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 50
FXUS61 KPHI 140059

Area Forecast Discussion
National Weather Service Mount Holly NJ
859 PM EDT Tue Mar 13 2018

Strong low pressure east of New England will move north into
the Canadian Maritime area and then remain near the lower St.
Lawrence Valley through Saturday. Meanwhile high pressure will
extend south from Canada across the Great Lakes and Ohio Valley,
maintaining a relatively cold northwest flow across our mid-
Atlantic region into the weekend. Another coastal may develop in
the early to middle part of next week, but as of now its track,
timing and intensity are quite uncertain.


Intense coastal low south and east of Cape Cod will lift into
the Canadian Maritimes tonight. Meanwhile, closed H5 low over
the Great Lakes tracks to the south and east and will be just
north of NYC by daybreak Wednesday.

Clouds have scattered out across the region and winds have
started to diminish as well. Temperatures have decreased well
with only one or two sites needing adjustments in the latest
hourly grids. We will keep the overnight lows as is with mostly
20s and close to 30 in Phi;adelphia.

Shortwaves approach the region late tonight as that 500 mb low
tracks east. Temperatures may hold steady late tonight and into
daybreak due to the increased cloud cover. A few snow showers
associated with the low could move into the southern Poconos
and far northwest NJ prior to daybreak, but any snow accumulations
will be light.


Westerly pressure gradient tightens up between low pressure
retrograding through the Canadian Maritimes and high pressure
over the Gulf Coast states. Meanwhile, several potent shortwaves
will pass through the region in the afternoon, and there will
be enough instability to touch off rain and/or snow showers
south and east of the Fall Line, and more widespread snow
showers in the southern Poconos, Lehigh Valley, and northwest
NJ. Snow accumulations will generally be up to an inch in the
heavier snow bands in the Poconos, otherwise, generally 1/2"
snow elsewhere. Highs should get into the lower 40s for most of
southern NJ and southeast PA, so would not expect much in the
way of accumulation.

West winds increase to 15-20 mph with 25-35 mph gusts in the


For the long-term period starting Wednesday night, the mid-
Atlantic region remains largely under the influence of an upper
low/trof over eastern Canada and the northeast U.S. This pattern
will be associated with NW flow aloft and generally below
normal temps, especially if the ECMWF guidance is to be

On Thursday a shortwv trof is fcst to rotate around the main
upper low and across the mid-Atlantic region, with an associated
cold front also crossing the area. This along with some low-
level instability may trigger some rain or snow showers during
the afternoon. At this time we are carrying only chance or
slight chance PoPs.

On Friday it will be colder behind the cold front, and another
shortwv is fcst to rotate through. There seems to be a bit less
instby and sfc reflection with this one and any snow showers
will likely be confined to the southern Poconos.

For the weekend the upper low remains invof Canadian Maritimes.
Temperatures are forecast to be a bit milder but still a few
degrees below normal. A back door cold front may push through on
Sunday but no assocd precip is expected. Temps will become
colder again for Monday and Tuesday as high pressure builds in
from the NW. Models are forecasting another low to develop off
the mid-Atlantic coast around mid week, but whether it will
track along the coast or move out to sea is unclear.



Tonight...VFR. West winds diminishing to less than 10 kt this

Wednesday...VFR. Scattered snow showers may impact KABE/KRDG, and
scattered rain and/or snow showers may briefly impact
KTTN/KPNE/KPHL. Best chances at KABE/KRDG. Brief MVFR conditions
possible. West winds increase to 15-20 KT with 25-35 kt gusts late
Wednesday morning.


Thursday...Mostly VFR. Occasional MVFR possible in snow or rain
showers during the day, more likely at ABE/RDG. Westerly winds
gusting to 20-25 knots. Moderate confidence.

Friday...Mostly VFR.  Northwest winds gusting to 20-25 knots.
High confidence.

Saturday and Sunday...VFR. Northwest winds gusting 15-20 knots
on Saturday. High confidence.


The SCA flag will continue on all the waters overnight. For the
ocean, it will also be in effect for Wednesday as winds once
again increase Wed. morning. Seas will remain at or above 5 ft.
On Delaware Bay, the SCA was extended in time earlier, and it
still appears that the SCA gusts will continue much of the
night. Fair weather expected tonight and a few snow showers
possible Wed.


A gale watch is in effect for Wednesday night. SCA conditions
may persist through Thursday and Friday with gusty NW winds. Sub
SCA condition are expected for Saturday and Sunday.


Surface flow will increase on Wednesday from the west, which is
an offshore flow. This will limit 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 high tide this evening. However, the
astronomical tide will be lower for the evening high tide,
likely limiting the threat.


MARINE...Gale Watch from Wednesday evening through late Wednesday night
     for ANZ430-431-450>455.
     Small Craft Advisory until 6 PM EDT Wednesday for ANZ450>455.
     Small Craft Advisory until 6 AM EDT Wednesday for ANZ430-431.


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