Year of the Umbrella Comes to a Close

There have been a number of major weather events in the Nation’s Capital over the course of 2018.  That ranges from DC’s earliest 80° on record on February 21, to record snow in March, and unprecedented rainfall that occurred so frequently from May through December.  The dominant weather headlines in the DC Metro Area has been the record rains of 2018.

Washington, D.C. broke a 129-year-old record for wettest year on December 15, when a daily record 2.55” of rain fell at National Airport.  Several days of rain occurred since then and more is occurring today, making DC’s 2018 rainfall total a record that will be hard to beat in the future.  That stands at 65.80” as of December 30 and could end up finishing more than 5” higher than the 1889 total, 61.33”.

There are several rainfall-related milestones this year.  Nine of the 12 months of 2018 have been wetter than average.  That by itself isn’t that unusual and occurred as recently as 2014.  However, for the first time DC had three months that finished with at least 8.7” of rain.  This year also had 24 days with at least one inch of rain, breaking the previous record of 21 set in 1878.

The plethora of rainy days led to some very wet months in the Nation’s Capital this year, including DC’s sixth wettest May, fourth wettest July, fifth wettest September and wettest November on record.  Weather records in Washington, D.C. date back to 1871.  Having four months rank in the Top 10 for wettest months in a single year is truly remarkable.

While there have been some dry periods in Washington, D.C. this year, they have been few and far between.  January and March 2018 were each much drier than average.  No measurable rainfall occurred in DC from July 1 through July 16.  That makes DC’s 9.73” of rain over the final two weeks of July much more impressive.  Over 40% of that total occurred on DC’s wettest day in nearly seven years, when 4” of rain fell on July 21.  There were 11 consecutive dry days earlier this month and that was noteworthy for being DC’s longest stretch without rain since September 2017.  However, since then, DC has almost doubled the December average of 3.05” of rain with 5.34” as of December 30.

Despite December’s above average rainfall, it has also been a warmer than average month with a monthly average temperature (combining daily high and low temperatures) almost 4° above normal.  In an unusual twist, Washingtonians had measurable snowfall in November for the first time in more than 20 years, with no December snow whatsoever for only the third time in the last 20 years.  The last time Washingtonians had measurable snow in November but none in December was in 1983. 

Ending 2018 on a Record Note

Flood Watches in effect for much of the DC Metro Area

It’s appropriate that 2018 comes to a wet conclusion since the Nation’s Capital set a record for wettest year with nearly five and a half feet of rain since January 1.  Just this morning, Dulles Airport in nearby Sterling, Virginia, broke its 2003 record for wettest year.  Eight of the first 11 months of 2018 have been warmer and wetter than average in Washington, D.C.  December has already been wetter than average, with 4.32” through December 27 compared to DC’s monthly average of 3.05”.  Over the same time period, DC has been 2.8° warmer than average.

The National Weather Service issued Flood Watches for the DC Metro Area with a total of 1” – 2” of rainfall forecast today.  That could make this DC’s wettest December since 2009 when Washingtonians finished with a total of 6.79” of rain, including liquid snow equivalent.  Unlike December 2009, however, which finished nearly 2° colder than average, December 2018 has been quite mild.  

Over the 20-year period from 1998 through 2017, Washington, D.C. had 11 Decembers that were at least 2° warmer than average.  During 7 of those Decembers, the Nation’s Capital had no measurable snowfall.  In similar fashion, there’s been no snow this December either.  Only eight of the 11 winters that had a very warm December went on to have average or below average snowfall in January and February as well.  This fact illustrate that we cannot accurately deduce what the rest of the winter will be like based on December’s weather alone.

There are many paths for Washington, D.C. to get its seasonal average of 15.4” of snow.  A series of small to moderate snowfalls (as in the 2014-2015 winter) or one major snow event (2015-2016) could make a winter snowier than average.  The two primary ingredients for a major winter storm are appropriate storm track combined with an adequate amount of cold air.

