The Start of Spring ?

Although many people consider the March 20 vernal equinox to be the official start of spring, meteorological spring began on March 1 and runs through May 31.  March is a highly variable and transitional weather much in the Nation’s Capital.  March can occasionally feature late-spring like warmth.

Average temperatures in Washington, D.C. range from 51°/34° on March 1 to 61°/42° on March 31.  The warmest March temperature on record in the Nation’s Capital is 93° on March 23, 1907.  The coldest temperature is 4° on March 4, 1873.  The difference between DC’s warmest and coldest observed March temperatures is the greatest of any month.  Over the last 10 years, there have been five warmer and five colder than average March’s.

Washingtonians average 3.48” of rain in March.  Half of the last 20 March’s were wetter and half were drier than average.  March 2006 was the driest on record in Washington, D.C. with only 0.06” of rain.  Meanwhile, March 2014 was DC’s snowiest since 1960 with 12.7”.  Snowfall records date back to the 1887-1888 winter in Washington, D.C. and in 23 of those 130 winters, March has been the snowiest month.  There is a four-way tie for the decade when March was DC’s snowiest month of the year with three in each decade (2010s, 1990s, 1940s and the 1930s).  

Not since 2008 have Washingtonians had a March without any snow.  Since February 2018 was DC’s third warmest on record according to NOAA, an earlier than average peak bloom of the famous cherry blossoms along the Tidal Basin is expected.  The National Park Service recently estimated that peak bloom will occur between March 17 – 20.  That’s compared to the average date of April 4.  The record for earliest peak bloom was March 15, 1990, while the latest peak bloom was April 18, 1958.  Some major factors that can adversely affect the cherry blossoms include episodes of very warm, very cold or very windy weather.

Being a transitional month, March often vacillates between warmer and colder than average weather in the DC Metro Area.  For example, Washingtonians had a temperature of at least 81° on four out of five days from March 27 – 31, 1998, and DC residents also enjoyed 81°/+ warmth on three consecutive days starting March 13, 2012.  In contrast, Washingtonians remained below freezing on consecutive days from March 2 – 3, 2009.  DC residents also had their snowiest St. Patrick’s Day on record in 2014 with 3.9” and a high/low temperature of only 32°/27°.

March Came in like a Lion

March 2018 has certainly entered like a lion across the eastern United States.  A powerful Nor’Easter brought the Mid-Atlantic Region a prolonged period of damaging winds.  Friday’s high wind event – with several gusts above 70 mph in the DC Metro Area – caused considerable damage and widespread power outages.  Virtually all school districts and the Federal Government were closed on March 2 as a precaution.

Winds are the result of differences between areas of high and low pressure.  The smaller the physical distance between areas of high and low pressure (known as a “gradient”), the higher the wind speeds tend to be.  What made Friday’s school closures especially noteworthy was the fact no accumulating snow occurred in the DC Metro Area with this storm.  The closures were caused exclusively by the high winds and ancillary power outages.  In turn, the power outages and downed trees caused delays and cancellations to road, rail and air traffic.

Some of Friday’s highest wind gusts (mph) in the DC Metro Area include:

Dahlgren, Va. – 75
Dulles Airport, Sterling, VA. – 71
Gaithersburg, Md. – 69
National Airport (DCA), Virginia – 62
BWI Airport, Baltimore, MD – 61

These wind gusts were similar to the June 29, 2012 derecho in the Nation’s Capital.  During the derecho, Dulles also had a wind gusts to 71 mph, while National’s peak wind gust was 70 mph and BWI’s was 66 mph.  They were all strong tropical storm force wind gusts and also met the criteria for a severe thunderstorm.  Yesterday’s wind gust in Dahlgren, VA, of 75 mph was equivalent to a minimal, Category 1 hurricane.  

There are differences between the June 2012 derecho and yesterday’s wind event.  The derecho was a very short-lived event that lasted a matter of minutes, while yesterday’s high winds lasted the entire day.  The other major difference is the time of year.  In late June the trees have a full canopy of leaves which make them susceptible to high winds.  Without any leaves yesterday, the trees were much lighter than they otherwise would be.  The first six months of 2012 all featured below average rainfall in the Nation’s Capital and June 2012 had also been a very hot month.  This combination created hard and dry ground conditions.  By comparison, after a very wet February the soil was much softer and it was easier for larger trees to be uprooted in yesterday’s high winds.

March is typically a very windy month in the Nation’s Capital.  It is the first month of “meteorological spring” that runs through the end of May.  Washingtonians can expect a high degree of weather variability during March.  For example, March 2012 was DC’s warmest on record, while March 2014 was DC’s snowiest March since 1960.  Meanwhile, last March was the snowiest month of the entire year. 

How Does This Winter Rank ?

The end of meteorological winter has arrived.  The three month period of December, January and February comprise “meteorological winter.”  NOAA uses a running 30-year average (1980-2010) that’s updated every decade to determine what average temperatures and precipitation amounts are in Washington, D.C.

The 2017-2018 winter season could be divided into roughly two different halves with respect to temperature.  The period from December 1 through January 15 was exceptionally cold in the DC Metro Area.  That includes an 11-day stretch where temperatures remained at or below freezing on nine days (December 28, 2017 – January 7, 2018).  Despite the frigid temperatures, only 2.7” of snow occurred during this six-week period.  That speaks to the larger trend of dry weather from September 2017 through January 2018, when the Nation’s Capital had a rainfall deficit of more than nine inches.

Following DC’s driest January since 1981, moderate to severe drought conditions enveloped almost the entire DC Metro Area earlier this month.  Fortunately, a dramatic change in the weather pattern developed with measurable rainfall on 15 of the first 25 days of February.  Despite this, February 2018 has also been significantly warmer than average and that has meant below average snowfall. 

January 2018 had a mild second half with above average temperatures on 11 of the final 15 days.  That warmer than average trend continued into February, as this month is poised to finish as the third warmest on record in Washington, D.C.  In addition, the high temperature of 82° on February 21 was not only the earliest in the year 80° warmth occurred, but was also DC’s first 80° February day since February 28, 1948.

Despite this flip flop from cold and dry over the first half of the 2017-2018 winter season to warm and rainy for much of the second half, the lack of snowfall has persisted.  A total of only 3.3” of snow fell in Washington, D.C. this season or roughly 20% of the seasonal average of 15.4”.  

Washingtonians longing for snow shouldn’t give up hope altogether for seeing a little snowfall.  While last winter was also warmer and drier than average in the Nation’s Capital, March 2017 was snowier than average with two inches at National Airport.  Despite the expected cooler and wetter than average start to March 2018, NOAA says there is a 33% chance that it will feature warmer than average monthly temperatures in the Nation’s Capital and near average precipitation. 

Weather Quiz

True or False.

With 3.3” of snow the entire winter, the 2017-2018 winter is the third consecutive winter season with below average snowfall in Washington, D.C.

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Answer to February 14 Weather Quiz question.

B.  Norfolk, Virginia saw 13.1” of snow in January 2018 that is roughly four times the amount Washingtonians had the entire 2017-2018 winter season (3.3”).  In a rare set of circumstances, Atlanta (4.7”) and Birmingham (4.0”) also saw more snow than the Nation’s Capital this winter.