Tuesday, September 1, 2009

DC Summer Temperature Recap

Images (click to enlarge):
- Washington, DC August 2009 daily temperatures vs. average
- June-August 2008-09 monthly temperatures
- 2000-09 90°+ days
- 2009 monthly cooling degree days vs. average
CapitalClimate charts from National Weather Service data, photo © Kevin Ambrose

See here for more Washington, DC weather records.

Sept. 2 Update: Added historical 90° data and chart; added links to previous data; added daily temperature chart.

PM Update: Added cooling degree data and chart.

Although June and July (especially the first half) were both relatively cool, August was by far the warmest of the 3 meteorological summer months, so Washington, DC is closing out the season with only the coolest summer in 5 years. The 2009 summer average of 76.8° is well above the 76° in both 2003 and 2004. Since the summers of 2000 and 2001 were also cooler than this one, 2009 is tied for the median summer temperature of the decade. Unlike last year, when all 3 months were above average, this summer started cool but finished with an August that was not only above the current July, but also above the long-term July average.

There were 2 days with 90° or higher temperatures in June, 7 in July, and 12 in August. The total of 21 was well below the average of 31. This was the lowest number of 90°+ summer days since the 8 recorded in 2004 and 20 in 2003. Other years in the current decade with lower numbers were: 2001 (16) and 2000 (9).

Monthly highs and lows were (normals in parentheses):
June   91 (95) 55 (54)   
July 96 (97) 62 (61)
August 97 (96) 62 (59)
Air conditioning bills were aided by the cool temperatures early in the season. Cooling degree days were as much as 17% below average in July, but the nearly 15% above average amount in August brought the cumulative seasonal total to exactly 4% below average. Monthly degree day totals were:
93 272 378 467

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