Meteorological Summer Gets Underway with June's Arrival

May 2018 finished as D.C.’s third warmest May with an average monthly temperature of 72.4°.  It was also the second warmest May on record at Dulles Airport.  Last month was also exceptionally wet.  D.C.’s May rainfall total of 8.73” made last month the sixth wettest on record, while Dulles experienced its third wettest May.  It was only the second time on record, and first since 1953, that May ranked both in the top 10 warmest and top 10 wettest in the Nation’s Capital.

The wet weather pattern that characterized the second half of May is continuing into early June.  June is D.C.’s second wettest month on average, with a monthly average of 3.78”, according to the National Weather Service.  It’s worth pointing out that 13 of the last 20 June’s have been wetter than average in Washington, D.C.

The D.C. Metro Area has seen significant June rainfall from former tropical systems, such as the remnants of Hurricane Agnes in 1972.  Also, a stagnant weather pattern favorable for persistent heavy rain can occur in June because atmospheric steering currents are often weak.  Such was the case on June 25-26, 2006 when a total of 9.41” of rain fell.  That contributed to making June 2006 the wettest June on record with 14.02” of rain in the Nation’s Capital.  By comparison, June 2017 was much drier than average with only 1.13” of rain.

Average high/low temperatures in Washington, D.C. range from 80°/62° on June 1 to 88°/70° on June 30.  D.C.’s hottest observed June temperature occurred relatively recently on June 29, 2012 (104°).  Meanwhile, D.C.’s coolest June temperature on record was on June 2, 1897 (43°).  National Weather Service data reveals that 12 of the last 20 June’s have been warmer than average in Washington, D.C.  That includes the current streak of eight consecutive June’s with above average temperatures.  This follows a 13-year stretch, from 1997 through 2009, when eight June’s were cooler than average in Washington, D.C.

An increased amount of urbanization and development has heightened the urban heat island effect.  That’s helped keep urban and suburban areas warmer than they used to be.  A good illustration of this trend is that Washington, D.C. has either tied or set new record high or record high/low temperatures 26 times in June over the last 20 years.  That’s compared to only two record low/high temperatures with no record low June temperatures during that time in the Nation’s Capital.  Currently, NOAA’s outlook for June 2018 is for warmer and wetter than average conditions in the D.C. Metro Area.