Reviewing the major models, at this time, it appears that the balance of December won’t have a pattern for snow in Philadelphia.
Short duration dips in the jet stream will bring cold periods, but moisture flow from the southwest will make these colder periods of moderate duration, allowing wet and mild weather to return along with deep storms whose tracks will be moving to our west instead of along the coast.
Today’s (Sunday) GFS and FV3-GFS differ significantly in the very long range with these similar models having very different forecasts by New Years Eve.
For this week— A storm for Friday is a now posing to be a significant rain storm and the storm potential mentioned for Sunday into Monday also appears to be wet instead of white.
The chance of seeing a white Christmas here have faded, at least for now.
The global models show very frigid air building in the polar region, Siberia and Greenland during the last week in December. A shift to much colder weather and stormer conditions (snow) is expected by the end of December into the first week of January.