18z Gfs has the 546 height line through northern Baltimore City while the Nam has it just south of DCA. IF the Nam is closer to correct with the cold air draining further south, that's enough to make a difference for some.
Gefs have not been great with snowfall this year, and downright lousy at 96+ hrs. This threat may not workout for this forum, but that remains an accurate critique of the Gefs snowfall predictions this year.