What are meteorological seasons?

Back tracking a bit, the astronomical seasons (what most of us learned in school) are tied strictly to our orbit around the sun and the tilt of Earth on its axis. But the temperatures do not perfectly match the astromical seasons. For example, astronomical summer begins within a day of June 21 each year (summer solstice). But the hottest three calendar months of the year are June, July, and August. To keep more straightforward weather records, we denote those three months as meteorological summer.

The reverse is true in winter. The coldest three months are December, January, and February. Thus, meteorological winter.

The months in between are meteorological spring (March, April, May) and meteorological fall (September, October, November) — regardless of the precise moment of the spring or fall equinox.