NWS Philadelphia/Mount Holly wrote its last area forecast discussion before the first event at Feb 12, 7:39 PM EST, 4 hours 21 minutes earlier.
Area forecast discussion, Feb 12, 7:39 PM EST, 4 hours 21 minutes before
Area Forecast Discussion
National Weather Service Mount Holly NJ
739 PM EST Mon Feb 12 2024
.SYNOPSIS...
An intensifying coastal storm is expected to tracks off the Mid-
Atlantic coast Tuesday morning. High pressure arrives for Wednesday
into Thursday, then a weak clipper system may move through late
Thursday into Friday. An area of low pressure may then track near
our area Saturday into Sunday.
&&
.NEAR TERM /THROUGH TUESDAY/...
Rather large changes were made to the forecast for the incoming
storm. Winter Storm Warnings were issued for Mercer, Monmouth,
and Middlesex County in NJ and for Lower Bucks County in PA.
Winter Weather Advisories were added for the remainder of SE PA
including Philadelphia and for Camden/NW Burlington/Ocean/western
Monmouth. Important to note that all of Ocean County will not
see Advisory-level snow, but the northern portion will, hence
the issuance.
With this update, snowfall totals came down in the northern
zones, though we are still expecting warning-level snow. 6 to 12
inches are expected in the southern Poconos and areas of New
Jersey along and north of the I-78 corridor. 4 to 8 inches are
anticipated within the Lehigh Valley, with anywhere from 1 to 4
inches in the I-95 corridor and lesser/zero accumulations south
and east. The reasoning for the rather large change has been a
decrease in QPF coupled with a further track storm track. There
is the potential for further headline changes later this
evening.
This has been a tremendously difficult storm to forecast due to
rapidly changing conditions/temperatures expected and the
difference in timing (plus or minus an hour or two) will have
large differences. The same goes for the storm track. Any
difference plus or minus a couple miles will have rather large
implications in snow totals. Previous full discussion follows...
All eyes are on the upper level low currently traversing the
mid Mississippi Valley and the surface low that is starting to
develop ahead of the upper level low. The surface low is
expected to pass off the Delmarva coast early tomorrow morning.
As it does so, it will bring impacts of snow/precipitation,
winds, and coastal flooding (more information on the coastal
flooding impacts is in the Tides/Coastal flooding section
below).
Model Guidance: Unfortunately there remains quite a bit of spread in
model guidance. Some of the global deterministic guidance
significantly backed off on QPF (total moisture equivalent precip)
on the northwest side of the storm, which would consequently mean
lower snow totals across the Poconos especially. On the flip side,
the southern track has held which could mean a longer period of snow
for areas closer to the I95 corridor. Although the surface low will
be in the process of deepening and intensifying, the upper level low
will actually be filling and weakening. Additionally, the best jet
dynamics never really seem to match up with the stronger low level
lift.
Precipitation type: Despite our region mostly staying on the cold
sector side of this low with little in the way of warm air
advection, we don't have much cold air already in place.
Consequently, expect the precip to begin as all rain for the region.
It should start changing over to snow in the higher terrain of the
Poconos and NW Jersey late this evening. Berks County, Lehigh
Valley, and the rest of NW Jersey should see the changeover coming
before sunrise. Near and along the I-95 corridor, the change to snow
will come around the time of the morning commute. The precipitation
should end from SW to NE from mid day through late afternoon.
Winter Weather Impacts: Aside from the usual traffic and surface
transportation impacts (especially with this coming at the time of
the morning commute), another concern is that it will be a heavy
snow, so some impacts on power lines and minor tree damage are
possible.
Wind impacts: winds gusting 45 to 50 mph are possible right along
the coast, primarily during the morning hours Tuesday. This could
lead to some minor tree damage in these areas.
&&
.SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY NIGHT/...
After the storm tonight through Tuesday, a brief period of quiet
weather is expected, the potential for additional active weather
returns. On Tuesday night, the low pressure that brings the
precipitation Monday night-Tuesday continues to move to the
northeast away from the area. This will lead to a northwest flow
across the area, and with a short wave/vorticity impulse moving
across the area, there could be some lake effect/enhanced snow
showers across the Poconos and higher elevations. While there could
be a dusting in some areas, it will likely not have much effect
since there will be snow already on the ground. One concern is winds
could become gusty overnight, which may lead to some blowing and
drifting snow.
