This post was revised
An Interesting and active weather period is unfolding for the next several days. Model differences promise to make the forecast more challenging.
Tonight’s NAM has snow developing early Sunday evening and extending into early Monday morning. QPF values have increased over the day and are now at 0.40 inches water. If the NAM is correct, 4-5 inches of snow will accumulate by early Monday morning in and around the immediate Philadelphia area.
The same event is depicted differently by the GFS, which has high pressure blocking the moisture’s northward movement. QPF values tonight are about 0.10 inches water, even less just north of Philadephia.
I’m leaning towards the NAM, which has done the best for the last two wintery weather events. So the current predicted amount is 3, possibly 4 inches of snow Sunday night, ending early Monday morning.
Another larger system will affect us late Monday afternoon through Tuesday. Let’s get through the first one before focusing on details, but the trend is for snow, several inches, changing to sleet and freezing rain Tuesday morning. An extended period of freezing rain is possible even in Philadelphia. An eventual change to all rain later Tuesday morning.
Further complications include the possibility of a secondary low formation.