The latest run of the HRRR (High Resolution Rapid Refresh) model (which is based off of the NAM model) shows 4-6 inches of snow in the immediate Philadelphia and surrounding areas by 7 PM, with the greatest accumulations occurring  between 3 and 7 PM.

I guess it’s taking that 0.47 QPF for the afternoon and assuming all snow at about a 1:10 ratio.

Don’t shoot the messenger.