The Washington PostDemocracy Dies in Darkness

After 20 long, hot weeks, we declare summer over. Fall weather is here.

(Zsaj via Flickr) (Zsaj)

Our lawns are parched. Our air conditioners are tired. And our summer wardrobes are worn out. But, finally, the weather regime has shifted, none too soon, and we can declare summer over and fall arrived.

The cooler, drier air is streaming into the region as we speak. By Saturday morning, temperatures will dip into the 40s to near 50, the lowest since last April. The change in conditions is sudden, especially considering the persistence of the warmth over the last 4½ months.

Starting in mid-May, when we declared summer had begun, high temperatures consistently reached the 80s or higher. The statistics tell the story: The heat was relentless:

Review: Our summer outlook was a failure

But we’ve now turned the corner, and, like the flip of a switch, the summerlike 80s and 90s have shut off. The forecast for the next week is for highs in the 60s and 70s:

Unlike the hot high-pressure zones that have been parked over the area in recent weeks, the jet stream is set to move faster and take more frequent dips, pushing cool fronts through the region routinely.

Our criteria for declaring summer over is no further risk of a heat wave, or three straight days at or above 90. We’re confident we’ve reached that point. Our average high temperature is now in the low 70s and slips into the 60s in just over a week.

But we are still likely to have more warm days. It’s common to see some 80-degree weather deep into October, hence the concept of “Indian summer.”

[What is ‘Indian summer’?]

We probably won’t hit 90 again, however. The latest Washington has ever hit 90 degrees is Oct. 11, and forecast models over the next 10 days don’t show us getting close. However, in this age of climate warming it would not shock us if, at some point in the future, we see 90-degree weather move later into October.

Since 2015, we’ve issued these end-of-summer declarations, based on the actual weather, rather than calendar definitions. The dates of these declarations have ranged from Sept. 11 to Oct. 12.

This year’s end-of-summer/start-of-fall declaration lies toward the end of the range.

For everyone eager to don sweaters and fleeces and enjoy a hot drink on a crisp autumn morning, your time is here. Enjoy. Before too long, the conversation will shift to snow. …