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Posted at 01:33 PM ET, 07/09/2012

Historic heat wave in hindsight: Hottest on record in Washington D.C., hotter than 1930


Hottest 11-day stretches in D.C. using daily maximum temperatures

Mercifully, Washington, D.C.’s 11-day heat wave is over. We’ve crunched the numbers - and by almost every measure - it ranks as the most intense in 141 years of records.

Let’s first consider all of the records established at Reagan National Airport - the official observing station in Washington, D.C. during the heat wave which spanned June 28 and July 8:


Most consecutive days of 95 or higher by year in Washington, D.C. (Ian Livingston)
* Hottest June day of 104 on June 29

* Longest stretch of highs at or above 95 of 11 days

* Most consecutive days over 100: 4 (tie with 1930)

* All-time hottest daily average temperature of 94 on July 7 (high of 105, low of 82)

* Record daily high of 105 on July 7; tied for second hottest high temperature all-time and among D.C.’s top 5 hottest days (2 days at 106, 3 days at 105)

* Record daily high minimum temperature of 82 on July 7

* Longest period at or above 100 of 7 hours on July 7 (tie with July 6, 2010 and July 21, 1930)

* Record daily high of 102 on July 8

* Record daily high low temperature of 79 tied on July 2

Was 1930 hotter?

Questions have swirled about how this year’s heat wave stacks up to 1930 which had its own suffocating stretch of sweltering temperatures. If you compared the two together as they evolved, they were neck and neck, but 2012 won the race with a strong finish.


(Ian Livingston)
The average high from June 28 through July 8, 2012 was an astounding 99.5 degrees, besting 1930’s most brutal 11-day stretch (the first big heat wave was 12 days long with a 95 to start) by 0.5 degrees.

When considering the average temperature (incorporating low temperatures as well as highs) for these segments of both years, 2012’s lead grows due to warmer overnight temperatures. 2012 finished with an average temperature of 88.0 degrees compared to 1930’s 87.0 over the 11 days.

Comparison of 2012 versus 2011

Examining the top-10 hottest 11-day stretches (see table at top of post), for only high temperatures, the span from July 22 through August 1 of last year (2011) also emerges near the top. It ranks third, with an average high of 97.9 degrees.

And it turns out, 2011’s 11-day stretch of horrid weather actually tops 2012 and 1930 by a full degree when analyzing the average (factoring both highs and lows) temperature, due to its extraordinarily warm nights.

Tracking 100+ degree days

The incredible 5 100-degree or higher temperatures during this year’s heat wave already puts 2012 in a tie for 4th when it comes to annual tallies of this metric. It’s also the earliest we’ve reached that mark, besting 1930 by over two weeks.


100-degree days by year. 2012 so far has 5 with more than half of summer remaining. (Ian Livingston)

Also note: we’ve already had two “top tier” 100+ days at 104 or higher (104 on June 29, and 105 on July 7). Only two other years have accomplished this feat-- 1918 and 1936. None have had more.

Thanks to this most recent spurt of 100-degree readings, the last three years now have a combined 14 days 100+, which outranks any other three-year stretch on record, including the one encompassing 1930 when all 11 occurred that same year.

Broader context

This most recent heat wave piles on numerous heat records to an eye-opening flurry of heat records established since 2010 in Washington, D.C.

Not to mention, NOAA’s National Climatic Data Center released the graphic below, showing the first six months of 2012 ranked warmest on record in Washington, D.C. by a wide margin (dating back to 1946, at least).


Temperature in Washington, D.C. in 2012 (red line) compared to other top 5 warm years (lighter red lines), top 5 cold years (blue lines) and all other years (gray lines). View big. (NOAA)
As discussed Friday, attributing changes in local temperatures and local temperature extremes to global warming is difficult and gets messy. But the more these kind of heat records are established, the less statistically likely they are happening due to chance alone.

Caveat

Comparison of modern Washington, D.C. temperature data from Reagan National Airport with data prior to the 1940s - when temperatures were measured near Georgetown - is complicated. The two observing stations have different environments and both areas experienced population growth and urbanization over time.

Due to the effect of urbanization and the station move to Reagan National (a somewhat warmer, lower elevation location), it’s likely somewhat “easier” to set warm records now versus earlier decades - especially for low temperatures. Thus, the 1930 and 2012 comparison above is not exactly apples to apples

By and  |  01:33 PM ET, 07/09/2012

Categories:  Latest, Local Climate, Extreme Heat

 
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