Missing: 90-degree high temperatures in D.C.


The Capitol near sunset on July 30, 2013. HDR image. (Ian Livingston)

It’s been 16 days and running (today is almost guaranteed 17) without a 90-degree or higher maximum temperature. In late July to early August no less!

Gotta be some kind of record, right? Well, not quite. But it is noteworthy.

In fact, it’s the coolest stretch of this sort since at least 2004. For a comparable stretch during the (near) hottest portion of the summer, you have to go back to at least 2003.

Cooler feels extra cool after scorching 2010-12

Before getting to the blissfully chilly details. Remember 2011? The lengthiest break from the 90s during July and August that year was five days. 2010 wasn’t much better, with the longest streak below 90 of eight days during summer’s hottest months.

Even last year only gave us a streak of 10 days off during July and August, and that came at the end of August.

Those were undeniably hot summers, as hot as they get around here — now ranking at #1 (2010), #2 (2011) and #3 (2012). Using those as a frame of reference for summer around here can be misleading. Even so, what’s occurred in the last 2.5 weeks is something special.

Current streak the longest mid-summer break in a decade


The lengthiest period without 90-degree days by year in D.C. since 1981, when the current climatological normal period begins. June was excluded from this analysis as it is not generally as consistent a 90-degree day producer given average temperatures. In about half of the years, June had a lengthier break than shown. The 35 in 1996 was the lengthiest of all summer months, including June, during the period.

We have to go back to 2004 to find a lengthier stretch of consecutive sub-90-degree days during July and August. That year had a 27-day stretch, running from August 5 through the end of the month.

2004 was extraordinarily lacking in 90-degree days, coming in with only 11 total for the year. That’s the least number since records began at Reagan National in the 1940s, and only a few more than the all-time low of seven in 1886 and 1905 from the observing station at 24th and M St.

The most comparable recent year to 2013 (thus far) might be 2003. That year brought a 17 day stretch of no 90-degree days from July 28 through August 13. The current stretch threatens to surpass that if we miss 90 on Thursday. Models are suggestive that we’ll get closer late week into the weekend.

Staying cool at the tail of our hottest time

July 22, the day the current streak began, is the final one of summer with a rounded normal high of 89 degrees, the toastiest of the year. The normal high only drops about two degrees into mid-August.

During the past two weeks (plus) we’ve seen only three days with highs near or just above normal. Even more atypical for this time of year, a number of these days — like August 4 and August 5 — featured plentiful sun and highs only around 80 degrees. Then there’s that record low max just yesterday.


High temperatures and norms for the past 16 days of no 90 degree heat. A record cool low maximum temperature thrown in yesterday (8/6) for good measure! Note: this graphic initially incorrectly showed a high of 80 on 8/5, which was corrected.

The recent conditions more closely resemble what we might think of as the beginning of fall around here. For reference: Monday’s mostly sunny afternoon temperature is what we should expect on September 15. However, by then we’re losing 1/3 to 1/2 a degree a day off our average high, as opposed to up to 1/10 in the current period.

Big targets ahead?

Even in just the most recent climatological period (1981-2010), 1996 provides a formidable target, with a 35 day streak of no 90 degree highs in July and August. It also happened in a similar time frame, running from July 18 through August 21.

1889, the year with the third least 90s on record – eight – appears to provide the loftiest goal (one unreachable this year) with a 47-day streak of no 90s. It ran from July 15 through August 30. Funny enough, a 90 closed out the summer and yearly tally on August 31.

We could, in theory, run the Jul-Aug (and summer) streak to 41. I’d put odds against that happening for now given climatology, though since we’ve failed to get there recently on several occasions, it’s hard to rule out the possibility.

Those odds might rise a good deal should we escape 90 this week, especially if the ideas shown by the Climate Prediction Center below are correct.  Extended autumn? I’ll take it.


6-10 and 8-14 day outlooks from the Climate Prediction Center show decent chances for cooler than normal weather through the period on average. We might have a bump of heat to get through first though. (NOAA)
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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45
90-degree days year-to-date
Yearly Average
36
Record Most
67 (1980,2010)
Record Fewest
7 (1886,1905)
Last Year
24

At a Glance

Tue.

partlycloudyday
72° /93°

Wed.

thunderstorms
75° /93°
Drop 20%

Thu.

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76° /92°

Fri.

thunderstorms
74° /91°
Drop 30%

Sat.

partlycloudyday
71° /85°

Sun.

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68° /88°
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Dan Stillman · August 7, 2013

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