Warm and Dry Start to Fall

Great Falls, Virginia

The first half of September has been remarkably warm and dry in the DC Metro Area.  All but three days this month have been warmer than average, including two days with record-setting heat.  That makes September 2019 DC’s first since 1991 to have at least two record highs.

Through September 16, DC’s average monthly temperature (combining daily high and low temperatures) is 4.5° warmer than average at 77.9°.  There have also been six days of 90° temperatures so far this month.  DC’s record high temperature of 98° last Wednesday, September 12, was not only the second hottest temperature of the year, but also DC’s hottest September day since 2016.

This month is well-positioned to continue a long-running streak in the Nation’s Capital.  There have been nine consecutive warmer than average September’s here.  DC’s last cooler than average September came in 2009.  That was also the last time Washingtonians didn’t experience any 90° September heat.

The fact September has gotten off to a dry start has been compounded by the fact August was also a very dry month.  With a total of only 2.1” of rain since August 1, DC has a rainfall deficit of 2.85” over the last 6+ weeks.  That’s quite remarkable considering how wet the previous 15 months have been in the Nation’s Capital.  Washington, D.C. had a rainfall surplus of an astounding 33.12” of rain for the 15-month period from April 2018 through July 2019.

Having an extended stretch of drier than average weather in late-summer and early-fall isn’t that uncommon in the Mid-Atlantic Region.  It would only take the remnants of one decaying tropical system to make up the rainfall deficit that’s developed over the last six weeks.  However, since January 1 DC’s annual rainfall surplus has fallen to 2.47”. 

Having a year-to-date rainfall surplus is impressive considering how dry the DC Metro Area has been since August 1.  But it’s nothing like last year.  Through September 16, 2018 the Nation’s Capital had 47.13” of rain and set a new record.  According to NOAA’s Climate Prediction Center, warmer and drier than average conditions are likely to continue through the rest of the month.