Sunday morning's low of 28 degrees was our first foray into the 20's this cold season in Philadelphia. While not our first official freeze of the cold season (that occurred back on October 31st), it was a late occurrence for our first low below 30 degrees. Since the climate site was moved to the Airport in 1940, only December 12th, 1998 featured a later arriving "first sub 30" low.
As you can tell by the list above (the list dates back to 1940 at the current Airport climate site), there is a clear recent trend in later arriving cold mornings. Blame the expanding heat island, blame climate change, blame the location as not representative of the city and/or the fact that the climate site is near the river...there's a little bit of truth to any of those buckets. However, the list does not indicate a bad trend for the coming winter. Two snowy winters populate the list -- 2009 and 2010...and 2006-2007 featured a rather brutal second half of winter that had a lot of us scraping and icing our way through February and March.
For history buffs, the last year that the official observations were taken in Center City (1939), it took until December 6th to get the first morning low in the 20's. That would not rank as the latest for Center City -- that honor belongs to December 15th, 1923, when the thermometer dropped to 27 degrees...the only time before the end of the calendar year in the cold season when the low was below 30 in Philadelphia. At least we've been below 30 each of the last three mornings -- that ugly record won't be approached this year!