A stronger La Niña has been affecting our weather recently we are currently in by what NOAA defines as a multi-year La Niña, where it began during the Summer of 2010. Normally a strong La Niña is followed by a strong El Niño event. Normally these cycles can be strong to neutral, last year they were predicting a moderate event and it started to weaken during the spring and then it had intensified by late summer.
Since La Niña is here to stay, they say we may end up having a mild winter, which translates to little or no snow accumulation for Southeastern PA.
A more recent article on the NOAA website states that there is another cycle called the "Arctic Oscillation", apparently this is being identified as the newest element for our warm winter and for unusually warmer temperatures in the far northern areas. This is the main cause of the diminishing polar ice that is melting away.
This was in part my own summary of a much bigger and impressive topic, to read on from the experts please visit; http://www.climatewatch.noaa.gov/image/2011/so-far-arctic-oscillation-favoring-mild-winter-for-eastern-u-s