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)

Weather Quiz

(Courtesy: Lee Laudicina)

When was the last time Washington, D.C. had measurable snowfall in November ?

A.  1978

B.  1987

C.  1996

D.  2014

Major November Hurricanes

Hurricane Lenny (Source: NOAA)

November is the final month of the Atlantic hurricane season when major hurricane are exceedingly rare.  However, there have been some significant ones over the course of history.  A major hurricane is defined as a Category 3 or higher on the Saffir-Simpson Scale with sustained winds of at least 111 mph.

Otto (2016):  Otto attained hurricane status in the Caribbean Sea on November 23 and intensified into a Category 3 hurricane with sustained winds of 115 mph.  Otto made landfall in Nicaragua on November 24 at peak intensity and was the latest landfalling Atlantic hurricane in modern history.  It was the first tropical system since 1996 to cross Central America and emerge in the Pacific Ocean.  Otto remains the most recent major November hurricane in the Atlantic Ocean Basin (that includes the Atlantic Ocean, Gulf of Mexico and Caribbean Sea).

Paloma (2008): Hurricane Paloma formed in the southwest Caribbean Sea, which is an area favorable for tropical storms and hurricanes late in the season.  Paloma reached its peak intensity on November 8 as a Category 4 hurricane with sustained winds of 145 mph and a minimum central air pressure of 944 millibars (mb).  By comparison, standard sea level air pressure is approximately 1013 mb.  The lower the air pressure, the stronger the storm is.  Hurricane Paloma was also significant because it marked the first known instance when major hurricanes formed in the Atlantic Ocean Basin in five consecutive months (July through November).

Michelle (2001):  According to the National Hurricane Center, Michelle became a Category 4 hurricane on November 3 with sustained winds of 140 mph and a minimum air pressure of 933 mb.  Hurricane Michelle caused major damage and claimed more than 20 lives across the Caribbean during its destructive lifespan.

Lenny (1999):  On November 17, Lenny made landfall on the island of St. Croix with sustained winds of 155 mph, nearly Category 5 intensity.  Although Lenny’s minimum central air pressure of 933 mb was the same as Michelle’s two years later, Lenny’s peak winds were higher.  Hurricanes normally track from east to west in the Northern Hemisphere.  However, being a late season storm, Hurricane Lenny tracked west to east across the Caribbean Sea.  Lenny was the first major November hurricane anywhere in the Atlantic Ocean Basin since Kate in 1985.

Kate (1985):  Kate reached peak intensity in the Gulf of Mexico on November 20 with sustained winds of 120 mph and a minimum central air pressure of 953 mb.  Kate weakened slightly to a Category 2 storm before making landfall on the Florida Peninsula on November 21.  That made it the latest landfalling hurricane on record in the contiguous United States.  Kate was also the fourth hurricane to impact the U.S. Gulf Coast during the 1985 season.

“Cuba Hurricane of 1932”: The strongest November hurricane on record occurred so long ago that it was before hurricanes were named.  Consequently, it’s referred to as the “1932 Cuba hurricane” and remains the Atlantic’s only Category 5 November hurricane on record.  On November 6, 1932 it reached peak intensity with maximum sustained winds of approximately 175 mph and a minimum central air pressure of 915 mb.  Since hurricane hunter flights didn’t begin until the early 1940s, the most accurate way to measure the intensity of an offshore tropical storm or hurricane were ships at sea.  These measurements weren’t made at the center of the storm, so the air pressure could have been even lower.

DC’s Wettest Years

NOAA's Precipitation Outlook for November 2018

November 5 was the 20^th day of 2018 with at least 1” of rain in the Nation’s Capital.  That’s just one off Washington, D.C.’s annual record of 21 – the highest number of 1” daily rainfalls in a given year occurred in 1878.  According to National Weather Service records, 1878 was also DC’s third wettest year on record.  By comparison, a total of 55.90” of rain has occurred at National Airport since January 1.  That already makes 2018 DC’s sixth wettest year on record as of November 6.

The period of April 2018 through September 2018 was the first period of at least six consecutive months that Washington, D.C. had above average rainfall since 2003.  DC’s rainfall surplus over this six-month period is 20.97”, compared to the average annual rainfall of 39.74”.  That means Washington, D.C.’s rainfall surplus over this rainy six-month period is roughly 53% of what DC averages over the course of an entire year.

Consequently, it should come as no surprise that 2018 will almost certainly finish among DC’s five wettest years on record.  With the exception of 2003, DC’s five other wettest years on record all occurred in 1948 or earlier.  Weather records in Washington, D.C. date back to 1871, while they date back to 1964 at nearby Dulles Airport.  Since January 1, Dulles Airport (IAD) has had 56.12” of rain compared to its annual average of 41.54”.

Although October 2018 was the first drier than average month in Washington, D.C. since March, November has gotten off to an exceptionally wet start.  From November 1 – November 5, a total of 2.22” of rain occurred at National Airport making it the third wettest first start of November on record.  DC’s rainfall total of 3.01” over the first six days of November is already more than the combined total of 2.76” from November 2016 and November 2017.  This rainy start to November means there is a good chance this month will become DC’s first wetter than average November since 2009.

January 2018 and March 2018 were also drier than average months in Washington, D.C.  Had merely average rainfall occurred during those months, than DC would have a year-to-date total of 59.33”.  Since NOAA’s outlook for November and its three month outlook both call for an increased chance of above average precipitation in the Mid-Atlantic Region, there is also a chance 2018 could become Washington, D.C.’s wettest year on record.  If D.C. were to see only average rainfall the rest of the year, then 2018 would finish with 61.55”.  

