Hazy, Hot and Humid

Although the average high for August 18 has cooled slightly to 87 degrees at National Airport, mid-August can still be quite hot.  On this date in 1995, Washington, D.C., set a record high of 97 degrees.   Like the summers of 2010-2012 that I wrote about recently, 1995 also featured an unusually hot summer (including a stretch of 25 consecutive days without measureable precipitation).

The 97 degree record high set 19 years ago today would stand for seven years until 2002, when the high climbed to a sultry 98 degrees.   Washingtonians experienced a rather unique occurrence in 2002 when August was hotter than July.  The average monthly temperature – combining daytime highs with nighttime lows - for August 2002 was 90.4 degrees, while it was “only” 89.7 degrees for July.  Also, August 2002 featured two days with triple digit heat (the first triple digit heat in the Nation’s Capital since July 1999).

The summers of 1995, 2002 and 2010-2012 saw a strong ridge of high pressure situated off the Southeast coast of the United States.  This high pressure ridge helped limit rainfall while pumping up the heat and humidity for the Mid-Atlantic Region.  However, the summers of 2013 and 2014 have not seen the same record heat and prolonged dry weather. 

In fact, the Mid-Atlantic Region had only 10 days of 90 degrees or hotter weather since July.  By comparison, from July 1 through August 18, 2010, Washington, D.C. (as measured at National Airport) observed 30 days of 90 degree or hotter high temperatures.  That helps illustrate the extreme variability in weather patterns in the Nation’s Capital – and makes forecasting the weather here challenging and exciting.