Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 130834

Area Forecast Discussion
National Weather Service Mount Holly NJ
434 AM EDT Tue Mar 13 2018

The strong coastal low will continue to move northeast offshore
of New England today, then continue into the Canadian Maritimes
tonight and linger there through the remainder of the week.
Several surface troughs or fronts will likely rotate around this
low through Friday. Canadian high pressure builds into the
region Friday night through Saturday. A back door cold front may
sink across the area Sunday into Sunday night, then high
pressure pushes into the area later Monday. Another coastal
storm is possible late Monday into late Tuesday.


330 AM fcst: Might have given up too soon on accums near and
north of VAY to ACY as banding is really getting going now but
we`re out there and staying with what we have until we know
we`re wrong. Recent model trends suggest snow will last 1-2
more hours than we currently have fcst in our zone and taf
products and there is going to be some 3/4 mi snow here and
there between now and 9 am.

While the primary forcing has shifted east slightly from
midnight to about 60 miles offshore as you can see from the
radar at 0830z... ie...a 50-60 NM westward shift in the storm
track would probably have meant a much more substantial
snowfall along the coast....not to be. Still, banding is
occuring and snow ratios are higher so at elevation, there is
going to be some significant accumulations with 5" amounts
expected aoa 1000 ft along and north of I80.

Otherwise at lower elevations...despite the surface temperatures
cooling early today, accumulations may be more difficult on
treated surfaces due to the lighter intensity. Most of the snow
accumulations will occur prior to 9 AM today with an additional
1-2 inches possible Monmouth to Morris and Sussex Counties in
nrn NJ after 12z. There should definitely be morning commute
impacts near and north of I78. The Winter Weather Advisory was
maintained as is, where an area of widespread 2-4 inches of snow
is expected. I did drop Mercer county due to the fcst being
under criteria

Snow ends slowly from southwest to northeast later this

Mixed clouds and sun and blustery this afternoon with a
northwest wind gusting 25-35 mph and maybe some scattered
flurries except scattered snow showers Poconos.


Becoming mostly clear. A westerly wind with scattered gusts
15-20 MPH.


The strong coastal low will continue to linger across the
Canadian Maritimes Wednesday, Thursday, and Friday. At the same
time, high pressure will be building across the Deep South and
southeastern states, as well as the Upper Mississippi Valley and
western Great Lakes. This will keep a strong northwest flow
across the area Wednesday, Thursday, and Friday. Each day, a
surface trough/frontal boundary is forecast to move across the
area as well. There will be a chance of showers each day from
Wednesday through Friday. However, each day the chances and
coverage get less.

Wednesday has the greatest chance of showers as the low level
lapse rates will be their greatest during the day Wednesday, as
well as the low-mid level moisture. Wednesday is also expected
to be the windiest day, with winds reaching at least 30-40 mph,
possibly even higher later in the day and into the evening. With
the strength of the winds, and the instability, we expect there
to be some snow showers/squalls developing to our west and move
into our area. Temperatures may warm into the upper 38s or low
40s for some areas, but with as hard and fast as the
precipitation will come down, it may be more snow or a rain/snow
mix for the warmer areas. The higher elevations of the Poconos
may very well see an inch or two as they will be colder and have
the greater potential to see snow. Any snow showers/squalls
should diminish after sunset as the lapse rates weaken and
moisture slides to our east.

On Thursday, another surface trough is expected to move across
the area while low level lapse rates increase again, along with
low-mid level moisture. It is possible again for another round
of snow/rain showers or squalls during the day. Again the
Poconos have the better chance of seeing any accumulation as
most other places may mix rain and snow. Although winds are not
expected to be as windy as Wednesday, we should still see wind
gusts 20-30 mph at times. Any precipitation that does form is
expected to diminish after sunset as the lapse rates weaken and
moisture slides to our east.

For Friday, yet another surface trough is forecast to move
across the area as the low to our northeast loses it`s grip on
our area. The lapse rates are not as strong everywhere on
Friday, and there is not as much moisture expected across the
area. Therefore the chance for snow is mainly expected across
the Poconos on Friday. By Friday night, high pressure begins to
approach from the west, and drier conditions are expected.

On Saturday, high pressure briefly builds across the area, then
pushes south of the area. This will lead to dry conditions
during the day Saturday. On Saturday night, an area of low
pressure is forecast to pass just to our south while a short
wave/vorticity impulse slides across the southern half of the
area. The expectation is that any precipitation will remain to
our south Saturday night. However, if any precipitation were to
occur, it would most likely occur across the southern Delmarva
in the form of rain.

On Sunday into Sunday night, a back door cold front is forecast
to move across the area from the north, before high pressure
noses into the area from the north on Monday. This is expected
to lead to dry conditions Sunday into Monday.

