What’s On Tap in May ?

D.C. residents experienced something last month that had not occurred in more than a decade.  April 2018 finished with an average temperature of 54.9° (1.9° cooler than average) and 3.59” of rain (0.53” above average).  Most of that rain (2.01”) occurred on April 15-16, which was D.C.’s highest two-day April rainfall total since April 29-30, 2014 (3.91”).  It was also the third cooler than average and second wetter than average month of the year in Washington, D.C.

May 2018 has gotten underway with significantly above average temperatures in the D.C. Metro Area.  However, the warmth of spring is usually without the sultry conditions so common in the Mid-Atlantic Region during the summer months.  For that reason, many people consider May to be the finest weather month of the year in the Nation’s Capital.  Average high and low temperatures in Washington, D.C. range from 71°/52° on May 1 to 80°/61° on May 31.

D.C.’s warmest May temperature on record is 99°, which occurred on May 31, 1991.  In fact, the daily record highs for the entire month of May are in the 90s, with today being the one exception.  Some record highs may be challenged this week, especially at Dulles Airport, with high temperatures approaching the 90° plateau.  Since 1993, the Nation’s Capital averages one to two days of 90° heat in May.  The D.C. Metro Area has had 90°-heat in seven of the last 10 May’s.

The coolest May temperature on record in Washington, D.C. is 33°, which occurred on May 11, 1906.  Weather records in the Nation’s Capital date back to 1871, and they have been kept at National Airport since it opened in 1941.  The coolest May temperature that occurred at National Airport is 35°, which occurred on May 2, 1945.  It’s not surprising that record high temperatures have become much more common than record low temperatures in recent decades as urbanization has increased dramatically.  That’s had the effect of enhancing the urban heat island effect.  Over the last 20 years, Washington, D.C. has either set or tied 18 record high temperatures during the month of May, compared to only four record low temperatures.

May is the third and final month of meteorological spring.  It is also the wettest month of the year in the Nation’s Capital with a monthly average of 3.99” of rain.  It’s important to start the summer months with a sufficient amount of rain and soil moisture.  In that way, local gardeners and farmers can endure the hot and sometimes dry conditions of summer without difficulty.  The last two May’s have been wetter than average in Washington, D.C.  

Record High / Record Low High Temperatures
* = also occurred in previous years

May 2:

Washington, D.C., National Airport (DCA): 89° (1930) / 71° (2010)
Dulles Airport, Sterling, VA (IAD): 88° (2010)* / 70° (2010)
Baltimore, MD (BWI Airport): 88° (1951)* / 72° (2010)

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May 3:

Washington, D.C., National Airport (DCA): 91° (1965) / 70° (2010)
Dulles Airport, Sterling, VA (IAD): 92° (1965) / 67° (2010)
Baltimore, MD (BWI Airport): 91° (1913) / 69° (2010)

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May 4:

Washington, D.C., National Airport (DCA): 93° (1928) / 68° (1942)
Dulles Airport, Sterling, VA (IAD): 90° (2001) / 60° (2012)
Baltimore, MD (BWI Airport): 90° (2001) / 71° (1942)