Needed Rainfall on the Way

Record Snowfall Occurs in the DC Metro in January 2016

Ironically, today is the second anniversary of DC’s fourth largest snowstorm on record.  That’s because the Nation’s Capital is mired in a growing drought resulting from a sustained stretch of drier than average weather.  Washington, D.C. has a rainfall deficit of more than 16”, dating back to August 2015.  In that time, 24 of the last 29 months have been drier than average according to NOAA.  Washington, D.C. hasn’t had more than 0.37” of rain since November 7 and that stretch of 76 days is the sixth longest on record.

Since September 1, 2017, DC’s rainfall deficit is approaching 9” at National Airport (“DCA” is DC’s official weather reporting site).  Since the start of meteorological winter on December 1, the rainfall deficit is nearly 4”.  That followed July and August which were both significantly wetter than average in the Mid-Atlantic Region with a rainfall surplus of 7.07” (at DCA).  Consequently, the DC Metro Region had no drought conditions on Labor Day weekend.  However, given how dry the fall and first half of winter have been, the latest Drought Monitor Index shows moderate drought conditions extend from parts of central Pennsylvania to South Carolina.  

Since only 0.67” of rain has occurred this month in Washington, D.C., meaning there is quite a bit of ground to reach the January average rainfall total of 2.81”.  In the Nation’s Capital, 14 of the last 20 January’s have been drier than average.  It’s somewhat ironic that January 2016 was drier than average in the Nation’s Capital despite it being DC’s eighth snowiest January on record with a monthly total of 18.8”.  That’s because outside of DC’s record January 22-23, 2016, snow event that brought 17.8” of snow, January 2016 was an otherwise dry month.  It will take several months of above average precipitation to alleviate the moderate drought conditions across the Mid-Atlantic and put a dent in DC’s growing rainfall deficit.

Fortunately, it’s not the growing season in the Mid-Atlantic Region and the arid conditions don’t have the same impact they otherwise would.  However, the combination of extreme cold and below average rainfall from late December through the first half of January has led to a lot of frozen ground in the DC Metro Area.  The current milder temperatures are allowing some of the ice to melt from area waterways and this thaw will help minimize any rainwater runoff.  

Some rain is actually expected tonight and tomorrow morning.  The storm track is such that much of the East Coast will be in the warm sector.  That means the precipitation will be rain and not snow, sleet or freezing rain.  Although snow-lovers are disappointed by this turn of events, they should take comfort that several of DC’s largest snowstorms have occurred in the month of February, including President’s Day 1979, 1983 and 2003.  NOAA’s Climate Prediction Center currently expects an equal chance for above or below average February precipitation in the DC Metro Area.  All it takes, though, is the right set of events to come together just once to create a significant DC snowstorm.

A Tale of Two Extremes

2018 Has Gotten off to a Frigid Start in Washington, D.C.  (Courtesy: Robin Beal)

The first half of January 2018 has been exceptionally frigid in the Nation’s Capital.  This month’s average temperature (combining daily high and low temperatures) is 29.5° (6.5° below average) through January 17.  That’s despite having three consecutive days in the 60s this past week.  

So far this month, there have been a total of 10 days with low temperatures in the single digits and teens.  High temperatures remained at or below freezing on eight days.  That’s the highest such total since January 2005.  Although no record lows were set in Washington, D.C., temperatures were below average on 13 of the first 17 days this month.

Official weather measurements for Washington, D.C. are made at National Airport.  Some may wonder where weather measurements for the Nation’s Capital were made prior to National Airport’s opening in 1941.  They were taken downtown in Northwest Washington and date back to the 1870s.

 

The vast majority of record low temperatures in the Nation’s Capital occurred before 1941 when measurements were made away from the Potomac River and when the city was much less developed.  The urban heat island effect was significantly less than it is today.  Only a third of the 62 record low January temperatures (including record low and record low-high temperatures) have occurred at National Airport.  

The last time a record low temperature occurred in Washington, D.C. in the month of January was in 1994.  By coincidence, today is the 24^th anniversary of the last time temperatures fell below zero degrees in the Nation’s Capital.  The observed high and low temperatures of 8°/-4° remain January 19 records.  That was also the last time a high temperature remained below 10° in Washington, D.C.  Since then, Washingtonians have had a total of 15 record high January temperatures (including record highs and record high-low temperatures).

Fortunately, for those tired of the cold, NOAA expects warmer than average weather in the DC Metro Region for over the next one to two weeks.  Several days over the next week will feature high temperatures in the 50s, compared to average high temperatures in the low 40s.  This milder than average weather will prevent January from finishing as an exceptionally cold month overall.  While 10 of the last 20 January’s been warmer than average, three of the past four have been colder than average in Washington, D.C.  

Over the last several weeks of up and down temperatures, Washingtonians have had very little snowfall.  Since December 1, DC residents have seen only 3.1” of snow, including 1.2” since January 1.  By comparison, southern cities like Atlanta, Georgia and Birmingham, Alabama received 4.7” and 4” of snow, respectively, since December 1.  That is not good news for local snow lovers.

What’s Better: A Few Small or One Huge Snowfall ?

January 2016 DC Snowfall

Accurate snowfall records date back to January 1888 in the Nation’s Capital and snow has been officially measured at National Airport since World War II.  Washington, D.C. averages 15.4” of snow annually according to NOAA.  Fifteen of the last 20 winters have had below average snowfall in the Nation’s Capital.

However, Washingtonians had two of their 10 snowiest winters on record since 2002.  The 56.1” of snow during the 2009-2010 winter season made it the snowiest winter on record in the Nation’s Capital.  That’s in addition to the seventh snowiest winter on record in DC when 40.4” of snow accumulated during the 2002-2003 winter.

More recently, the Nation’s Capital has experienced record winter cold, record warmth and record snowfall.  For example, although February 2015 was DC’s coldest February since 1979, December 2015 was DC’s warmest on record.  The 2013-2014 winter season was DC’s 18^th snowiest on record with a total of 32”.  Daily snowfall exceeded an inch on 10 days during the 2013-2014 winter season.  By comparison, the 2015-2016 winter season was also snowier than average with 22.2” of snow at National Airport.  However, 17.8” of that occurred during the record-setting January 2016 storm, or roughly 80% of the seasonal total.

There were only three days with at least one inch of snowfall during the 2015-2016 winter in Washington, D.C., unlike the 2013-2014 winter.  That illustrates how DC residents can exceed the average seasonal snowfall total: with one major winter storm or with a series of smaller snowfalls. 

Although the month of March averages less snow than December, January and February in Washington, D.C., there have been seven winters where March has been the snowiest month dating back to the 1992-1993 season.  Some may remember the March 1993 “Superstorm” that brought record snowfall the much of the Mid-Atlantic Region.

By comparison, the 1989-1990 winter was the opposite of the 1992-1993 winter season.  That’s because a total of 12.5” of snow fell in Washington, D.C. in November and December 1989, while only a combined 2.8” occurred during the rest of that winter.  This winter has been similar to the 1989-1990 winter so far.  Both December 1989 and December 2017 were colder than average and had measurable snowfall in the Nation’s Capital.  The high temperature of 23° on December 31, 2017, was DC’s coldest December high temperature since December 24, 1989.  

Following temperatures at or below freezing on eight of the first 15 days of January, another significant shift in the weather pattern is expected later this week.  March-like temperatures in the mid to upper 50s are expected by this weekend.  However, a weak system will first bring some light snow to the DC Metro Region later today and tonight.