DC’s Unofficial Start to Summer

 

Great Falls is a good place to keep cool !

Meteorological summer officially got underway on June 1 and continues through August 31.  This is the first June that average daily high/low temperatures and precipitation will be measured against the National Oceanic and Atmospheric Administration’s (NOAA) new 30-year climate benchmarks for the period of 1991-2020.  This new data set replaces the previous 30-year period of 1981-2010. 

Consequently, there are significant changes as the Nation’s Capital has grown warmer and wetter over that last decade.  Average daily high/low temperatures now range from 81°/63° on June 1 to 89°/71° on June 30.  The previous averages were 80°/62° on June 1 and 88°/70° on June 30. 

Ten of the last 20 June’s have been warmer than average in the Nation’s Capital.  The trend for warmer than average weather over the last decade is in particular led to NOAA’s updated climate statistics.  DC’s warmest June temperature on record remains the sweltering high of 104° on June 29, 2012.

The Nation’s Capital also averages more June rainfall that it did previously.  The new June rainfall average of 4.20” is 0.42” greater than the 1981-2010 average.  Three of DC’s five wettest June’s (2006, 2013 and 2015) have occurred in the last 15 years.  June can also be a dry month as local residents experienced in 2017, when only 1.13” of rainfall occurred.  That made June 2017 DC’s third driest on record.

Although rare, the DC Metro Area can feel the impacts of decaying tropical systems in June.  Longtime Washingtonians may remember the record flooding of June 1972 due to the remnants of former Hurricane Agnes.  June 1972 now ranks as DC’s third wettest.  However, there isn’t anything currently brewing in the tropical Atlantic.

Another key trend in the DC’s Metro Area has been the disproportionate number of record highs in recent decades compared to record lows.  For example, the month of June has had 11 record highs in the last 20 years.  Meanwhile, you have to all the way back to June 22, 1992, for the last time the Nation’s Capital experienced a record low temperature.  A key reason for that is the increasing amount of urbanization and automobile traffic that’s enhanced the urban heat island effect.  The higher volume of traffic has also produced a larger concentration of greenhouse gases, which only serves to help intensify the “greenhouse effect.”  NOAA’s outlook for June 2021 is for warmer and wetter than average conditions in the D.C. Metro Area.