D.C.’s Fall Transition

 

August 2022 finished as a warmer and drier than average month in the Nation’s Capital for the first time since 2019.  Not only did the month finish 1.0° warmer than average at Reagan National Airport, but it was even warmer at Dulles Airport, finishing 1.8° warmer than average (combining daily high/low temperatures).  It was also drier than average with 2.42” of rain, well below D.C.’s August average of 3.25”.

September features some of the nicest weather of the year in the Nation’s Capital as fall officially gets underway.  Average daily high/low temperatures drop from 85°/69° on September 1 to 75°/59° by the end of the month.  The amount of daylight also continues to fall throughout September and sunset will occur at 6:53 p.m. on September 30.  The combination of a reduced amount of daylight and a lower sun angle contributes to the cooler temperatures as September wears on. 

D.C.’s hottest September temperature on record is 104° on September 7, 1881.  Triple-digit heat during the month of September is a rarity in the Nation’s Capital and has occurred only four times since 1871.  The most recent was 101°on September 2, 1980.  By comparison, D.C.’s coolest September temperature on record is 36° from September 23, 1904.  Seven of the last 10 September’s have been warmer than average in the Nation’s Capital.  To add to that, 5 of D.C.’s 10 warmest September’s on record have occurred since 2005.

Although Washington, D.C. averages 3.93” of September rainfall, the amount of rain can fluctuate wildly year-by-year.  September can be a very wet month if decaying tropical systems bring appreciable rainfall.  Such was the case with Floyd in 1999, Isabel in 2003 and Florence in 2018.  This month can also be very dry in the Nation’s Capital.  D.C.’s driest September on record in 2005 (0.11”) was followed by the wettest October on record (9.41”).  There has been an even 50/50 split between wetter and drier than average September’s in the Nation’s Capital over the last 20 years.

The cooler autumn weather will be a relief to many Washingtonians following another warmer than average summer.  The first half of September often sees a continuation of summer-like heat in the D.C. Metro Area as summer weather only gradually gives way to fall.  Such was the case yesterday with a high of 91°.  September has an above average chance for warmer than average temperatures combined with an equal chance for above or below average rainfall, according to NOAA’s Climate Prediction Center.