Stellar Fall Weather

 

Many DC Area residents would tell you that the autumn is the best season with lots of sunny, warm days along with comfortable relative humidity.  Those are especially welcome weather conditions after the notoriously hot and humid summers in the DC Metro Area.  Although much of September often features summer-like heat, DC’s weather can pivot to fall at different times.

For example, last month was DC’s first cooler than average September since 2009.  DC’s last 90° day this fall was September 4.  That’s in contrast to last year when DC’s last 90° didn’t occur until October 2, when it was a sizzling 98°.  That made October 2019 DC’s second consecutive October with 90° heat, following the high of 90° on October 4, 2018.  Prior to 2018, the Nation’s Capital only experienced 90° heat once during the month of October dating back to 2004. 

Much more common during October are several days of high temperatures in the 80s.  DC’s October 7 high temperature was 81°, guaranteeing October 2020 will continue the recent trend of 80° warmth in October.  The warmest daily average high temperature in the Nation’s Capital during October is 74° on October 1. 

Eight of the last 10 October’s have been warmer than average in the Nation’s Capital so it’s not unusual there has been a lot of warm October weather in recent years.  Part of that can be attributed to the urban heat island effect that’s increased in recent decades as many urban/suburban areas have gotten more developed.  This is also the last year that NOAA will use the 30-year average from 1981–2010.  Starting next year, NOAA’s temperature and precipitation averages will be updated to reflect the 30-year period from 1991-2020.  

Several of DC’s warmest months on record have occurred during the last 10 to 15 years and updated the averages will be more representative.  There is much more urbanization now than there was in the 1980s, along with significantly more automobile traffic and a higher population.

NOAA’s temperature outlook through the middle of October calls for warmer than average temperatures in the DC Metro Area.  My colleagues and I on the WUSA9 Weather Team have forecast highs in the 70s on several days over the next week.  That’s several degrees warmer than average as average high temperatures are only in the 60s in the Nation’s Capital in mid-October.  Most Washingtonians won’t mind temperatures in the 70s after the cooler than average second half of September 2020.