Late March Snow in DC

March 21 Snowfall Forecast  (Source: WUSA9)

Accumulating snow in the second half of March is relatively rare in the Nation’s Capital.  That said, the DC Metro Area is poised to experience its largest accumulating snow event since the record January 2016 blizzard.  Several inches are likely tomorrow inside I-495.

Washingtonians had very little snowfall last winter and for much of this season.  In fact, the meteorological winter of 2017-2018 (December 1 through February 28) finished with only 3.3” or roughly 20% of the seasonal average of 15.4”.  However, a coastal storm has developed in the ideal position to bring the Mid-Atlantic Region its largest snowfall in more than two years.  Although Washington, D.C. averages 1.3” of snow in March, significant snowfall is quite rare in the second half of March.  That’s because there are environmental and meteorological factors which combine to make significant snow hard to come by (e.g. increasing sun angle).  

March is the first month of meteorological spring (March 1 through May 31) and the sun angle is a lot higher than in December or January.  That’s important because it leads to warmer temperatures – even on cloudy days.  Average high and low temperatures in Washington, D.C. range from 51°/34° on March 1 to 61°/42° on March 31. 

Large temperature fluctuations are quite common in the DC Metro Area during the month of March.  For example, it was 70° in Washington, D.C. on March 15, 2014, before temperatures fell dramatically late on March 16.  St. Patrick’s Day 2014 was a frigid and snowy day in the Nation’s Capital with a total of 7.2” of snow, which began late on March 16.  However, that snow wasn’t around long as temperatures were in the low 60s on March 20, 2014.

There are no 60° temperatures expected in the Nation’s Capital until next week at the earliest.  That could make this March unusual for another reason.  Through March 20, DC’s average monthly temperature (combining daily high and low temperatures) is more than 2° below normal at 42.4°.  That makes it quite likely this month will finish cooler than average and cooler than February (45.3°).  March 2017 was cooler than February 2017 and that hasn’t happened in consecutive years since 1890-1891, according to National Weather Service data.  

Last month was DC’s third warmest February on record, so this month feels especially chilly by comparison.  Washingtonians experienced their earliest 80° temperature on record on February 21, 2018, but the warmest temperature this month has only been 59° on March 1.  My colleagues and I on the WUSA9 Weather Team will continue to refine the forecast both on-air and on the WUSA9 mobile app.

Washington, D.C.’s largest snowfalls in the second half of March:

March 27-28, 1891: 12”
March 28-29, 1942: 11.5”
March 15-16, 1900: 10”
March 14-16, 1937: 8”
March 16-17, 2014: 7.2”

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March 21 Daily Snowfall Records for the DC Metro Area

Washington, D.C. (Reagan National Airport - DCA): 5.3” (1924)
Dulles Airport, Sterling, VA (IAD): 2.3” (1964)
Baltimore, MD (BWI Airport): 9.7” (1964)