Monday, October 15, 2012

First Sub 40 Morning Earlier Than Past Years

Saturday morning's low of 37 degrees equaled the earliest morning low of under 40 degrees in Philadelphia since 2006 and was the earliest sub 40 degree start in the city since October 3rd, 2003 (when we dropped to 39).  October has historically featured our first sub 40 degree morning, with nine of the last ten years featuring an October morning with a low in the 30's.

There isn't much correlation between a cold morning in October on its own and the following winter...there is, however, a correlation between a cold October overall and the proceeding winter.   Typically, a colder October compared to long-term climo suggests a colder than normal winter about two out of three times whereas a warmer October compared to long-term climo puts us in a warmer winter about 70 percent of the time, according to Tony Gigi at the National Weather Service.

The dividing lines between cold and warm October are among the top third warmest and top third coldest....historically, those dividing lines are about 1.5 degrees above and 1.2 degrees below our current 30 year average, with the balance falling in the middle based on our 140 plus year dataset of monthly data.

This October, as of yesterday, is ever-so-slightly above average.  Odds favor us probably above average for the duration of October but we should not finish too terribly warmer than normal overall at month's end.   October temperature isn't the be-all and end-all given there's a one in three shot or a three in ten shot in either side of the fence that the opposite of reality will some respect similar to the NAO state in October being opposite of the winter about 60 percent of the time.   As we march through the coming weeks, more pieces will come into place to allow us to get a sense in what will happen this coming winter.