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Posted at 10:30 AM ET, 06/ 1/2010

Capital Weather Gang's 2010 Summer outlook

By Matt Ross

Hot, dry summer anticipated

* P.M. t'storms likely, less humid tomorrow: Full Forecast *
* Where's the rain now? Radar & more: Weather Wall *

After an epic, record-breaking winter, can we expect similar extremes this summer? We present our annual Summer Outlook. This summer we're predicting above average temperatures. While not historic, the heat this summer should be classically D.C., similar to the summers of 2005-2008: consistently hot, and perhaps quite dry.

The task of doing a summer outlook is no easy one. First, with few exceptions, summer in the D.C. area is mainly hot. Do we really care if it's 88 and humid or 93 and humid? Also, the weather varies less during the summer than it does during the the rest of the year (especially compared to winter), with the vast majority of summer months finishing within a few degrees of normal. So, it follows that when putting together a summer outlook we're less likely to see the signals for extreme warmth or cold that we sometimes see in advance of winter.

Nevertheless, we will do our best to convey what we expect for summer 2010...

Keep reading for the full summer outlook, but first vote in our 90-degree poll. On average, we get 31 days at or above 90. Last year we had only 21 and in 2008 we had 29. By comparison, we had 55 in 1988.


This summer is likely to be similarly hot to the summers of 2005-2008 and may be quite dry as well like the summers of the late 1980s. There will be long stretches of oppressive heat and humidity. While there will be occasional reprieves, there is likely to be a handful of heat waves (maximum temperatures of 90 or higher for 3+ days), with perhaps 2 or 3 lasting more than a week. It is quite hard to predict precipitation totals as a day of heavy thunderstorms or remnants of a tropical storm can skew the statistics, but overall we expect a dry summer with long stretches of no rain. This will be a classic D.C. summer: hazy, hot and humid.



June: 1 to 2 degrees above average
July: 1 degree above average
August: 1 degree above average

Overall: 1 to 2 degrees above average

Number of 90-degree days for June/July/August: 40-45 (Normal is 31.3)

Number of 100-degree days: 1-2

Longest Streak of 90+: 10-12 Days


Below normal. Perhaps, well below.


The main methodology for creating the outlook was the use of analog years. Analog years are past years in which conditions leading up to summer most closely resemble conditions leading up to summer 2010. Analog years are far from a perfect predictor due to the complexities of weather, as no two years are exactly alike. However, they can be of considerable value in giving us a general idea of what to expect.

The following factors were given the most consideration in preparing the outlook. It should be noted that any one factor does not necessarily correlate with a particular kind of summer (e.g., warm, cool, dry or wet).

El Niño/La Niña:

After a moderate El Niño episode this past winter, we have rapidly transitioned to neutral conditions this spring. Modeling suggests we may transition to a La Niña episode as we head towards the fall. We are operating under the assumption that conditions will be in a neutral or weak La Nina state throughout the summer.

This Spring's Conditions:

For most of April and May there has been a significant trough in the west and a ridge in the east. As such, temperatures have been well above normal in DC. Indications are that this pattern will persist through much of June, though the warmest temperature anomalies for the summer overall are likely to be in the center of the country from the Northern Plains down through Texas.

Analog Years:

The Analog Years, or the years where many of the above factors were also apparent, are: 1964 and 1970

The weather during these summers served as the basis for our outlook.

Enjoy summer 2010. Hope your A/C is working!


CWG's 2008 Summer Outlook
2008 Outlook Evaluation
CWG's 2009 Summer Outlook
2009 Outlook Evaluation

By Matt Ross  | June 1, 2010; 10:30 AM ET
Categories:  Capital Weather Gang, Extreme Heat, Local Climate  
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Posted by: hereandnow1 | June 1, 2010 10:44 AM | Report abuse

So--CWG is going with 40-45 90-degree days. How many do you expect?

Posted by: CapitalWeatherGang | June 1, 2010 11:06 AM | Report abuse

My guess: 30 or so *actual* 90-degree days; probably over 50-60 (total -- so 20-30 more than that) will feel like it.

Welcome to DC summer....

Posted by: | June 1, 2010 11:16 AM | Report abuse

I second that Ugh! Sounds like it's going to be a dreadful summer.

With five months of below-average precipitation already (at DCA), a drier-than-normal summer does not bode well.

Perhaps the forecast for an above-average hurricane season will send the juicy remnants of a tropical storm or two north to DC to remedy our rainfall deficit!

