Looks to me like the NWS laid out their reasoning why what we have been seeing modeled (and discussing these last few days) is not all that accurate in TRUE forecasting on this event for the following reasons:
(1.) Persistent above freezing surface temperatures that will help temper/melt the majority of the snowfall. The exception to the rule may be areas closer to the VA/NC border, however, these are the areas that will likely see far less QPF throughout the event
(2.) 10:1 snow to liquid ratios are not likely in an event like this, expect closer to 3:1 at precipitation changeover onset, 5:1 toward the middle of the event, and perhaps ending in vicinity of 10:1
(3.) While the CAA process will be key in the original changeover, it will also become the ultimate limiting factor through the frozen ptype portion of the event. This will work to greatly reduce QPF from northwest to southeast in general.
Oh yeah, they also mention a "cold initialized NAM"