Meteorological Fall Comes to a Close

Fall 2019 Comes to its Unofficial Conclusion Today

Meteorologists refer to the three-month period of September, October and November as "meteorological fall."  That differs slightly from "astronomical fall" that spans the period from the fall equinox to the winter solstice.  Astronomical fall is based on the position of the earth in relation to the sun, while the meteorological seasons are based on temperature cycles.

November 2019 is poised to finish as a cooler and drier than average month.  Through November 29, DC's average monthly temperature (considering daily high and low temperatures) was 3.6° below average.  Although last November finished 3.1° colder than average, it was also DC's wettest November on record with 7.57" of rain.  By comparison, only 1.37" has occurred so far this month, well below DC's November average of 3.17".  DC's warmest November temperature was 69° on November 11, while the coldest temperature was 26° on November 13.  The last time DC had two or more consecutive cooler than average Novembers was 2012 - 2014.

October 2019 was a tale of two weather extremes in the Nation's Capital.  It began as a very warm and dry month with 14 of the first 15 days warmer than average.  Washingtonians also endured the warmest October temperature on record with a sweltering 98° on October 2.  October also continued September's dry trend with only 0.14" through October 15.  Fortunately, the second half of the month was significantly wetter with a total of 6.52”.  That erased the moderate to severe drought conditions that had enveloped much of the DC Metro Area after a dry three-month period from July 15 - October 15 (when DC had a combined 7.01” rainfall deficit).

September 2019 finished as DC's third warmest and fourth driest on record.  Two record high temperatures were set in September for DC's highest such total since 1991.  September’s above average temperatures (25 out of 30 days warmer than average) only served to worsen the dry conditions in the Mid-Atlantic Region.  Only 0.25" of rain fell in September after a drier than average August.

Fall weather swung between extremes in the Nation's Capital this year.  Periods of warm and wet weather alternated with drier than average conditions and colder than average temperatures.  However, fall weather has little bearing on what the upcoming winter will be like.  For example, DC had four colder than average Novembers since 2010, with three of the subsequent winters finishing snowier than average (2013-2014, 2014-2015 and 2018-2019).  However, two of those winters were also warmer than average.  This November is well positioned to be DC’s coldest since 1997 and longtime Washingtonians may remember that the 1997-1998 winter had only 0.1” of snow.

NOAA's three-month outlook for December, January and February (meteorological winter) is for warmer and wetter than average conditions in the DC Metro Area.  Yet, the right ingredients have to come together only once to create an appreciable winter storm.