By Wednesday, the pressure gradient remains across the area as high
pressure builds to our west. This will keep gusty winds across the
area through the daytime Wednesday. But as we go into Wednesday
night, the pressure gradient begins to lessen as the high pressure
builds a little closer to the Mid Atlantic region, although it will
fully build to our south overnight.
&&
.LONG TERM /THURSDAY THROUGH MONDAY/...
On Thursday, the high pressure system to our south builds offshore,
before a clipper-like low pressure system moves out of the Great
Lakes region and moves to our north. This will pull a cold front
across the Mid Atlantic region Thursday evening. This will bring a
chance of precipitation to the area, and depending on temperatures
and location, there will be a chance of rain or snow for many areas.
This system will be fairly quick moving and will exit the region by
daybreak Friday.
Another brief quiet period can be expected during the day Friday as
one low pressure system continues to move to the north of the area
and high pressure briefly builds to our south, before another
clipper-like low pressure system possibly impacts the area Friday
night into Saturday, followed by another later Sunday into Sunday
night; although the system later Sunday may remain just to our north.
After this period of potentially active weather, quiet weather
returns again by Monday as high pressure builds back across the
region.
&&
.AVIATION /01Z TUESDAY THROUGH SATURDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE,
KRDG, KILG, KMIV, KACY and surrounding areas...
Rest of Today...Mainly VFR with increasing cloud cover. Light and
variable winds. High confidence.
Tonight...VFR conditions to start at 00Z will quickly give way to
MVFR then IFR before the second half of the period. Mainly -RA/RA
through the period for most sites, though KABE/KRDG will likely
see RA change over to RASN around 08Z. Light SSE/E winds to
start the period will gradually pick up and shift to the NE with
time. NE winds of 15-20 kts with gusts up to 30 kts expected by
09Z. Moderate confidence.
Tuesday morning...LIFR/IFR conditions with RASN and SN. NE
winds of 15-20 kts with gusts up to 30 kts will shift towards
the N/NNW with time. Moderate confidence.
Tuesday afternoon...Lingering LIFR/IFR conditions to start will
quickly give way to VFR conditions. RASN and SN ceasing for most
sites by 18z. NNW winds of 15-20 kts with gusts up to 30 kts
diminishing with time. Moderate confidence.
Outlook...
Tuesday night-Wednesday...VFR conditions expected. Northwest winds
10-15 knots, with gusts 20-30 knots. High confidence.
Wednesday night...VFR conditions expected. Northwest winds 5-10
knots. High confidence.
Thursday...VFR conditions early, possibly lowering to sub-VFR
conditions later in the day as rain and snow move into the area.
Southerly winds 5-10 knots. Moderate confidence.
Thursday night...Sub-VFR conditions possible early, improving
overnight. Southernly winds 10-15 knots early, shifting to west then
Northwest overnight with gusts 20-30 knots possible. Moderate
confidence.
Friday...VFR conditions. Northwest winds 10-15 knots with gusts 20-
25 knots. Moderate confidence.
Friday night...Sub-VFR conditions possible with rain or snow showers
possible. Moderate confidence.
Saturday...VFR conditions. Northwest winds 10-15 knots with gusts 20-
30 knots.
&&
.MARINE...
A period of gales is expected on the Delaware Bay and the Atlantic
coastal waters early Tuesday morning into Tuesday afternoon. A few
hours of small craft advisory conditions are likely ahead of the
gales developing.
Some model guidance even has wind speeds on the cusp of storm force.
However, I think this may be overdone given the persistent
temperature inversion which will limit mixing. However, will be
keeping a close eye on trends overnight into the morning.
The wind direction will be changing through this period. Starting
late tonight when gales first develop, winds will be out of the
northeast. During the strongest winds mid to late morning, winds
will be shifting to more NNE. Winds will start to shift to NW around
mid day. With the NW shift, could see an initial period of gales
before it starts to diminish.
Outlook...
Tuesday night-Wednesday night...Small Craft Advisory conditions
expected through the period, before diminishing later Wednesday
night. Winds may gust near Gale force on Wednesday.
Thursday...Conditions begin below advisory levels early on Thursday,
before increasing to advisory level winds later on Thursday.
Thursday night-Friday...At least Small Craft Advisory level
conditions, with the potential for Gale force winds.
Friday night-Saturday...Small Craft Advisory level conditions
continue across the area.
