How Unusual Has D.C.’s Weather Been during May 2018 ?

May Rainfall has its benefits

Wetter than average months with lots of rainy days tend to be cooler than average months as well.  Such has been the case more often than not during Washington, D.C.'s ten wettest May’s.  However, that’s exactly what makes this May so unusual in the Nation’s Capital.  Washington, D.C. has had 7.37" of rain since May 1 and that's almost double the May average of 3.99". Meanwhile, D.C’s average May temperature (combining daily high and low temperatures) is 71.4° through May 23 (6.6° above average).

In addition to already being a unique weather month given D.C.’s warm and wet conditions, May 2018 has also featured some very streaky weather.  Ten of the first 11 days of May were warmer than average in Washington, D.C.  That includes four 90° days at National Airport (D.C.'s official weather reporting site).  By comparison, D.C.'s fourth day of 90° heat didn’t occur until June 11 last year.

D.C.'s first measurable rainfall this month didn't occur until May 12.  Washingtonians then had measurable rainfall on nine of the following 11 days with multiple rainfall records set in the process.  However, six of the 11 days from May 12 through May 22 were warmer than average in Washington, D.C. despite the rainy weather. That, combined with the very warm start to the month, has put May 2018 in a strong position to rank among D.C.’s Top Five warmest May’s on record.

According to the National Weather Service, eight of the ten warmest May's in Washington, D.C. were drier than average (the only exceptions were in 1953 and 1975). For example, while May 1953 tied for D.C. wettest, it was also the seventh warmest on record in the Nation's Capital.

A similar pattern exists at Dulles Airport where seven of its ten warmest May’s on record were also drier than average.  Dulles Airport has had 6.5" of rain (above the May average of 4.55") with an average monthly temperature of 68.2° through May 23. That would put May 2018 among the ten wettest and warmest on record at Dulles Airport. 

D.C.’s Wettest May’s on Record (National Airport - "DCA")

1.  10.69" (1953, 1889)
3.  10.66" (2008)
4.  10.60" (1886)
5.   8.87" (1948)
6.   8.05" (2009)
7.   7.77" (1989)
8.   7.06" (2003)
9.   6.99" (1946)
10.  6.97" (1897)
3.99” - Average

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D.C.’s Warmest May’s (DCA - in Degrees Fahrenheit)

1.  73.2° (2015)
2.  73.0° (1991)
3.  71.8° (2004)
4.  71.6° (1944)
5.  71.4° (2012)
6.  70.5° (1880)
7.  70.1° (1953)
8.  70.0° (1911)
9.  69.8° (1959)
10.  69.7° (1975)
66.0° - Average

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Dulles Airport's Top Ten Wettest May’s (IAD)

1.  10.26" (2009, 1988)

3.  9.38" (2008)
4.  8.71" (2003)
5.  8.49" (2017)
6.  8.47" (1971)
7.  7.71" (1989)
8.  7.07" (1996)
9.  6.34" (2014)
10.  6.08" (2016)
4.55” - Average

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Dulles Airport's Top Ten Warmest May’s

69.8° (2004)
69.3° (1991)
68.9° (2015)
68.5° (2012)
67.0° (2010)
66.9° (1965)
66.8° (1982)
66.3° (2011)
66.1° (2007, 1960)

63.2° - Average