Great, albeit lengthy writeup by Kyle Elliott at MU last night. Essentially, he believes the most likely scenario is pretty much what the GFS is showing...the ridge axis out west looks to set up to the west of Boise, Idaho. For the LSV to get a major snowstorm we'd want the ridge axis set up to the east of Boise. This would allow the low to plow northward through PA and bury the Appalachians. So, he's giving the GFS full props at this point.
On terms of percentages, this is where he's at:
Track through CPA: 45%
Track up the coast: 30%
Southern slider/out to sea: 25%
He emphasized (obviously) that there are a ton of moving parts and things can/may change quickly and significantly; HOWEVER, he believes that the pattern supports the storm heading up through PA.