Can Fall Weather lead to Snowy Winters ?

Given the slew of winter weather outlooks recently issued for the Nation’s Capital, it’s a good time to analyze whether fall weather is a reliable indicator of what the upcoming winter will be like.  September and the first half of October were significantly warmer than average in Washington, D.C., while the second half of October was appreciably cooler than average.  While September was much wetter than average, October was the first drier than average month in the Nation’s Capital since March.

On the other hand, November 2018 has already exceeded its monthly average amount of rainfall in Washington, D.C.  While November’s average temperature (combining daily high/low temperatures) has been within 0.1° of average through November 13, NOAA expects cooler than average temperatures over the second half of the month.  That would make November 2018 a cooler and wetter than average month in Washington, D.C.

The 10 snowiest winters on record in the Nation’s Capital span three centuries, ranging from 1891-1892 to 2009-2010.  Five of the 10 autumns prior to DC’s 10 snowiest winters were wetter than average, so that does not point to a trend.  However, the preceding autumns do share some commonalities.  Eight of the 10 autumns prior to DC’s 10 snowiest winters were cooler than average.  Washington, D.C. also had snow in eight of those 10 Novembers.  

The Nation’s Capital averages 0.5” of snow in November, but having a colder than average November with snow doesn’t necessarily mean anything about the upcoming winter.  For example, more than 80% of DC’s near average seasonal snowfall total (15.3”) for the 1989-1990 winter occurred prior to December 31 and that includes the 3” of snow that occurred in November 1989.  Meanwhile, the rest of the 1989-1990 season had below average snowfall.  Conversely, the 0.5” of snow that fell in November 1995 foreshadowed the 1995-1996 winter that became DC’s third snowiest on record.

Since DC’s snowiest November on record in 1987, Washingtonians have had a trace or more of snow in 15 of the last 30 Novembers.  However, 23 of the last 30 winters have had below average snowfall.  Three of DC’s snowiest winters (1957-1958, 2002-2003 and 2009-2010) occurred during a moderate to strong episode of El Nino.  Two of the three preceding autumns prior to those winters were wetter and cooler than average in the Nation’s Capital.  

NOAA expects a moderate episode of El Nino to develop this winter.  El Nino winters have a more active southern branch of the jet stream and that often translates to wetter than average weather in the southern United States.  On occasion, a coastal storm can develop and head up the east coast.  If there is sufficient cold air in place, then the DC Metro Area could see significant snowfall.  The January 2016 blizzard, which tied for DC’s fourth largest snowstorm on record, also occurred during an El Nino winter.

As a whole, the fall 2018 season is poised to finish warmer and wetter than average in Washington, D.C.  With the arrival of the anticipated El Nino, it will be interesting to see what happens during the upcoming winter.  My colleagues and I on the WUSA9 Weather Team recently issued our 2018-2019 winter weather outlook.

Washington, D.C.’s Ten Snowiest Winters (Source: National Weather Service)

1.  56.1” (2009-2010)
2.  54.4” (1898-1899)
3.  46” (1995-1996)
4.  42.5” (1921-1922)
5.  41.7” (1891-1892)
6.  41” (1904-1905)
7.  40.4” (2002-2003), (1957-1958)
9.  40.3” (1960-1961)
10.  37.7” (1978-1979)