Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

FXUS61 KPHI 181143

Area Forecast Discussion
National Weather Service Mount Holly NJ
643 AM EST Mon Feb 18 2019

Low pressure will pass through the region today, with High
pressure building back in from the north and west on Tuesday.
High pressure will move away from the area Tuesday night with a
complex area of low pressure moving through the Northeast
Wednesday through Thursday. High pressure builds in from the
north and west to close out the week. Low pressure will likely
impact the area next weekend.


630 AM Update:
The precipitation is making its way out of our area. While it
may not look like much on radar in the advisory area, it`s
likely that some very light mist/drizzle is falling so we will
leave the headline up for now. Once the precip moves out,
things should start to clear out fairly quickly.

Temperatures are gradually rising but there are still some
colder spots out there right around freezing so expect
hazardous conditions to continue through this morning.

Previous Discussion:
Winter Weather Advisory remains in place this morning as looking at
the mesonet temperatures, we see them continue to hover right around
32 degrees across much of the advisory area.

The main issue remains freezing rain. While there may be a little
bit of snow that falls, the profiles have remained warmer overall
and we are seeing much more in the way of liquid precipitation as
opposed to frozen precipitation. Regardless of the fact that less
snow will fall, the impacts remain the same. Hazardous travel
conditions will continue through the advisory areas through this

Precipitation, mostly rain, will continue to move through the
forecast area this morning. As the parent low pulls offshore, we
should start to see the precip end from west to east this morning,
Some lingering showers may continue, especially across eastern
zones, through mid-morning but the bulk of the precipitation should
be over by the time the morning rush has ended.

Clearing will start to occur as the precip departs and much drier
air moves into the region. Skies may remain cloudy through at least
mid day but expect some sun to start peeking out this afternoon,
especially across our southern areas.

Winds pick up in the westerly flow and may become quite gusty
through the afternoon and into this evening. Wind gust up around 25
to 30 mph with some gusts around 35 mph possible across the forecast

Temperatures will gradually rebound today and should start to war
appreciably toward this afternoon. Expect highs to reach into the
upper 40s to lower 50s across Delmarva, mid to upper 40s through the
Delaware Valley and along the I-95 corridor, and in the upper 30s to
lower 40s across the Lehigh Valley, southern Poconos and
northwestern New Jersey.


High pressure will start to build into the region tonight and we are
expected to stay dry. Skies will clear out overnight and we should
radiate well, especially once the winds start to die down.

Overnight lows will be cold with teens across the northern zones and
20s every where else.


Big Picture

The large-scale synoptic pattern will be more or less static
through the long term period with longwave troughing over the
western US and a mid-lvl ridge over the sub-tropical Atlantic.
Various shortwave disturbances will eject from the western
trough and generally track north and west of the area due to the
mean ridge position. An upper level jet will generally be
centered just north of the area however it will meander at
times into favorable locations to enhance ascent over the
forecast area. The sfc.low track to the northwest of the area
will result in precipitation events being largely driven by
ejecting shortwaves interacting with moist isentropic lift advection
to the SE of the low center.


Tuesday: High pressure will reside over or just north of the
forecast area on Tuesday with quiet sensible weather as a
result. As the high moves overhead northerly winds should be
noticeably weaker than Monday. A fairly cool airmass will keep
temps about 5-10 degrees below normal. Cloud cover increases
from S-N Tuesday night into Wednesday morning as flow aloft
backs more southwesterly advecting moisture into the area.

Wednesday: The main precipitation event of the long-term looks
to impact the area Wednesday as shortwave energy interacts with
increasing isentropic lift and moisture advection ahead of a
sfc.low over the Midwest. Guidance has slightly slowed the
onset of precipitation with precipitation now arriving in
Delmarva early Wednesday morning and then spreading
northeast...finally reaching NW NJ/the Poconos by early Wed
afternoon. As is typical with overunning events ptype will be
 challenging with typical model biases coming into play (e.g.
the GFS scours out the low- lvl cold air too quickly, while the
NAM likely keeps the sfc. too cold). Additionally there is quite
a bit of spread among guidance over how much a secondary low
developing near/south of the area Wed PM will impact the
kinematic and thermal fields.

