Morning view on Aug. 30. (George Jiang via Flickr)

Out of nowhere, seemingly, summer left Washington in late August. By Labor Day weekend, many passed on dips at the pool and flocked to apple orchards in the unusually crisp air that was more typical of a month later.

But summer isn't over. An extended stretch of warm weather is arriving.

Before getting into the details of what's coming up, let's first look back. We haven't seen a start to September this cool in most of our lifetimes.

Washington's average temperature of 68 degrees over the first third of September ranks as the coolest since 1935, some six degrees below normal. All of the cooler starts to September concentrated in the late 1800s and early 1900s.

Just one day this month (Sept. 5) has been warmer than normal. The high temperature has averaged 76 degrees (normal is in the low 80s), while the low has averaged 61 degrees (normal is in the mid-60s).

Washington has taken on early September temperatures most comparable to what's normal in Boston, according to the Southeast Regional Climate Center.

But just as fast as the weather turned autumnlike, summer is coming back.

The signs emerged Tuesday, when Washington hit 80 for the first time in a week. Models suggest that temperatures should be near and above 80 for the next 10 days or so.

Temperatures predicted by group of simulations from the European model for the next 15 days. (

We can attribute this summer renaissance to a radical alteration in the jet stream pattern. From late August until the past couple of days, it dipped in the east and bulged north in the West (recall San Francisco's all-time high of 106 degrees and all of the smoke and fires). Now the opposite configuration has emerged and may persist for the next couple of weeks.

"It's a monster change out West," said Matt Rogers, a Capital Weather Gang contributor who specializes in long-term forecasting. "It was a pretty large shift in the North Pacific, which has led to the cool trough in the Pacific Northwest and western Canada, which is creating a ripple effect to a warmer East."

Change in jet stream as portrayed by NAM model between late August and mid-September. (UnisysWeather)

While the average high temperature from the group of simulations comprising the European model is around 80 over the next couple of weeks, Rogers said we may have some hotter days into the low to mid-80s or even a low-humidity 90-degree day.

So you can put away the fall fleeces and jeans for a bit, and bring back out the shorts and bathing suits.

For fall lovers, your turn will come again. Like a seesaw, Rogers said that pattern may flip back to autumnlike by the end of September or early October.