Like most statistic posts we have here, there's the usual blend of good news and not-so-good news that can be gleaned from the article.
First, the good news. Saturday morning's low of 55 degrees was the earliest 55 degree or cooler low in Philadelphia since 2000. It's also only the tenth time since 1983 where we knocked out a 55 or cooler start by September 7th.
Unfortunate, there's very little statistical correlation between a singular cool morning and the proceeding winter.
Over the past 30 years, some of those "early cool" morning years include 1997 (one of the warmest winters on record), 1994 (a rather warm, snowless winter), and 1991 (another warm and snowless winter). One example to counter the correlation is how 2002, given its late start, also provided a rather cool winter overall. 2002 is the last year where we went through September without dropping to 55 or cooler at any point!
The last year where Philadelphia dropped to 55 or below in August was 1994 -- August 6th, low of 55. During the 1980's, we had a seven year stretch in eight years where we dropped to 55 or below during August at the Airport. Times have changed the heat island is a bit stronger...but Saturday's low of 55 is a reminder of what it can do early in September in a cool airmass...but it doesn't mean much for the forthcoming winter.