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Posted at 10:45 AM ET, 06/23/2010

Relentless heat threatens D.C.'s June record

By Ian Livingston

Why us? Does it mean anything for the rest of summer?

* How long is it going to stay this hot? Full Forecast | NatCast *

June temperature departures across the D.C. area range from 4 to 6 degrees above average. Image as of June 21, 2010. Courtesy: High Plains Regional Climate Center.

Six months ago we commenced what became our snowiest winter in recorded history with our snowiest December ever. While the regular calendar indicates summer has just begun, D.C. has already suffered through (counting today's certain addition) 17 days of 90-degrees or higher since the first instance in April, and 12 this month alone. Our summer outlook called for a hot and dry one, but it's fair to say that June has performed above (or below depending on your perspective) most -- or all -- expectations.

There are at least several ways of examining both this month's heat and the heat we have seen for the entirety of 2010 thus far. The metrics examined here will largely pertain to June's heat in the context of meteorological summer.

Keep reading for more on June heat and how it may or may not correlate to a hot summer. Let us know how this summer ranks in your book thus far.

June 2010 upper-level height anomalies (through the 20th) show above average heights centered over the south-central U.S. Much of the nation has seen warm temperatures this month. Source: NOAA Physical Sciences Division Daily Mean Composites.

What's to blame for this June heat? The yellowish blob over the south-central U.S. to the right has a lot to do with it. It is an anomalous upper-level high pressure area that has been centered (shifting east or west during shorter time periods) over the southern-tier of the country for much of the month - pumping warm air to the north and east. This has lead to widespread heat across a good portion of the nation.

Dallas, Tx., is currently about 6 degrees above normal for June and has seen 90-degree or greater high temperatures on all but two days this month, including numerous upper 90s and several 100-degree days. Other locales in the Midwest and Ohio Valley, like Paducah, Ky. and Dayton, Oh., are also experiencing positive temperature departures from 3 to 6 degrees above normal.

One relatively cooler region has been north of here into New England. The monthly departure in New York City is only around 2 degrees above average, and parts of Maine are witnessing slight negative departures.

Top-10 Warmest June's on Record in D.C.
D.C. 2010 thru June 21: 79.0 +5.5. (compared to mtd average)
Dulles thru June 21: 75.2 +5.4. (Hottest: 76.1 in 1994)
Baltimore-Washington thru June 21: 77.0 +6.2. (Hottest: 79.8 in 1943)

In the 139 June's since records began in 1871 and running through last year, the monthly range for average temperature at D.C. spans from a record low of 65.9°F in 1907 (8.6°F below average) to a record high of 79.4°F in 1994 (4.9° above average) . The record high June temperature from 1994 was about equivalent to an average July in the city. In recent history (from 2000-2009) about 22% of the 90°F+ days have occurred during June with 39 percent in July and August, respectively.

Top 10 year-to-date years with days at or above 90-degrees at D.C. *As of June 23 (assuming today is 90°F+ prior to it happening).

1943 stands out as the year with the most 90°F+ days in June with 18. The runner up is 1994 when 17 were observed. Washington also saw its greatest streak of 90-degrees or higher in 1994 when the area was treated to 14 days of such heat in a row. During that stretch, the highest temperature recorded at National was 101°F (1-degree shy of the all-time June record set on June 9, 1874). With raw daytime heat like that, there is little wonder June 1994 is currently the warmest on average!

Our 12 days (including today) at-or-above 90°F this June puts us on pace to finish with about 16 to 17, unless we get unlucky and it rolls through the month uninterrupted. 13 90°F+ June days would put this year in the top 10 (tied) while 14 brings it into top 5 (tied).

When we add our 90°F+ days from April and May into the mix, the stats are even more impressive. Year-to-date 90+ numbers have us running at number #2 (tied) all-time as of yesterday. Record astronomical springtime warmth records (spanning March 20 to June 20) at D.C. and Dulles have surely carried over to the beginning of summer (June 21).

