2018 Reaches Uncharted Territory

NOAA's Temperature Outlook for Christmas Week

Having broken DC’s longstanding record for wettest year on December 15, any additional rain before the end of the year will only pad the new record.  The old record for wettest year was set in 1889 (61.33”) and ironically featured DC’s driest December on record (0.19”).  With 3.76” of rain through December 17, December 2018 this month has already exceeded its average of 3.05”.  Since January 1, a total of 64.22” of rain has occurred in the Nation’s Capital.

DC will finish 2018 with a remarkably long and wet stretch of weather, with eight of the final nine months of the year wetter than average.  With the exception of October, every month since April has been wetter than average and this year’s rainfall has been spread out fairly evenly over much of the year.  May 2018 was DC’s sixth wettest on record, July 2018 was DC’s fourth wettest, September 2018 the fifth wettest and last month was DC’s wettest November on record.

That’s unlike some past years that have been wetter than average, but the majority of the rainfall was concentrated around a particular weather event.  For example June 1972 was DC’s third wettest on record due to the flooding rainfall from the remnants of Tropical Storm Agnes.  Meanwhile, September 1999 was DC’s fourth wettest September on record due the remnants of Hurricane Dennis followed by Hurricane Floyd.  August and September 2011 were a combined 11.11” wetter than average in Washington, D.C., largely the result of former Hurricane Irene and Tropical Storm Lee.  By comparison, the DC Metro Area has had above average rainfall over a long period of time this year and that makes 2018’s record more impressive.

With Christmas a week away some may wonder what the odds are for a White Christmas in the Nation’s Capital.  The National Weather Service defines a “White Christmas” as having “…at least 1 inch of snow on the ground on December 25.”  The last time there was snow on the ground in Washington, D.C. on Christmas Day was in 2009.  That was the result of the record December 18-19 snow event.  Washingtonians haven’t had actual snowfall on Christmas Day since 2002 (0.2”).

Washingtonians have already had the first measurable snowfall of the season with 1.4” on November 15.  Unfortunately for snow lovers in the DC Metro Area, the weather pattern is not favorable for any snow on Christmas this year.  NOAA’s temperature outlook for December 23 – 27 is for near average temperatures in the DC Metro Area along with near to slightly below average precipitation.  The average high/low temperatures in Washington, D.C. on December 25 are 44°/30°. 

2018 Has Become DC’s Wettest Year Ever !

Weather ducks would love !

Residents of the Nation’s Capital are in the midst of a very wet mid-December weekend that has made 2018 DC’s wettest year on record.  The Nation’s Capital officially broke its longstanding record (61.33” set in 1889) at 6:26 AM, when a total of 61.34” had accumulated at National Airport since January 1.  The rain has continued for much of the day since then, which only pads the 2018 record.  By comparison, Washington, D.C. averages 39.74” of rain in a given year so Washingtonians are currently at approximately 150% of the annual average.  

It has been a stunning turnaround in the DC Metro Area after one of the longest dry periods in recent memory in this part of the country.  From August 2015 through March 2018, Washington, D.C. experienced drier than average weather in 25 of those 31 months.  That produced a combined rainfall deficit of 16.42” in the Nation’s Capital, with intermittent periods of moderate drought in parts of the Mid-Atlantic Region.  

DC’s weather pattern then proceeded to change rather dramatically in April 2018.  Washingtonians experienced wetter than average conditions in six of the seven months from April 2018 through November 2018.  A slew of rainfall records were set during that time, including DC’s wettest November on record, as well as the fifth wettest July day on record.  The 4” on July 21 also made it DC’s wettest day, overall, since September 30, 2010 (4.66”).  With 1.42” of rain on November 24, Washington, D.C. also set a new record for highest number of days (22) in a calendar year with at least one inch of rain.  (The previous record of 21 such days occurred in 1878).  

Today became DC’s twenty-third day with at least one inch of rain.  Prior to today, Washington, D.C. hasn’t had a December day with at least one inch of rain since December 6, 2016 (1.03”).  You have to go back more than seven years to December 7, 2011 for the last time DC had at least 2” of rain on a December day (3.1”).  The Nation’s Capital averages 3.05” of rain in all of December.

Aside from putting DC over the top and breaking its annual rainfall record, today’s rainfall is also significant for coming after DC’s longest stretch of dry weather in more than a year.  No rainfall occurred in Washington, D.C. from December 3 through December 13.  The last time DC had 11 or more consecutive days without rain was September 15 through October 6, 2017.

