The Unofficial Start of Summer

NOAA's Temperature Outlook for June 2020

Although astronomical summer doesn’t get underway until the summer solstice later this month, meteorological summer began yesterday.  “Meteorological summer” runs from June 1 through August 31.  Following a cooler than average April and May in the Nation’s Capital, many are eager for warmer weather.  They’ll get their wish as high temperatures will reach 90°/+ for the first time of the year tomorrow.

Average temperatures rise in the Nation’s Capital throughout the month of June from a high/low of 80°/62° on June 1 to 88°/70° by the end of the month.  June has the third highest average monthly temperature (combining daily high/low temperatures) of the year in the DC Metro area, behind only July and August.  Since 2000, 14 of the last 20 June’s have been warmer than average in Washington, D.C., including the last 10.  DC’s hottest June temperature on record of 104° occurred relatively recently on June 29, 2012.  By comparison, DC’s coolest June temperature of 43° occurred more than 120 years ago on June 2, 1897.  Meanwhile, the earliest Washingtonians have experienced triple-digit heat was when it reached 100° on June 5, 1925.

June has been a rainy month more often than not over the last two decades with 13 of the last 20 being wetter than average.  That’s saying something since June is DC’s second wettest month of the year, with a rainfall average of 3.73”, behind only May’s 3.99”.  Several of DC’s 10 wettest June’s have also been warmer than average.  Such was the case in 2013 and 2015.  Both years ranked among DC’s Top 5 rainiest, while being warmer than average.  June 2015 also happened to be DC’s sixth warmest June. 

It’s also significant that six of DC’s 10 warmest June’s have occurred since 2008, while three of DC’s wettest June’s have occurred since 2006.  Although rare, the DC Metro Area can feel the impacts of decaying tropical systems.  Longtime Washingtonians may remember the record flooding of June 1972 from the remnants of Hurricane Agnes.  That was DC’s wettest June until 2006 and has since fallen to third place. 

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 has been the increasing amount of urbanization and automobile traffic that’s enhanced the urban heat island effect.  NOAA expects June 2020 to again be warmer and drier than average.