DC Area Snowfall

December 9 Snow in Germantown, Maryland

Washingtonians have had a total of 3.1” so far this winter or roughly 20% of the annual average of 15.4” of snow, according to NOAA.  That’s despite the unusually frigid weather which enveloped the Mid-Atlantic Region from late-December through mid-January.

However, the storm track hasn’t been favorable for any significant rain or snow in the DC Metro Area for a long time now.  The last time at least 0.5” of rain occurred in Washington, D.C. was on November 7.  Area snow lovers shouldn’t fret, though, as February remains the snowiest month on average with 5.7” of snow.  February has featured some of the largest snowstorms on record in the Nation’s Capital, such as in 1979, 1983 and 2003.  There are some parallels between those winters and this one.  For example, a total of only 6.6” of snow fell in the Nation’s Capital between December 1, 1982 and January 31, 1983.  But, the record February 1983 winter storm brought 16.6” of snow and the month ended with a snow total of 21”.

More recently, the 2013-2014 winter season featured some of DC’s coldest weather in decades, including DC’s first high temperature of less than 20° on January 22, 2014 (19°) since January 20, 1994 (18°).  A total of 8.1” of snow occurred at National Airport from December 2013 to January 2014.  However, February and March 2014 brought Washingtonians roughly three times that amount for a total of 23.9” of snow.  In a relatively rare feat, March 2014 was the snowiest month of the entire 2013-2014 winter (12.7”) and DC’s snowiest March since 1960. 

Similarly, the 2015-2016 winter season got off to an awful start for area snow lovers with the warmest December on record in the Nation’s Capital.  However, the January 22-23, 2016 snowstorm (17.8”) helped the winter season finish with above average snowfall in Washington, D.C.

Following the 3.4” of snow that fell during the entire 2016-2017 winter season in the Nation’s Capital and the 3.1” so far this winter, there are quite a few despondent snow lovers in the DC-Area.  The last time the DC Metro Area saw a total of less than 10” of snow during consecutive winters was the 2011-2012 and 2012-2013 winters when only 5.1” was recorded.  

It’s worth remembering that it only takes one significant storm to change the course of an entire winter.  NOAA expects above average temperatures with near average precipitation for the DC Metro Area in February.

Weather Quiz

January 2018 in the Nation's Capital  (Courtesy: Robin Beal)

True of False. 

With a total of only 0.94” of precipitation this month, January 2018 not only ranks as DC’s driest since 1981 but also one of the driest on record.

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Answer to the January 15 Weather Quiz question.

True.  There were only three days with high temperatures =/<32°F in Washington, D.C. during the entire 2016-2017 winter season.

Can One Month be Warm, Cold and Near Average ?

As January 2018 comes to a close, it’s a good time to discuss some of its weather extremes.  As of January 27, this month has had seven days with high temperatures in the 20s and another eight days with highs in the 60s.

Although January got off to a frigid start with colder than average temperatures on 10 of the first 15 days, DC temperatures have been warmer than average on eight of the last 12 days since January 15.  That’s left this month’s average temperature at 35.0° (only one degree below average).  Official weather measurements for Washington, D.C. are made at National Airport (DCA).

A major shift in the position of the jet stream has caused milder than average temperatures over the second half of January across the DC Metro.  Unfortunately for snow lovers, it has been a relatively dry month with no significant winter storms during the unusual cold wave earlier this month.  There has only been 1.2” of snow this month, well below DC’s January average of 5.6”.

The eight days this month with high temperatures at or below 32° was DC’s highest such total since 2005.  Amazingly, this month has also had eight days with high temperatures in the 60s for the highest such total since 2006.  January 2018 joins a rather elite club of only nine other months with eight or more 60°/+ days dating back to the 1870s.  Eight of those months rank in DC’s Top 10 warmest January’s according to the National Weather Service.  January 1950 had a record 14 days of 60° or warmer and remains DC’s warmest January on record.

Since January’s temperatures will ultimately finish close to average, it’s important to mention what has become January’s primary weather story in the Mid-Atlantic.  That is the moderate to severe drought conditions which now exist for almost the entire DC Metro Area.  As of January 27, Washington, D.C. has a rainfall deficit of nearly 9” since September 1, 2017.  Fortunately, the DC Metro Area had some much needed rainfall today.  NOAA expects roughly equal chances of above or below February precipitation for the DC Metro Area.

The Challenge of Forecasting Snow

Some of DC’s largest snowstorms have occurred during the second half of January, including the infamous “Knickerbocker” Storm of 1922 and, more recently, DC’s fourth largest snowstorm just two years ago.  A high degree of skill is required when forecasting snow in the DC Metro Area given the complexity of winter storms and the unique geography of the Mid-Atlantic Region.  

Several of the record snow events in the Mid-Atlantic Region over the last 20 years were well-forecast in advance.  For example, the January 22-23, 2016 event that tied for fourth largest snowfall in the Nation’s Capital and was first mentioned in forecasts the previous weekend.  Also, area meteorologists, including my colleagues and I on the WUSA9 weather team, gave area residents several days advance notice for high impact storms in December 2009, February 2003 and January 1996.  

These storms were all such blockbuster events that the computer models meteorologists use were able to identify the seeds that became the storms days in advance.  The farther out from an event you are, there is a higher degree of fluctuation between computer model runs.  That leads to an old weather adage in the weather community that “the trend is your friend.”  If several models show a particular storm or event over several model runs, then meteorologists have more confidence that said event might occur.

There has also been an incredible amount of improvement in the forecasting models as computers have become more powerful and the mathematical equations used have been refined to account for bias.  But there still remains an inherent amount of uncertainty in weather forecasting, with each model having its own bias.  That’s why meteorologists are so important since they recognize the bias associated with each model and can adjust their forecasts accordingly.

Despite the increased accuracy in forecasts due to advances in numerical weather prediction, forecasting “busts” do occur on occasion when an anticipated winter storm either doesn’t materialize or more snow than originally expected occurs.  For example, some computer models were suggesting on March 2, 2001 that a major winter storm with possible blizzard conditions would develop in the DC Metro Area on March 5-7.  While snow totals of 12”/+ did eventually occur, they were further north in New York and New England.  Many DC Area school districts had closed in anticipation of a significant winter storm, but only 0.2” fell at National Airport on March 5, 2001.

Ironically, today is also the 18^th anniversary of another numerical weather prediction failure.  On January 23, 2000, a storm was expected to be too far east to have any significant impact on the DC Metro Area.  However, by 11:00 pm on January 24, local meteorologists recognized that it would be a high impact storm for the Nation’s Capital.  Most people had already gone to bed and woke up to a surprise snow day on January 25.  Snow totals of 9” to 18” were common from I-81 to the Chesapeake Bay.  Many residents held local media outlets and meteorologists responsible for the unwelcome surprise.  This remains one of the more significant numerical weather prediction failures in recent memory for the Mid-Atlantic Region.

Some take-away lessons are that while weather forecasting continues to improve, forecasting “busts” do happen.  People need to pay attention to the latest forecasts for any changes.  Weather forecasting is an evolving process and it’s vital to get the latest updates from reputable sources.