When did summer really start?

seasonsrgbhiresSummer “officially” started yesterday, June 21. That’s what we all learned in school. But as we get older, we realize there are often many “right” versions of the same thing, and the first day of summer is one of those things. For meteorologists and climatologists, we already three weeks into summer. For them, the first day of summer is June 1.

The astronomical calendar is based on the rotation of the Earth around the sun. We learned about the Earth’s tilt and the sun’s alignment over the equator, about solstices that start winter and summer, and equinoxes that start fall and spring.  But, because the Earth takes  its time circling around the sun, requiring that extra day every fourth year to even things out, and because the Earth’s orbit is elliptical, not round, the lengths of the astronomical seasons vary between 89 and 93 days. Seasons don’t have a consistent start date on the astronomical calendar, either.

Enter the meteorological  seasons, with consistent dates that make it easier to compare climatological statistics from year to year.

Meteorologists and climatologists label seasons based on the annual temperature cycle and the calendar. Folks think of summer as the warmest time of the year and winter as the coldest time of the year. Spring and fall are transitions between them. For meteorologists, summer is June, July and August, and winter is December, January and February. Spring is March, April and May, and fall is September, October and November.

It makes sense. We’re thinking and shivering  “winter” long before Dec. 21 or 22,  and most years the weather has been “hot enough for you” before June 21.

The meteorological calendar has less variation in the length of seasons and makes it easier to calculate seasonal statistics from monthly statistics. And really, where would Iowa farmers be without seasonal statistics?

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