More Like Winter

Residents across the Mid-Atlantic Region and much of the country, have noticed a major shift in the weather pattern.  Gone is the warmer and drier weather that’s dominated much of the fall.  Instead, they are experiencing a significant amount of frigid air that’s been reinforced by arctic air from Alaska and northern Canada.  Although no significant wintry precipitation is expected in the DC Metro Region during the upcoming week, it remains important for people to rely on their favorite source of weather information (such as my colleagues and I on the WUSA9 weather team) for the latest updates.

The Nation’s Capital hasn’t seen measureable snow the way cities in the Upper Midwest and Great Lakes Region – like Chicago, Cleveland and Buffalo have, but it has been cold enough for regional ski resorts in West Virginia, Maryland and Virginia to make their own snow.  Meanwhile, there are a few chances this week for residents in the DC Metro Region to see a few flurries or light snow showers.

Although this month has been slightly warmer than average during its first 10 days, there has been a palpable change in the air.  With a high and low temperature of 39/26 degrees on Saturday, December 10 was the coldest December day in the Nation’s Capital in nearly three years (since December 25, 2013’s high and low temperature of 33/22).  During the first 10 days of this month, there have been four days with high temperatures in the 40s and 50s, with one day of high temperatures each in the 30s and 60s.  That compares to the same period last year when there were six days with high temperatures in the 50s and two each in the 40s and 60s.  The fact that last December was the warmest on record in Washington, D.C. by a wide margin makes the comparison to this December even more dramatic.

The latest Drought Monitor Index (released on December 8) shows moderate drought conditions remain across much of the Mid-Atlantic Region.  In spite of 1.4” of rain so far this month at National Airport, Washington, D.C. still has an annual rainfall deficit of 7.28”.  Helping illustrate just how dry this fall has been is that a total of only 1.66” of rain fell in Washington, D.C. during all of October and November.

Some beneficial rain has occurred earlier this morning.  This will also be the mildest day of the week with high temperatures in the low 50s.  Another cold front will approach the East Coast on Wednesday, helping usher in an even colder blast of arctic air for the end of the work week.  High temperatures will struggle to reach the freezing mark under full sunshine in the Nation’s Capital on Thursday and Friday.  The last time Washingtonians had a daily high temperature that remained below freezing in December was on December 16, 2010 (27F).

Putting This Week’s Cold Into Perspective

NOAA's Temperature Outlook for Mid-December

Although it will be colder than average over much of the next week in the Nation’s Capital, the cold won’t approach record levels.  But, the combination of gusty winds and below normal temperatures will produce especially cold wind chills.

Unless you’re a snow lover, you will be happy no snow will accumulate with these below average temperatures.  That’s not to say the occasional snow flurry won’t occur in spots, but no accumulating snow is on the horizon in the DC Metro Region.  That’s unlike recent Decembers, such as in 2009 when the largest December snowstorm on record occurred in Washington, D.C. (with 16.4” at National Airport on December 18-19).

Over the last 25 years, December has had some dramatic temperature swings in the Nation’s Capital.  For example, Washingtonians experienced two separate streaks in December 1995 when high temperatures remained under 40 degrees (December 10 – 14 and 19 – 28).  That contributed to making the month more than four degrees colder than average.  One of the warmest December’s on record occurred just three years later.  That warm trend was set early in the month with four consecutive days with high temperatures in the 70s (December 4 – 7).  In fact, the high temperature of 79F on December 7, 1998 was Washington, D.C.’s warmest December temperature on record.

By comparison, with an average monthly temperature of 31.8 degrees (combining daily high and low temperatures), National Weather Service data indicates December 2000 was the fourth coldest on record since National Airport opened in 1941.  Just a year later, December 2001 tied for third warmest on record in the Nation’s Capital.  Both the 2000-2001 and 2001-2002 winters featured less than half the average amount of annual snowfall in Washington, D.C.  This illustrates the fact that December temperatures are not a good indicator of what the entire winter will feature.

Both November and December 2015 were significantly warmer than average in the Nation’s Capital, but last winter went on to become snowier than average.  In fact, it was the snowiest January in two decades.  While the Upper Midwest and Great Lakes Region have already seen some significant snowfall this month, the DC Metro Region will not see any over the next week.  However, my colleagues and I on the WUSA9 weather team are expecting below average temperatures for much of the next week.  Also, today is poised to be Washington, D.C.’s first day since March 20 that high temperatures remain below 45 degrees.

