Coastal Flood Warning 3, NWS Philadelphia/Mount Holly

Area Forecast Discussion
National Weather Service Mount Holly NJ
306 PM EST Sun Feb 11 2024

.SYNOPSIS...
Low pressure moving into the Tennessee Valley later tonight and
Monday will then give way to an intensifying coastal storm that
tracks off the Mid-Atlantic coast during Tuesday. 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 MONDAY/...
Weak high pressure will continue to nose in the Mid Atlantic region
tonight. The remaining showers will move offshore this afternoon,
and the rest of this evening and overnight will remain dry across
the area. Some drier air may make its way into the western and
northern areas, so some partial clearing could move in to those
areas, but most places will remain at least partly to mostly cloudy
tonight.

For Monday, we start out dry as high pressure moves out. Rainfall
associated with the upcoming winter storm will begin to move in
from southwest to northeast by the mid- afternoon, getting to
the Philadelphia metro by the early evening or so. Temperatures
will be far too warm to support any snow at onset, and highs
Monday will get into the upper 40s with some spots touching low
50s.

&&

.SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY/...
Broad low pressure will lie along and just west of the Appalachians
Monday evening, but a secondary low looks to form just over the Mid-
Atlantic. This new low will track through Delmarva and towards Cape
May and Atlantic City by Tuesday morning. Upper trough along with
the primary low then approaches from the west, merging with the
secondary low off the New Jersey coast. This system then passes
south of Long Island and moves out to sea during the day Tuesday.
Canadian high pressure then builds in from the west Tuesday night
and Wednesday.

In terms of the overall forecast, not much change for the Monday
night portion. Rain overspreads the region, and may be locally heavy
at times for the majority of the forecast area. Exception will be
far northern portions of Carbon and Monroe counties, where
temperatures should be cold enough for snow not long after the
precipitation starts, and then the rain/snow line moves south
towards the Lehigh Valley late at night and towards daybreak
Tuesday.

From there, latest model guidance has the low just a bit farther
north from previous runs. Temperatures are just a bit warmer, and as
a result, snowfall amounts are just a shade less. Will keep Winter
Storm Watches in place with this forecast package. For the first
zone in the Watch, which includes Carbon, Monroe, and Sussex (NJ)
counties, snowfall totals should be in the 6 to 10 inch range. For
the next tier of counties south, snowfall totals look to be in the 3
to 5 inch range, and the Watch may be converted to a Winter Weather
Advisory if that trend holds. For that third tier of counties in the
Watch, including Berks, Upper Bucks, and Hunterdon counties,
snowfall amounts are now in the 1 to 3 inch range. Will keep the
Watch in effect, though it is possible that an Advisory will not be
needed should this warmer trend continue.

Rain and/or snow tapers off by Tuesday afternoon as the storm system
departs. A tight northeast pressure gradient develops over the area
Tuesday morning with winds 15 to 20 mph with 25 to 35 mph gusts with
40 to 45 mph gusts possible along the New Jersey coast. Winds turn
northwest in the afternoon as the low departs.

Skies clear out for Tuesday night, and then partly to mostly cloudy
skies expected Wednesday as a shortwave passes through the region.
Breezy and colder with lows mostly in the 20s Tuesday night and then
highs will mostly be in the 30s on Wednesday. Wind chills will be in
the single digits and teens Tuesday night and in the 20s on
Wednesday.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
Summary...Temperatures close to average overall. A weak system may
move through later Thursday into Friday, followed by a low
pressure system possibly over the weekend.

Synoptic Overview...An upper-level trough from the Canadian
Maritimes to the Northeast U.S. continues to shift eastward
Wednesday night with some ridging to follow into Thursday. A
shortwave trough sliding across the Great Lakes may toss a clipper
system our way later Thursday into Friday. A stronger upper-level
trough may develop across south-central Canada which then amplifies
south and eastward Friday and over the weekend. It is possible this
taps into some southern stream energy with surface low pressure
getting pulled farther north. This may result in a shield of
precipitation advancing toward or across our area during the
weekend. There is much less certainty with the evolution of these
features.

For Wednesday night through Friday...An upper-level trough is
forecast to continue shifting out of the Northeast Wednesday night
with some ridging aloft to follow into Thursday. The latter will
result in weak surface high pressure building in during Thursday
before settling to our southeast by early Friday morning. There is
the potential for a weak system sliding across the region later
Thursday into Friday, however this looks moisture starved. This may
still bring at least some rain/snow showers to the region. High
temperatures are forecast to be closer to average each day, although
Friday is forecast to be a bit milder than Thursday.

For Saturday and Sunday...An upper-level trough may amplify south
and eastward from south-central Canada. The southern portion of this
trough may tap into southern stream energy, helping to support
surface low pressure farther north. While there could be some
confluent flow out ahead of this system, a deeper trough approaching
from the west may tend to dampen that and therefore have a surface
low more organizing and shift farther north. It still looks to be an
overall faster moving system. It is uncertain though how the
incoming trough evolves with time and therefore the location and
strength of the associated surface low. Given the uncertainty
especially at this time range, our PoPs are pretty much the National
Blend of Models (NBM) which includes PoPs right about 30 percent
Saturday then decreasing into Sunday.

