Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 132035
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
335 PM EST Wed Dec 13 2017

.SYNOPSIS...
A fast moving low pressure system will move across the area tonight
and then offshore Thursday. A ridge of high pressure will build over
the area later Thursday through Friday. A low pressure system will
move up along the coast Friday night. More high pressure will affect
the area much of this weekend. Another few disturbances will be
across the area beginning later Sunday and lasting into early next
week.

&&

.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
Winds will diminish going into this evening to less than 10 mph
shortly after sunset, and then will become light and variable as the
evening progresses.

Clipper low moving through the Great Lakes will be over the Ohio
Valley after midnight, and then will pass through New Jersey and
move offshore just after daybreak Thursday. The low looks to weaken
as it approaches the spine of the Appalachians between midnight and
daybreak Thursday, but seems to strengthen a bit once it is through
the Appalachians in the pre-dawn hours.

As a result, light snow develops this evening, first over the Lehigh
Valley, and then spreads east through midnight. Around an inch or so
of snow accumulation is expected over the Lehigh Valley and into the
Poconos, but then the snow really gets going as the low intensifies.
Best lift and dynamics will be to the north, where an additional 1-
2" of snow is expected across the Lehigh Valley, Pocono Mountains,
and into northern New Jersey for a total of 2-3". Temperatures will
be cold enough to support 15-20:1 snowfall ratios, so it will not
take much liquid QPF to result in accumulating snow.

Although borderline for a Winter Weather Advisory, feel it is
prudent to issue one for Berks, Lehigh, Northampton, Warren, Sussex,
Carbon, and Monroe counties, as this snow will accumulate just prior
to and during the Thursday morning commute. For the rest of northern
New Jersey and into southeast Pennsylvania, around an inch of snow
is expected, perhaps close to 2" in parts of northwest New Jersey.
For these areas, we will issue a Special Weather Statement
highlighting the impacts to the morning commute. For southern New
Jersey and the Delmarva, accumulations should be less than an inch,
and not nearly as widespread as the accumulations will be to the
north.

Lows tonight range from the teens in the Poconos to the 20s
elsewhere.

&&

.SHORT TERM /6 AM THURSDAY MORNING THROUGH 6 PM THURSDAY/...
Snow tapers off fairly quickly after sunrise Thursday morning, but
not before dropping up to 1/2" of additional snowfall across
northern zones. Behind strengthening and departing low, west to
northwest winds will increase to 15-20 mph with gusts up to 25 mph
starting in the late morning hours. The pressure gradient relaxes
during the afternoon.

Temperatures moderate a bit Thursday afternoon compared to highs
today, but will still be below normal.

&&

.LONG TERM /THURSDAY NIGHT THROUGH WEDNESDAY/...
Weak high pressure will be across the Middle Atlantic region
Thursday night and Friday. It will bring mostly fair and continued
cool weather to the area. Temperatures will remain some 5 to 10
degrees below normal. A quick moving low pressure system will move
just off the NJ/DE coastal areas Friday night. This could bring some
light precipitation (most likely snow) to parts of SE NJ Friday
evening. Overall, confid in this is low however with the system
looking disorganized and the trends are to minimize any qpf over the
area. We`ll just keep the slgt chc pops for now, with this low and
an upper trough crossing the area.

Much of the upcoming weekend will be fair, with high pressure
building over the area. Sunny weather is expected most of Saturday
and much of Sunday before clouds increase later Sunday. Temperatures
will still be a little below normal Saturday before moderating back
to normal levels Sunday. A few showers are possible Sunday afternoon
in a warm advection pattern, but again confid in this is rather
low attm, so we`ll just have slgt chc or small chc pops only
for this time.

A better chc for rains (a some higher elevations snows) will develop
Sunday night and last into Monday as a upper trough begin to affect
the area. We`ll have chc pops for Sunday night and slgt chc pops for Monday.
We`ll carry the low pops into Tuesday as well, with the different
models having varying solutions for this period. Most of the precip
will be rain with the temperatures Monday and Tuesday having
moderated back to above normal by then. A few snow showers
across the southern Poconos are possible however.

&&

.AVIATION /21Z WEDNESDAY THROUGH MONDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.

Tonight...Snow develops this evening, resulting in MVFR/IFR CIGs and
IFR VSBYs at KRDG-KABE-KTTN-KPNE-KPHL, though the lowest CIGs/VSBYs
will be at KRDG/KABE, where the snow will be heaviest. At these
terminals, around 2" of snow will accumulate. At KTTN-KPNE-KPHL,
around an inch of snow is expected. For KILG-KMIV-KACY, snow will
not be as widespread and long-lived, but brief IFR conditions are
possible.

NW winds 15-20 KT with gusts up to 30 KT will diminish fairly
quickly to 5-10 KT early this evening, and then will become LGT/VRB
tonight.

Thursday...Snow tapers off fairly quickly from west to east just
after 12Z Thursday, and conditions improve to VFR between 13-15Z.
Winds shift to the NW and increase to 10-15 KT with 15-20 KT gusts,
perhaps a few KT higher at KACY.

Outlook...
Thu night thru Fri...VFR.
Fri evening thru Sat morning...Mostly VFR. Few showers psbl.
Sat afternoon thru Sunday...Mostly VFR.
Sunday night thru Monday...Mostly VFR. Slgt chc showers.

&&

.MARINE...
Gales will diminish fairly quickly going into this evening over DE
Bay and the DE coastal ocean waters, and SCA conditions expected for
the rest of tonight. There may be a brief lull in SCA conditions on
DE Bay. For the NJ coastal ocean waters, gales continue through this
evening, before diminishing to SCA levels.

As low pressure approaches from the west, there looks to be another
surge in Gale force winds late tonight and into Thursday morning.
Otherwise SCA conditions will prevail through Thursday.

Snow will develop late tonight and into Thursday morning, mainly on
the NJ coastal ocean waters, and this will result in VSBY
restrictions.

Outlook...
Thu night...SCA conditions early, diminishing. Fair,
Fri thru Fri evening...Sub-SCA. Chc rain/snow.
Fri night thru Sat...SCA with low end Gale psbl. Chc rain/snow.
Sat night thru Sunday...Mostly sub-SCA. Mostly fair.

&&

.TIDES/COASTAL FLOODING...
The strong west to northwest winds have lowered water levels on the
tidal Delaware River. Although winds will diminish this evening,
water levels may be low enough (i.e., around or below 2 feet below
MLLW) to cause some navigation issues during low tide into this
evening. We have issued a special weather statement to address this
concern. Water levels will return to more typical values later
tonight.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Winter Weather Advisory from 8 PM this evening to 10 AM EST
     Thursday for PAZ054-055-060>062-070-071-101>106.
NJ...Winter Weather Advisory from 8 PM this evening to 10 AM EST
     Thursday for NJZ001-007-009.
DE...None.
MD...None.
MARINE...Gale Warning until 10 PM EST this evening for ANZ450>453.
     Gale Warning until 6 PM EST this evening for ANZ430-431-454-
     455.

&&

$$
Synopsis...O`Hara
Near Term...MPS
Short Term...MPS
Long Term...O`Hara
Aviation...MPS/O`Hara
Marine...Miketta/MPS/O`Hara
Tides/Coastal Flooding...



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