Watch Out for Winter Weather

 

NOAA’s winter weather outlook for the upcoming 2020-2021 season expects warmer and drier conditions along the southern tier of the United States along with cooler and wetter conditions in northern areas.  A large consideration in its forecast is the episode of La Nina that’s developed.  La Nina is characterized by cooler than average sea surface temperatures in the tropical east Pacific Ocean – off the west coast of Ecuador.  That often has global repercussions, much like El Nino, though in opposite ways.  For example, El Nino conditions tend to create unfavorable conditions for development in the tropical Atlantic, while the current La Nina conditions have helped enhance the active 2020 Atlantic hurricane season.

La Nina winters in the DC Metro Area are often warmer than average with near average precipitation.  However, that can fluctuate depending on the intensity of the La Nina with weaker La Nina’s having less of an influence.  Washingtonians usually get below average snowfall during La Nina winters.  While the presence of El Nino or La Nina play significant roles in seasonal forecasts for winter, there are other factors to consider such as the status of the North Atlantic Oscillation (NAO).

Over the last two decades there have been some key winter weather trends in the Nation’s Capital.  For example, 14 of the last 20 winters have had below average snowfall, but four of DC’s 10 largest snowstorms have occurred in that time.  They include President’s Day 2003, December 2019, “Snowmageddon” in February 2010, and the epic January 2016 winter storm.  While DC averages 15.4” of snow annually, the perception of a winter can vary widely depending on whether that snow occurs during one large winter storm or with a series of smaller storms.

Thirteen of the last 20 winters have also been warmer than average in the DC Metro Area, including the last five winters.  However, a warmer than average winter doesn’t necessarily mean it will have below average snowfall.  A good example of that was the 2015-2016 winter that featured DC’s warmest December on record.  DC residents didn’t see the first measurable snowfall that winter until mid-January, shortly before its fourth largest winter storm on record – the epic “Blizzard of 2016.”  However, if you subtract the 17.8” that occurred at National Airport during that storm, DC only saw a combined 4.4” of snow the rest of the winter.

Washingtonians haven’t had more than three consecutive snowier than average winters (2013 – 2014 through 2015 – 2016) or more than three consecutive colder than average winters (2008 - 2009 through 2010 – 2011) over the last 20 years.  Last winter was largely ENSO-neutral (meaning an absence La Nina or El Nino) and finished as DC’s third least snowy winter on record with a seasonal total of only 0.6”.  Based on NOAA’s outlook, residents of the DC Metro Area can expect warmer than average temperatures and near average precipitation.