&&

.AVIATION /20Z SUNDAY THROUGH FRIDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE,
KRDG, KILG, KMIV, KACY and surrounding areas...

Rest of this afternoon...VFR. A few showers remain possible from
KMIV/KACY southward. No significant restrictions are expected.
North-northeast to north-northwest winds 5-10 knots or less.
Moderate confidence.

Tonight...VFR. Northwest winds around 5 knots, becoming light
and variable overnight. High confidence.

Monday...VFR through the daytime hours. Light and variable
winds early, becoming northeast during the morning, then
southeast by the afternoon 5-10 knots. Moderate confidence.

Outlook...

Monday night...Sub-VFR conditions in RA Monday night for most
terminals. RA should change to SN after midnight Monday night at
KRDG/KABE, and RASN possible at KTTN prior to daybreak Tuesday.
Light N winds on Monday, becoming E 5 to 10 kt late. Winds
become NE 15 to 20 kt with 25 to 35 kt gusts by Tuesday morning.
Low confidence.

Tuesday through Tuesday night...Sub-VFR in RA or SN, tapering
off with improving conditions later in the day. VFR Tuesday
night. N winds 15 to 25 kt with 25 to 35 kt gusts, though gusts
over 35 kt possible at KACY. WNW winds 10 to 15 kt Tuesday
night. Low confidence.

Wednesday...VFR. NW winds 15 to 20 kt with 25 to 30 kt gusts.
High confidence.

Thursday and Friday...VFR overall, however there is a low chance for
a few rain/snow showers later Thursday into Friday. West to
southwest winds around 10 knots Thursday, becoming west-northwest 15-
20 knots with gusts to around 25 knots Friday. Moderate confidence
overall.

&&

.MARINE...
No marine headlines are anticipated through Monday. Winds out of the
north/northwest tonight 5-10 kt with east/northeast winds 5-10 kt
Monday. Seas 2 to 3 feet.

Outlook...

Monday night...E winds 5 to 10 kt, becoming 20 to 25 kt with gusts
up to 30 kt late. VSBY restrictions in rain Monday night. Seas
building to 4 to 6 ft.

Tuesday through Tuesday night...Gale Watch in effect for Tuesday. NE
winds 20 to 30 kt with gusts up to 40 kt, backing to the NW in the
afternoon. Winds become W 15 to 20 kt with gusts up to 30 kt Tuesday
night. Seas 6 to 9 ft. VSBY restrictions in rain or snow on Tuesday.

Wednesday...SCA likely with gales possible W winds 20 to 30 kt with
30 to 35 kt gusts. Seas 4 to 6 ft.

Thursday...The conditions should be below Small Craft Advisory
criteria.

Friday...A period of Small Craft Advisory conditions probable,
mainly due to west-northwest wind gusts to around 25 knots.

&&

.TIDES/COASTAL FLOODING...
The Coastal Flood Advisory remains in effect into early this
evening for the tidal portion of the Delaware River.

Minor coastal flooding is forecast to continue occurring with
the morning to early/mid afternoon high tides through Tuesday 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. If additional widespread minor flooding
occurs with the Monday high tide cycles, an additional advisory
may be needed.

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
more 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 Tuesday morning. This is anticipated to result in a
threat for moderate flooding impacts from around Atlantic County
and north into Monmouth and Middlesex Counties. A Coastal Flood
Watch was issued for the Tuesday high tide in these areas to
highlight this threat.

Elsewhere along the Atlantic coast, Delaware Bay, and the tidal
Delaware River, widespread minor flooding is currently forecast
to occur with the Tuesday high tide. There is a possibility
(30-40% chance) of localized moderate coastal flooding impacts
in some back bays of Cape May and Sussex Counties with the
Tuesday high tide, however confidence at this point is too low
to justify a Watch for those areas. Additionally, the
widespread rainfall of 1-1.5" 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.

No coastal flooding is currently forecast for our eastern shore
of Maryland portions of the northern Chesapeake Bay through
Tuesday.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Winter Storm Warning from 6 PM Monday to 6 PM EST Tuesday for
     PAZ054-055.
     Winter Storm Watch from late Monday night through Tuesday
     afternoon for PAZ060>062-105.
     Coastal Flood Advisory until 6 PM EST this evening for PAZ070-
     071-106.
NJ...Winter Storm Warning from 6 PM Monday to 6 PM EST Tuesday for
     NJZ001.
     Winter Storm Watch from late Monday night through Tuesday
     afternoon for NJZ007>009.
     Coastal Flood Watch from Tuesday morning through Tuesday
     afternoon for NJZ012>014-020-022-025>027.
     Coastal Flood Advisory until 6 PM EST this evening for
     NJZ017>019.
DE...None.
MD...None.
MARINE...Gale Watch from Tuesday morning through Tuesday afternoon for
     ANZ430-431-450>455.

&&

SYNOPSIS...Gorse
NEAR TERM...Hoeflich/Robertson
SHORT TERM...MPS
LONG TERM...Gorse
AVIATION...Gorse/MPS/Robertson
MARINE...Gorse/MPS/Robertson
TIDES/COASTAL FLOODING...PHI

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