A Record Setting August

1600 Pennsylvania Avenue, NW., Washington, D.C.

July’s heat has continued in the Nation’s Capital for much of August and that’s broken a variety of records.  We’ve seen the first August stretch of three consecutive days at/above 100 degrees since 1930.  Potentially, August’s number of 90 degree days will set record.

Through August 29, there have been 21 days at or above 90 degrees in Washington, D.C (measured at National Airport or DCA).   With high temperatures expected today and tomorrow around 90 degrees, there is a distinct possibility that the Nation’s Capital could break the record.  National Weather Service data indicates the existing record for highest number of August days at/above 90 degrees in Washington, D.C. is 22 from 1980.

August 1980 was also the hottest August on record in the Nation’s Capital with a monthly average temperature (combining daily high and low temperatures) of 82.8 degrees.  Through August 29, this month’s average temperature is 82.8 degrees.  Even if Washingtonians don’t set a new overall record, this month is all but assured of a second place finish for warmest August.  To date, Washington, D.C. has had 49 days at/above 90 degrees in 2016 – above the annual average of 36 days.  In fact, the Nation’s Capital is approaching the total of 52 days at/above 90 degree days that occurred during all of 2015.

What separates 2015 and 2016, though, is the frequency of the heat.  Through July 4, 2015 a total of 19 days at/above 90 degrees occurred in Washington, D.C., while only five such days occurred through the same period this year.  Washingtonians have had high temperatures of 90 degrees or hotter on 44 of the last 56 days since July 5.  Of those 44 days at/above 90 degrees, 17 were at least 95 degrees – including four days of triple-digit heat.  

The increased amount of urbanization in the Mid-Atlantic Region in recent decades has contributed to warmer overnight temperatures as well.  According to the Capital Climate blog, Washington, D.C. experienced 79 consecutive days and counting of low temperatures of at 64 degrees or higher since June 11.  This month’s average high temperature through August 29 is 91.8 degrees.  According to the National Weather Service, that would put August 2016’s average high narrowly behind the August’s 1980 record of 92 degrees.

The increased urbanization in the Washington, D.C. area includes downtown and the entire corridor to Dulles Airport, which is significantly more developed than it was in 1980.  The higher concentration of atmospheric pollution and greenhouse gases from the increased development has also contributed to the higher number of warmer than average days and nights.  As a result, if you include this summer, four of the warmest summers on record have occurred since 2010.

Warmest Augusts (Combined Average Daily Highs/Lows, Degrees Fahrenheit at DCA – Source: NWS)

1.  82.8 (1980), 82.8 (2016 – through 8/29)

3.  81.3 (1995), (1978)

5.  81.1 (2002)
6.  81.0 (2012, 1983)
8.  80.7 (1988)
9.  80.6 (2006)
10.  80.3 (1959)

Most 90-degree August Days (Washington, D.C. – Source: NWS)

1.  22 (1980)
2.  21 (1943), (2016 through 8/29)
4.  20 (1988, 1983)
6.  19 (2002, 1995, 1966)
9.  18 (1900)
10.  17 (1968, 1872)