December’s Cold and Dry Start in DC

NOAA Expects a Moderating Trend Next Week

Early December has been colder and drier than average in the Nation’s Capital, with a near miss by a major snowstorm.  Through December 11, this month has been 2.2° colder than average.  It has also had below average rainfall so far.  That’s significant since Washington, D.C. hasn’t yet broken its longstanding record for wettest year.  The Nation’s Capital has sat with an annual total of 60.78” of rain since December 3.  That’s only 0.55” away from the 1889 record of 61.33”.  But an expected storm on Friday afternoon continuing into the weekend is expected to make 2018 DC’s wettest year on record. 

In the meantime, area residents have been fortunate to enjoy a dry stretch of weather not seen in some time.  Last week was DC’s first dry work week (Monday, December 3 through Friday, December 7) since July 9 through July 13.  DC’s dry streak will reach 11 consecutive days because it will remain dry in the Nation’s Capital until Friday.  That would be DC’s longest dry stretch since a 22-day stretch from September 15 – October 6, 2017.

The major local weather story this month will likely be that the Nation’s Capital has set a new record for all-time wettest year.  DC weather records date back to 1871 and are kept by NOAA.  There are some parallels between December 1889 – the final month of the current record holder for DC’s wettest year – and December 2017.  Despite being a very wet year prior to December 1, 1889 had the driest December on record in the Nation’s Capital with only 0.19” of rain.  By comparison, last December was DC’s fifth driest with only 0.5” of rain.

As if DC setting a new record for wettest year isn’t impressive enough, there is something else that makes all the rain this year even more noteworthy.  Prior to April 2018, Washingtonians had been languishing in an extended period of drier than average weather.  From August 2015 through March 2018, the Nation’s Capital had accrued a rainfall deficit of 16.42”.  However, during the seven-month period from April 2018 through November 2018, DC had a rainfall surplus of 25.03” that more than wiped out that deficit.

This month’s colder than average start in the DC Metro Area is expected to come to an end as NOAA expects milder than average temperatures to arrive early next week and continue through Christmas.  That means the odds are against having a White Christmas this year in the Nation’s Capital.

DC’s December Record Snow and Warmth

Broomes Island, Maryland (Courtesy: Kayce Kerr)

The storm that brought significant snow and rain to much of the southern United States has been tantalizingly close to bringing the Nation’s Capital appreciable snowfall today.  So close that DC's southern suburbs have had small accumulations while nearby southern Virginia has had double-digit snow totals.  It’s worth pointing out that Washingtonians have had both record snow and record warmth during the month of December over the last 20 years.  However, such conditions often have had little bearing on the rest of the winter barring, the presence of El Nino or La Nina or phase of the North Atlantic Oscillation (NAO).

The Nation’s Capital averages 2.3” of snow in this month and measurable December snowfall has occurred in 16 of the last 24 years – including last year.  December 2009 was the snowiest on record in Washington, D.C. (16.6”).  Longtime Washingtonians may remember the record December 18-19 snow that year which remains one of DC’s 10 largest snowstorms.

DC residents also experienced the warmest December on record just three years ago.  December 2015 finished with a total of 14 days with high temperatures in the 60s and 70s, while low temperatures only fell at or below freezing twice with no snow.  Washingtonians also experienced the warmest four-day stretch on record on December 4 – December 8, 1998, when high temperatures ranged between 73° and 79° (setting records on three of the four days).  Not surprisingly, four of DC’s warmest Decembers have occurred since 2001.  That’s compared to nine of DC’s ten snowiest Decembers that occurred in 1966 or earlier.

Having a warm start to winter doesn’t necessarily mean the rest of the winter will be warmer than average with below average snowfall.  Area residents may recall that following DC’s warmest December in 2015, DC’s fourth largest snow storm occurred in January 2016.  At the opposite end of the spectrum was December 1989, which finished 11.8° colder than average with nearly four times the average monthly amount of snowfall (9”).  In addition, 1989 remains DC’s only year that had snow on the ground on both Thanksgiving and Christmas.  Meanwhile the rest of the 1989-1990 winter was warmer than average with below average snowfall.  

Having one storm give the DC Metro Area a glancing blow should not be discouraging to area winter weather enthusiasts.  That’s because the right elements have to come together only once to bring Washingtonians a classic winter storm capable of producing the seasonal average of snow in just one event (15.4”).  For example, a sufficiently cold air mass combined with the appropriate storm track close to the East Coast could bring the requisite moisture into the DC Metro resulting in a winter wonderland.

Weather Quiz

True or False.

Washingtonians have not had a “White Christmas” in the last 20 years.

---

Answer to the November 13 Weather Quiz question.

C.  Prior to last month, the last time the Nation’s Capital had measurable snowfall in November was in 1996 (0.2").  However, last month’s 1.4” was DC’s highest November total since 1989 (3.5”).

Rare December Severe Weather

Source: NOAA

Severe weather in December is relatively rare in the United States.  According to NOAA’s National Center for Environmental Information, the month of December averages the fewest number of tornadoes of any month with 24.  Despite this, there have been a few noteworthy December severe weather outbreaks.  Severe weather refers to a thunderstorm that contains any of the following: wind gusts of at least 58 mph, hail 1”/+ in diameter, or a tornado.

