Friday, April 13, 2012

Weather History: Talking The Titanic Weather Pattern

Sunday marks the 100th anniversary of Titanic's sinking in the wake of striking an iceberg in the North Atlantic waters east-southeast of Newfoundland.  You've probably seen the movie (perhaps enough times) and know the story...we don't need to retell it here although you can now see it in 3-D if you wish.  However, the backstory behind the sinking...the weather pattern the prior winter that lead to icebergs hanging out around 41 degrees north latitude...is worth discussing.

Icebergs aren't uncommon off of Canada's coastal waters -- the cold Labrador current that pushes down from the high latitudes near Greenland combined with the historically cold reaches of Eastern Canada combine to provide an annual journey of icebergs down along the Labrador and Newfoundland coastlines.  According to the Canadian Ice Service, about 800 icebergs a year drift south of 48 degrees latitude and some can reach as far south as 40 degrees latitude.  That number can vary based on sea ice extent, climate, ocean temperatures (colder oceans can support icebergs a bit longer), and atmospheric conditions (cold winters can help generate more sea ice).  In recent years, that average number has been lower thanks to the combination of warming arctic, thinner sea ice, and not as much southern extent of sea ice development in the winter.  The farthest south an iceberg has been spotted is near Bermuda back in 1926.

100 years ago, however, things were quite cold compared to our recent winter.

The January-March period was rather cold for much of the central and eastern US...and one could argue Canada as well.  While the core of the cold in the US dove into the Midwest and Great Lakes, the East Coast was dinged with cold that has set records, one of which still sticks in Philadelphia to this day.  January 1912 was a particularly cold stretch for the US -- Minneapolis set its second coldest January on record (-2.7 degrees for an average temperature...an average high of 4.3 degrees!), with Philadelphia coming in with its tenth coldest January on record (25.4 degrees for an average temperature, over 7 degrees below our modern average and exactly seven degrees below the 1881-1910 norm).

Not quite coldest winter ever material but January-March 1912 were much colder than historical averages for much of the Eastern US.

The middle portions of January were undoubtedly the brunt of the cold for much of the US -- highs on the 11th topped out at -19 in Minneapolis and on the 13th a record cold high (that still stands) of 12 was set in Philadelphia, with a record low (since tied) of 0 here in Philly.

The cold continued into February, easing in the Midwest but shifting to the East Coast during the month.  Philadelphia averaged a temperature of 30.9 degrees in February, a touch more than four degrees below our modern average for the month and 2.1 degrees below the 1881-1910 averages, with lows of 4 degrees on the 10th and 11th of the month (not records, still cold though).   For the winter overall, a mild December was negated by a very cold January and cold February to provide temperatures that were anywhere from one to five degrees below modern averages.

This cold look persisted into March in the Eastern US though.  Temperatures in Philadelphia did not break 60 degrees until March 15th, with lows below 20 on the 3rd and 4th of March.  Snow fell in Philly on three occasions during the month, all of which minor in accumulation, but it brought a third consecutive cold month to the Eastern US.  The monthly temperature of 39.5 degrees in Philadelphia was nearly four degrees below our modern averages and 1.3 degrees below the running 30 degree average of the era (40.8).

While 1912 was not the coldest ever, temperatures were still below the 1881-1910 running averages by one to three degrees across the East (which would put them into a two to five degree departure in our modern era).  The prevalent cold pattern contributed to oceanic temperatures running around one to two degrees below average Celsius (between just under two to four degrees Fahrenheit) for various portions of the North Atlantic.   Oceanic temperature estimates just southeast of Newfoundland in February 1912, for instance, ran 2.05 degrees C below average, 1.52 below in March, and 1.32 below average in April.   This cold environment likely helped to sustain icebergs on their slide south from the Arctic...whether one wants to blame the chicken (cold ocean) or the egg (cold airmasses reinforcing the chilled water) is up for debate...but the prevalent and dominant pattern in the North Atlantic was much colder than average...and one that supported iceberg sustenance that led to the fateful night.