December's Foggy Freeze

I wanted to talk today about the recent weather here on Long Island and in the northeastern United States as a whole.  The area is experiencing an extended cold spell, with the current forecast calling for a fairly significant weather event later on in the week followed by even colder temperatures.  I will wait until the end of this month to see how January plays out, but I think it's worth discussing the cold December we've had in the context of our weather history over the last half-century.

I looked at temperature records for the month of December going back to 1965 from the weather station located at LaGuardia Airport, using the Weather Underground site.  The mean temperature for December 2017 was 36°F.  How does that compare to Decembers of previous years?  The graph below plots the monthly mean December temperatures since 1965, with the most recent data point being December 2017.  As you can see, this past December was indeed cool compared to recent Decembers.  It wasn't the coldest December on record, though; nor would it have been that abnormal relative to the early part of the data set.   The decadal means for December temperatures were 36.6ºF from 1965-1969, 37.3ºF for the seventies, and 36.4ºF for the eighties.  In other words, it wasn’t that long ago when this December would have been considered very close to average.  Temperatures have risen noticeably since then, however.  The decadal mean December temperature was 39.9ºF in the nineties and 38.6ºF in the 2000s.  This decade, even given this past month, has seen a mean December temperature of 41.1ºF.  It is also worth pointing out that December 2015, with an average temperature of 51°F, was far more anomalously high than 2017 was anomalously low.  (My vegetable garden was still going strong that December, and I even had broccoli growing into the new year.)

So I think a little perspective is required when discussing the current cold spell.  Weather happens, and sometimes things get cold in the winter regardless of the overall trends in temperature.

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