Impressive Weather Trends

As March 2019 comes to a close, it will be remembered as a relatively benign weather month in the Nation’s Capital.  Average temperatures are well-positioned to finish within a degree of average for only the third time in the last 20 years.  When the National Weather Service measures a monthly average temperature for a given location, both daily high and low temperatures are used.

While the first 10 days of March were exceptionally chilly with temperatures at or below freezing on five consecutive days, above average temperatures during the middle of the month largely offset them.  That’s why it’s sometimes misleading to look solely at average temperatures.  While this month’s warmest temperature was 78° on March 15, DC’s coldest temperature was 22° on March 6.

According to NOAA, there have been a combined 14 record high / record high-low March temperatures in the Nation’s Capital over the last two decades.  No record cold has occurred in Washington, DC during the month of March since 1996.  It’s a different story, however, at Dulles Airport in more rural Sterling, Virginia, where a total of 36 record high / record high-low March temperatures have occurred since 1999.  But, Dulles did have a total of 21 record low / record low-high March temperatures over the same time period.  A record “high-low” temperature means the low temperature on a particular day remained much warmer than average, while a “low-high” temperature is the opposite.

Two primary factors can account for that large difference.  In the Nation’s Capital weather records date back to the 1870s, so it’s often more difficult to break weather records.  Meanwhile, weather records at Dulles Airport only date back to the 1960s when it opened.  To add to that, the amount of urbanization in and immediately adjacent to the Nation’s Capital contributes to a more pronounced urban heat island effect compared to the more rural Dulles Airport.

Washingtonians have experienced no shortage of cold and snowy weather during the month of March in recent years.  Washington, DC had measurable snowfall in seven consecutive March’s (2013 – 2019), the longest such streak on record.  Not only was March 2014 DC’s coldest since 1996, but it was also the snowiest since 1960 with 12.7” of snow.  March 2014 was also the coldest and snowiest (19.8”) on record at Dulles Airport.

Despite the wide variation in March weather in recent years, one thing has remained constant over the last year.  March 2019 will finish with above average rainfall in the Nation’s Capital.  Since April 1, 2018, the Nation’s Capital has had 69.41” of rain.  That would make the 12-month period from April 1, 2018 through March 31, 2019, DC’s wettest 12-month period on record.  2018 was also DC’s wettest calendar year on record.  Washington, D.C. averages 39.74” of annual rainfall.