Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

Current Version | Previous Version | Text Only | Print | Product List | Glossary On
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
FXUS61 KPHI 161321

Area Forecast Discussion
National Weather Service Mount Holly NJ
921 AM EDT Fri Mar 16 2018

Low pressure remains over the Canadian Maritimes through Saturday,
then weakens as it moves eastward. Meanwhile, a cold front moves
through the region early this morning followed by high pressure
slowly building toward our area by late day. A weak area of low
pressure will quickly slide to our south Saturday, then high
pressure arrives for Sunday. Low pressure in the Central Plains
later Sunday and Monday tracks eastward, and should result in
another coastal storm impacting the area for Tuesday into Wednesday
before moving to off the New England coast Thursday.


A few snow showers associated with the surface cold front and
mid-level shortwave moving through the region popped up in parts
of southeast PA and NJ. Will go ahead and bump up PoPs to
isolated/scattered this morning, as coverage is not widespread,
and dewpoint depressions are high enough that most of the snow
is not reaching the ground, and only a few ASOS stations are
picking up on it. A dusting or so is possible across the
Delaware Valley and into southeast NJ.

A reinforcing shot of colder air will spread into the region
later today.

Forecast high temperatures range from the upper 20s in the
Poconos to mid 40s along and S/E of I-95. The readings are about
15 degrees below normal for the middle of March for the higher
elevations of NE PA/NW NJ and more representative of climo for
January. Elsewhere, highs will be about 10 degrees below and
more representative of mid February.

High pressure over the Upper Midwest will nose southeastward
toward the central Appalachians, helping to strengthen the
pressure gradient across our region today with the low stalled
over eastern Canada. The result will be a breezy W-NW wind
around 20 mph, gusting 30-35 mph this afternoon.

Flurries may linger across the southern Poconos through the
morning and possibly early afternoon before forecast soundings
show significant drying in the low-levels as subsidence
strengthens overhead.


High pressure builds to our S/W tonight with the surface ridge
axis extending SEwd from the Upper Midwest to the central Mid-
Atlantic region.

The pressure gradient will relax a bit as the ridge axis shifts
ever- so-slightly closer to our region but it will still be
breezy in the evening. The gradient may weaken enough across far
SE PA, E MD and S DE to allow for winds to become light late
tonight. Accordingly, a sharper drop in temps may occur before
daybreak across these southern zones under increasingly
favorable radiational cooling conditions. Low temperatures range
from the mid teens in the Poconos to the mid 20s along and S/E
of I-95, which are roughly 5-10 degrees below climo.


Saturday through Sunday night...

Persistent pattern remains in place with an upper level trough
situated over eastern Canada putting the area in a broad, cyclonic
flow. To start the period Saturday, the tail end of a cold
front will move south and brush across the area but this will be
a dry front with no major impacts on sensible weather other
than helping provide breezy conditions (though not as windy as
Friday). However what will have to be watched is a wave moving
out of the midwest and skirting by just south of the area. The
GFS continues to be most robust with this feature indicating
upwards of a quarter inch of QPF over the southern Delmarva on
the northern edge of this system while the NAM keeps precip just
south of the area. GEM Regional is in between these two
extremes. Current forecast for POPs/QPF doesn`t change much from
previous one and basically follows this middle ground solution
bringing some precip into the Delmarva with even some slight
chances for rain brushing far south NJ near Cape May. As such,
expect some rain to break out across the Delmarva Saturday
afternoon with temps initially in the low to mid 40s. What will
have to watched though is that the air will be quite dry at the
surface and depending on how much precip falls, there may be
enough wet bulb cooling to change precip over to wet snow before
it moves out by early evening. Confidence not high regarding
this and even if it occurs, there probably wouldn`t be much if
any snow accumulation. Elsewhere for Saturday, SE PA and central
and northern NJ will see a dry day with sunshine filtered at
times by mid and high clouds from the aformentioned system to
the south. Highs will be generally in the 40s except 30s across
the southern Poconos.

For Saturday night, system quickly moves out in the early evening with
an otherwise clear and chilly night on tap as high pressure
noses back into the Ohio Valley resulting in a NW flow. This
high will bring sunshine with continuing seasonally cool weather
for Sunday with highs once again mainly in the 40s except 30s
across the southern Poconos. Another clear and cold night will
follow for Sunday night.

Monday through Thursday...

