April 2012 was the third warmest April since 1895 on a national level, which is counter to our rather pedestrian 1.5 degree above average departure. The Plains and central portions of the US were responsible for a chunk of that warmth in April nationally, which has helped the US roll to a national record for warmth so far this year.
Philadelphia is off to its warmest start on record (since 1872) this year, buoyed by our near record warmth in March and very mild January and February. Our average year-through-April (YTD) temperature for Philadelphia is 46.6 degrees, which is four tenths of a degree higher than the previous record from 1921. The graph below shows the March, April, and year-to-date temperature marks for the eight warmest years so far on record as well as our "norm" for the 1981-2010 period. We're running 5.1 degrees warmer than our normal and 0.4 degrees ahead of the 1921 "gold standard" for warmth to this point.
Our record warmest year is 1931, which through April only averaged out to 42.3 degrees and isn't even among the ten warmest years out of the gate. 1931 ended up averaging to a temperature of 58.1 degrees thanks to a very warm September through December, which featured top five warmest months on record to close out that year. 1921, the gold standard of heat through April ended up as 11th warmest on record by the time the year was done. 1998, 2002, and 1990 (the next three on the list) finished the year as 2nd, 6th, and 3rd warmest years on record respectively. Lots can change before the year is out but a warm start usually puts you to the finish line in the top few years of warmth on record. Barring any arctic intrusions this summer we probably will end up with another top ten year of warmth in Philadelphia...the question is simply "how high" we can get.
Philadelphia is one of 28 cities that are off to their warmest starts on record. That list also includes Washington, Atlanta, Boston, Buffalo, Chicago, and NYC.