A July for the Record Books

The first half of July 2018 was the driest on record in Washington, D.C. with no measurable rainfall.  The second half of the month has been the complete opposite and has propelled July 2018 to rank among DC’s Top Five wettest on record.

Since April, May and June were wetter than average in the DC Metro Area, it was quite noticeable how dry the first half of July was.  However, given the above average rainfall during the previous three-month period, no drought conditions developed in the Nation’s Capital.  Fortunately, the record rainfall that occurred on July 17 (2.79” at National Airport) was gone before the Major League Baseball All-Star Game got underway at Nationals Park.

The five-day period from July 21 – July 25 was one of the wettest on record for the DC Metro Area.  A total of 6.4” fell at National Airport, 7.7” at Dulles Airport in Sterling, Virginia and Baltimore, Maryland (BWI Airport) had 11.17” of rain.  By comparison, the National Weather Service says Washington, D.C. averages only 3.73” of rain for the entire month of July.  National Weather Service records in the Nation’s Capital date back to 1871.

The frequent, heavy rainfall had an impact on temperatures during the second half of the month.  High temperatures reached the 90° mark only twice in the Nation’s Capital since July 17.  On the other hand, a total of five days in the last two weeks had high temperatures of 85° or cooler, several degrees below average.  Nevertheless, July 2018’s average monthly temperature will finish almost a full degree warmer than average.  The last cooler than average July in Washington, D.C. was in 2014.

Many of the wettest months on record in Washington, D.C. saw the influence of decaying tropical systems, such as the remnants of Hurricane Agnes in June 1972.  However, none of this month’s heavy rain can be attributed to a current or former tropical system and that makes July 2018 that much more unique.  Absent the widespread heavy rain that commonly occurs with tropical systems, this month’s rainfall has been more localized.  Washington, D.C. had 9.73” of rain so far this month, good for fourth wettest July on record.  Dulles and BWI Airports have also had their wettest July’s with 11.21” and 16.73” of rain, respectively.

Washington, D.C.’s Wettest July's (Source: NOAA)

1.  11.06” (1945)

2.  10.63” (1886)

3.  9.95” (1905)
4.  9.73” (2018)

5.  9.59” (1922)

6.  9.44” (1969)

7.  9.41” (1917)
8.  9.15” (2017)

9.  8.40” (1891)

10.  8.37” (1878)