Thursday, December 06, 2012

Flipping The Switch

December has been off and running with a rather mild start.  Taking out today's chill (temperatures averaging out a couple of degrees below average), the first five days of December have featured temperatures nine degrees above normal and an average temperature of 50.6 degrees.   That's over six degrees warmer than how November averaged throughout the course of the month, a rather impressive reversal of temperature fortune.

December will not be as warm as it's started throughout the course of the month.  Today and tomorrow are going to put a nice dent into that 50.6 and bring it down a few notches.  That said, the overall trend for at least the next ten days is for more above average temperatures in the Mid Atlantic, so it lead me to research how close of a temperature spread we've had between November and December.

Historically, no December has ever finished warmer than its preceding month in a given year.  It's been close a few times over the city's 140 years of good climate records, though.  In fact, the closest spread was just two tenths of a degree in 1873, where November finished with an average of 38.0 degrees and December came in at 37.8 degrees.  In the last fifty years, we've had two years with pretty close November to December temperature drops.  November 1996 was just 1.1 degrees warmer than December and November 1972 was just 3.7 degrees warmer than December that year.

The 'average' December should be 10.2 degrees colder than the average November and it is the third largest change from month to month in the calendar year (only March to April and September to October have greater changes...either warmer in the Spring, colder in the Fall)

If we end up averaging 40.2 degrees this month, or 3.8 degrees above average, we would end up at the four degree threshold of separation and it would rank us eighth closest in temperature drops from last month to this.