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Posted at 11:00 AM ET, 09/23/2010

Comparing, defining D.C.'s record summer heat

By Ian Livingston

2010 and 1980 lead the pack, but which was warmest?

* No. of 90+ days so far: 64 | Record: 67 (1980, final of yr on Sept 23) *
* How much more heat is in our future? Full Forecast *

Comparison between astronomical summer and meteorological summer in D.C. Image rotates every 7 seconds.

We're pros at heat, yesterday's high of 95 was 18 degrees above average for the date and not even one of the hottest temperatures this year (though impressive for so late). After a warm spring, Washington, D.C. and many nearby localities recorded their hottest meteorological summer (Jun-Aug) on record.

Since then, other notable warmth marks have been surpassed, like the 90+ days record at Baltimore. At D.C., we're headed ever closer to that record as well. Even falling short would be an achievement, leaving the previous No. 2 at least 5 (as of yesterday) 90-degree days behind. Summer heat is pretty typical around here, but this one had staying power and disregard for the calendar unlike just about any other.

Keep reading for more on astronomical summer, how it compares to meteorological summer, and how it ranks in Washington D.C. And really... Which "summer" matters the most anyway?


There is little question that this summer's overall heat, despite the hottest days falling short of the extreme readings of the 1930s, has risen above all others but perhaps one -- 1980.

When it comes to meteorological record keeping, 2010 blew 1980 out of the water by well over 1 degree. But, much of 1980's major heat was tail-end loaded, exemplified by the record 14 90+ days in September that year.

Daily average temperature comparison for 1980 and 2010. Covers the period April 1 through Sept. 22 in order to capture all 90+ days (through Sept. 22) in 2010. The 175-day average for 1980 was 74.7 degrees compared to the 175-day average in 2010 of 74.9 degrees.

So... Which summer was the warmest? What "summer" matters?

A vast majority of the heat for an average year occurs in the Jun-Aug period, and 2010 was no exception with July tying for the hottest on record and also the first-ever occurrence of an average Jun-Aug high temperature greater than 90 degrees. But, we can't ignore that 1980 had a very strong finish.

Thanks to its late heat surge, 1980 had an average astronomical summer (94 days from June 21 'til September 22) temperature of 81.7 degrees. Quite warm, even compared with this year's 80.4. The average high during this period in 1980 was a toasty 91.0 compared to this year's 89.7. As important but less watched, lows in 1980 were also slightly higher during the same period, 72.5 in 1980 compared to 71.2 this year.

In the 94 days of this astronomical summer, D.C. reached 90 degrees or higher on 50 occasions. The same periods of 1980, 1966 and 1983 finished equal or higher, coming in with 61, 52 and 50 days, respectively.

As with the graph above, but more focused on "prime" heat months, the period of June 1 through Sept. 22 brought an average temperature of 80.0 in 1980 and 80.1 in 2010. Very similar numbers, with a slight (assuming no rounding errors) edge to this year.

In the end when talking "hottest summer," it might be a tossup -- for some reason, our biggest records seem to cluster (for example, while winter 2009-2010 was significantly snowier than numbers 3-10 of the top snow years, it was only the snowiest ever by 1.7").

If you're one who likes to go by the "official" story, as Bob Ryan seems to be, then it's hard to say 2010 is not the warmest summer on record.

However, if you must go by the kitten calendar hanging on your wall at home and want to declare this summer "not as hot as 1980," at least consider the larger warm season and how this one stands out in multiple categories over a considerable period of time.

Then again, it's always good to leave a few records out there still to beat. Though I'm sure most won't be longing for a repeat of this summer anytime soon...


Seasonal temperature records: Warmest ever June, tied warmest ever July (and any month all-time), warmest ever summer

64 90-degree days: (with at least 1 or 2 to add) April, 2; May, 3; June, 18 (tied for record); July, 21; August, 13; September (thru 9/22), 7. See comparison to 1980. See running year-to-date comparisons with other top years. (Graph re-posted from

7 heat waves (3 or more days in a row 90+): June 12-14, June 19-29, July 4-9, July 14-25, Aug. 4-6, Aug. 8-11, Aug. 29-Sept. 3. Another in progress?

5 record highs: 100 on June 24, 99 on June 27, 102 on July 7, 101 on July 24, and 98 on Aug. 10.

6 record high minimums: 76 on June 21, 78 on June 24, 80 on July 7 and 8, 81 on July 24, and 80 on Aug. 11.

