DC’s Seasonal Transition Continues

Freeze Warnings for much of the DC-Baltimore Corridor  (Source: NWS)

Late October and early November is often when the DC Metro Region experiences its first freezing temperatures of the fall season.  Such is the case this fall with the coldest temperatures of the season on tap tonight.  Freeze warnings are in effect for much of the Mid-Atlantic Region tonight and some record lows will be challenged tomorrow morning.

Average low temperatures on November 11 range from 43° at National Airport to 37° at Dulles Airport.  However, today and tomorrow will feel more like January than mid-November, with significantly colder than average temperatures.  Longtime residents may remember that DC’s largest November snowstorm occurred on Veteran’s Day 30 years ago.

Fortunately, no snow is expected this weekend and Washingtonians haven’t had measureable snowfall in November since 1996.  The big story this weekend will be the temperatures.  The last time Washingtonians had temperatures at or below freezing was on March 23, 2017 (30°), while the last time Dulles was that cold was April 9, 2017 (32°).  Tonights below freezing temperatures will put us a few weeks ahead of last year.  The first sub-freezing temperatures at National Airport last fall didn’t occur until November 23, 2016 (32°).  However, Dulles Airport was 30° on October 26, 2016.

There is often several weeks’ difference between when the first subfreezing temperatures occur at National vs. Dulles Airports.  That can be attributed to the local geography as National Airport is located adjacent to the moderating influences of the Potomac River, as well as downtown.  The “urban heat island effect” often keeps urban areas warmer than suburban or rural areas.  Although the Dulles corridor is more developed than 20 to 30 years ago, it’s still significantly more rural than National Airport and away from the Potomac River.  

While weather records for Washington, D.C. date back to 1871, Dulles Airport didn’t open until 1960.  No record lows have been set at National Airport in November since 1976.  However, Dulles Airport has had five record lows in November just since 2003.

November 11 Record Low Temperatures

Washington, D.C. (National Airport – DCA): 26° (1973)
Dulles Airport, Sterling, Virginia: 16° (1973)
Baltimore, MD (BWI Airport): 21° (1973)

Significant Off-Season Atlantic Hurricanes

Hurricane Epsilon on December 5, 2005  (Source: NOAA)

Hurricane season runs from June through November in the Atlantic Ocean Basin, which includes the Gulf of Mexico and Caribbean Sea.  September is the busiest month of the hurricane season because conditions are most favorable for development.  However, there have also been a handful of noteworthy off-season hurricanes in the Atlantic Ocean.

Alex (2016) – Alex was a minimal Category 1 hurricane with peak winds of 85 mph and a minimum central air pressure of 981 millibars (mb) on January 14 while south of the Azores.  Although a weak hurricane, the mere fact it developed in the central Atlantic in January is a rare occurrence.  Alex was the Atlantic’s first January hurricane since Alice in 1955.  Ironically, the second named storm of the 2016, Tropical Storm Bonnie, also developed before the official start of hurricane season in late May.

Epsilon (2005) – The 2005 hurricane season saw a record number of tropical storms (28) and hurricanes (15) in the Atlantic Ocean.  Epsilon was significant not for its intensity, but for being the final hurricane of the record season.  Since the 2005 season had so many named storms, the entire list of assigned names was used up and names from the Greek alphabet had to be added.  Epsilon reached hurricane intensity on December 2 and had sustained winds of 85 mph and a minimum pressure of 981 mb at peak intensity.  Epsilon became the Atlantic’s longest lasting December hurricane on record, remaining at hurricane intensity for five days.

Lili (1984) – Lili was the Atlantic’s first December hurricane since an unnamed 1951 storm.  At peak intensity over the central Atlantic Ocean, Lili had sustained winds of 80 mph and a minimum central pressure of 980 mb.  This version of Lili was a relatively benign storm when compared to the 2002 version.  Some may recall that 2002 version of Hurricane Lili was a damaging and deadly hurricane that ultimately made landfall in Louisiana on October 3.  The name “Lili” was subsequently retired by the World Meteorological Organization before the start of the 2003 season.

Alma (1970) – Alma was the last Atlantic hurricane to develop during the month of May.  Alma reached its peak intensity on May 20 with sustained winds of 80 mph and a minimum central air pressure of 993 mb, while located near the Cayman Islands and Jamaica.  Eventually, the remnants of Alma spread appreciable rainfall from Florida to Virginia. 

Off-season hurricanes are noteworthy for the fact they occur so infrequently.  That said, an off-season tropical storm or hurricane has occurred in 11 of the last 20 years in the Atlantic Ocean – including Tropical Storm Arlene this past April.

Will DC's October’s Warmth Linger in November?

September and October were both warmer and drier than average in the DC Metro Area.  November is the third and final month of meteorological fall in North America.  This month has already gotten off to a warmer than average start with a balmy high temperature of 78° at National Airport on November 3.  Although today’s high temperature of 61° is appreciably cooler, it’s much closer to average. 

The average high/low temperatures in Washington, D.C. fall from 63°/45° on November 1 to 52°/37° by the end of the month.  According to NOAA, November’s warmest temperature in the Nation’s Capital (86°) occurred on November 1, 1974.  By comparison, DC’s coldest November temperature on record (11°) was on November 30, 1929.  Some may know that weather records in Washington, D.C. date back to 1871 and that official weather measurements are made at National Airport. 

Weather records that predate National Airport (that opened in 1941) were made in NW D.C.  The coldest November temperature observed at National Airport occurred on November 26, 1950 (17°).  Since Dulles Airport is located in a more rural location away from the moderating influence of the Potomac River, temperatures there often get colder than at National Airport.  November’s coldest temperature at Dulles Airport (9°) occurred on November 24, 1989.

National Weather Service data shows that Washington, D.C. averages 3.17” of rain and 0.5” of snow in November.  November largest snowstorm in the Nation’s Capital occurred on Veteran’s Day in 1987 when 11.5” of snow occurred.  However, the Nation’s Capital hasn’t had measurable November snowfall since 1996.  That’s D.C.’s longest stretch without accumulating snowfall in November.  However, November snowfall has little bearing on the upcoming winter season.

Washingtonians had an average amount of snow (0.5”) in 1995, while the 1995-1996 winter remains the third snowiest (46”) on record.  Meanwhile, November 1989 was a colder and snowier than average month that brought a total of 3.5” of snow to the Nation’s Capital.  By comparison, more snow fell in Washington, D.C. in November 1989 than in January, February and March of 1990 combined (2.6”).

NOAA is expecting the warmer than average conditions of the fall to continue over the course of the month with near average rainfall in the DC Metro Area.  The last seven Novembers have been drier than average in Washington, D.C., while the last two have also been warmer than average.