Deciding just when summer ends is often attempted but not so easy. Summer’s end is cultural as well as meteorological. It involves Labor Day, the start of school and the occurrence of the equinox.

But this year, a case can be made for Sunday, Sept. 8. As it turned out, it was a warm Sunday, with the high at Reagan National reaching 91 degrees. But the mercury may not reach 80 on Monday. That will be the day the regular National Football League season opens for Washington, and football is not yet regarded as a summer sport.

There is something else: Summer is a season of extremes, in which the temperature in Washington can reach 100 degrees. Washington residents are accustomed to 90-degree heat, and in fact Wednesday may hit 90 or above, according to forecasts.

But the true thermal menace of summer is the torment of the triple-digit reading. And none of those have ever been recorded here later than Sept. 8.

Labor Day is often described as the “unofficial” end of summer, and that was a full week ago. Meteorological summer is said to end on the last day of August. The day of the equinox is widely considered to be the “official” end. But that does not come this year until the 22nd, which is almost two weeks away. Washington’s normal high temperature for that date is 77 degrees, which is not as summerlike for this region.

The normal high for Sept. 8 is 82. The figure falls into the 70s on Sept. 17, which is thus also a candidate for the start of fall.