Mt. Holly and Upton still have all their warnings, but they trimmed snowfall back to the bare minimum that could ever justify warnings, i.e., 3-6" for the NJ counties along the 95 corridor in NJ/EPA from Wilmington up through SE Bucks/Montco and Mercer/Middlesex/Somerset (for Mt. Holly, where 4" is the criterion for a warning for counties S of 276/195, i.e., Philly-Burlington-Ocean and south) and the warnings are for ~6" of snow for NENJ (Union up to Bergen)/NYC metro/Nassau and 5-8" for Suffolk/E CT.
Would love to know if they saw the 6Z NAM before issuing, as the 6Z NAM is back to where the 18Z was ,showing the 6" line running right up the Delaware from Philly to Trenton and then to NYC and 4-6" for 20-25 miles NW of there and 6-7" SE of there. But the RGEM showed a general 1-3"/2-4" event still at 6Z and the GFS is still 2-4" for most, so who knows. NWS-Philly's discussion is below. Ok, back to sleep, lol.
National Weather Service Mount Holly NJ
305 AM EST Sun Feb 7 2021
NEAR TERM /THROUGH TODAY/...
Summary: A quick hitting winter storm will impact the area today,
with most of the precipitation confined to the daylight hours.
Meteorological Overview: Latest
sfc. analysis depicts an area of
weak (but
deepening) low pressure off the South Carolina coast,
while on water vapor a mid-
lvl shortwave trough was evident
upstream
of this feature over southern Tennessee. This low is
progged to
quickly move NNEwrd during the day today, with the low intensifying
significantly as it moves underneath the right-
entrance region of a
strengthening UL
jet. To highlight both the rapid intensification
and quick forward speed of the low, by this time tomorrow it is
progged to have a central pressure around 975
mb, and be located in
the Canadian Maritimes. Precipitation will overspread the area from
SW-NE this morning, as ascent increases in association with the
incoming
shortwave, the UL
jet, and finally (and most importantly) a
region of 600-700mb FGEN associated with the axis of the 700mb wave.
Current observations: A deck of thick
cirrus blankets our area, with
light winds and temperatures ranging from around 20 in the Poconos
to the low 40s in Delmarva. Of importance to ptypes,
sfc. wet-
bulb temps range from the low teens in the Poconos to the mid
30s in Delmarva, with most of the area seeing Tws in the mid 20s
to low 30s. As of 2 AM, Rain has (based on
ASOS obs and mPING
reports) nearly reached the MD/VA border, with snow being
observed in western Virginia and North Carolina. Some
radar
returns (aloft) are approaching southern Delmarva, but these
will
likely just be
virga initially due to the dry low-lvls
Forecast:
Timing... In general the system`s timing looks very similar to what
was advertised in previous forecasts, with precipitation entering
our area early this morning and moving out of the area between 5-
7PM. The heaviest precipitation looks to impact the area from mid-
morning to early afternoon.
Precipitation Types... Very similar to thinking to previous
packages, i.e. almost all snow NW of I-95, mostly snow but some rain
mixed in during times of lighter precip rates near I-95, and then a
messier rain/snow mix
likely towards the coast.
Precipitation & Snow Amounts... Forecast
QPF amounts were heavily
based towards the 00Z HREF
Probability-matched
mean and WPC
guidance, resulting in a forecast of 0.2-0.5 inches of water from I-
95 northwestward and 0.5-0.9 inches of water from I-95 to the coast
with the
QPF gradient oriented SE. These amounts are about 25% lower
than the previous forecast, and physically this reduction primarily
stems from the consensus low position being a bit further east/less
amplified, which keeps most of the "prime" FGEN forcing confined
near the coast, with weaker (more synoptic-driven) lift NW of I-95,
along with perhaps some compensating
subsidence on the cool side of
the boundary. All that being said, our
fcst QPF is still about 50%
higher than most of the coarser guidance (which generally have about
0.1-0.5 inches of total liquid) as suspect these are underplaying
the heavier rates present in the FGEN band.
All the above discussion leads us to the most important forecast
element of the day... snow amounts. The reduction of
QPF naturally
did contribute to a reduction of snow amounts across the board.
Generally have 3-6 inches along and near I-95, with the axis of
higher amounts tilting SEwrd a bit to account for the FGEN band`s
positioning towards the Coast. Amounts are largely 2-3 inches I-78
and northward, and a sharp
gradient remains present near the coast,
due to the ptype concerns there. These snowfall amounts are still a
bit above consensus... probably a nearer to the 75th percentile
outcome than the 50th. The general reasoning for leaning on the high
side is that the potential for locally heavy snowfall does exist,
particularly near or just SE of I-95 where the
mesoscale lift
associated with the FGEN band will be favorably placed within the
DGZ. Heavy rates associated in this zone would result in better
ratios and accumulations despite the marginal temperature profiles.
All that being said, would not be shocked to see this being a mostly
2-4 inch event near I-95, with some total "shutout" potential in
Delmarva and along the NJ Coastal Plain if rates never get high
enough to compensate for the poor
thermal setup. Up north,
QPF looks
to be the main limiting factor, but typically in these events
(provided there is not a dry arctic airmass in place), the
precipitation shield extends a bit further northward than
progged.
Therefore am not totally gutting amounts up there despite some
models having only about 0.1 inch of
QPF.
Despite lowering amounts, have no plans to significantly modify
headlines as the heavier rates may make up for (from an impact
perspective) total snow amounts potentially being under official
warning criteria.
