Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 230746

Area Forecast Discussion
National Weather Service Mount Holly NJ
346 AM EDT Wed Aug 23 2017

A cold front will slowly cross our region through the morning
hours before moving off shore late today. High pressure is then
expected to build towards the northeastern U.S. and remain over
our region into early next week. A low pressure system off the
East Coast could affect our weather mid week next week.


As of 3 AM EDT, the cold front is on the door step of SE and E
Central PA. It has been making steady progress over the last 6
hours. Based on the observed trends, expect it to move into our
region within the next hour, and into the I-95 corridor by 6 AM.
It will then likely slow its progress east thanks to increased
daytime mixing and may linger on the coastal Plains (especially
southern Delmarva) through mid day. Adjusted PoPs to keep a
mention of showers and thunderstorms along and ahead of where we
expect the front to be. Though shower activity has mostly
diminished for now, expect to see some additional development
ahead of the front near or after sunrise (though do not expect
as widespread coverage as what we saw overnight).

MOS guidance doesn`t appear to be handling the front and the
effect on highs very well, so went with a blend of operational
models which show below normal highs along and west of the fall
line. Even for the eastern Coastal Plains which may stay in the
warm sector until just before peak heating, clouds could limit
highs through the day.


Clearing skies and cold air advection will promote below normal
temperatures across the region. The one question will be if we
will see any fog development overnight. At this point, have not
mentioned it in the forecast as we should also see considerable
dry air advection behind the front.


500 MB: a -2SD trough begins the long term period in the Great
Lakes region, then weakens slightly as it moves into the
northeast Friday- Monday. Thereafter, we will monitor the
northeastward progress of what should be a split flow low of
tropical origins, having moved ashore along the Gulf Coast by
early next week.

Temperatures: Calendar day averages Thursday...near or slightly
below normal, then 2 to 6 degrees below normal daily Friday-

Forecast basis: a 50 50 blend of 12z/22 GFS/NAM MOS was used
Wednesday night-Thursday night, then the 12z/22 GFS MEXMOS was
applied Friday and thereafter the 15z/22 WPC D4-8 gridded
elements of max/min T, 12 hr POP 6 hrly dew/wind/sky.

Thursday...Scattered light showers possible late Thursday in e
PA with considerable afternoon cloudiness.

Friday-Monday...High pressure shifts southeastward into the
Great Lakes Thursday through Saturday,then eastward into
southeastern Canada/Northeast U.S. Sunday and Monday. This
expansive high will control our regional weather pattern across
the Mid Atlantic during this time. The trough aloft could result
in a shower north of I-78 Friday afternoon and there should be
considerable cloudiness at that time. Otherwise, for now, good
weather is predicted.

Tuesday...WAA overrunning clouds, if not rain, from a potential
tropical remnant moving northeastward from the Gulf coast.


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

Once showers and low clouds move off shore later this morning,
expect mostly VFR conditions for the remainder of the TAF

A cold front will be moving through the region between 09 and
18Z. Behind this cold front, expect northwesterly winds around
10kt with some higher gusts especially just behind the front.
After 00Z, wind speeds should diminish below 10kt.

Thursday through Sunday...VFR. Generally light winds from the N
or NW, possibly becoming N-NE on Saturday and Sunday. small
chance of a light shower vicinity KABE/KTTN/KRDG Thursday
afternoon and Friday afternoon.


Winds have dropped below 25 kt on the Delaware Bay, so the Small
Craft Advisory has been cancelled for the bay. On the Atlantic
Coastal waters, waves and winds are diminishing, but there are
still some locations reporting SCA conditions, so will keep the
SCA going for now. Once the winds and waves diminish this
morning, expect sub-SCA conditions for the remainder of today
and tonight. For locations that still have southwesterly winds,
expect a wind shift to northwesterly by mid day as a cold front
moves through.

Thursday through Saturday...Winds and seas below SCA criteria.

Sunday...For no SCA headline but chance that northeast flow
will increase and cause hazardous seas to develop along the S NJ
and DE coasts Sunday (5 feet).

Wednesday... At this point we are forecasting a low risk of rip
currents today as earlier elevated seas are diminishing quickly.


MARINE...Small Craft Advisory until 6 AM EDT early this morning for


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