Stunning reversal: March 2013 was 13 degrees colder than March 2012

marchtemprankingsMarch 2013 was cold – strikingly cold compared to last year, but not all that cold in a historic sense.

The month ended up as the 59th coldest March on record (since 1871) and tied for second coldest since 2000.  You can see the rankings relative to the 2000s to the right

To me, the month’s most amazing statistic is that the average temperature was 13 degrees colder than last March.  The year-to-year change ties 1946-1947 for biggest on record.  The size of the swing mostly reflects 2012′s crazy March warmth (10 degrees above average) which was comparable to a typical April. But the March 2013 difference from average of 3 F on the cold side made the swing all that much more impressive.

The 3 F cold anomaly was the biggest since November (also 3 F cooler than average).  Considering February was also colder than average, we had our first colder than average back-to-back months since December 2010 and January 2011.

The month’s warmest temperature of 63 F joins a group of only 5 years in the entire period of record (since 1871) with a peak temperature so low.  (Those other years were not recent:1891, 1906, 1915, 1931, and 1958).  It was also the first time D.C. failed to reach at least 65 F in March since 1958 according to the Capital Climate blog.

A few other interesting stats:

  • The high temperature of 39F on March 25 (just last Monday!) marked just the 6th instance of a high in the 30s so late in the month (on that day or later).
  • For the first time since 2001, we failed to reach 70 (or higher) during  the month.
  • March was 1.5 F cooler than December.  On average, March 7.1 is degrees warmer than December.  This was the first March colder than December in D.C. since 1959-60.

The cooler than average temperatures occurred disproportionately during the day. National’s high temperature was 4.4 F colder than normal while the low temperature was only 1.5 F colder than the the thirty-year (1981-2010) benchmark.

Precipitation was below normal and one of the driest of the 2000s, but wetter than last year.

marchprecip

The cold temperatures were sometimes conducive for snow, especially north and west of the District. The difference in amounts between the three airports was impressive given their proximity.  See the comparisons below.

marchsnow

Dulles Airport set two daily snowfall records with the 3.3 inches and 3.2 inches that fell on March 6 and 25, respectively.  BWI also set a daily snowfall record with the 3.2 inches it logged on March 25.

While  Reagan National Airport did not set any snowfall records, the 1.4 inches that accumulated on March 25 was the most so late in the season since 2 inches fell in 1990 on March 24-25.

The daily details for temperature and precipitation reveal cold weather dominating all but one week with substantial but scattered precipitation events.

dcatempchartmarch2013

dcaprecipchart032013

Below are some point-by-point comparisons to last year.  There are really some dramatically stark differences between the two years.  March 2012 put last year on track to be the warmest on record for D.C.  This year, we are nowhere close to that pacing.

fixedcomparechart

Cause of the cold

What was to blame for all of this cold? A powerful atmospheric “blocking” pattern set up early in the month across the far northern latitudes.  Whenever strong upper level ridging builds around the polar regions, cold air is flushed down to the middle latitudes like Europe, Asia, and North America.  Many areas of the Northern Hemisphere saw a colder, snowier March due to this blocking regime which may have been partially triggered by a powerful stratospheric warming event that occurred way back in January.

Related: Record blocking patterns fueling extreme weather: detailed look at why it’s so cold

You can see the blocking pattern that dominated March here with the cold trough that got trapped underneath it over eastern North America.

marchupperlevel

A look ahead

The big, bad, winter-extending block is now collapsing and setting the stage for more frequent warmer weather after this first week of April.  The National Weather Service final call for April favors warmer than normal temperatures with an uncertain precipitation outlook.  This seems reasonable given the blocking breakdown and warmer pattern trends expected starting next week.

For Further Information:

The National Weather Service publishes nice monthly assessments usually within a week of the close of each month (should be available shortly):

You can click on your closest airport location here:

Reagan National (DCA)

Dulles Airport (IAD)

Baltimore-Washington (BWI)

Ian Livingston and Jason Samenow contributed to this post.

Also on Capital Weather Gang

D.C. area forecast: One last winter gasp