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Washington, D.C., eclipses warmest December on record by an enormous margin

December 2015 in Washington was the epitome of weird weather. It will be remembered not for its steadily decreasing temperatures and occasional flurry, but for its humid, foggy days with high temperatures in the 70s, and lows that could masquerade as normal highs.

Some cherry trees, irises, roses and daffodils bloomed straight through the month, painting a surreal portrait next to evergreen trees and red bows. Instead of curling up in front of a fireplace, many in Washington turned to air conditioning rather than heat on Christmas.

This month has been more typical of November — or March, for that matter — and rarely felt like meteorological winter. This December was far from normal.

In fact it was record-warm by an enormous margin and now ranks as the largest departure from normal out of any month in any year. With an approximate average temperature of 51.2 degrees, this month will end 11.5 degrees warmer than normal in Washington — 5.5 degrees warmer than the previous warmest December.

It was 1.5 degrees warmer than an average November and 4.3 degrees warmer than an average March. The lowest temperature we had this month was 30 degrees — which is now that warmest low temperature ever in the month of December, beating last year’s record of 29 degrees.

And for the first time since 2001, there was no snow — zilch — in the entire month.

In so many ways, December 2015 was off the chart.

The list of warm weather milestones and records established this month is simply astonishing:

  • Two record high temperatures: 71 degrees on Dec. 13 and Dec. 24
  • Four record warm low temperatures, including 60 degrees on Dec. 24, and 57 on Dec. 25
  • The 60-degree low on Christmas Eve was the warmest minimum temperature on record for the entire month.
  • 26 days at or above 50 degrees, beating the record of 24 from 1889
  • 14 days at or above 60 degrees, beating the record of 10 from 1971, 1951 and 1932
  • Three days at or above 70 degrees, which falls just short of the record of five in 1982 — also a super El Niño year
  • Two days at 32 degrees or colder, which beats the old record of four days from last year
  • 20 days at 40 or warmer (2/3 of the month!) which easily beats the old record of 15 from 2001
  • For the season, we’ve seen only three freezing temperatures in November and December, which is the lowest on record thus far.

Of course, the warmth was seen well beyond the immediate Washington area. Baltimore set six record high temperatures this month, and three record warm lows. Dulles reported three record highs and three record warm lows. On Dec. 24, the 63-degree low temperature was the all-time warmest low for the month of December at Dulles.

All across the Northeast, warmest Decembers have been logged.

Precipitation in Washington was 4.84 inches for the month, which was 1.79 inches above normal and the wettest December since 2013, when 5.53 inches fell. Dulles and Baltimore-Washington International Airport were also wetter than normal with totals of 3.76 inches and 5.85 inches, respectively.

No snow was recorded at Washington D.C. (one trace report in Baltimore and at Dulles), and the combined months of November and December are the least snowy since 2001.

The super-warm pattern

A combination of the strongest El Niño on record (by some measures) and a few other factors drove the super-warm pattern over eastern North America. The prevailing jet stream featured an incredible, warm ridge of high pressure over the entire eastern half of the continent — a complete reversal from last year’s winter pattern.

All of these large-scale patterns worked together to create impressive warmth in the Eastern United States.

+WPO Positive Western Pacific Oscillation (warm Eastern U.S. signal)

+EPO Positive Eastern Pacific Oscillation (warm Eastern U.S. signal)

-PNA Negative Pacific-North American (warm Eastern U.S. signal)

+AO Positive Arctic Oscillation (normally a warm Eastern U.S. signal)

+NAO Positive North Atlantic Oscillation (normally a warm Eastern U.S. signal)

The resulting surface temperature anomaly was astonishing.

Year in review

Our super-warm December catapults 2015 to the second warmest year of the 21st century — falling short of 2012 when a very warm spring and hot summer pushed it to the warmest year in Washington. This year will also end as the third-warmest of all-time too after 2012 and 1991 (which was just o.1-degree warmer than 2015).

Warmer low temperatures did a lot of the work early this year before a station correction. December’s periods of unusually high humidity also played a role.

The wet December also advances 2015 to sixth position for the 21st century.

For further information

The National Weather Service publishes nice monthly assessments about five days into the start of the next month. You can click on your closest airport location here:

Reagan National Airport (DCA)

Dulles International (IAD)

Baltimore-Washington International (BWI)

Ian Livingston contributed to this report.