However, the forecast then turns to the potential for...yet
another coastal storm late Monday night through late Tuesday. As
usual, there is uncertainty with the details, but the GFS,
Canadian, and ECMWF all show the coastal storm with varying
degrees of coldness and QPF. Still, there is the potential for
some of the area to see another round of snowfall.


The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.

Early this morning...VFR CIGS occasionally IFR conds in snow
with TAFS attempting to time the end of the IFR risk in snow
beginning 08z-10z ILG and arriving RDG PHL MIV ard 11-13z and
ABE TTN ard 13-15z. North to northwest wind with scattered gusts
around 20 kt.

Today after 15z....VFR sct-bkn aoa 4000 ft. Northwest winds
12-18 knots with gusts up to 30 knots. A few late afternoon snow
showers are possible in the vicinity of RDG and ABE.

Tonight...VFR conditions expected with westerly winds scattered
gusts 15-20kt.


Wednesday...VFR CIGS early may lower to MVFR during the day.
Snow or rain showers/squalls possible during the day. If snow
showers/squalls occur, they would likely lead to temporary lower
conditions. Westerly winds gusting to 25-30 knots.  Moderate

Wednesday night...MVFR CIGS possible early for some areas,
becoming VFR overnight. West winds gusting to 30-35 knots.
Moderate confidence.

Thursday...Mostly VFR. However, snow or rain showers/squalls
possible during the day, but not as widespread as Wednesday. If
snow showers/squalls occur, they would likely lead to temporary
lower conditions. Westerly winds gusting to 20-25 knots.
Moderate confidence.

Thursday night...VFR conditions overnight. Northwest winds may
gust 20-30 knots.  High confidence.

Friday...Mostly VFR. However, snow or rain showers/squalls
possible during the day, but not as widespread as Thursday and
mainly for northern areas. If snow showers/squalls occur, they
would likely lead to temporary lower conditions. Northwest winds
gusting to 20-25 knots.  Moderate confidence.

Friday night...VFR conditions overnight. Northwest winds may
gust 20- 30 knots.  High confidence.

Saturday...VFR. Northwest winds gusting 15-20 knots.  High


Gales in progress most of the waters at this time with NAM MOS
guidance a better indicator of gust transfer reality. The winds
become northwest during the day and gales should gradually
diminish later today. WW3 seas were very poor for this evening
and we increased the seas by 3-5 feet this morning. We have no
SJSN4 data so we`re not exactly sure of winds speeds over the
upper part of DE Bay

Tonight...SCA expected with isolated gale force west northwest
gusts possible.

Wednesday-Wednesday night...Gale Watch in effect. Moderate-high

Thursday-Friday night...Small Craft Advisory conditions
expected.  High confidence.

Saturday...Conditions may lower below advisory levels.  High


Still a risk of coastal flooding this mornings high tide Ocean
County to the DE Atlc coast area but at this time our merged
TWL guidance still says just below. Wind direction near the 6am
high tide will ultimately determine how much surge at high tide
which is currently anticipated to be around 2 feet. We may need
a last minute 430 am issuance there based on surge trends as
the tide cycle marches up to high tide.

An examination of the latest gridded ETSS and ESTOFS (GFS-
based) and multi-model ensemble guidance indicates that coastal
flooding is expected to be at worst, minor. On the coast of
Delaware Bay, spotty minor flooding is forecast during the
Tuesday morning high tide. Levels will be elevated on the tidal
portions of the Delaware River, but they are expected to remain
below advisory levels at this point.

Beyond this morning, surface flow is expected to become strong
and offshore, limiting the threat of flooding with subsequent
high tides. However, confidence is a little lower on the NJ
coast where surge will be higher, so coastal flooding cannot be
ruled out for the Tuesday evening high tide. However, the
astronomical tide will be lower for the evening high tide,
likely limiting the threat.


PA...Winter Weather Advisory until 10 AM EDT this morning for
     Winter Weather Advisory until noon EDT today for PAZ055.
NJ...Winter Weather Advisory until 10 AM EDT this morning for
     Winter Weather Advisory until noon EDT today for NJZ001-008-
MARINE...Gale Watch from Wednesday afternoon through Thursday morning
     for ANZ430-431-450>455.
     Gale Warning until 6 PM EDT this evening for ANZ450>455.
     Small Craft Advisory until 6 AM EDT Wednesday for ANZ430.
     Gale Warning until 5 PM EDT this afternoon for ANZ431.


Near Term...Drag 433
Short Term...Drag 433
Long Term...Robertson
Aviation...Drag/Robertson 433
Marine...Drag/Robertson 433
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