A High Degree of Variability

Although winter arrives this month, December occasionally has some fleeting moments of fall-like warmth.  There have also been instances of mid-winter chill during the month.  Over the last 25 years, the Nation's Capital has averaged one day with high temperatures in the 70s three out of every four Decembers.  There has also been roughly the same frequency of days with high temperatures in the 20s.  Bear in mind that average high temperatures during December range from 52° at the start of the month to 44° by December 31 in the Nation's Capital.

Seven of the last eight Decembers have been warmer than average.  That includes December 2015, which was DC's warmest on record with a total of 14 days of temperatures in the 60s and 70s.  By coincidence, the Nation’s Capital set its all-time record for warmest December temperature on this date 21 years ago.  On December 7, 1998 the thermometer climbed all the way to 79°, which is DC’s average high temperature on May 28! 

By comparison, December 2017 was DC's first colder than average December of the decade.  Although it had three days with high temperatures in the 60s, it also finished with some of DC's coldest December weather since the late 1980s.  DC's high/low temperature of 23°/16° on December 31, 2017 was DC's coldest December high temperature since Christmas Eve 1989 (also 23°).  More recently, December 2017 was 1.9° warmer than average as late as December 26.  However, the final five days of 2017 were particularly frigid with temperatures remaining at or below 33°.  That caused December 2017 to finish 0.5° colder than average.  A net swing of more than 2° in less than a week is quite rare.

This month has gotten off to a benign start with two cooler and wetter than average days and seasonal weather since then.  That will change, however, as the upcoming week will transition from a mild and wet start to drier and colder than average by mid-week.  Such a roller coaster of temperatures is not uncommon in early winter. 

Snowfall has been common in the Nation’s Capital in recent years.  Since 2002, DC has had accumulating December snowfall 10 times.  December 2009 was DC’s snowiest on record with 16.6” during the snowstorm of December 18 - 19.  NOAA expects above average precipitation and near to below average temperatures to continue in the DC Metro Area over the next two weeks.