Earth Day Weather

April has been exceptionally warm in the DC Metro Region so far.  In fact, April is poised to finish among the warmest on record in the Nation’s Capital.  Through April 21, this month’s average temperature is 63.0 degrees (combining daily high and low temperatures) at National Airport.  If the month were to end today, it would shatter the existing record for warmest April of 62.1 degrees from 1981 in Washington, D.C. 

Two primary factors have contributed to making April so far above the monthly average of 56.6 degrees.  All but four days since April 1 have featured warmer than average temperatures.  Over the last 25 years, Washingtonians have averaged only three to four days each April with temperatures in the 80s.  The six that have occurred so far this month have already surpassed that mark.  DC residents also had their warmest April day since 2013, when it was 89 degrees on April 16, 2017.

Moreover, overnight low temperatures have also been above average.  Only three days this month had cooler than average low temperatures (April 7 – 9).  The combination of warmer than average high and low temperatures has put this month in the conversation for warmest April on record.  According to NOAA, Washingtonians have experienced five of their warmest months on record just since 2011, including July 2011, March 2012, May 2015, December 2015 and February 2017.  Last August, finished within 0.1 of a degree of tying the existing record for warmest on record in the Nation’s Capital (1980).

In recent years there have been many more record high than record low temperatures in the Mid-Atlantic Region.  The increase in urbanization around Washington, D.C. and other major cities has enhanced the urban heat island effect.  That’s kept cities warmer than they used to be before development and suburban sprawl increased dramatically in the 1980s and 1990s.

This weekend’s cooler and wetter than average conditions in the DC Metro Region will have two major effects.  It will put a dent in the ongoing rainfall deficit of more than 10” that dates back to August 2015.  The cooler than average temperatures this weekend will also lower the average monthly temperature slightly.  However, my colleagues and I on the WUSA9 weather team are tracking a dramatic warm-up during the second half of next week that should position the Nation’s Capital to set a new record for warmest April.

Warmest Aprils on Record in Washington, D.C. in degrees Fahrenheit (Source: NOAA)

1.  62.1 (1981)
2.  62.0 (1994)
3.  61.6 (1985)
4.  61.2 (1960)
5.  60.9 (2010)
6.  60.6 (1941)
7.  60.1 (1980, 1977)
9.  60.0 (2002)
10.  59.9 (1976)