The Wettest Day in the Nation’s Capital ?

Historic Rainfall in the Mid-Atlantic Region  (Source: NOAA)

Yesterday will go down in the record books as not only the wettest July 21 on record in Washington, D.C., but one of the wettest days for many places in the area.  Widespread rainfall totals of 2” to 6” were common with isolated higher amounts.  National Airport had 4” of rain, Dulles Airport had 5.02” of rain and BWI had 4.79”.

A rare coastal storm, more characteristic of late-fall or winter, brought an all-day rain to much of the Mid-Atlantic rainfall.  In addition to the daily rainfall records that were set yesterday at the three DC Area airports, Dulles Airport also set a monthly record yesterday.  That means July 21, 2018 was not only the wettest July 21 on record, but the wettest July day, overall, at Dulles Airport since it opened in the early 1960s.

The entire week has been very wet in the DC Metro Area.  On July 17, National Airport had a daily record 2.79”, of rain followed by the 4” that occurred yesterday.  Ironically, DC had earlier set a record for driest first half of July.  No measurable rainfall occurred in Washington, D.C. from July 1 through July 16.  Normally, the Nation’s Capital averages 3.73” of rain for the entire month of July.

According to National Weather Service data, Washington, D.C. has never had two July days with at least 2.79” of rain in the same year.  If July were to end today, the 6.79” of rain that’s already fallen would make this the twentieth wettest July on record.  However, with scattered showers and thunderstorms likely during the upcoming week, the Nation’s Capital will no doubt climb higher on the list.

The July 21 rainfall total of 4” made for DC’s fifth wettest July day overall.  Yesterday was also DC’s wettest day since September 30, 2010 (4.66”).  Although weather records in the Nation’s Capital date back to 1871, they have been kept at National Airport since it opened in 1941.  Prior to that, weather measurements were made downtown.  Looking at weather records kept only at National Airport, yesterday was the thirteenth wettest day to occur there. 

Washington, D.C.’s Overall List of Wettest Days on Record (Source: NOAA)

1.  6.39” (August 23, 1933)
2.  6.14” (August 2, 1944)
3.  6.11” (June 21, 1972)
4.  5.97” (August 11, 1928)
5.  5.44” (August 12, 1955)
6.  5.19” (June 25, 2006)
7.  5.16” (September 2, 1922)
8.  4.92” (August 12, 1898)
9.  4.83” (August 20, 1963)
10.  4.76” (September 16, 1976)
11.  4.69” (July 9, 1970)
12.  4.66” (September 30, 2010)
13.  4.49” (September 4, 1939)
14.  4.45” (September 5, 1935)
15.  4.35” (July 22, 1969)
16.  4.25” (July 30, 1878)
17.  4.22” (June 26, 2006)
18.  4.16” (June 22, 1886)
19.  4.15” (September 16, 1874)
20.  4.12” (July 30, 1876)
21.  4.07” (September 14, 1966)
22.  4.03” (August 8, 1942)
23.  4.02” (September 12, 1934)
24.  4.00” (July 21, 2018)