Washington, D.C.’s Ten Wettest Years (Source: NOAA)

1.  61.33” (1889)

2.  60.83” (2003)

3.  60.09” (1878)

4.  58.17” (1886)

5.  57.54” (1948)

6.  54.49” (1937)

7.  52.95” (1891)

8.  52.92” (1906)

9.  52.59” (1877)

10.  52.03” (1942)

Average: 39.74”

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Dulles Airport’s Five Wettest Year’s (Source: NOAA)

1.  65.69” (2003)
2.  59.05” (1972)
3.  58.09” (1996)
4.  55.43” (1979)
5.  52.64” (1975)

Average: 41.54”

November's Warm Start

November 2 Severe Weather Reports  (Source: NOAA)

This month got off to a milder than average start in the Nation’s Capital with highs in the 70s on each of November’s first two days.  However, a cold front subsequently brought heavy rain and severe weather to the DC Metro Area on Friday.  

Friday’s rain broke a November 2 rainfall record at Dulles Airport with 1.32”.  The 0.75” of rain that occurred at National Airport helped push 2018 higher on the list of wettest years in the Nation’s Capital.  With 53.67” of rain since January 1, Washington, D.C., has already had its seventh wettest year on record.  There are several chances of rain in the DC Metro Area over the upcoming week so the annual rainfall total will only continue to grow. 

 

The National Weather Service also confirmed that an EF-1 tornado occurred in the Dundalk area of Baltimore, Maryland on Friday night and caused two fatalities.  That made it Maryland’s first November tornado fatalities on record.  Another EF-1 tornado was also confirmed in Mt. Airy, Maryland.  Although the Mid-Atlantic Region has tornadoes on occasion in September and October, severe weather frequency decreases dramatically in November.

November’s warm start has already extended an impressive streak in Washington, D.C.  The 70s on November 1 and 2 made November 2018 the eighth consecutive November with at least two days in the 70s.  The last November without any 70° temperatures in the Nation’s Capital was in 2010.  In addition to 2010, there has been only one other November in the last 25 years that hasn’t featured any 70° warmth in the Nation’s Capital (1997).  In that time, Washingtonians have experienced an average of between three and four November days in the 70s.  DC’s warmest daily average high temperature during the month of November is 63° on November 1.

The DC Metro Area has also averaged between three and four days with low temperatures at or below freezing since 1993.  Area residents may also know that November is the first of five consecutive months that Washington, D.C. averages measurable snowfall (0.5”).  Nevertheless, measurable November snowfall is a rarity in the Nation’s Capital and hasn’t occurred since 1996. 

Having winter-like days with high temperatures less than 40° are a little more common, locally, during the month of November.  There have been a total of 12 such days in Washington, D.C. since November 1993.  The most recent occurrence was on November 11, 2017 when the high temperature was only 39° (significantly colder than the average high for the date of 60°).  
  
Temperatures in the 80s are even rarer during the month of November with only five such occurrences since 1993; or one every five years.  The most recent occurrence was on November 3, 2016 when Washington, D.C.’s high temperature was a more September-like 83°.    

Washington, D.C.’s Ten Wettest Years (Source: NOAA)

1.  61.33” (1889)

2.  60.83” (2003)

3.  60.09” (1878)

4.  58.17” (1886)

5.  57.54” (1948)

6.  54.49” (1937)

7.  52.95” (1891)

8.  52.92” (1906)

9.  52.59” (1877)

10.  52.03” (1942)

November Weather Trends in the DC Metro Area

NOAA's Temperature Outlook for early November

Average daily high/low temperatures in Washington, D.C. decrease from 63°/45° on November 1 to 52°/37° on November 30.  Despite average high temperatures in the low 60s in early November, there will be several warmer than average days to kick off November in the Nation’s Capital.  That should be pleasing to many DC Area residents who endured a cooler than average second half of October. 

Despite October’s cooler than average finish, October 2018 still finished 3.1° warmer than average.  That made last month the fifth October since 2013 to finish with a monthly average temperature (combining daily high/low temperatures) at least 2.9° above average.  Not since the early 1970s has there been a similar stretch of significantly warmer than average Octobers in Washington, D.C.  The Nation’s Capital had four Octobers that were at least 3° warmer than average between 1970 through 1975.

NOAA expects the warmer than average temperatures to continue in the DC Metro Area until the middle of November.  That’s not to say a chilly day or two isn’t possible, but the trend over much of the first half of the month will be for above average temperatures.  That’s not unusual as 14 of the last 20 November’s have been warmer than average in the Nation’s Capital.  That’s despite three recent cooler than average Novembers in Washington, D.C. from 2012 through 2014. 

November’s warmest temperature on record in Washington, D.C. occurred on November 1, 1974 (86°).  Meanwhile, DC’s coldest November temperature is 11° (November 30, 1929).  While the Nation’s Capital averages 3.17” of rain this month, 15 of the last 20 Novembers have been drier than average.  The last wetter than average November in Washington, D.C. occurred in 2009. 

NOAA’s outlook for November 2018 calls for an increased probability for above average precipitation in the DC Metro Area.  Part of that can be attributed to NOAA’s expectation of a developing El Nino event.  Meanwhile, October 2018 finished with 3.06” of rain making it DC’s first drier than average month since March.  Nevertheless, a total of 52.89” of rain has occurred in the Nation’s Capital since January 1.  That already makes 2018 the ninth wettest year on record with two months left in the year to add to that total.

November is the first of five consecutive months Washington, D.C. averages measurable snowfall with 0.5”.  Longtime Washingtonians might remember that DC’s largest November snowfall occurred on Veteran’s Day in 1987 (11.5”).  However, there is no reliable correlation between measurable November snowfall in Washington, D.C. and what the upcoming winter season will be like.  Measurable November snowfall hasn’t actually occurred in Washington, D.C. since November 1996.