2nd paragraph from NWS Winter Weather discussion from 3:15 today might explain why they are bullish on totals. I'm no meteorologist though just lurking and learning on here.
By 12Z Saturday, most guidance is in agreement that the 500mb
shortwave takes on a more neutral tilt (oriented N-S) over the TN
Valley and becomes a closed low over GA. PVA becomes maximized
over the Southeast while a surface low spawns along a coastal
front east of the Carolinas. As the 850mb low deepens over northern
GA and heads east into SC, easterly 850mb theta-e advection will
direct low-level moisture around the 850mb low and support a band
of moderate-to-heavy snow from northern GA to central SC. Farther
north, the same tongue of 850mb theta-e is funneling along the
850mb front to the north of the 850mb low track from northern SC
on east through the heart of NC. This is where the deformation zone
is likely to form, pivoting over central NC and northern SC with
1-2"/hr snowfall rates likely. This band of heavy snow is likely to
ensue farther east into southeast VA, where 700mb FGEN is more
ideally placed to support strong vertical velocities within a fully
saturated DGZ. Similar to NC, look for intense bands of heavy snow
over southeast VA to form late Saturday afternoon and persist into
Saturday night. These bands of heavy snow in eastern NC and
southeast VA depict 700-500mb lapse rates >6.5C/km Saturday
afternoon and evening. It is here where not only are 2"/hr snowfall
rates achievable, but so is the likelihood for thundersnow. The
intense vertical velocities in eastern NC and southeast VA may
result in some subsidence in north-central NC and south-central VA.
Snowfall is still likely to reach warning criteria, but these
regions are potentially susceptible to lesser snowfall amounts as
they are caught between the influence of the strong upper-low to
the south, and the strengthening coastal low.