September snow, and Philly winter
What near-record Northern Hemisphere snow might mean for Philly snow.
Following up on Tuesday's post about the prodigious snow cover in the Northern Hemisphere last month – the third-largest for a September on record -- we found some data to warm the hopes of snow-lovers.
The 45 years of available records suggest a correlation between hemispheric September snow and winter snowfall in Philadelphia – albeit with some dramatic exceptions.
A few cautionary notes:
David Robinson, keeper of Rutgers University's Global Snow Lab, says he knows of no serious work that examines any link between September snow with the subsequent winter.
We will go out on a sturdy limb and say that if David Robinson, a living snow encyclopedia, doesn't know of such a study, it doesn't exist.
As for the data, itself, it dates to 1968, the era of satellite surveillance. But a few years are missing, so we have 45 in the set.
The snow totals are Philadelphia's official measurements, which came from three different locations (and probably different methodologies) during the period.
The median annual snowfall in Philly for the period was 18.3 inches --- half the seasons above, half below. The average, bulked up by recent mega-snow season, was higher, 22.6 inches.
The median Northern Hemisphere snow cover in September is about 5.2 miliion square miles, give or take a few flakes.
Now, for the results:
In the 22 seasons that followed above-median hemispheric snow cover in September, 14 -- two-thirds --finished above the median for snowfall in Philly.
In all 45 seasons, only 16 had above the average snowfall amount in Philly – and 12 of those came after above-median September snow.
The average snow totals after the above-median Septembers: 30.2 inches. Average for the below-median snow-cover years: 19.1.
Not to throw too much cold water on the possible links, we point out that September 2009 weighed in with the ninth-lowest snow cover. That was followed by 78.7 relentless inches of snow in Philadelphia.
September 1997 had the third-highest snow-cover extent; less than an inch fell here during the entire subsequent winter.