Aching for autumn? A cool down is on the way

It’s hard to argue that we haven’t had it nice this summer. So far this year, D.C. has only racked up 21 days of 90-plus degree heat, when our average tally is 36, and four of those have come in the past five days. At Dulles, the 90-degree count drops to 10 days. July temperatures were cooler than average, and even though we ended up around normal in D.C. in August, the suburbs enjoyed below average temperatures.

But if this past week’s sizzle has you aching for autumn anyways, then you might get your fix next week.


850 mb temperature forecasts show a plume of cold air diving south in to the lower 48 next week. (ECMWF/WeatherBell)

In the D.C. region, highs will start to cool off on Monday. Said the National Weather Service in their forecast discussion on Friday morning, “one thing is true about the extended part of the forecast — the warm temps of this week will not be repeated next.” Flow from the ocean, as well as some lingering clouds, will keep highs around the upper 70s in the first part of the week.

Mid-week highs could reach the low 80s, but won’t climb much hotter than that.

While our Mid-Atlantic temps are cooling off in the early week, the jet stream is forecast to take a dip south into the lower 48, bringing with it a strong cold front, cool Canadian air, and the first taste of fall weather for much of the central U.S.

Starting Tuesday, this chilly air will push into the northern Plains states. By Wednesday morning, lows in North Dakota and Montana will struggle to reach 40, and in some locations, could bottom out below the freezing point.


200 mb jet stream forecast valid Friday from the ECMWF. The jet stream starts to take a plunge early next week. (WeatherBell)

By Friday, this cool surge will really get its teeth as lows plunge into the upper 20s in the northern states. Minneapolis could bottom out around 30 degrees on Friday morning, while Chicagoland sees lows around 40. Daytime temperatures in the central Plains will be running 25 to 35 degrees below normal.

Here in the D.C. area, things could really cool off on Friday, with morning lows in the 50s and high temperatures around 70 degrees.


GFS forecast temperatures for Friday morning. (WeatherBell)

The NWS Weather Prediction Center is even hinting at the chance for snow in the northern states by mid-week:

Weather Channel meteorologist Linda Lam writes that this week could be an early frost for some locations:

It is possible that by late next week many locations could see their first frost of the season. If low temperatures drop to 32 degrees or below, frost would be about two to three weeks early in Billings, Montana (average date is Oct. 3), Bismarck, North Dakota (average date is Sept. 21) and Rapid City, South Dakota (average date is Sept. 27).

While it’s good to take the long-range model forecasts with a grain of salt, a cool-down is on the way, for certain.

Angela Fritz is an atmospheric scientist and The Post's deputy weather editor.
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Heat Tracker

19
90-degree days year-to-date
Yearly Average
36
Record Most
67 (1980,2010)
Record Fewest
7 (1886,1905)
Last Year
24

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Sat.

rain
71° /78°
Drop 90%

Sun.

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70° /83°
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Tue.

thunderstorms
68° /86°
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Wed.

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71° /89°
Drop 40%

Thu.

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