Tropical Downpours in the Nation’s Capital

 

Photo Credit: Robin Beal

The National Oceanic and Atmospheric Administration (NOAA) recently updated its running 30-year average temperature and precipitation totals for the United States.  The 30-year period of 1991-2020 was appreciably warmer and wetter than the previous 1981-2010 period in the Nation’s Capital.  That’s no more apparent than during the month of July.

Previously, July was DC’s third wettest month of the year with an average of 3.73” of rain.  However, things changed dramatically with the updated climate statistics that saw the decade of the 2010s replace the 1980s.  July is now the wettest month of the year in the Nation’s Capital with a new monthly rainfall average of 4.33” – 0.6” greater than the previous average.  If you look at how rainy the last few July’s have been in the D.C. Metro Area, it’s easy to see why there was such a significant increase in the new average.

2020:  The monthly rainfall total of 6.51” was above average.  What made this July significant was that 3.93” or 60% of the monthly rainfall occurred on just two days.  A daily rainfall record of 2.04” occurred on July 7, while another 1.89” fell on July 23.  

2019:  July got off to a wet start two years ago with measurable rainfall on five of its first eight days.  The signature rainfall event occurred on July 8 when a daily rainfall record of 3.44” occurred at National Airport.  That accounted for more than half of DC’s monthly total of 6.49”.  Most of that rain fell in less than two hours, snarling the morning commute across the D.C. Metro Region.

2018:  An astounding 4” of rain fell at National Airport on July 21.  Not only was it a new daily record, but was the wettest day in the Nation’s Capital since September 30, 2010.  Although there was no measurable rain prior to July 17, 8.52” of rain fell during the eight-day period from July 17 – July 24.  It finished among DC’s Top 5 wettest July’s with 9.73”.

2017:  This July finished with 9.15” of rain making it DC’s wettest since 1969.  During an eight-day period from July 22 – July 29, a total of 6.15” of rain fell that accounted for a little more than two-thirds of DC’s monthly total.  The wettest day of the month occurred on July 28 when a daily record 3.31” of rain was observed at National Airport.