There was a significant tornado outbreak in Illinois this past Saturday, December 1, where more than three dozen tornadoes developed and caused extensive damage.  According to the U.S. Storm Prediction Center, the strongest tornado was an EF-3 tornado with winds of 155 mph in Christian County, IL.  It was the first EF-3 tornado to develop anywhere in the United States since July 28.  Fortunately, there weren’t any reported fatalities during this rare December tornado outbreak but some injuries were reported.  Based on NOAA data, this was the largest December tornado outbreak in Illinois state history.

More broadly, Saturday’s tornado outbreak was the largest in the United States during the month of December since 2015.  Between December 23 and December 28, 2015, a total of nearly 100 tornadoes were reported in the United States, primarily from the Ohio Valley to the Deep South.  The busiest severe weather day during this outbreak was December 23 when a total of 50 tornadoes occurred that led to four fatalities and 10 injuries.  Contributing to this severe weather was that December 2015 was the warmest December on record in many eastern cities, including Washington, D.C.

The deadliest U.S. tornado outbreak in December over the last 10 years occurred on December 23, 2014, when a total of 19 tornadoes developed in the Deep South that led to eight fatalities in Mississippi.  However, December’s largest single-day tornado outbreak in the last 10 years was on December 31, 2010, when a total of 66 tornadoes developed from Illinois to Mississippi.

The DC Metro Area has had only one tornado during the month of December over the last decade.  On December 1, 2010 a relatively weak and short-lived EF-0 tornado developed in Charles County, Maryland.  That was the third and final day of a severe weather outbreak that extended from the Deep South on November 28, 2010 to the Mid-Atlantic on December 1.  A total of 37 tornadoes developed, but no fatalities were reported.  

Some people may remember a more recent late-November severe weather outbreak between November 28 and November 30, 2016.  A total of 79 tornadoes developed, with an overall total of 348 severe weather reports (including severe wind and hail reports along with the confirmed tornadoes) from the Midwest to the southeastern United States.  Eight fatalities were reported during this outbreak.  NOAA’s Storm Prediction Center doesn’t expect any severe weather in the United States through tomorrow.

What Kind of December Weather Can Washingtonians Expect ?

December is the first month of “meteorological winter” that runs through the end of February.  Average temperatures continue to fall throughout this month as DC’s coldest month, January, looms on the horizon.  Although Washingtonians have had significant snowfall and frigid temperatures historically during the month of December, occasional spring-like warmth can occur as well.

DC’s average temperatures this month range from a high and low of 52°/37° on December 1 to 44°/29° on December 31.  The coldest temperature on record in Washington, D.C. this month is -13° on December 31, 1880.  DC’s warmest December temperature on record occurred more recently on December 7, 1998 (79°).  Six of the last seven December’s have been warmer than average in Washington, D.C., including DC’s warmest December on record in 2015.

Over the last 25 years, DC has averaged one 70° day roughly four out of every five years.  That’s about the same frequency with which Washingtonians have experienced December days when high temperatures remained in the 20s.  Area residents may recall the frigid end of December 2017.  The high temperature on December 31, 2017 in the Nation’s Capital was only 23° - DC’s coldest December high temperature in more than 20 years.

The Nation’s Capital averages 3.05” of rain during the month of December.  Ten of the last 20 Decembers have been drier than average, including the last two.  DC also averages 2.3” of snow in December and snow has occurred in 18 of the last 20 December’s.  December 2009 was DC’s snowiest on record with 16.6”.  Almost all of that can be attributed to DC’s eighth largest snowstorm that occurred on December 18-19, 2009, when 16.4” of snow fell at National Airport. 

 

While DC Area residents had snow on the ground Christmas Day in 2009, it was leftover snow from the storm the week before.  The National Weather Service defines a “White Christmas” as “…at least 1 inch of snow being on the ground on December 25.”  The last time measurable snow occurred on December 25 in Washington, D.C. was in 2002 with 0.2”.

The overall weather pattern in the Nation’s Capital at the start of this December is significantly different then it was a year ago.  The first 11 months of 2017 featured eight drier than average months in Washington, D.C.  By comparison, eight of the first 11 months of 2018 have been wetter than average.  Last month became the wettest November on record in the Nation’s Capital with 7.57” of rain breaking a 141 year-old record.  

So far this month, Washingtonians have had 0.32” of rain.  The yearly total is 60.78” since January 1.  The Nation’s Capital is on the verge of setting a new record for all-time wettest calendar year.  DC’s existing record for wettest year of 61.33” was set back in 1889.  Ironically, December 1889 was also DC’s driest on record.