Washingtonians have seen winter seasons like 1997-1998, which was a typical El Nino winter with a series of coastal storms and an active southern branch of the jet stream.  It was also a milder and wetter than average winter with only 0.1” of snow in DC.  By comparison, the 2015-2016 winter season also had a strong El Nino event, but the right ingredients came together and produced the epic January 2016 blizzard.

NOAA is on “El Nino Watch” and there is a 90% chance that El Nino will “…form and continue through the Northern Hemisphere winter 2018-19.”  In the meantime, December 2018 will end on a wet note in the DC Metro Area with more rain expected on New Year’s Eve.  NOAA expects near average temperatures and precipitation in the Mid-Atlantic Region during the first week of 2019.

Weather Headlines of 2018

I recently co-wrote a story for the WUSA9 website discussing some of the DC Area weather highlights for 2018.  I also want to emphasize two significant national weather headlines for 2018: devastating hurricanes, Florence and Michael; and the role weather had in the deadly Duck Boat disaster in Missouri.  Fortunately, Christmas Day weather in the DC Metro Area was largely quiet.

A Warm and Wet December

December 14 - 16, 2018 Rainfall Totals (Source: NWS - LWX)

The first three weeks of December 2018 couldn’t have been more different than last December.  Through December 21, DC’s average monthly temperature (combining daily high and low temperatures) was 2.2° above average.  The final five days of December 2017 were unusually frigid in the Nation’s Capital and remained at 33° or colder.  With a high/low temperature of 23°/16°, December 31, 2017 was also DC’s coldest December day since 1989.  By comparison, DC’s high/low temperature of 67°/47° made for the warmest December day in the Nation’s Capital since December 27, 2016 (68°/49°).  

NOAA’s temperature outlook over the next six to 10 days is for above average temperatures over much of the eastern United States through the end of the year.  That will disappoint local winter weather enthusiasts who were hoping for a “White Christmas.”  There hasn’t been snow on the ground in the DC Metro Area on Christmas Day since 2009.  December 2018 will finish as a warmer than average month.  That’s not unusual considering seven of the last 10 Decembers have been warmer than average in Washington, D.C., including DC’s warmest December on record in 2015.

 

One of DC’s more significant weather headlines this month occurred on December 15 when 2.55” of rain fell at National Airport, breaking the existing 129-year-old record for wettest year.  The 61.33” of rain that occurred in 1889 stood as DC’s wettest year until last Saturday.  DC’s rainfall total since January 1 now stands at 64.75”.

Winter weather enthusiasts might wonder what clues, if any, a warm and wet December offer for the rest of the winter.  Looking at DC’s 10 snowiest winters on record, seven of the 10 Decembers in those winters were colder than average.  That includes December 2009, which featured DC’s largest December snowfall on record with 16.4” of snow on December 18-19.  Six of the 10 Decembers in DC’s 10 snowiest winters were also wetter and snowier than average.  

The fact is, however, that a multitude of factors go into a seasonal forecast.  Winter weather in the United States can be influenced by the presence of El Nino or La Nina and other things like the North Atlantic Oscillation.  December weather by itself isn’t a reliable indicator of what the rest of the winter will feature.  For example, December 1989 finished tied with 1917 as the second coldest on record in the Nation’s Capital – almost 12° colder than average.  It was also a very snowy month with 9”, compared to the December average of 2.3”.  By comparison, the rest of the winter was warmer than average with a combined snow total of only 2.8”.

On the other hand, December 2015 was DC’s warmest on record with no snow.  There was a major shift in the weather pattern by mid-January of 2016 when the right elements came together to produce the epic “Blizzard of 2016.”  That storm made the 2015-2016 winter season snowier than average in Washington, D.C.  Given the warm weather prevalent in the DC Metro Area in December 2015, a snowier than average winter seemed like a pipe dream in early January 2016.  

My colleagues and I on the WUSA9 Weather Team will keep DC Area residents apprised of the latest weather headlines both on-air, online, and on the free WUSA9 app.

Weather Quiz

A rare double rainbow in Gaithersburg, MD (Source: Emi Marinari)

True or False.

The high temperature of 67° on December 21 was DC’s warmest December temperature in nearly two years.