Because monthly records are measured in averages, the 90°F+ day category may not be as truly meaningful as it is a quick and simple metric for "hot" days in general. To the state the obvious, a 90-degree day does not equate to a 102-degree day but they are both treated the same on such a scale.

Despite the plethora of 90°F+ day, we have yet to record a 100-degree day. There have been 15 such days in the history of the month.

A big story this year, in addition to the persistence of the heat, is the anomalously warm low temperatures and their role in the average temperature day-to-day.

Since the 1940s, when temperatures began being recorded at National, the record high average monthly minimum temperature is 70.3°F set in 1981. Number two and three in this time frame are 1989 and 1994, with 68.9°F and 68.7°F respectively.

As of yesterday, this June is averaging right around the National record of 70.3°F for its monthly low temperature. Considering that all but three days this month have had positive temperature departures compared to average, with many of those being near-and-past double digits (potentially including today and tomorrow), it seems likely this record will be tested or broken.

Scatter plot and linear best-fit line comparing June average temperature and summer average temperature.

When analyzing June temperature averages (1871-2009) against the resulting overall summer temperature averages, there is a fair amount of spread, but the trend does seem to indicate that a warm June has a decent chance of portending a warmer than normal summer (average temperature 77 for June-August).

Also of note in the graph above, the coolest June on record led to the coolest summer on record. However, the warmest summer on record (1980) had a relatively "average" June with a departure of +.3 degrees, ranking it number 42 all time. 1980s heat was not evident at this point in the year on the 90-degree day scale either.

Looking forward: When plugging in readings from moderately reliable temperature guidance (00UTC GFS MOS from June 23) for the rest of the month, an average temperature right around 80F seems very possible (which would be a new record), though it could come down to the wire. This "prediction" immediately assumes today and tomorrow are way above average, which is quite likely if not a given. Much of the period after may end up at or above 90. But it seems as if Friday could fail to surpass the upper 80s and that we may see at least a short-lived break in the heat as the month finishes. Being cautious, plugging in significantly below average day on the 30th following a near-average day on the 29th still yields a record breaking temperature for the month for D.C.

By Ian Livingston  | June 23, 2010; 10:45 AM ET
Categories:  Extreme Heat, Local Climate  
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Next: PM Update: Steamy heat enjoying local stay


In Seattle we have yet to hit 75 degrees this spring/summer a new record. Last time it was 75 was in September. We are used to moderate temperatures in the Pac NW, but this is pretty brutal.

This comes after one of the warmest winters on record. The atmosphere really reversed itself in March/April.

Posted by: where_is_snowmonster | June 23, 2010 11:04 AM | Report abuse

It sure been a hard, hard winter
My feet been draggin' 'cross the ground
And I hope it's gonna be a long, hot summer
And the light of love will be burnin' bright

Posted by: blasmaic | June 23, 2010 11:24 AM | Report abuse

"How long will it stay this hot?"
As a long time metro area resident I can answer that question.
The answer is "September".

Posted by: FIREDRAGON47 | June 23, 2010 11:45 AM | Report abuse

The word hot usually goes with summer. Its in the 90s at least one day every summer in DC, even when its in the 80s people complain.

LMAO at all these charts to show that its hot in the summertime in DC and its always been hot.

Posted by: Redial1 | June 23, 2010 12:08 PM | Report abuse

What? Only 2 of the 10 hottest Junes have been since 1994? But what about global warming and warmest decade ever?

Oh, never mind...East Anglia.

Posted by: silencedogoodreturns | June 23, 2010 12:20 PM | Report abuse

So to summarize your post: It will be one hot and long summer? Just because June usually sets the precedent for the rest of the summer-- ("a warm June has a decent chance of portending a warmer than normal summer").

Can you put out a blurb for the numbers of 90+ days in July and August? I want to mentally prepare myself for one long and hot summer...

(And I have to be honest-- yes it is hot today, but it is not oppressive. It is just like walking around in desert *in California*-- the usual humidity is slightly low, to my relief, so I don't get it when people are complaining about the hot days. At least, just wait until August to get what a "hot day" really means.)

