D.C.’s Warm and Dry September

 

Lake Needwood, Derwood, Maryland

Residents of the D.C. Metro Area are in the midst of a prolonged stretch of mostly sunny and stellar fall-like weather.  That follows a recent period of wet weather in the Nation’s Capital that’s becoming an increasingly distant memory.  Washington, D.C. had an official total of 1.90” of rain between September 5 and September 12, with higher totals further north and west of town (e.g., 2.78” at Dulles Airport).

Washington, D.C. averages 3.93” of rain for the entire month of September.  Last year, NOAA updated the temperature and precipitation averages for the United States.  NOAA’s weather “averages” through 2020 were based on the 30-year average for the period of 1981 – 2010.  However, they now reflect the period of 1991 – 2020.   

The updated weather averages in the Nation’s Capital are generally warmer and wetter because the 2010’s were a largely warmer and wetter decade than the 1980s.  Consequently, D.C.’s September rainfall average is wetter than it used to be (3.72”) in the old data set through 2010.  The Nation’s Capital felt the impacts of former tropical systems in September 2011 (Tropical Storm Lee) and September 2018 (Hurricane Florence) and each rank among D.C.’s 10 wettest on record.

NOAA’s Climate Prediction Center expects D.C.’s dry weather to continue well into next week.  Although three of the last four September’s have been wetter than average, September 2019 finished as D.C.’s fourth driest on record with only 0.25” of rain. 

Temperatures over the first half of September have been at or above average on all but one day (September 14).  My colleagues and I on the WUSA9 Weather Team are tracking the potential for additional 90° temperatures next week.  The Nation’s Capital has already had two days in the 90s so far this month and has averaged three to four days of 90° September heat over the last 30 years.

NOAA expects warmer than average temperatures to continue through the second half of September in the D.C. Metro Area.  If that holds true, then that would be unlike last year.  September 2021 finished with six cooler than average days in the Nation’s Capital over the final eight days of the month.