Ranking Autumn 2017

The months of September, October and November make up meteorological fall.  All three months for the second consecutive year were warmer than average in the Nation’s Capital.  All three months were also drier than average for the third consecutive year.  That’s added to the ongoing rainfall deficit Washingtonians are experiencing.  Do the dominating weather patterns of the fall foreshadow the upcoming winter weather?

Although no record high temperatures were set in the Nation’s Capital this fall, four consecutive record high/low temperatures were set (starting October 8).  That means the daily low temperature remained at record high levels for four days.  By comparison, Washingtonians got their first taste of record November cold since 1976 last month.  A record-tying low temperature of 26° was observed at National Airport (DC’s official weather reporting site) on November 11, 2017.

Washingtonians have been dealing with an ongoing rainfall deficit since August 2015.  In that time, 22 of the last 28 months were drier than average, including eight of the first 11 months of 2017.  DC Area residents had a 4.84” rainfall deficit during the fall 2017.  Since August 1, 2015, DC’s rainfall deficit is 12.61” but it is only 1.59” since January 1, 2017, because July and August of 2017 finished with a surplus of 7.07” of rain.

Does a warmer and drier than average autumn foreshadow a particular type of winter weather?  Not necessarily.  Meteorologists look at large-scale weather patterns when issuing seasonal weather outlooks such as the presence of El Nino or La Nina and the status of the North Atlantic Oscillation or NAO.  These large-scale events create more favorable conditions that the upcoming winter season will be warmer and drier than average, colder and wetter, or a combination of each.  A season can be warmer and wetter than average, but also feature above average snowfall and/or a few days of frigid temperatures.

Autumn 2015 was drier than average in the Nation’s Capital and finished 2.5° warmer than average.  Although October 2015 was 0.6° cooler than average, December 2015 was DC’s warmest on record.   However, January 2016 was DC’s third consecutive cooler than average January and included an historic snowstorm.  

DC’s 17.8“ of snowfall during the “Blizzard of 2016” tied it for the city’s fourth largest on record and made up the majority of the 22.2” of snow that occurred during the entire winter.  Although the 2015-2016 winter season finished 3.8° warmer than average according to NOAA, it also finished with 22.2” of snow (nearly 7” above the seasonal average of 15.4”).  

In short, a warmer and drier than average fall doesn’t necessarily mean the winter will be warmer than average with below average snowfall.  A winter season can be relatively snowless, but one major winter storm can make the entire winter snowier than average, such as occurred in 2015-2016.  By comparison, the 2003-2004 winter was 2.2° colder than average in Washington, D.C., but also finished with 3” less snow than average.  NOAA expects above average temperatures this winter with near average precipitation in the DC Metro Region.