Decade in Review

 

NOAA weather averages are based on 30-year periods that are updated every decade.  For example, Washington, D.C.’s current weather averages have relied on the 30-year period of 1981 through 2010.  However, starting next month that will be updated to reflect the period of 1991 – 2020.  There have been a number of memorable weather events and trends in the Nation’s Capital over the last decade.

Although weather records in the Nation’s Capital date back to the 1870s, six of DC’s warmest months have occurred in the last decade.  They include February (2017), March (2012), April (2017), May (2015), July (2011) and December (2015).  Those months ranged from 4.7° warmer than average in July 2011 to an astounding 11.5° warmer than average in December 2015.  Longtime Washingtonians may recall the 2011 summer that featured bountiful 100° heat and ranked among DC’s hottest on record.  December 2015 was also memorable in the Nation’s Capital with 14 days of high temperatures of at least 60°, including three days in the 70s.  In fact, temperatures only fell to 32° or colder twice during that month. 

There have been some memorable cold months over the last decade, such as February 2015 that was DC’s coldest since 1979.  March 2014 was DC’s coldest since 1996 and finished as DC’s snowiest March since 1960.  However, the trend has clearly been for more warmer than cooler than average weather over the last decade.  Given the increased amount of urbanization and automobile traffic in recent decades, it’s much easier to reach warm weather benchmarks than cold weather milestones due to more significant urban heat island effect.

There have also been alternating rainy vs. dry periods in the DC Metro Area over the last decade.  The 32-month period of August 2015 through March 2018 had 25 drier than average months.  During that period, DC accrued a rainfall deficit of 16.42”, or nearly half of DC’s annual average (39.74”).  The subsequent 32-month period from April 2018 through November 2020 was remarkably wet with a rainfall surplus of 46.48”.  That’s more than a year’s worth of extra rainfall in DC during that time.  It also includes DC’s wettest year on record, 2018.  At the same time, 2020 is already in seventh place for DC’s wettest years and could climb to sixth place with more rain in the forecast on New Year’s Eve.

Those are some of DC’s overall temperature and rainfall trends of the last decade.  There have also been several major stand-alone weather events in the Nation’s Capital such as the June 2012 Derecho, “Superstorm” Sandy, and the record-setting January 2016 blizzard.  It will be interesting to see NOAA’s updated weather averages for the Nation’s Capital in 2021, as well as what major weather events are in store for Washingtonians over the next decade.