toward or away from the sun, respectively.
When Earth’s axis isn’t tilted in favor of either direction, it’s referred to as an equinox, or the start of spring or fall.
The days that the solstices and equinoxes fall on vary year-by-year because Earth takes slightly more than 365 days to revolve around the sun, hence why you’ll see slight adjustments in the changing of the astronomical seasons.
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The National Oceanic and Atmospheric Administration says meteorological seasons were developed because of the ever-changing dates produced by the astronomical calendar.
So when the calendar switches over to December, don’t be shocked if your favorite FOX Weather meteorologist is welcoming everyone to winter.
Meteorological winter will start on Dec. 1 and run through Feb. 28.