The period between January 12th and 25th marks our coldest to average from a climate perspective in the city. The average high is 40 and the average low is 25, yielding a daily average temperature of 32.5 degrees. Putting everything to perspective, getting the season's coldest weather in late January is neither unusual nor unprecedented. It's the equivalent of getting your hottest day of the year in July.
Since 2000, cold has been fleeting in general but there have been some rather cold days historically in comparison to what's average. The list below shows the coldest days on record in Philadelphia since we flipped the calendar into the 2000's.
Philadelphia, keep in mind, hasn't had a subzero low since January 1994 but we've flirted pretty close in the city on two occasions -- lows of 3 on January 24th, 2005 and 4 on January 10th, 2004. In fact, the daily high and low of 16 and 4 on 1/10/2004 is the coldest day we've had in the city since 2000.
The coldest we've come in the last couple of years to reaching this list of ten is on January 24th, 2011...our last morning of lows below 10 in Philadelphia. That day's high and low of 25 and 8 yielded an average of 16.5 degrees.
To show how "relaxed" our winters have been compared to past years, January 10th 2004's average for the day of 10 degrees is the only day with an average temperature of 10 or colder since 1996. There have been 86 such days on record in Philadelphia and most decades have more than one such day...some "warmer" decades like the 1920's, 1950's, and the 2000's have just one. This decade has yet to see one of those gold standard cold days.