How Wet Has 2018 Been in DC ?

A total of 1.51” of rain fell on October 11 due to the combination of a cold front and remnants of Hurricane Michael.  It was the 19^th day since January 1 that the Nation’s Capital got more than an inch of rain.  It was also DC’s first measurable rainfall since September 28 and highest daily rainfall total since September 9 (1.59”).

Washington, D.C. has had a total of 51.55” of rain since January 1.  That’s nearly 12” more than the yearly average of 39.74”.  As of October 15, DC has an annual rainfall surplus of 19.77” of rain.  Making this rainfall total especially impressive is that January and March were each considerably drier than average in the Nation’s Capital.  Washingtonians saw a combined total of only 2.86” of rain in January 2018 and March 2018, less than half of the average total of 6.29”.  

Although February 2018 was wetter than average, it wasn’t until April that the weather pattern took a significant shift in the Nation’s Capital.  For the first time since 2003, Washington, D.C. has had at least six consecutive wetter than average months.  According to NOAA, the months of May, July and September each had more than 8” of rain.  That’s the first time on record that a calendar year has had three such wet months.  Weather records in Washington, D.C. date back to 1871.

July 2018 is another good example of how unique the rainfall has been in the Nation’s Capital. Although the month finished with 9.73”, roughly 55% of that occurred during the two-day period of July 21-22.  In fact, July 21 was one of DC’s wettest July days on record with a daily total of 4” and the month finished as the fourth wettest dating back to 1871. 

September 2018 had the most days with rain (21) in the Nation’s Capital of any month so far this year.  The period from July 15 through September 30 was exceptionally wet with rain on 48 of the 77 days resulting in a total of 24.65”.  It’s hard to imagine that DC had more than 60% of its annual average amount of rainfall in only two and a half months.  It’s also remarkable since the DC Metro Area only saw limited effects from the remnants of Hurricane Florence last month.

Washington, D.C. only needs to have average rainfall during the rest of the year for 2018 to finish among the Top 5 wettest on record.  Making that even more unusual is that 25 of the 32 months from August 2015 to March 2018 were drier than average in Washington, D.C.  The Nation’s Capital accrued a rainfall deficit of 16.42” in that time, but has a rainfall surplus of 21.03” since April 1, 2018. 

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

1.  61.33” (1889)

2.  60.83” (2003)

3.  60.09” (1878)

4.  58.17” (1886)

5.  57.54” (1948)

6.  54.49” (1937)

7.  52.95” (1891)

8.  52.92” (1906)

9.  52.59” (1877)

10.  52.03” (1942)