Another Warm and Wet December

This December will finish as a warmer and wetter than average month in the Nation’s Capital for the fifth time in the last six years.  Through December 30, DC’s December average temperature (combining daily high and low temperatures) is 2.1° above average.  Washingtonians also exceeded the December rainfall average (3.05”) with 3.28”.  December 2019 won’t finish as wet as last December (5.82”) or as warm as December 2015 (11.5° warmer than average). 

DC had no measurable snowfall occurred in December 2014, 2015 and 2018.  However, each of the subsequent winters (2014-2015, 2015-2016 and 2018-2019) finished with above average snowfall.  That means there’s good news for snow lovers in the DC Metro Area longing for appreciable snowfall.  It’s true that Washingtonians officially saw 0.4” of snow this month, well below DC’s December average of 2.3”.  However, once the calendar changes to January, there can be a dramatic change in the weather pattern.  For example, a significant dip in the jet stream occurred in early January 2015 that coincided with the passage of a vigorous Alberta Clipper that brought the Nation’s Capital a robust 2.4” on January 6.  What’s more, February 2015 was DC’s coldest February since 1996 and finished with 9.8” of snow. 

December 2015 was DC’s warmest on record and featured more days with highs in the 70s (three) then had lows at or below freezing (two).  It was also a wet month with rain on nine of its final 10 days that helped it finish 1.79” wetter than average.  The first measurable snowfall of the 2015-2016 didn’t occur until January 17 and set a record for DC’s latest first accumulating snowfall.  DC’s fourth largest snowstorm occurred a few days after that. 

December 2018 was another warm and wet month with 5.82” of rain (nearly double DC’s December average of 3.05”) that helped 2018 finish as DC’s wettest year on record.  However, a significant winter storm that spanned three days brought the Nation’s Capital 11.5” of snow the following month – DC’s largest snow event since the record January 2016 storm.

The only colder than average December in recent years occurred in 2017.  However, the 2017-2018 winter finished with half of DC’s seasonal average of 15.4” of snow.  That helps illustrate that a cold December doesn’t always foreshadow a snowy winter, just as a warm and wet December doesn’t portend a warm winter.  Although NOAA’s January outlook is for near average temperatures and above average precipitation in the DC Metro Area, the right ingredients need to come together only once to produce a significant snowfall.