Wednesday, November 14, 2012

A Cool November After A Warm October

Through yesterday, we are still running over four degrees below average on temperatures in Philadelphia for the month and the likelihood of us having a below average month on temperatures is pretty high at this point given how the trends in temperature look for the duration of the month.  I think it'll be pretty tough for us to get enough warmth between now and November 30th to get back to average.  We probably end up a couple of degrees below average before all is said and done.

Assuming that takes place, it marks a relatively rarer occurrence where we follow a warm October with a cooler than average November.  Using a benchmark of 46.5 degrees for November, which is 0.6 degrees below our current normal and right around the historical average back to 1874, it's only happened 14 other times after a mild October (59 or warmer for an average monthly temp).

How did those winters end up?  Well, there isn't a terribly huge consensus one way or the other!

If you look at those 15 years, you see some really good winters for snow lovers -- 1995-96 sticks out as one of those years.  You also see 2007-08, which was a pretty awful winter from a snow standpoint.  Temperatures and snowfall average out to slightly above our current "norms" of 35.3 and 21.8, respectively but there is no clear trend one way or the other.  Temperatures were below 35.3 on six of the occasions, above on eight.  Snowfall was below average on seven, above average on six, and right at average in 1959-1960.

A couple of interesting nuggets -- the "winter" of 1914-15 was really more a Spring freak show in terms of snowfall -- 27.6" of that 33.1 fell after March 1st.  Second, the winter of 1932-33 featured the third warmest January on record but then followed it up with eleven inches of snow the next month.

There isn't much to be gleaned from this -- cool to cold Novembers when coupled with October don't lend much statistical weight to what winter can do.  A colder November with a colder October certainly has some weight to it (the winters of 76-77 and 77-78 were both in this data set but there are exceptions like 1996-97 that end up rather mild and snowless) but with a mixed bag Fall there's a general consensus of mixed bag winters that result when November ends up colder than average.