The main story during this period will be the east coast storm
threat for the Tuesday through Wednesday period. In the meantime,
the period starts off dry for Monday under the influence of high
pressure with sunshine giving way to increasing high clouds by late
day. Highs will be mainly in the 40s except 30s over the southern
Poconos. Beyond this time, attention turns to the next east coast

Forecast models continue to show a strong signal for an east coast
storm during the Tuesday - Wednesday period of next week. In fact
the latest trends are for the storm to be a little slower to arrive
but to potentially be very slow moving with an extended period
of precip and winds for the middle of next week over the mid
Atlantic. The other potential hazard that will need to be
monitored is coastal flood threat, especially given this slower
trend which could bring a prolonged period of strong NE winds.
General trend has also been for the low to be farther south and
east favoring a colder, potentially snowier solution. Both the
GFS and latest ECMWF track low pressure east into Tennessee by
next Tuesday and then indicate secondary development will occur
near the North Carolina coast by late day. Precip should move
into the area during the day either as rain, snow or a mix of
rain/snow. At this early juncture, rain looks to be favored
along and S/E of the I-95 corridor with snow or a mix possible
farther north/west, but again, it`s early so we are not yet
confident in these forecast details. Winds will also strengthen
out of the northeast through the day.

Heading into the Tuesday night into Wednesday period, the
secondary low looks to take over as it deepens and slows down
near or just off the coast as the system begins to close off
aloft. This slower movement could keep precip in place over the
area right through much of Wednesday. A big forecast challenge
at this time will continue to be precip type. The lift and
precip with the system along with winds becoming more northerly
as the low moves off the coast could result in a change to
mainly snow later Tuesday night or Wednesday. But again, it`s
early to have much confidence in these forecast details. Also,
wet snow falling during the daytime at this time of year with
marginal temperatures may have a hard time accumulating. Despite
these uncertainties, in the big picture confidence continues to
grow that there will be a coastal storm impacting the area
around the middle of next week but it`s going to take at least a
couple more days until we can be more confident in details such
as precip types and amounts.

The storm should finally move north and east of the area by next
Thursday with precip over the area diminishing but cool temperatures
lingering in its wake with a NW flow. So no warm up for the
next week as pattern we`ve been stuck in remains in place.


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

Today...Some virga, possibly even flurries or a brief snow
shower, is possible at the terminals through 16Z or so. Latest
KDIX radar, as well as nearby ASOS stations, are picking up on
some light snow showers. Cannot rule out a brief reduction in
VSBY to MVFR. Otherwise, VFR. Variable mid-level deck today with
CIGs varying between 4500-7000 ft AGL. W-NW winds 10-15 kt with
gusts up to 20 kt will increase to 15-20 kt with gusts up to 30
kt as the morning progresses and will continue through the day.

Tonight...VFR with clearing skies. W-NW winds will gradually
decrease throughout the night with gusts diminishing at a faster
rate after sunset.


Saturday through Sunday...Mainly VFR. A little light rain could
brush KMIV and KACY late Saturday but this should not bring any

Monday...Clouds increase especially late day and at night, with
possible MVFR/IFR conditions developing overnight if precipitation

Tuesday...Widespread MVFR/IFR conditions with rain/snow possible.
Low confidence with the details.


Strong Small Craft Advisory conditions on the waters today, and
there may be a period from around 4pm-8pm for a few gale force
gusts on the ocean waters. Confidence in widespread gales is
low, so opted to keep the SCA going.

The SCA, which also includes the DE Bay, will continue into


Saturday and Sunday...The conditions should be mostly below Small
Craft Advisory criteria, however a northerly wind surge with gusts
20-25 knots may occur Saturday night. Winds may also be near
SCA levels during the first part of Saturday.

Monday...The conditions are anticipated to be below Small Craft
Advisory criteria, although winds should start to increase from an
easterly direction later Monday night.

Tuesday...Winds increase as a coastal storm approaches and
should at least be at strong SCA levels by late day. The
magnitude of the winds and seas will depend on the track and
strength of a coastal storm.


MARINE...Small Craft Advisory until 6 AM EDT Saturday for ANZ450>455.
     Small Craft Advisory until 4 AM EDT Saturday for ANZ430-431.


Near Term...Klein/MPS
Short Term...Klein
Long Term...Fitzsimmons
Marine...Fitzsimmons/Klein/MPS is the U.S. government's official web portal to all federal, state and local government web resources and services.