Meteorological Fall Comes to a Close

 

Meteorologists have a different benchmark for measuring seasons than the standard astronomical calendar most people are familiar with.  For the sake of climate records, meteorologists break up the four seasons into equal, three-month segments.  For example, “meteorological fall” began on September 1 and comes to a close today, November 30.  Meteorological winter officially gets underway tomorrow and continues through the end of February.  Since the fall comes to its unofficial conclusion today, we can reflect upon the D.C. Area weather headlines of the last three months.

November 2021 has been a cooler and drier than average month.  That couldn’t be more different than last November, which finished as one of D.C.’s warmest and wettest on record.  Temperatures this month have been streaky with several consecutive warmer than average days alternating with cooler than average days.  However, this month will finish with 20 out of 30 days that were colder than average.  It’s also been a dry month with measurable rainfall on only seven of the last 30 days.  D.C.’s November rainfall total will be 0.98”.  That’s the third November during the last decade with less than an inch of rain. 

By comparison, October 2021 was a very warm month in the D.C. Metro Area.  It finished as the second warmest, behind only 2007.  Meanwhile at Dulles Airport, October 2021 tied 2007 for warmest on record.  Rainfall was also very streaky last month.  Although only 0.42” accumulated at National Airport through October 24, two significant rainfall events during the final week of October produced a two-day rainfall total of 2.70”.  That helped October 2021 finish close to average instead of finishing among the driest on record.  D.C.’s most impressive weather statistic during all of October is that 28 of the 31 days last month were warmer than average.

D.C.’s trend of streaky 2021 fall weather began in September when accumulating rainfall was spotty.  The majority of September’s rainfall total occurred on only two days.  The remnants of Hurricane Ida brought the Mid-Atlantic Region heavy rain and severe weather on September 1 with 1.34” at National Airport.  Another 1.30” fell on September 23.  September’s average monthly temperature (combining daily high/low temperatures) finished nearly 1° above average.  It was also slightly wetter than average (0.10”). 

This fall will finish a warmer than average season overall, but with below average rainfall.  Seven of the last nine autumns have had below average rainfall in Washington, D.C.  That follows a stretch of four consecutive autumns (2009-2012) when Washingtonians had above average rainfall.  NOAA’s outlook for the upcoming winter season weighs heavily on the current episode of La Nina and expects the Mid-Atlantic Region to have warmer than average temperatures with near average precipitation.  Four of the last five winters have had below average snowfall in the Nation’s Capital.

November 2021: Cold and Dry

 

November 2021 is on track to finish as a cooler and drier than average month in the Nation’s Capital.  That would make this month D.C.’s fourth colder than average November in the last five years.  However, it will be remembered for its streaky weather with alternating stretches of warmer and cooler than average temperatures.

This month’s average monthly temperature (combining daily high/low temperatures) in Washington, D.C. is 2.0° cooler than average.  That’s in contrast to November 2020, which finished 4.4° warmer than average and tied for D.C.’s fourth warmest November on record.  So far, this month had four days with highs in the 70s in the Nation’s Capital, compared to the most recent 30-year average of roughly three such days.  The warmest temperature this month was 74° on November 18.  D.C.’s coolest temperature was 30° on November 24.  

This has also been a dry month with only 0.98” of precipitation at National Airport.  That’s approximately a third of D.C.’s November rainfall average of 2.91”.  D.C.’s wettest day of the month was November 12 with 0.64”.  This could be the third November in the last decade to finish with less than an inch of rain.  Meanwhile, two of the last three November’s have been wetter than average in Washington, D.C.  That includes November 2018, which finished as D.C.’s wettest on record (7.57”), and last November (6.14”), which was D.C.’s sixth wettest.

Despite being a colder and drier than average month, no snowfall has occurred in the Nation’s Capital.  Accumulating November snowfall is a relative rarity, with only one such occurrence over the last two decades (2018).  No direct correlation exists between November’s dominant weather pattern in the D.C. Metro Area and what the upcoming winter will be like.  My colleagues and I on the WUSA9 Weather Team issued our “Winter Weather Outlook” earlier this month.  

 

D.C.’s Driest Novembers (Source: NWS)

1.  0.29” (1981)
2.  0.37” (1965)
3.  0.53” (2001, 1917)
5.  0.55” (1922)
6.  0.60” (2012, 1908)
8.  0.76” (2016, 1936)
10.  0.79” (1930, 1890)

 

2021-2022 Winter Weather Outlook

January 2016 D.C. Area Blizzard

Many people wonder what the upcoming winter season will be like during the final days of November.  That’s fitting since meteorological winter runs from December 1 through February 28.  My colleagues and I on the WUSA9 weather team recently released our outlook for the upcoming winter, taking such factors into account as the presences of La Nina/El Nino and climatology.  Check out this link for more details.