Ending 2018 on a Record Note

Flood Watches in effect for much of the DC Metro Area

It’s appropriate that 2018 comes to a wet conclusion since the Nation’s Capital set a record for wettest year with nearly five and a half feet of rain since January 1.  Just this morning, Dulles Airport in nearby Sterling, Virginia, broke its 2003 record for wettest year.  Eight of the first 11 months of 2018 have been warmer and wetter than average in Washington, D.C.  December has already been wetter than average, with 4.32” through December 27 compared to DC’s monthly average of 3.05”.  Over the same time period, DC has been 2.8° warmer than average.

The National Weather Service issued Flood Watches for the DC Metro Area with a total of 1” – 2” of rainfall forecast today.  That could make this DC’s wettest December since 2009 when Washingtonians finished with a total of 6.79” of rain, including liquid snow equivalent.  Unlike December 2009, however, which finished nearly 2° colder than average, December 2018 has been quite mild.  

Over the 20-year period from 1998 through 2017, Washington, D.C. had 11 Decembers that were at least 2° warmer than average.  During 7 of those Decembers, the Nation’s Capital had no measurable snowfall.  In similar fashion, there’s been no snow this December either.  Only eight of the 11 winters that had a very warm December went on to have average or below average snowfall in January and February as well.  This fact illustrate that we cannot accurately deduce what the rest of the winter will be like based on December’s weather alone.

There are many paths for Washington, D.C. to get its seasonal average of 15.4” of snow.  A series of small to moderate snowfalls (as in the 2014-2015 winter) or one major snow event (2015-2016) could make a winter snowier than average.  The two primary ingredients for a major winter storm are appropriate storm track combined with an adequate amount of cold air.

Washingtonians have seen winter seasons like 1997-1998, which was a typical El Nino winter with a series of coastal storms and an active southern branch of the jet stream.  It was also a milder and wetter than average winter with only 0.1” of snow in DC.  By comparison, the 2015-2016 winter season also had a strong El Nino event, but the right ingredients came together and produced the epic January 2016 blizzard.

NOAA is on “El Nino Watch” and there is a 90% chance that El Nino will “…form and continue through the Northern Hemisphere winter 2018-19.”  In the meantime, December 2018 will end on a wet note in the DC Metro Area with more rain expected on New Year’s Eve.  NOAA expects near average temperatures and precipitation in the Mid-Atlantic Region during the first week of 2019.