2013 in Washington, D.C. will not be known as an exceptionally extreme year in terms of overall temperature and precipitation.
The 12-month average temperature of 58.8F was 0.6F warmer than the 30-year running normal, the product of eight warmer and four colder-than-normal months. 2013 was 2.7F colder than 2012, which was the warmest year on record due to an exceptional March and very hot summer. Overall, it was the coolest year since 2009 and it ranks basically in the middle of the 2000s.
Precipitation was also right in the middle of the 2000s with the 44.28″ total coming in 4.54″ wetter-than-normal. However, it was an impressive 11.83″ wetter than last year, a big turnaround for a non-El Nino year.
You can see how 2013 gets sorted out in the context of the other 13 years of the 2000s here:
Here is how all three major reporting stations in our area fared for the final month of last year:
The temperature anomalies were very close to each other as were the precipitation totals; however, snow was the big differentiator as Baltimore got nearly twice as much as National with 2.9″ and Dulles picked up 4.7″. National came in at 1.5″. It has certainly been a slow-go for snow since the big 2009-10 season.
Temperatures in detail
December 2013 can be characterized by its very high degree of volatility. The range from warmest to coldest temperature was a solid 50 degrees (and only three days apart!). The month was nearly evenly split between cold and warm days, but the warm days were stronger, especially just ahead of Christmas when National hit 72F twice. While this is comparable to 2012’s peak of 72F, the colder low of 22F on Christmas Day beat 2012’s coldest by seven degrees. You can see the daily temperature differences from normal (anomalies vs. 30-year 1981-2010 normal) below:
In context with the rest of the 2000s, December 2013 was the fifth warmest of the batch. Tracking the years shows very little overall trend though:
2001, 2011, and last year were three big warm Decembers with very few days below freezing at National (we did it thirteen days this time), while 2000 was the powerhouse cold December that outperformed all the 1990s too with an average temperature below freezing. Even the relatively recently colder December 2010 was not nearly as cold as that.
Temperature records around the area were broken in the December 21-22 weekend when we surged into the low 70s and had a very warm low on Sunday. The pair of 72s at National Airport on those days bested or tied records from 1923 (68F) and 1889 (72F). Both Baltimore and Dulles broke high temperature records on those days too, but the bigger story for those two locations was the record warm minimum readings. Baltimore’s 62F was the warmest low temperature ever recorded in December (beating Dec 1950), and it exceeded the warmest of any meteorological winter month warmest low (Jan 1950’s 61F). At Dulles, the record warm minimum was 62F, beating 1990’s 61F for warmest low of the month and matching 1998’s value for warmest of the entire winter.
December was definitely a wet month with five days reporting over a half inch of liquid equivalent. Of course, in December, our attention is more on the snow side, but National again struggled to keep up with Dulles and even Baltimore. National’s 1.5″ total was comprised of two events just two days apart (Dec 8th’s 0.9″ and Dec 10th’s 0.6″). Here is the daily rundown of precipitation at National for December:
Compared to the rest of the 2000s, 2013 offered the second wettest December following the 2009 snow-crazy month. That 5.53″ total actually ranks in the top ten wet Decembers of all-time too at number nine on the list. 2009 is the second wettest of all time. Looking at the history of 2000s Decembers, we see there is no strong trend; however, there is a tendency to see slightly more wetter vs. drier months so far.
From a records standpoint, Dulles had some daily ones including .97″ December 6 beating 1983’s .75″. And the 1.27″ December 29 shattered 1991’s .51″. We undoubtedly had plenty of moisture, but the highly volatile temperature pattern was the bigger story.
The weather pattern
December 2013 was defined by lots of pattern volatility nationally and locally. For our Mid-Atlantic area, the volatility was fueled by a “conflict of influencers” with a cold weather signal from strong Alaskan area upper level ridging and a warm weather signal from upper level troughing over the North Atlantic. This unusual pattern combination (negative Eastern Pacific Oscillation and positive North Atlantic Oscillation) gave us alternating currents of warm and cold conditions this December as shown below.
That same weather pattern “battle” described above continues to impact our first half of January at least. A massive surge of ridging up through Alaska and even toward the North Pole see-sawed down some very cold weather over the past couple of days, offering the Mid-Atlantic region its coldest temperatures since 1996. However, that Alaskan ridge is forecast to crumble and allow the Southeast warm ridge to re-buckle to trend us back warmer again for the second week of the month. Long term indications for the second half of January are at odds, but the thinking right now is that we may again edge warmer than normal overall. Either way, we should expect a high degree of volatility to continue.
With such volatility, we will have to track precipitation closely too. This winter reminds me a little bit of the 1993-94 story when we received cold air outbreaks with very little to no atmospheric blocking on the Atlantic (Greenland) side and the 1995-96 winter when we saw a large degree of temperature volatility from week-to-week. We had one big snowstorm in the 1995-96 winter amidst all that volatility, but it will take getting the cold and precipitation ingredients to work out just right, which is always a big challenge around here. I’d recommend staying reasonably skeptical about bigger snowstorm prospects at this point.
The National Weather Service only has the D.C. area in the EC category meaning equal chances for above, below, or normal temperatures and precipitation just like they did last month. This is once again not very helpful for our area. You can see their depiction here.
For further information
The National Weather Service publishes nice monthly assessments:
You can click on your closest airport location here:
Capital Weather Gang’s Ian Livingston contributed to this post.