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Summer 2014 in D.C.: 90-degree days running 40 percent below normal

Sunrise at the WWII Memorial in early August 2014. (Navin Sarma via Flickr)

There’s one constant about D.C. summer, and that’s a lot of hot days. Right?

Not always.

While 2014’s average temperature for meteorological summer (Jun-Aug) is running fairly close to “normal,” as defined by the 1981-2010 climate period, it’s undoubtedly been among the more pleasant in recent memory when it comes to daytime heat.

90 degree days since 2004. 90 degree days since 2004.

With only 16 days featuring high temperatures at or above 90 degrees this year, we’re a week behind last year’s tally year-to-date, and 32 days (more than a month!) behind the pace of the scorching 2010-2012 summers.  The average year-to-date total is around 29.

Of course, the crazy summers that kicked off the 2010s averaged about three weeks more 90 degree days than the average around 36 days. 2010 even gave us a tie for the most on record at 67.

On the low end, 2004 sets the recent low mark when it comes to cumulative 90 degree days, at only 11. It reached that number prior to mid-August, and stayed there for the entire warm season. 2009 was more or less on par with this year at this point, having only racked up 15 by mid-August. It finished with 22.

Over the entire D.C. history going back to the 1880s, D.C. seeing so few 90 degree days through mid-August is about a one in five chance. However, two thirds of the years in which this happened occurred before the switch of observation location from downtown to National Airport in the mid-1940s.

90 degree days over the D.C. historical record.

There have actually been 17 years dating back to 1872 that finished with only 16 days at or above 90 degrees during the extended summer months, many were fewer. Three of these years with missing 90s occurred since 2000 (2001 had 16, 2000 had 12, and 2004 had 11). 2004’s tally is the record holder for lowest in a year at National.

Going way back, in 1886 and 1905 we only managed 7 days in the 90s or higher. Those are low marks that are almost undoubtedly safe for eternity.

Finally, during the 10-year period prior to this one, D.C. recorded about 80% of its 90 degree or warmer days by August 15. It’s roughly the same for the longer climatological average. That would put us on pace for about 20.

Where do you think we’ll finish this year?

Ian Livingston is a forecaster/photographer and information lead for the Capital Weather Gang. By day, Ian is a defense and national security researcher at a D.C. think tank.
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