End of Meteorological Fall

 

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 tomorrow, November 30.  Meteorological winter officially gets underway on Thursday and continues through the end of February.  Since the fall comes to its unofficial conclusion this week, we can reflect upon the D.C. Area weather headlines of the last three months.

November 2022 had very streaky weather conditions.  The first 12 days of the month were more than 10° warmer than average with record warmth on November 6, 7 and 11.  The month also got off to a dry start with only 0.70” of rain through the first half.  A hard pivot ensued with below average temperatures from November 13 – 22, including D.C.’s coldest November temperature (26°) in three years on November 21. Ultimately, the Nation’s Capital will finish with above average November temperatures and near average rainfall.

The Nation’s Capital had a very cool and wet start to October.  Measurable rainfall occurred on the first five days of last month and coincided with below average temperatures.  There was a rare record low-high temperature of 55° on October 4.  Although temperatures rebounded, including a September-like high of 81° on October 7, last month finished 2.6° cooler than average.  Consequently, October 2022 was D.C.’s coolest since 2003, according to NOAA.  It was also a drier than average month, giving Washington, D.C. its first cooler and drier than average October since 2015.

September 2022 finished with near average temperatures in the Nation’s Capital.  It was also the 11^th consecutive September to feature 90° heat with two days in the 90s.  There was no record heat or cold.  However, D.C.’s first temperature in the 50s since June occurred on September 16.  The remnants of destructive Hurricane Ian approached the Nation’s Capital on September 30 and brought appreciable rainfall and gusty winds.

The 2022 fall season will finish with near average temperatures in the Nation’s Capital.  That’s largely due to how cool October was compared to November’s milder than average weather.  It has also been a drier than average fall, with below average rainfall in September and October.  Depending on how much rain occurs tomorrow, November could also finish with slightly below average rainfall in Washington, D.C.  NOAA’s Climate Prediction Center expects December to get off to a relatively benign start with near average temperatures and rainfall.

November’s Streaky Weather in the Nation’s Capital

 

November 2022 is well-positioned to finish as a warmer than average month in the Nation’s Capital in contrast to last November that finished 2° colder than average.  Although this month will finish within 3° of average, that doesn’t tell the story of how streaky this month’s weather has been for Washingtonians.

Not only were the first 12 days of November each warmer than average in the Nation’s Capital, but seven of those days were at least 10° above average.  D.C. residents enjoyed nine days of high temperatures in the 70s this month for the highest such total since 2001.  That’s well above D.C.’s average of between three and four such November days over the last 30 years.  Four of those nine days were at least 75° for the highest such total since November 1994.  The icing on the cake was D.C.’s record high of 81° on November 7.  That was D.C.’s first November day in the 80s since 2016.

The weather then changed dramatically with cooler than average temperatures in Washington, D.C. on 10 consecutive days through November 23.  Low temperatures were at or below freezing on five consecutive days through November 22.  D.C.’s low of 26° on November 21 was the coldest November day in the Nation’s Capital since November 13, 2019 (also 26°).  As cold as the last two weeks have been, November 2022 is still 2.5° above average in the Nation’s Capital as of November 25, underscoring how warm the first 12 days of the month were.

A total of 2.09” of rain has fallen in the Nation’s Capital so far this month, with more beneficial rainfall in the forecast tomorrow.  D.C. averages 2.91” of November rainfall, according to NOAA.  However, rainfall has been fairly streaky so far this month with measurable rainfall on only five days.  The wettest day at National Airport occurred on November 15 with 1.22”, which accounted for nearly 60% D.C.’s monthly rainfall to date.

Regardless of the final overall weather statistics for November 2022, it has already been a memorable month with some of the warmest weather in decades combined with the coldest weather in several years.  It’s worth remembering how rare 80° November warmth is with only six such occurrences (including this year) dating back to 1993.  That averages to one such day roughly every five years.  

Rare November Severe Weather

 

November 4, 2022 Severe Weather Reports (Source: NOAA)

Some notable November severe weather outbreaks have occurred in recent years, including earlier this month.  The National Weather Service changed the criteria for severe hail in 2010.  Prior to this, hail 0.75"/+ (penny-sized) in diameter was considered severe.  However, in order to reduce confusion and the number of severe thunderstorm warnings, the criteria for severe hail was raised to 1”/+ (quarter-sized). 

November 4-5, 2022:

Over 60 tornadoes occurred over a two-day stretch from Texas to Illinois, along with a slew of severe wind and hail reports.  This event was unusual for the sheer number of intense tornadoes that occurred relatively late in the season with multiple EF-3 and EF-4 tornadoes.  Six confirmed fatalities were reported by NOAA, along with dozens of injuries. 

November 12-13, 2021:

What stands out about this severe weather outbreak aside from occurring in mid-November is where it occurred.  An eye-popping total of 16 tornadoes developed over a two-day period in New York, Connecticut and Rhode Island.  Long Island, N.Y. was particularly hard hit with tornado damage and severe wind gusts.  A wind gust of 79 mph was observed in Suffolk County on November 13.  Despite occurring in densely populated areas, no injuries or fatalities were reported during this outbreak.

November 10, 2020:

Numerous severe weather reports were observed over a relatively concentrated area in Illinois, Wisconsin and Michigan.  Over a dozen confirmed tornadoes occurred in Illinois alone, with multiple severe wind gusts.  Most notable were wind gusts of 78 mph at Chicago’s Navy Pier, as well as 79 mph in Sugar Grove, IL.  Fortunately, no injuries or fatalities were reported.

