Winter Weather Averages

January 13, 2018 in Bethesda, Maryland

The DC Metro Area had its ninth largest January snowfall on record this past weekend with 10.3” at National Airport.  The snow fell for an unusually long period of time at National Airport: 35 consecutive hours from 3:00 Saturday afternoon, January 12, to 2:00 Monday morning, January 14.  It was the DC Area’s largest overall snow event since the record January 2016 storm.

Temperature and precipitation averages are kept by the National Weather Service and are updated every 10 years.  DC’s current annual snowfall average of 15.4” is based on the 30-year period from 1981 through 2010.  While the Nation’s Capital had 10 snowier than average January’s between 1981 and 2010, there have been only two since 2011.  However, January 2019 also became a snowier than average month in Washington, D.C. with this past weekend’s storm.

There are a few more chances to add to DC’s snow total in the next few days.  The month of January is DC’s second snowiest month of the year with an average of 5.6”, narrowly behind February’s 5.7”.  Three of DC’s 10 largest snowstorms occurred in January, while six occurred in February.  Also, five of DC’s 10 largest snowstorms have occurred relatively recently in the last 23 years since the January 1996 blizzard.

Something a lot less frequent in recent decades has been record cold.  The Nation’s Capital hasn’t set a record low temperature in January in nearly 25 years, since it was -4° on January 19, 1994.  Temperatures have only fallen to the single digits in Washington, D.C. four times in January during the last 20 years.  Washingtonians did set a record low of 5° on February 20, 2015, and that was DC’s first record low in February since 1970.

DC’s official weather measurements have been made at National Airport since 1942.  As urbanization has increased, there has been a commensurate increase in the urban heat island effect.  That means it’s a lot harder for temperatures to fall to levels seen decades ago when there was less development and urbanization.  By comparison, Dulles Airport, in the more rural Sterling, VA, has been below 0° as recently as last winter (-1° on January 7, 2018) and has set multiple record low temperatures over the last five winters.

This coming Monday, January 21, is poised to be DC’s coldest day of the winter season so far with high temperatures only around 20°.  That’s less than half the daily average high temperature of 43°.

Last Time High Temperatures Below 30°

Washington, D.C. (National Airport – DCA): 28° (January 14, 2018)
Dulles Airport, Sterling, VA (IAD): 26° (January 14, 2018)
Baltimore, MD (BWI Airport): 27° (January 14, 2018)

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Last Time High Temperatures Below 20°

DCA: 19° (January 22, 2014)
IAD: 19° (January 6, 2018)
BWI: 18° (January 6, 2018)

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Last Time Low Temperatures </=10°

DCA: 8° (January 7, 2018)
IAD: 9° (January 15, 2018)
BWI: 1° (January 7, 2018)

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Last Time Below 0°

DCA: -4° (January 19, 1994)
IAD: -1° (January 7, 2018)
BWI: -1° (February 5, 1996)