Posted by: TominMichiganParkDC | June 1, 2010 12:08 PM | Report abuse

Please do not wish for tropical storms!! TP Hanna gave us 13 inches of water in our house. Some rain, fine, but I can do without the tropical storms!

Posted by: erbele | June 1, 2010 12:44 PM | Report abuse

Yipee!! As an expat from SoCal, temps in the 90's are right up my alley. Bring it on!

Posted by: moneel | June 1, 2010 12:47 PM | Report abuse

Ugh-plus. We need rain, not heat. But not rain this afternoon, at least until I get where I'm going.

Posted by: JerryFloyd1 | June 1, 2010 12:51 PM | Report abuse

It's not starting out like a "dry" summer, since "much-needed-rain" seems to be doing everything they can to throw downpours & lightning at me whenever I have an errand, a meeting or a dance to go to.--El Bombo

As for the "analog years" they both seem to be prior to my arrival in Washington in 1973. Is it possible the hot dry summer of 1988 is another such year?

Posted by: Bombo47jea | June 1, 2010 1:20 PM | Report abuse

I love the heat, as well, moneel, but SoCal heat is a lot different and usually more bearable than DC heat. Here, we've got the humidity making it feel much hotter than it actually is, whereas dry heat in SoCal can actually feel okay. Of course, I also love fantastic lightning shows and tropical downpours, so bring on the humidity!

Posted by: crzytwnman | June 1, 2010 1:25 PM | Report abuse

Anyone remember the summer of 1980 with its record of straight 90 degree days. It seemed like 50 days straight. Best aprt I was in full plaster leg cast from does to my upper thigh from the second week of June when it started to the first week of August. Summer of 80 was one hot humid nasty summer. Its about time for one like that.

And don't forget Agnes in June 72.

Posted by: sheepherder | June 1, 2010 2:19 PM | Report abuse

For the "we need rain" crowd. Please keep in mind that this so-called deficit you speak of is very localized. Dulles is exactly 0.10 "below" normal. I wouldn't call that much of a deficit at all.

And I have mushrooms popping up in my yard. So, I can safely say that in my neck of the woods, we DON'T need the rain. But, I hope for your sake, you get all you want at your house. :)

Posted by: ThinkSpring | June 1, 2010 2:19 PM | Report abuse

@ThinkSpring, DCA, the death valley of weather gauges is about 5" inches below normal for the year. So go pick your mushrooms and let the rest of us have the rain we need here in nearby D(rought) C(ity).

Posted by: JerryFloyd1 | June 1, 2010 3:39 PM | Report abuse

Question for CWG re: humidity - why is it that whenever I check the humidity of D.C. v. Los Angeles (where I used to live)it's usually about the same - in fact, L.A. is sometimes even higher - when it feels so much stickier and more humid here?

For example, see this:

v. this:

Posted by: javachip | June 1, 2010 4:16 PM | Report abuse


Relative humidity, which is the variable shown at the links you provide, says very little about how humid the air feels to us (the key word in there is "relative"). Dew point is a function of the absolute humidity, and is the best indicator of how humid the air feels. See a previous post of ours on this for more. -Dan, CWG

Posted by: CapitalWeatherGang | June 1, 2010 5:23 PM | Report abuse

err on the side of misery, safe bet for DC summers.

Posted by: grinbear | June 1, 2010 6:36 PM | Report abuse

Here's a graph of 90+ for June/July/Aug.

Posted by: Ian-CapitalWeatherGang | June 1, 2010 6:55 PM | Report abuse

I'm voting 16-25 out of hope, despite the sound analysis from my colleagues.

Posted by: Ann-CapitalWeatherGang | June 1, 2010 8:56 PM | Report abuse

Thanks for the quick answer! Now I know to keep my eye on the dew point.

As for over 90 days, I'm going for the middle range.

So *not* looking forward to the summer, weatherwise...

Posted by: javachip | June 1, 2010 9:31 PM | Report abuse

"This will be a classic D.C. summer: hazy, hot and humid."

OK, does anyone really think that this sentence would ever have read "This will be a Seattle-like summer..."

DC = H3 so if you can't stand the heat (and haze and humidity), get outta DC. DC was a swamp originally if I recall so we get what we get. This is why we have AC. Personally, after living in the DC area for 45 years, I have to say I have gotten used to it.

Posted by: amaranthpa | June 3, 2010 5:59 PM | Report abuse

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