How Wet Has 2020 Been ?

Glen Echo Park, Glen Echo, Maryland

As of December 20, there has been 55.82” of rain in the Nation’s Capital since January 1 giving Washingtonians a rainfall surplus of 17.07”.  If there were no more rain the rest of the year, then 2020 would finish as DC’s seventh wettest year on record.  It was only two years ago that 2018 became DC’s wettest year on record, so two of the last three years will have the distinction of ranking among DC’s rainiest.

Some interesting comparisons can be made between 2018 and 2020.  The Nation’s Capital had a record 24 days in 2018 with at least an inch of rain.  Of those 24, four days had at least 2” of rain and those four accounted for 16.1% of DC’s annual 2018 rainfall.  Of the 24 days, 19 had between 1” and 1.99” of rain.  One of DC’s wettest, overall, days on record occurred on July 21, 2018 when 4” occurred at National Airport.

By comparison, there were 15 days so far this year with at least 1” of rain.  That rainfall accounted for nearly half (47.6%) of DC’s 2020 rainfall total.  While eight days so far this year had between 1” and 1.99” of rain – less than half of DC’s 2018 total of 19 – this year surpassed 2018 on a different rainfall statistic.  There has been a record seven days so far this year with between 2” and 2.99” of rain, compared to only four such days two years ago.  Those seven days this year have accounted for 29.4% of DC’s year-to-date rainfall total of 55.82”.

As in 2018, there were drier than average periods of the year mixed in with the exceptionally rainy periods.  Ironically, 2018 got off to a drier than average start.  For the 32-month period through March 31, 2018, the Nation’s Capital had a combined rainfall deficit of 16.42”.  However, Washingtonians followed that up with a rainfall surplus of 27.8” for the nine-month period from April through December 2018.  Not only did that surplus eliminate the rainfall deficit, but it made 2018 DC’s wettest year on record.

In similar fashion, Washingtonians have a rainfall surplus of 15.22” for the five-month period from July 1 through November 30, 2020.  This surplus, in combination with DC’s wet spell last week, helped push 2020 into the Top 10 for DC’s rainiest years.  That surplus was also more than enough to offset the fact that four of the first six months of 2020 were drier than average.  DC would need another 1.72” of rain in 2020 to reach sixth place on the list of DC’s rainiest years.

Washington, D.C.’s Ten Wettest Years (Source: NOAA)

1.  66.28” (2018)
2.  61.33” (1889)

3.  60.83” (2003)
4.  60.09” (1878)
5.  58.17” (1886)
6.  57.54” (1948)
7.  55.82” (2020)
8.  54.49” (1937)
9.  52.95” (1891)
10.  52.92” (1906)