Currently it appears most areas (outside of maybe far southern
Delware) will experience all snow with the initial burst of
precipitation Wed AM, with a gradual (SW-NE) transition to mixed
precipitation then finally to rain Wednesday afternoon into
Wednesday night. Naturally the speed in which this transition
occurs will have significant impacts on snow and ice
accumulations. The current snow accumulations represent a
compromise between the GFS which is both the fastest to warm the
column and also has the lowest QPF, and the NAM which has the
highest QPF and the coldest profiles. It must be emphasized the
uncertainty associated with these amounts is higher than usual
both due to spread in ptype forecasts and spread in QPF

Thursday/Friday: By Thursday AM the sfc. warm front will have
passed through the entire area with any lingering precipitation
being all rain. The area will dry out fairly quickly into
Thursday afternoon as the cold/occluded front passes with brisk
but not particularly strong westerly winds in its wake. Friday
looks generally quiet as high pressure builds to the north of
the area. Expecting seasonable temperatures although some weak
mid-lvl waves may result in some passing cloud cover.

Saturday/Sunday: The next storm system takes aim at the area
this weekend with plenty of uncertainties regarding detail. At
this time the signal is for another warm advection driven storm,
with little to no CAD in place beforehand. Consequently am
currently leaning on a primarily rain event Saturday PM into
Sunday AM but there is still some uncertainty.


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

Today...Rain across the terminals will move off to the east through
this morning. IFR conditions will improve to MVFR this morning with
a return to VFR expected to occur by mid morning. Light winds
this morning will turn to the west around 15-16Z, increasing to
around 10 to 15 knots with gusts up to 25 to 30 knots through
this afternoon.

Tonight...Mainly VFR conditions expected. Northwest winds around 10
to 15 knots early will drop down to around 10 knots or less
overnight. High confidence.Outlook...


Tuesday...VFR. N/NW winds 10 kt or less. High confidence.

Tuesday night through Wednesday night...Cloud cover increasing
Tuesday night with VFR conditions transitioning to MVFR and then
IFR Wednesday morning into early afternoon as snow arrives.
Precipitation type will transition to wintry mix and then rain
from south to north Wed afternoon/evening. East to southeast
winds around 10 knots or less. Low confidence with respect to
precipitation type.

Thursday...MVFR or lower conditions in the morning, improving
to VFR late in the day. West to northwest winds around 10-15
knots. Moderate confidence.

Friday...VFR. N winds 5-10 kt.


Small Craft Advisory is in effect for all waters from this afternoon
through tonight.

Winds will be generally light this morning before starting to pick
up out of the west/northwest by the afternoon. A fairly tight
pressure gradient will allow winds to gust above 25 knots for this
afternoon and evening before the gradient starts to relax overnight.

Seas around 2 to 4 feet this morning will build to 3 to 6 feet this
evening. Seas will subside back down to 2 to 4 feet overnight.


Tuesday...Sub-SCA conditions with Seas generally around 2 to 4

Wednesday through Wednesday night...Increasing easterly winds
Wed PM with gusts > 25 knots possible. Transition from snow,
wintry mix to rain expected.

Thursday...Seas building to SCA levels by Thursday AM on ocean
waters with winds shifting to the West/NW by Thursday

Friday...Seas/winds dipping below SCA by Friday morning with
sub-SCA conditions prevailing through Saturday.


A Coastal Flood Advisory remains in effect for this morning`s
high tides along the coastal areas of New Jersey and Delaware.

It appears as though at least some spotty minor flooding may occur
with the morning high tides into the mid week period. We will
continue to monitor the water level trends.

The full moon occurs on Tuesday.


PA...Winter Weather Advisory until 10 AM EST this morning for
NJ...Winter Weather Advisory until 10 AM EST this morning for
     Coastal Flood Advisory until 11 AM EST this morning for
DE...Coastal Flood Advisory until 11 AM EST this morning for
MARINE...Small Craft Advisory from noon today to 6 AM EST Tuesday for


Near Term...Meola
Short Term...Meola
Long Term...Carr
Tides/Coastal Flooding... is the U.S. government's official web portal to all federal, state and local government web resources and services.