Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 181855

Area Forecast Discussion
National Weather Service Mount Holly NJ
255 PM EDT Wed Oct 18 2017

High pressure remains in control of the weather for much of the
rest of the week into the weekend. A dry frontal boundary may
move into the area Thursday into Friday. A front and low pressure
moving along it will bring unsettled conditions for later Monday
into Wednesday.


High pressure remains over the mid-Atlantic region. However, this
high will undergo gradual weakening tonight as an upstream shortwave
trough approaches from the Ohio Valley.

This upper shortwave trough will be associated with increasing high
clouds responsible prior to its arrival. Do not anticipate these
clouds to have a significant impact on radiational cooling given the
high base of the cirrus. Accordingly, temperatures should drop
rather quickly this evening once the boundary layer decouples and
winds become calm. Compared to recent nights, higher dewpoints
tonight will (1) raise the floor for how low temperatures can bottom
out, (2) inhibit frost formation and (3) increase the risk for
radiational fog. At this point, am skeptical to think fog will be
much more than patchy in coverage and shallow in depth (mainly
ground fog). Forecast lows range from the upper 30s/lower 40s in the
sheltered valleys of NE PA/NW NJ and the NJ Pine Barrens to the
lower 50s for the urban I-95 cities and along the coast.


High pressure sinks southward toward the Southeast U.S. on Thursday.
Modest pressure (height) falls at the surface (aloft) occurs across
the northern mid-Atlantic region as a weak upper shortwave trough
and surface cold front progress eastward.

The aforementioned cold front will trail the upper trough enough to
remain upstream of the forecast area through the period. The setup
will allow us to remain situated in the pre-frontal warm sector and
for this warming trend to continue into tomorrow. Sided closer to
the warmer MAV guidance for temperatures, yielding forecast highs in
the lower to middle 70s (except cooler in the higher elevations of

Filtered sunshine with high clouds during the morning will give way
to sunny skies by the afternoon. Meanwhile, SW winds 5-10 mph in the
morning are forecast to increase to 10-15 mph by afternoon.


Thursday night thru Monday...High pressure at the surface and
aloft will be in control of the weather with fair weather
expected. Temperatures generally 5 to 10 degrees above normal.

Monday night thru Wednesday...A pattern change with a sharp h5
trough moving into the ern part of the country. Low pressure
and a slow moving front associated with the upper trough will
affect the area with occasional rains. Locally heavy rains are
possible with an upper trough beginning to take a negative tilt
as it crosses the area. The 12Z NA models are showing QPF
totals generally in the 1 to 3 inch range across the area for
the period Mon_Wed. The higher totals are across the wrn
counties. Much colder temperatures will be ushered in behind
the system with below normal temperatures for the middle part of
next week.


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

Generally VFR Thursday. However, patchy ground fog may develop at
the fog-prone, rural TAF sites between 05Z-11Z Thursday which could
result in a brief period of MVFR visibility. Confidence in fog
development was too low to mention in 18Z TAFs except at MIV.

SW winds 5-8 kt this afternoon will diminish to 5 KT or less after
sunset this evening. SW winds continue on Thursday, gradually
increasing to from 5-8 kt in the morning to 8-15 kt in the

Thu night thru Monday...VFR expected thru the period.


Winds this afternoon are generally from the W-SW between 5 and 10
kt. However, winds are backed locally out of the S in the nearshore
NJ waters owing to the formation of a sea breeze front. Winds may
briefly increase to 10-15 kt late this afternoon and early evening a
few miles farther off the NJ coast in association with an Ambrose

SW winds 5-10 kt will continue into tonight and Thursday morning,
then increase 10-15 kt across the coastal Atlantic waters during the
afternoon. Wind field may become locally enhanced to 15-20 kt off
the coast of Ocean and Monmouth Counties via Ambrose jet late in the
day. Held off on a SCA at this juncture since poor mixing profiles
should inhibit higher winds aloft to reach the surface. Accordingly,
capped gusts to below 25 kt.

Seas will generally be around 3 ft in the coastal waters and 2 ft or
less in the Delaware Bay.

Thu night...Near SCA winds across the nrn NJ coastal waters Thu
    evening, but not confid enough for a flag attm. Fair.
Friday thru Sunday...Sub- SCA conditions thru the period with
    fair weather.




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