Well, I clearly guessed wrong on the NWS in both Philly and NYC as they just issues watches for most of the area (except NWNJ/NEPA and SE NY north of the Tappan Zee) for 5" or more of snow just now, not waiting for 4 am - maybe they were looking at the 18Z NAM, lol. See the map for counties in blue with watches - those watches might easily extend NW if we see more consensus on heavier snows to the NW. NWS-Philly also put out a snowfall map, below (not yet for NWS-NYC).
https://www.weather.gov/phi/
5 pm edit: the NWS-NYC also just posted their snowfall map, which is similar to the NWS-Philly...
Nice write-up by NWS-Mt. Holly on the storm. They do mention the chance for 8-12" in some areas wherever the heaviest deformation bands set up (impossible to predict this far out or even 6 hours in advance, really).
https://forecast.weather.gov/produc...&format=CI&version=1&glossary=1&highlight=off
National Weather Service Mount Holly NJ
419 PM EST Fri Feb 5 2021
SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/...
The main story for this period will be the coastal storm as it
moves up the coast Sunday.
To start the period Saturday evening low pressure will be developing
near the Gulf coast in response to
shortwave energy diving south to
near the base of the long wave
trough. Meanwhile weak ridging will
still be present across the mid Atlantic though there will already
be some increasing mid and high cloudiness but it will be dry.
The system will start moving up the coast through Saturday night
with low pressure located near or just east of
Cape Hatteras by
12z Sunday. Similar to many systems in recent years, the main
question will be the exact track and strength of the low. One of
the determining factors influencing this will be how much
phasing occurs between two pieces of
shortwave energy...the main
one rounding the base of the
trough over the SE then moving up
the coast with another piece of energy diving SE through the
midwest. The general trend has been for a stronger system
tracking farther north and west with the
NAM being the strongest
while the
GFS is still be a bit weaker and farther S/E. However
GFS trend has also generally been N/W with time. Given the
model trend and also that the models are sometimes a bit slow to
catch on to rapid self development of coastal storms we have
increased
QPF and snow amounts and issued a Winter Storm for a
fairly broad swatch of the
CWA excluding our NW zones and
Atlantic coastal areas from Atlantic County southward.
In terms of sensible weather with the storm, expect snow to develop
SW to NE near or shortly after midnight Saturday night. The precip
could start as rain over southern Delmarva and parts of southern NJ
but as cooling effects take hold it will change to all snow. The
brunt of the storm looks to hit into Sunday morning as
deepening low
pressure tracks northeast off the coast. There should be strong
forcing for ascent over the area due to right
jet entrance
dynamics
and also the mid level low looks to track right near the area as it
start to close off. The upshot is we expect snow, heavy at times,
through the morning with still some question on exactly where the
heaviest bands set up. Heaviest bands of snow will
likely be near or
just north of the mid level low in the strongest F-
Gen forcing.
Rates in the heaviest bands are
likely to be 1-2 inches per
hour creating significantly reduced
visibility. Most of the
forecast area should be all snow Sunday with the exception being
southern Delmarva and parts of coastal NJ where a mix with or
change to rain and sleet will be possible. But this will depend
on the exact track of the storm. A track closer to the coast
will result in more mixing near the coast with the heaviest snow
near or even north of I-95 while a track farther east will
result in mostly all snow even at the coast potentially bringing
the highest snow amounts here. Generally favoring a track close
enough to the coast to bring at least some mixing here with our
highest snow amounts of 6+ inches currently forecast in a swath
near the I-95 corridor. But again, confidence still fairly low
on these exact details despite growing confidence of the storm
impacting the region. Also, within the area we are currently
forecasting 6-8 inches there will
likely be an area that gets
8-12+ inches in the heaviest bands.