November 16, 2010:

This event was concentrated on the east coast from South Carolina to New York.  The dominant type of severe weather on this day was severe wind gusts.  There was, however, a confirmed EF-1 tornado in Baltimore, Maryland.  Three injuries were reported from the tornado, which had wind speeds between 86-110 mph.  The Fujita Scale, originally created in the 1970s, was updated and became the "Enhanced Fujita Scale" or “EF Scale” in 2007.

November 5-6, 2005:

Similar to the November 2010 outbreak, the overwhelming majority of severe weather reports during this outbreak were for high winds.  This event covered a large area from Arkansas to New York.  On November 5, a deadly tornado claimed 22 lives and caused over 200 injuries in the town of Evansville, Indiana.  It was rated an F3 tornado on the original Fujita Scale with estimated wind speeds of 158-206 mph.

Weather Quiz

 

True or False.

Washington, D.C. has never had a snowy Thanksgiving and Christmas.

A Closer Look: Thanksgiving Day Weather, Washington, D.C.

 

Thanksgiving has been the rare holiday in the Nation’s Capital that can feature snow and winter-like cold, as well as spring-like warmth.  Check out this story I wrote for the WUSA9 website for more details.

D.C.’s Hard Pivot to Winter

 

D.C.’s unusually warm start to November has quickly become a distant memory following a particularly cold week.  Yesterday’s high of 41° made for the coldest day in the Nation’s Capital since March 28 (40°).  Following another cold day today, temperatures will start to moderate and reach the 50s by tomorrow.  Highs for much of the upcoming Thanksgiving holiday weekend will be near average in the mid-50s for the Nation’s Capital.  That will feel balmy compared to the January-like chill that’s enveloped so much of the eastern United States over the last week.

These large fluctuations in temperature can be attributed to a shift in the position of the jet stream.  According to the National Weather Service, jet streams are “…relatively narrow bands of strong wind in the upper levels of the atmosphere. The winds blow from west to east in jet streams, but the flow often shifts to the north and south. Jet streams follow the boundaries between hot and cold air.”  The major shift from warmer than average weather when the jet stream was well north of the D.C. Metro Area changed to cooler than average when a “dip” in the jet stream occurred that allowed the colder than average weather to move south.

It’s been so cold in the Nation’s Capital that D.C.’s average monthly November temperature (combining daily high/low temperatures) went from being 10.8° above average for November 1 – 12, to being 3.4° above average as of November 20.  A drop in monthly average temperature this great over the course of a week is dramatic and underscores how unusually warm the first 12 days of November were in Washington, D.C.

Given that NOAA’s temperature outlook is for near average temperatures in the D.C. Metro Area for the rest of the month, November 2022 should finish as a warmer than average month.  Some may wonder whether November weather trends can foreshadow what the upcoming winter season will be like.  There have been some winters when November’s weather in the Nation’s Capital did, in fact, do that.  Such was the case during the 1995-1996 winter season.  November 1995 was 6.5° colder than average in Washington, D.C. with 0.5” of snow.  As longtime Washingtonians may recall, 1995-1996 was D.C.’s third snowiest winter on record with 46” – roughly triple the seasonal average of 15.4” at the time.  That winter was also 2.9° colder than average and featured a moderate episode of La Nina.

On the other hand, November 2009 was 2.6° warmer than average in Washington, D.C. and gave way to what became D.C.’s snowiest winter on record.  A total of 56.1” of snow fell in the Nation’s Capital during the 2009-2010 winter.  The 2009 - 2010 winter was also 2.4° colder than average.  However, unlike the 1995-1996 La Nina winter, it featured one of the strongest El Nino’s on record.  Thus, while November’s weather can sometimes foreshadow what the upcoming winter season will be like, there are too many variables to rely solely on November weather as a predictor.

D.C.’s Unusually Warm Start to November

 

The first 12 days of November were warmer than average in Washington, D.C.  Highs reached 70° or higher on 10 of those days, with a record high of 81° at National Airport on November 7.  That was D.C.’s first November day of 80° warmth since 2016.

The Nation’s Capital has averaged between three and four November days with highs in the 70s dating back to the early 1990s.  What is truly rare in D.C. during the month of November are high temperatures in the 80s.  In fact, there has been a combined total of only five such days since 1993, prior to this month.  The first 12 days of this month were so warm that D.C.’s average monthly temperature (combining daily high/low temperatures) for that period was 10.8° above average, while Dulles was 12.1° warmer than average.

While this November has gotten off to an incredibly warm start, it traditionally is a fairly cold month in the Nation’s Capital.  Four of the last five Novembers were colder than average in Washington, D.C.  In fact, November 2019 was D.C.’s coldest since 1996.  Accumulating snowfall occurred in the Nation’s Capital in November 2018, making it the first November since 1996 to do so.

Despite the string of recent colder than average November’s, D.C.’s 10 coldest November’s all occurred in 1917 or earlier.  That’s long before National Airport became D.C.’s official weather reporting site.  Prior to that, weather measurements for the Nation’s Capital were made downtown.  At that point in time, “downtown” was vastly different.  Washington, D.C. was largely undeveloped with lots of green space and little or no automobile traffic.  In other words, there wasn’t a significant urban heat island effect the way there is today.

The Potomac River plays a significant role in moderating temperatures at National Airport by helping keep them cooler in the summer and fall and warmer in the depths of winter.  Also, suburban sprawl and urbanization since the 1940s has helped make the D.C. Metro Area warmer than it was prior to World War II.  Weather records in the Nation’s Capital date back to the 1870s.

No strong correlation exists between D.C.’s November weather and what the upcoming winter season will be like.  For example, the Nation’s Capital had more snow in November 1989, then it did in January, February and March 1990 combined.  NOAA’s outlook for the next one to two weeks is for significantly colder than average weather in the D.C. Metro Area with near to slightly below average precipitation.