&&
.TIDES/COASTAL FLOODING...
Minor to moderate coastal flooding is forecast to occur with the
high tides Monday through Tuesday night along Atlantic coastal New
Jersey and Delaware, Delaware Bay, and the tidal Delaware River. The
astronomical tides are lessening with time as we get farther away
from the New Moon, which occurred on Friday. Thus, the flooding with
subsequent high tides through Monday may not be quite as widespread
or cause as many impacts as occurred over the weekend.
A strong coastal system pushing offshore early Tuesday is forecast
to result in increasing surge values upwards of 2-3 feet above the
astronomical tides, which will result in widespread and impactful
coastal flooding issues with the high tides on Tuesday. The peak of
the surge appears to coincide with the high tide along much of the
Atlantic coast of New Jersey and Delaware Tuesday morning. This is
forecast to result in moderate coastal flooding impacts for much of
Atlantic coastal New Jersey and Delaware. A Coastal Flood Warning
was issued for all of Atlantic Coastal New Jersey for the Tuesday
high tide in these areas to highlight this threat. Sussex County,
Delaware was upgraded to a Coastal Flood Warning as well with
moderate flooding now forecasted for the Atlantic coast and back
bays.
Elsewhere along the Delaware Bay and the tidal Delaware River,
widespread minor flooding is currently forecast to occur with the
Monday through Tuesday night high tides. The greatest impacts and
inundation will occur with the Tuesday high tide as the
aforementioned strong coastal system moves offshore. A Coastal Flood
Advisory was issued for the Monday through Tuesday night high tides
to highlight the threat for minor coastal flooding in these areas.
Additionally, the widespread rainfall of near 1" will lead to
increased fresh water runoff on Tuesday. This may lead to elevated
water levels, especially along tidal tributaries of the tidal
Delaware River. Thus, there is a possibility of localized moderate
coastal flooding impacts in some areas along the tidal Delaware
River with the Tuesday afternoon high tide as well.
For sake of simplicity, the Coastal Flood Warnings and Advisories
were issued with a longer than usual duration to cover all of the
impacted high tides Monday through Tuesday night. The greatest
impacts will be experienced with the Tuesday daytime high tide as
the coastal system moves offshore.
No coastal flooding is currently forecast for our eastern shore of
Maryland portions of the northern Chesapeake Bay through
Wednesday.
&&
.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Winter Storm Warning from 11 PM this evening to 3 PM EST
Tuesday for PAZ054-055.
Winter Storm Warning from midnight tonight to 3 PM EST Tuesday
for PAZ060>062-105-106.
Winter Weather Advisory from 3 AM to 3 PM EST Tuesday for
PAZ070-071-101>104.
Coastal Flood Advisory until 10 AM EST Wednesday for PAZ070-
071-106.
NJ...Coastal Flood Advisory until 4 PM EST Tuesday for NJZ016.
Coastal Flood Advisory until 3 AM EST Wednesday for NJZ021.
Coastal Flood Warning until 3 AM EST Wednesday for NJZ012>014-
020-022>027.
Wind Advisory from 5 AM to 5 PM EST Tuesday for NJZ014-024>026.
Winter Storm Warning from 11 PM this evening to 3 PM EST
Tuesday for NJZ001.
Winter Storm Warning from midnight tonight to 3 PM EST Tuesday
for NJZ007>010-012-013-015.
Winter Weather Advisory from 3 AM to 3 PM EST Tuesday for
NJZ014-018>020.
Coastal Flood Advisory until 10 AM EST Wednesday for
NJZ017>019.
DE...Coastal Flood Advisory until 4 PM EST Tuesday for DEZ001.
Coastal Flood Advisory until 3 AM EST Wednesday for DEZ002.
Coastal Flood Warning until 3 AM EST Wednesday for DEZ003-004.
Wind Advisory from 5 AM to 5 PM EST Tuesday for DEZ004.
MD...None.
MARINE...Gale Warning from 4 AM to 6 PM EST Tuesday for ANZ430-431-
450>455.
&&
SYNOPSIS...Gorse/Johnson
NEAR TERM...Hoeflich/Johnson
SHORT TERM...Robertson
LONG TERM...Robertson
AVIATION...Hoeflich/Robertson/Wunderlin
MARINE...Johnson/Robertson
TIDES/COASTAL FLOODING...Staarmann