Putting a Dent in DC’s Rainfall Deficit

Warmer than Average weather Expect in August 2017  Source: NOAA

Washingtonians are on the verge of reaching a significant milestone as we enter the final week of this month.  August 1 will be the second anniversary of what has been a very warm and dry period in the Nation’s Capital.  As of this past Friday, Washington, D.C.’s rainfall deficit had swelled to 14.3” dating back to August 1, 2015.  That shortfall represents about one-third of the 39.74” of rain that DC averages in an entire year.

Prior to this month, only four months have been wetter than average in Washington, D.C. during the last two years.  In that time, the Nation’s Capital has set multiple record high and record high-low temperatures that contributed to the warmest December on record (2015) and a series of months finishing among the warmest on record.  Washingtonians also experienced the first 100° temperature in four years last summer, including a rare streak of three consecutive 100° days.  

The warmer than average temperatures combined with the below average rainfall contributed to moderate drought conditions for parts of the Mid-Atlantic Region earlier this year.  Fortunately, a wetter than average second half of April and month of May eliminated the drought conditions, but not the rainfall deficit.  This month has featured several days with significant rainfall in the DC Metro Area that have ensured this month will finish as only the fifth wetter than average month in the last two years.

July has also been a warmer than average month in the Nation’s Capital with 18 of the 22 days so far this month in the 90s.  High temperatures today and tomorrow are expected to reach the 90s, with several more chances during the upcoming week to pad that total.  The record for highest number of 90° days in Washington, D.C. during the month of July is 25 from 2011.  By comparison, following a cooler than average start, July 2016 finished with 23 of its 27 final days at 90°/+.  

There are several more rain chances the next few days that could provide some relief from the heat and make a dent in the ongoing rainfall deficit.  However, it will take several consecutive wetter than average months to make up the deficit entirely.  NOAA’s Climate Prediction Center is expecting near average precipitation for the Mid-Atlantic Region in August 2017.