Is December’s Weather an Accurate Predictor for Winter?

NOAA's Temperature Outlook for December 2016

Washingtonians can expect an average of 2.3” of snow in December.  Although less snow than what January and February average, December is the first month of meteorological winter and can set the trend for the entire season.  There have been winters when December has been warm and wet that have gone on to be snowier than average, while there have been winters when December was the coldest and snowiest month of the entire season.

Just last year there was a 180-degree turnaround between the warmest December on record in the Nation’s Capital and January 2016, which was more than a degree colder than average.  Last January also saw 18.8” of snow that made it the snowiest January in Washington, D.C. since 1996.  The majority of that fell during the fourth largest snowstorm on record on January 22-23, when 17.8” fell at National Airport.

Last winter ended up being the third consecutive snowier than average winter in Washington, D.C.   Ironically, this happened even though a strong El Nino event contributed to making the 2015-16 winter more than three degrees warmer than average in the Nation’s Capital.  The combination of one record snowstorm during a warmer than average winter shows that one significant storm can make an entire season snowier than average.  The last time the Nation’s Capital had three consecutive winters with at or above average snowfall was 1985 – 1988.

The 1989-90 winter saw the opposite extreme from last winter.  December 1989 was the coldest in the Nation’s Capital since 1917, when the monthly average temperature was also 27.9 degrees.  A total of 12.5” of snow fell in November and December 1989, making it the only year that Washington, D.C. had both a white Thanksgiving and Christmas.  However, once the calendar changed to 1990 the weather changed dramatically in the Mid-Atlantic Region.  January and February were both appreciably warmer than average.  So while the 1989-1990 winter season finished within 0.1” of average snowfall (15.3” vs. 15.4”), over 80% of that occurred in November and December.

NOAA’s outlook for this month calls for a slight chance of above average temperatures and precipitation.  However, for the next one to two weeks its outlook is for cooler than average temperatures.  My colleagues and I on the WUSA9 weather team are tracking the coldest weather of the season which is poised to arrive by the end of the week.  Although the arctic front may bring a few flurries and some light snow showers on Thursday, Washingtonians longing for significant snow will have to wait.

Changing Seasons

Autumn 2016: One for the Record Books

Meteorological fall, which runs from September 1 through November 30, was an especially warm and dry three-month period in the Mid-Atlantic Region.  In fact, November 2016 put an exclamation point on a record setting fall season in the Nation’s Capital.  The annual rainfall deficit in Washington, D.C. ballooned from 1.47” on September 1 to 6.13” by November 30. Only 4.16” of rain occurred during the fall in Washington, D.C. and that made it the seventh driest autumn on record and the driest since 2001 (2.65”).

The combination of a September that tied for third warmest, the tenth warmest October and a warmer than average November made the 2016 fall season the warmest on record in the Nation’s Capital.  The seasonal average temperature of 63.9 degrees (combining daily high and low temperatures) surpassed the previous record from 2007 by more than half a degree (0.6).  Despite being much warmer than average, there were some cold days this fall such as on November 23 when the low temperature reached 32 degrees at National Airport and 20 degrees at Dulles Airport.

Now that December has begun, what constitutes average weather in the Mid-Atlantic Region?  Average high and low temperatures at National Airport on December 1 are 52/37 degrees and drop to 44/29 degrees by New Year’s Eve.  The winter solstice occurs on December 21 and is the first day of “astronomical” winter in the Northern Hemisphere.  Washington, D.C. averages 3.05” of rain and 2.3” of snow during the month of December based on NOAA’s running 30-year average from 1980 – 2010.

Another interesting December trend in the Nation’s Capital is that since 2000, nine of the last 15 Decembers have been warmer than average.  Some many find that ironic because measureable snowfall has occurred in 10 of the last 15 Decembers.  However, a warm and wet December (such as in 2015) doesn’t always indicate what the entire winter will be like.  For example, while Washingtonians didn’t see their first measureable snow last winter until January 17 (0.3”), the season was still the third consecutive snowier than average winter in the Nation’s Capital.

NOAA’s outlook for December calls for a slight chance of above average precipitation in the Mid-Atlantic Region.  That coincides with some encouraging changes in the weather pattern.   My colleagues and I on the WUSA9 weather team expect an increasing potential for appreciable (and much-needed) rain on Tuesday.  That would be excellent news for the entire DC Metro Region.