What is “Indian Summer?”

Great Falls, MD (October 2016)

Washingtonians are in the midst of a major change in the weather pattern following their warmest October week in more than three years.  Today’s high temperatures of only 61 degrees made it the coolest day in Washington, D.C. since May 22 when it was 58 degrees.  61 degrees isn’t the average high in the Nation’s Capital until November 7.

Seven of the first nine months of 2016 have been warmer than average in Washington, D.C.  October has been no exception as temperatures have been 4.7 degrees above average through the 21^st.  That’s largely because of this week’s four consecutive days in the 80s at National Airport.  There haven’t been four or more consecutive October days at or above 80 degrees in Washington, D.C. since October 1 – 6, 2013.  Although no record highs occurred downtown, Dulles Airport saw four record highs and Baltimore had two records highs (officially observed at BWI Airport). 

This week’s warmest day was October 19 when it was 87 degrees at National Airport (Washington, D.C.’s average high on August 18).  That was the warmest October temperature in the Nation’s Capital since it was 91 degrees on October 6, 2013.  Some may wonder if this week’s warmth meets the official criteria for “Indian Summer.”  The National Weather Service defines Indian Summer as “An unseasonably warm period near the middle of autumn, usually following a substantial period of cool weather.”  Last weekend was cooler than average in the DC Metro Region with low temperatures in the 30s north and west of town.  So this week has featured some “Indian Summer” warmth in the DC Metro Region.

This year’s dry weather has continued with only 0.87” of rain over the first three weeks of the October (1.47” below average at National Airport).  By comparison, seven of the last ten Octobers in the Nation’s Capital have been wetter than average.  People may not mind the dry weather as much when they consider the Nor’easter that brought record rainfall and cold temperatures to the Nation’s Capital from October 15-18, 2009 and the severe weather that occurred on October 27, 2010.

People may wonder what typical Halloween weather is in the Nation’s Capital as October 31 draws closer.  Halloween’s average high and low temperatures at National Airport are 64 and 46 degrees respectively.  The last five Halloweens have featured near average temperatures with no measurable rainfall.  NOAA’s outlook for the next 1 to 2 weeks in the Mid-Atlantic Region is for a 33% to 40% chance of drier than average weather.  My colleagues and I on the WUSA9 Weather Team will keep you apprised of the latest weather forecasts.