By Chris Spears

DENVER (CBS4) – For a meteorologist or a climatologist the first of December is an important date because it marks the start of meteorological winter.

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Those who work in the fields of weather and climate break the seasons down into three month segments based on annual temperature cycles as well as the calendar.

Snow in Highlands Ranch (credit: CBS)

The meteorological seasons are as follows…

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Winter (coldest time of the year) – December, January, February
Spring (transition season) – March, April, May
Summer (warmest time of the year) – June, July, August
Fall (transition season) – September, October, November

(credit: CBS)

The astronomical calendar, which says winter will arrive this year on December 21, is based on the natural rotation of Earth around the sun and it defines the seasons with two solstices and two equinoxes.

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Meteorologist Chris Spears travels weekly in the CBS4 Mobile Weather Lab reporting about Colorado’s weather and climate. Check out his bio, connect with him on Facebook or follow him on Twitter @ChrisCBS4.