Posted by: SanDieganLostinDC | June 23, 2010 12:35 PM | Report abuse

Considering we had only 22 90+ days all last year and we are approaching that number already and it's ONLY June, it's not a stretch to expect a much "hotter" summer this year, probably "hotter" than most I can remember in the last decade.

For the record, the hottest period temperature wise for most Northern Hemisphere locations is mid to late July, not August. August being the warmest month is a common misconception, albeit a slight one.

Posted by: LoudounGeek | June 23, 2010 1:38 PM | Report abuse

I just feel the need to point out that the dewpoint here in my new home of southern Indiana is 80 degrees right now. 80 DEGREES. And the temps are only 3 degrees lower than yours right now.

When I moved, I never thought I would find myself envying DC's dewpoint.

Also, I miss you CWG!

Posted by: LaurainNWDC | June 23, 2010 1:51 PM | Report abuse

I am in Alexandria, VA and our building just swayed back and forth. I can't find anything online, but are there any reports of small tremors/earthquakes in the area?

Posted by: sara5209 | June 23, 2010 1:55 PM | Report abuse

I hope you excluded June temperatures from your Summer Average Temperatures on the Y-axis above-- otherwise, you have an endogeneity problem.

Posted by: MB_202 | June 23, 2010 1:58 PM | Report abuse

Sara - I just read about an earthquake in Canada that shook up New England.. maybe you felt that?

Posted by: CuseFan07 | June 23, 2010 2:50 PM | Report abuse


Got an e-mail a little while ago from a friend who lives in Cleveland. She said they'd just had an small earthquake out there - supposedly 5.5, centered in Ontario/Quebec.

I didn't feel a thing here in Lake Ridge, and the cat (my best weather barometer) didn't start acting weird.

Posted by: meta2 | June 23, 2010 2:55 PM | Report abuse

Speaking of heat, is forecasting a high of 107(!) tomorrow for Williamsburg VA, followed by three more days of 100+ degrees. That's considerably higher than the NWS forecast.

CWG - curious as to the reason behind such an aggressive forecast...the Burg's all-time high is 104, I believe.

Posted by: McLean76 | June 23, 2010 3:59 PM | Report abuse

CuseFan07, thanks for the link. I love sweet New England, where I spent a happy decade so hope I can share without offense that it uncannily recalls a 70s parody of the Boston Globe, wherein the front page headline blares: "Bostonians Missing, feared dead in New York City" Only deep into the [phony] report, do you learn the Soviets have nuked NYC. Anyway, I trust no Canadians were injured :)

Regarding earthquakes here in NoVa, we had one centered in Fairfax County, only a few years ago, which we heard rather than felt. Owing to the kind of quake it was, it sounded like a sonic boom. Sound doesn't travel far, so it makes, however that a quake from a distance would be felt as Sara felt.

Posted by: jhbyer | June 23, 2010 4:23 PM | Report abuse

I'm no fan of the hot weather. But I'm even more concerned about the lack of rain. What are the prospects for some moisture, other than scattered thundershowers?

Posted by: ah___ | June 23, 2010 5:19 PM | Report abuse

In reply to silencedogoodreturns: If there is one thing the climate change denial crowd really excels at, it's grasping at straws. Oh, and also non sequiturs.

Posted by: fall_line | June 23, 2010 11:12 PM | Report abuse

Alright, so the yellow blob is the reason for the hottest June on record. How long is that thing going to hover us? I'd like the blue one back if you don't mind.

Posted by: RedCherokee | June 24, 2010 5:16 AM | Report abuse

SanDieganLostinDC, sorry for delay in response. I was not around much yesterday. I can put together some info on July and Aug and perhaps put it in a PM Update soon.

Posted by: Ian-CapitalWeatherGang | June 24, 2010 10:08 AM | Report abuse

I really would like just a normal year... something boring would be nice for a change.

Posted by: nlcaldwell | June 24, 2010 5:24 PM | Report abuse

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