4 100-degree days: 100 on June 24, 102 on June 6 and 7 (first back-to-back 100s since 1999), 101 on July 24. The 4 100+ degree days ranked #5 (tied) all time.

Other random tidbits: 2010 is the first time D.C. has seen 4 or more lows of 80 degrees or higher in one year. The top-10 high temperatures averaged 99.6 degrees. Cooling degree days (1,994 in 2010 thru 9/22) are set to surpass their previous record of 2,006 set in 1980 (hat tip, CWG commenter JerryFloyd1).

By Ian Livingston  | September 23, 2010; 11:00 AM ET
Categories:  Latest, Local Climate  
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Next: Weather Channel: D.C. had worst summer in U.S.


thanks for the great summary and comparisons, especially the graphs.

Posted by: meteorolinguist | September 23, 2010 11:20 AM | Report abuse

Thank you! Thank You for pulling all these stats together in one place and making it easy to understand! This is one of the reasons I follow CWG. I love the forecasts, analysis and stats like these! I think you may have mentioned this before but what was the latest (in the year) 90 + degree day recorded in DC? And the latest heat wave?

Posted by: soleil2000 | September 23, 2010 11:22 AM | Report abuse

Thanks for the summary. Now I feel even more miserable.

Posted by: prayforsnowDC | September 23, 2010 11:25 AM | Report abuse

And one more record not mentioned. First year ever where 3 months have averaged at least 80 degrees (June, July, and August) at Reagan National. What a year it's been. And I don't think Mother Nature is done yet!

Posted by: cloudking1 | September 23, 2010 12:33 PM | Report abuse

This is a terrific comprehensive analysis. I would, however, like to see one more statistic: The number of days where the heat index exceeded 90 degrees. A report using the heat index would provide a more realistic picture of what those of us living here actually experienced this summer.

Posted by: rsalts01 | September 23, 2010 12:49 PM | Report abuse

I don't know the stats, but in the area of Alexandria where I live, we have barely had any rain in months. Even the days when it has rained, it has barely wet the soil (and did not wet it at all beneath trees). This drought combined with the heat has been atrocious for trees and plants. I am seeing the effect on trees all over our community.

FWIW, though we didn't get the water, we also were spared the t'storms and wild weather that came with some of the rain, so at least we had power.

Posted by: egengle | September 23, 2010 1:23 PM | Report abuse

Please see my post regarding Bruce F. Watson's 1975 weather almanac for the Minneapolis/St. Paul area. I'm not sure if WCCO is continuing to publish annual weather almanacs, but Bob Ryan apparently didn't continue his series for this area...though it is possible that he and Doug Hill might collaborate on an online version for Channel 7 in the future.

The hottest summers within my memory include 1988 here and 1955 in Wisconsin when I was growing up. I believe there were more 100-degree days in 1988 than this summer.

As I remember, 1954 and 1955 were great years for Atlantic hurricanes, and the sea surface temperature in the tropical Atlantic/Caribbean region was above normal as it was this year. The names for those years: Carol, Dolly, Edna, Hazel, Janet, Connie, Diane, etc. are still remembered by meteorologists; many of those names have been retired. BTW I'm no fan of "permanently" retiring specific tropical storm names, though names of notable hurricanes ought to be retired for 100 years or so. That should provide enough time to allow for recycling of hurricane names.

Posted by: Bombo47jea | September 23, 2010 1:57 PM | Report abuse

soleil2000 - I can pretty much answer both of your questions with one answer (Responding to "what was the latest 90 + degree day recorded in DC? And the latest heat wave?") = 1919. That year we hit 90F on the latest day of the year, October 11.

Posted by: Camden-CapitalWeatherGang | September 23, 2010 2:18 PM | Report abuse

Soleil2000 and Camden, the latest heat wave (defining heat wave as 3 or more 90 degree days) was October 7-9, 2007, when it was 92, 91, and 94 degrees respectively. Looks like unless we can eck out a 90 on Saturday on a west wind, that 67 days is going to be safe another year.

And Bombo47jea, you are absolutely right about 1988 having more 100 degree days. There was 7 that year. That was a heckuva hot summer not just here, but nationwide.

Posted by: cloudking1 | September 23, 2010 2:36 PM | Report abuse

Great analysis, Ian, and I hope the book you and Kevin are putting together includes an "Endless Summer" chapter about this year. I just wish we had more comparative data from the hot 1930s summers.

