Dulles Airport just recorded its longest “heart of summer” cool streak on record

Opening night of the Montgomery County Fair. (Dan Lawrence via Flickr)

Opening night of the Montgomery County Fair. (Dan Lawrence via Flickr)

D.C. is in the midst of a tame summer, with 40 percent fewer than normal 90-degree days (as described in a post last week). That’s only some of the story. Other parts of the area are seeing even cooler conditions.

At Dulles, a location representative of much of the western portion of the D.C. area, a three and a half week stretch of below normal temperatures came to an end Saturday.

Such a stretch of temperatures in the heart of summer seems unheard of. And as far as official records go, it is.

The first 15 days of August were the third coolest on record at Dulles and BWI. (NWS)

The first 15 days of August were the third coolest on record at Dulles and BWI. (NWS)

Over the weekend, the National Weather Service office serving Baltimore/Washington reported that the first 15 days of August came in at third coolest on record for both Dulles and BWI.

Of course, the first half of this month was only part of an extraordinary streak of below normal daily temperatures at Dulles. Every day in August through the 16th came in below normal. Even more incredible, the below normal streak ran all the way back to July 24.

Related: Daily normals at Dulles (based on 1981-2010 data)

That’s 24 days in a row of below normal temperatures. All during basically the hottest time of the year.

Many a comment has been made that it’s hard to remember a summer quite like this. And if you go by this metric in the western suburbs, you’re quite right.

Longest below normal temperature streaks by year at Dulles, based on 1981-2010 normals. (Author using NCDC data)

Longest below normal temperature streaks by year at Dulles, based on 1981-2010 normals. (Author using NCDC data)

I’m calling July and August the “heart of summer,” because that’s when the highest temperatures of the year occur on average. Since Dulles began hosting temperature readings in 1963, a below normal stretch like this has never occurred in the heart of summer.

There aren’t even that many instances of streaks getting close. We also created some distance from the nearest contenders before it came to an end. Impressive all around.

Based on the 30 years prior to this one, our normal streak of below average temperature days in July-August is about a week in length. Both 2010 and 2011 only had four day streaks of cooler than normal temperatures, tied for the smallest stretches of such on record.

2014's below normal temperature streak compared to previous. A list of years, and the start/end dates: 2014, Jul 24 - Aug 16; 2000, Jul 11-29; 1996, Jul 20 - Aug 5; 1976, Jul 1-20.

2014′s below normal temperature streak compared to previous. A list of years, and the start/end dates: 2014, Jul 24-Aug 16; 2000, Jul 11-29; 1996, Jul 20-Aug 5; 1976, Jul 1-20. (Author using NCDC data)

Only three other years have seen a below normal temperature streak of greater than 15 days. 1976 featured a 20-day streak, 2000 saw 19 days below normal in a row, and 1996 pulled off 17.

The July 30, 2014, daily temperature was 13.5 degrees below normal, greater than any departure in any of the other lengthiest streaks, and among the top 20 greatest July-August temperature departures on record at Dulles. Brr!

When it comes to below normal days overall across the two months, it appears we won’t quite get the records there, but it should be close. 1996, while falling short of this year’s below normal streak, tallied up 49 days below normal in the two month period.

While current guidance suggests we won’t be tallying up below normal days as quick in the time ahead, there is also no major warmth on the horizon. 2014: The Summer of Bliss?

h/t to CWG reader 4seamed for bringing up this idea in the discussion of record rain the other day. Your inklings were right!

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