2011 DC Astronomical Summer Temperatures

[RodneyS]

There was an interesting contrast between overall average and average maximum temperatures for this year's astronomical summer,* and an even more interesting contrast between the first 54 days of summer and the last 41 days. The 2011 DC overall average daily summer temperature was 79.2 degrees, which placed this year third over the 140-year period of record, behind only 1980 (81.7) and 2010 (80.5). However, the average maximum daily summer temperature was 87.5, which placed 2011 only 17th on that basis. Using average daily maximums, 1980 is still the hottest (90.9) and 2010 is still second (89.7), but a whole slew of other years, including 1930 (third, at 89.3) beat out 2011.

The most striking thing about 2011 DC astronomical summer temperatures was the contrast between June 21-August 10 and August 11-September 23. During June 21-August 10, temperatures were the hottest in DC history almost any way you measure it (average maximum of 92.4 compared with 92.2 in 2010, 92.0 in 1980, and 92.1 in 1930; average minimum of 74.6 compared with 73.71 in 2010, 73.69 in 1980, and 69.6 in 1930; and overall average of 83.5 compared with 82.94 in 2010, 82.85 in 1980, and 80.8 in 1930). During August 11-September 23, however, temperatures were actually slightly below the historical average with respect to maximums (average maximum of 81.7 compared with 82.3 during 1872-2010 inclusive, 86.8 in 2010, 89.7 in 1980, and 86.0 in 1930; average minimum of 66.9 compared with 64.9 during 1872-2010 inclusive, 68.3 in 2010, 71.2 in 1980, and 64.7 in 1930; and overall average of 74.3 compared with 73.6 during 1872-2010 inclusive, 77.6 in 2010, 80.4 in 1980, and 75.3 in 1930).

*As I'm sure most everyone here knows, astronomical seasonal periods vary slightly from year to year. This year, the Northern Hemisphere summer (Southern Hemisphere winter) began at 1:16 P.M. EDT on June 21st and ended at 5:05 A.M. EDT on September 23rd. For consistency in making year-to-year comparisons, I am using for each year the 95 days between June 21-September 23 inclusive, even though the Northern Hemisphere summer is actually only about 93.7 days.