July 8 Update: Added month-to-date chart. Today's cool high of 81° and low of 66° keeps the monthly average so far essentially unchanged at 73.4°.
Images (click to enlarge): July 2009 month-to-date average temperature vs. monthly normal and records; top 10 coolest, long-term normal, and warmest July average temperatures in Washington, DC; CapitalClimate charts from National Weather Service data
With a daily high matching the long-term normal of 88°, Washington DC is closing out a very cool first week of July. The monthly average so far of 73.5°, if continued through the month, would put this July firmly in the top 10 coolest. The current average is just 0.1° ahead of the third place holder, 1888. The coolest July of this century has been the one in 2000; at an average of 74.7°, it's tied with 1909 for tenth place, ahead of all but 2 other years in the 20th Century, 1904 and 1918, both at 74.4°.
The long-term normal for July is 80°, and the warmest ever recorded was 83.1° in 1993.
The Bottleneck Years by H.E. Taylor – Chapter 70
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