I spent a lot of time in 1980 outdoors in the blazing sun, tending my garden. This year I've walked on the shady side of the street. ; ))

Posted by: JerryFloyd1 | September 23, 2010 3:25 PM | Report abuse

Surpised MR Q. hasn't chimed in telling us us that it's all in our imaginations. I'm sure he can provide a link showing us that the temps recorded is some kind of a lie.

Posted by: VaTechBob | September 23, 2010 4:15 PM | Report abuse

Thx all. cloudking1, the three mo above 80 is a good stat -- forgot to include here, did in the met summer recap.

Posted by: Ian-CapitalWeatherGang | September 23, 2010 6:57 PM | Report abuse

rsalts01, that might be interesting to know about.. it would be a bit harder to get though. I'll have to see if there are any records on that info.

Posted by: Ian-CapitalWeatherGang | September 23, 2010 6:58 PM | Report abuse

Going to repost 95+ stats (asked about in forecast post today)... we may pick up another tomorrow.

Regarding 95+ days and how it matches up... I see 26 this yr including yesterday rather than 27, though maybe I'll double check. 1980 had 28, 1991 had 27, 1930 had 26. So we're up there...

Posted by: Ian-CapitalWeatherGang | September 23, 2010 7:00 PM | Report abuse

CWG, thanks for the shoutout re: Cooling Degree Days, which indeed did break the record today; now up 2,011, with perhaps 17 more CDDs on Friday.

Of course, there haven't been any heating degree days since July 1, so we're starting to build up a small deficit there, along with the much more serious precip deficit.

Posted by: JerryFloyd1 | September 23, 2010 7:31 PM | Report abuse

Thanks for posting the running total. It was beyond neat. What I see: this year was #1 in 90 degree days or tied for #1 a in cumulative 90 degree days good chunk of the summer. Also, 1980 would be near the bottom of the top except for that late season surge. The real champs (this year, 1980, 1991) also have more, and longer heatwaves.

Posted by: kperl | September 23, 2010 8:35 PM | Report abuse

Oh. I should have just said longer heatwaves.

Posted by: kperl | September 23, 2010 8:36 PM | Report abuse

@kperl, 1980 was hot from late July on and then it was blast furnance hot for two months. That was not a summer to be taken lightly and this year has beaten it with a safety in overtime. In 2010, the heat lasted longer but during the most intense heat, 1980 was often worse.

Posted by: JerryFloyd1 | September 23, 2010 9:01 PM | Report abuse

I'd pretty much agree with that Jerry. I was actually somewhat surprised when looking at the avg high for astro summer in 1980... 91 is pretty intense, and it's a slightly longer (2 days) period than the 90.2 JJA avg high we just saw here as well. But we should also consider that spring was #2 warmest met and #1 astro, so there's been little if any break since winter ended.

Persistence is probably the top story for the last yr. It has been a good theme in many regards.. few initially believed in Feb before it happened but it had already shown itself in Dec. Interestingly enough much of it since then can probably tie into the -NAO pattern that's been well established.

Posted by: Ian-CapitalWeatherGang | September 23, 2010 9:18 PM | Report abuse

Bombo47, we don't agree politically or on climate-warming, but I totally agree with your wiew of the summer of 1988. It had, by my memory, the longest string of 90+ days I can remember, with several days when Dulles reached 104. It was like a blast furnace/sauna outside then...the dew points seemed higher then than this year. I don't remember a dew point over 75 this year locally, while in some summers we see a dew point of 78 or even 80. When it gets to be a dew point of 80 outside, the heat is not only just is dangerous. And precipitable water can run 3" or more, with big thunderstorms droppping several inches of rain.

Posted by: MMCarhelp | September 23, 2010 11:25 PM | Report abuse

1988 had a very impressive shorter run at high heat. Only 5 days were sub 90 of the 46 from 7/4 to 8/18, including a 21 day heat wave and an instance of 3 100s in a row. 93.9 was the avg high temp in that period, with 6 days total over 100 during the stretch and 1 prior in June. Temps cooled pretty decently by mid-Aug though, some feature a flip to more typical D.C. fall weather 70s/80s earlier than others.

Posted by: Ian-CapitalWeatherGang | September 23, 2010 11:49 PM | Report abuse

yep Ian your right,of course, I misscounted the 95+ days in August which is why I had an extra day.

Posted by: minerdude | September 24, 2010 7:32 AM | Report abuse

yep Ian your right,of course, I misscounted the 95+ days in August which is why I had an extra day.

Posted by: minerdude | September 24, 2010 7:33 AM | Report abuse

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