Feeling Like Fall

 

September 2020 was first cooler than average September in the Nation’s Capital since 2009.  Last month’s average temperature was 70.2° -- nearly a full degree below the 30-year average of 71° (1981 – 2010).  It was also a wetter than average September, with 5.53” at National Airport – nearly 2” above the monthly average.  That made September 2020 DC’s first cooler and wetter than average September since 2006. 

There are two weather headlines that stand out for Washingtonians from September 2020.  First, was the record daily rainfall that occurred at National Airport on September 10 of 2.88”.  That produced significant flooding in parts of DC and Prince George’s County in Maryland.  Also, DC’s coolest September weather in decades occurred during the second half of last month.  Washingtonians experienced low temperatures in the 40s on four consecutive mornings between September 19 and September 22.  That’s in contrast to September 2019, which finished as DC’s third warmest.

October has also gotten off to a much different start compared to last year.  Washingtonians set a new record for warmest October temperature ever last October 2 when it was 98°.  By comparison, no 90° heat has occurred this year since September 4, with cooler than average temperatures this weekend.  Average high/low temperatures in October range from 74°/56° on October 1 to 64°/46° on Halloween.  DC’s hottest October temperature on record is 98°, while DC’s coolest October temperature is 26°, most recently on October 31, 1917.  Since 2000, 12 of the last 20 October’s have been warmer than average in the Nation’s Capital, including the last four.

DC averages 3.4” of rain in October.  Rainfall during October can be influenced by the remnants of tropical systems such as former Hurricane Sandy in 2012.  The DC Metro Area also experienced flooding during the wettest October on record in 2005 when a cold front combined with the remnants of Tropical Storm Tammy.  Although rare, the Nation’s Capital has seen snow in October, most recently on October 29, 2011, when a trace occurred (too little to measure).

NOAA’s outlook for October 2020 is for near to slightly warmer than average temperatures in the DC Metro Area – despite the cool start.  Meanwhile, below average rainfall is also expected this month.  That wouldn’t disappoint most residents of the DC Metro Area given how wet the last few months have been.  Washingtonians had a rainfall surplus of 10.39” for the three month period from July 1 – September 30. 

If August and September were drier than average, the colors of the fall foliage wouldn’t be as vibrant.  However, since there was a rainier than average late summer and early fall, the foliage has the potential to be especially colorful during the next few weeks.