An Exceptional Weather Month Comes to a Close

May 2018 will finish as one of the warmest and wettest on record in the Nation’s Capital.  That’s somewhat unusual because months with ten or more rainy days tend to be cooler than average.  This month has had 11 days with measurable rainfall in Washington, D.C. and could finish with 12.

However, Washingtonians didn’t see the first measurable rainfall of the month until May 12.  As fate would have it, May 12 would be the first of eight consecutive days of rain in Washington, D.C.  That was D.C.’s longest streak since measurable rainfall occurred on 15 consecutive days ending May 11, 2016.  A total of 7.41” of rain has occurred so far this month in the Nation’s Capital.  Despite above average rainfall this month, temperatures were above average on 27 of May’s first 30 days in Washington, D.C. 

Washington, D.C. has a monthly average temperature of 72.2° through May 30 and that ranks as the third warmest May on record.  This month got off to a warm start with above average temperatures on ten of the first 11 days of the month.  That included D.C.’s first heat wave of 2018 with high temperatures in the low 90s from May 2 through May 4.  By comparison, Washingtonians didn’t experience the first heat wave of 2017 until June 11 – 14.

Severe weather also occurred in the D.C. Metro Area on May 14.  That was also D.C.’s wettest day of the month with a daily record 1.49” of rain at National Airport.  Aside from May’s warm temperatures and record rainfall, this month’s other major weather headline in the D.C. Metro Area is the flooding that occurred in Ellicott City, MD on May 27.  Many consider this week’s flooding in Ellicott City to be comparable to, if not worse than, the epic July 2016 flooding.  In both cases, the flooding resulted from the combination of a slow moving cluster of thunderstorms that trained, or moved over the same area over and over again, combined with favorable topography for flooding.

If May were to end yesterday, this month would finish as the third warmest and eighth wettest May on record in Washington, D.C.  However, with additional rainfall possible this afternoon, it is possible for this month to become D.C.’s seventh wettest May on record. 

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)
Average: 3.99”

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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)
Average: 66.0°