“Finally fall,” Sept. 25. ( DCbmyers via Flickr )

It was a long, hot summer. But on Saturday, the swelter abruptly left town. Fall is here and seems intent on holding its ground.

We declare summer over when we no longer see a reasonable chance of a heat wave — that is, three straight days at 90 or above.

D.C. hit 90 degrees Friday, but odds are it was the last time. The chance of a conventional heat wave at this point is close to zero.

If D.C. somehow manages a freak 90-degree day in October, it wouldn’t be without precedent. In weather records dating back to the late 1800s, D.C. averages one 90-degree day every five Octobers. The latest it has hit 90 in the month is Oct. 11 (in 1919).

But we don’t see a strong signal for more 90-degree weather. Mostly — for the next one to two weeks — we expect highs in the 70s.

Average forecast from simulations of the GFS model shows highs mainly in the 70s for the next two weeks in D.C. area. (WeatherBell.com)

A wrinkle is that long-range models favor warmer-than-normal air through mid-October. So we think it’s reasonably likely we haven’t seen the last of 80-degree weather.

Even after it turns chilly during October, temperatures mount brief comebacks in many years, hence the concept of “Indian summer.”

But we can say with confidence sustained heat is over.

The summer weather we endured outlasted all conventional definitions for the season — which spans June 1 to Aug. 31 according to meteorologists, and June 20 (summer solstice) to Sept. 22 (fall equinox) using the astronomical definition.

After a cool, gloomy spring, summer arrived suddenly in late May on the 24th and didn’t cave until Sept. 23.

June, July and August were all warmer than normal, and the differences from normal increased each month. Using the meteorological definition, it was the third-hottest summer on record in D.C.

Unusually warm weather persisted through much of September. Only one day so far has been cooler than normal and, month-to-date, it ranks as the second warmest on record, about 6 degrees above normal.

The number of 90-degree days has climbed to 58, which ranks as 8th most on record, and 22 more than normal.

The summer period featured the longest streaks on record at or above 65 and 70 degrees, and second longest streaks above 60 and 80 degrees.

The period of summer weather was comparably long to the previous summer, lasting about four months. In 2015, we declared an earlier start to summer — on May 8 — but also an earlier end, on Sept. 11.

Now it’s time to unpack your jeans, fleeces and flannels and enjoy all the fall season has to offer.