Much Needed Rainfall

Latest Drought Conditions  (Source: U.S. Drought Monitor Index)

Washingtonians are finally seeing appreciable rainfall today.  Widespread rainfall totals of 0.5” to 1”/+ are likely.  That’s impressive since the last time DC had at least 0.5” of rain was over two months ago on August 7 (0.9”). 

Although July 2019 finished with an above average monthly total of 6.49”, the bulk of that occurred during the first half of the month on July 8 when a daily record 3.44” occurred.  But, for the three-month period from July 15 through October 15, Washington, D.C. had a rainfall total of only 3.05”.  That’s more than 7” less than the average of 10.19” of rain for that three-month period in the Nation’s Capital.  

Having such a high rainfall deficit in conjunction with above average temperatures for late-summer and early-fall have combined to produce moderate drought conditions for much of the Mid-Atlantic Region.  There have been other instances in recent decades where a very dry late-summer and early-fall have produced similar drought conditions.  For example, the six-month period of July 1998 – December 1998 saw a combined rainfall total of only 7.45” in the Nation’s Capital (12.55” below normal).  That caused 1998 to finish as a drier than average year in the Washington, D.C.

The two-year period of 2001-2002 produced a combined total of 64.28” of rain in Washington, D.C.  That’s 15.2” below average and led to drought conditions in parts of the DC Metro Area by the summer of 2002.  Fortunately for DC Area residents, the drought conditions were short-lived as the last three months of 2002 were wetter than average.  Similarly, 2012 was also an exceptionally hot and dry year with 10 months that were drier than average.

The Nation’s Capital has a history of going through stretches that can be significantly wetter or drier than average.  For example, the 32-month period from August 2015 through March 2018 DC had a combined rainfall deficit of 16.42”.  That was followed by a wetter than average 15-month stretch through July 2019, when DC had a rainfall surplus of 33.12”.  Although today’s rainfall won’t completely make up the deficit that’s developed over the last three months, it will provide some short-term relief.

DC’s Ten Wettest October Days (Source: National Weather Service)

1.  3.98” – October 4, 1877
2.  3.85” – October 29, 2012
3.  3.67” – October 8, 2005
4.  3.63” – October 7, 2005
5.  3.36” – October 14, 1995
6.  3.31” – October 23, 1878
7.  3.27” – October 14, 1953
8.  3.12” – October 25, 1872
9.  3.11” – October 23, 1890
10.  2.97” – October 20, 1910

DC’s Ten Driest October’s (Source: NWS)

1.  Trace – 1963
2.  0.02” – 2000
3.  0.28” – 1930
4.  0.29” – 1874
5.  0.34” – 1892, 1896
7.  0.40” – 1920
8.  0.44” – 1924
9.  0.53” – 1882
10.  0.59” – 1998