Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 010242

Area Forecast Discussion
National Weather Service Mount Holly NJ
942 PM EST Wed Nov 30 2016

Low pressure moving eastward across the Great Lakes into New England
will drag a cold front through our region overnight. This low
pressure will elongate and move slowly north through New England and
Atlantic Canada through Friday night. High pressure over the Ohio
Valley on Saturday will move into the mid-Atlantic on Sunday.
Meanwhile, a complex low pressure system stretching from the midwest
to the Gulf of Mexico will impact our weather during the early into
perhaps the middle of next week.


It appears that we will have at least two more rounds of showers
and thunderstorms. One ill-defined line moving into western
portions of our region now. A second area over western and central
PA is just ahead of the cold front. As for the thunderstorm
potential, we did have one cell that produced occasional
lightning earlier (has since weakened), but it appears that the
warm front has stalled, so do not expect any increase in the
instability. Therefore, kept mention of isolated thunderstorms,
but it will remain the exception, most of the precip should just
be showers.

Showers will clear out behind the cold front, mainly after midnight
and from west to east. Dense fog will be possible again tonight,
especially in advance of the cold front and possibly just behind the
front before the winds start to pick up. Westerly winds will become
breezy overnight and persist through early morning.

A mild night temperature-wise as lows will range from the 40s to
lower 50s across the region. Adjusted the temps slightly with this
update now that it looks like the warm front will likely not make
much more progress north.


The front exits offshore and conditions should clear out fairly
rapidly. Relatively clear skies with breezy conditions are expected
through the day Thursday. Clouds will push into our northwestern
zones by the afternoon and there will be partly to mostly cloudy
conditions expected in those areas.

Cooler air will start to make its way to the region but overall near
normal temperatures are expected with highs in the 50s across the
area. The strong northwest flow will allow for lake effect
precipitation to develop but the flow across our area will become
more westerly (as opposed to northwesterly) which should prevent any
precipitation from making its way into our forecast area.


A cyclonic flow aloft will be maintained over the region through at
least Friday, w/Friday night being the inflection point/transition
to an anticyclonic flow. Mid-level ridging will be prominent across
the area through Saturday night, with the eventual breakdown of the
ridge and subsequent unsettled weather being the primary source of
uncertainty for the remainder of the long term. This uncertainty
derives from the models` handling of multiple shortwave impulses
over the midwest, and the resultant degree of phasing between the
northern and southern streams.

There are two camps of model solutions for Sunday and beyond: GFS
/UKMET/Canadian, and the Euro. The GFS/UKMET/Canadian show minimal
stream phasing, which leads to a flatter eastern conus ridge, and
allows a quick moving clipper-like system to move through the
mid Atlantic Sunday into Monday. The Euro/Canadian indicate a more
robust phasing between the streams, leading to a higher amplitude
eastern conus ridge, and a primary storm system moving from the
lower Mississippi Valley on Sunday to the mid Atlantic in the Mon-
Tue time frame.

A look at both the ECENS and GEFS ensemble means tell a similar
story to the operational runs, with no additional clarification as
to which of the two solutions may be favored. Given the degree of
model disparity, it`s also unrealistic to compromise between the
extremes. Per WPC, the operational ECMWF appears to be the outlier,
so this forecast will lean more toward the GFS/UKMET/Canadian camp.
The end result is the best chance of precip focused in the late
Sunday into Monday period. Temperature-wise, dailies will not stray
too far from their climatological means, ending up near normal.

Daily details...

Thursday night through Saturday night...
The cyclonic flow aloft will eventually transition to shortwave
ridging over the region by Saturday. Friday is shaping up to be
a nice day with dry weather. Cannot rule out patchy fog Thursday
night in the normally prone locations where the boundary layer
decouples more, especially given the recent rainfall. With the
cyclonic flow aloft and westerly downsloping flow off the Great
Lakes, expect extensive stratocumulus across the far northwest,
otherwise mostly sunny. By Friday night, a shortwave swings by
just northeast of the area, with little in the way of moisture
and lift. Just an increase in cloudiness expected, in addition
to the upper jet cirrus over the area. On Saturday, similar to
Friday in terms of sky conditions. Cannot rule out a flurry in
northwest NJ and the Poconos, given greater low-level moisture
and instability across this area.

Clipper-type system approaches the region, but enough short-
wave ridging should be maintained aloft to stave off precip
during the day. At this point, an increase in cloudiness is
expected thru the day.

Sunday night thru Monday...
A weak shortwave moving quickly thru the northwest flow aloft
will traverse the region. There is inherent uncertainty in
the timing of this feature, given it`s over four days out,
but the primary period of impact is expected to be Sunday
night. Given the origins of the system and the absence of
Atlantic inflow (northwest flow), feel the precipitation
will be light, focused northwest of the area closer to the
Great Lakes. The thermal profile is supportive of snow, but
with limited moisture, amounts will be light. The primary
concern is the timing, as a minor shift forward could lead
to impacts for the Monday morning rush hour. Otherwise, a
clearing trend will take hold from southwest to northeast
during the day.

Monday night thru Wednesday...
At this time, fair weather is expected the first half of
this period, Monday night thru Tuesday. As the mid-level
ridge crests over the region late Tuesday, precipitation
could make it into the region as early as Tuesday night.
Model profiles indicate a warming trend, but cannot rule
out some wintry precip, especially at the onset given a
cold air damming signature. Given the time frame, above
average model uncertainty, and borderline thermal profile,
it`s too early to speculate any further on the sensible
weather details.


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

Widespread IFR conditions should continue through at least 06Z.
There have been temporary breaks in the low clouds from KPHL to
the south, but do not expect this improvements to be long lived
especially with another round of showers moving in from the west.
Visibilities will be variable and will lower at times in heavier
rain showers and fog. There may be isolated thunderstorms, but
confidence is too low to include in the TAFs at this time.

The cold front is expected to arrive between 06 and 09Z. Behind
the cold front, expect conditions to quickly return to VFR as low
clouds break up and rain moves off shore.

VFR conditions are expected during the day tomorrow, but gusty
northwesterly winds are expected (gusts near or above 20 kt possible
between 15 and 00Z.

Thursday night thru Sunday...Predominantly VFR conditions expected.
Winds out of the west-northwest may gust up to around 20 to 25
knots at all TAF sites both Friday and Saturday afternoons.

Sunday night and Monday...Predominantly VFR conditions. A brief
period of light snow is possible Sunday night into Monday morning,
especially to the northwest of I-95.

Monday night and Tuesday...Predominantly VFR.


The marine dense fog advisory has been extended through 3 AM EST.
There may be areas where fog has dissipated south of the warm
front, but it looks like fog is persisting along the shore for
many locations and now that we are past sunset, do not expect much
additional improvement.

Otherwise...the Small Craft Advisory remains in effect through
Thursday. Seas have risen above 5 feet and are expected to remain
elevated through Thursday afternoon. In addition, winds will
increase later this evening and gusts around 25 to 30 knots
overnight, mainly in the vicinity of and just behind a cold front.
The gusts should subside once the cold front has moved further to
the east of our region on Thursday. There is a chance for some brief
gale gusts overnight but there is also a slight chance of
some convection occurring with the frontal passage and this may be
short lived enough to be handled with an SMW as opposed to a longer
fused gale warning.

The gradient will start to weaken on Thursday and winds and seas
should both start to subside as we head into Thursday evening.

Thursday night...The current SCA expires at 23Z Thu, and this may
need to be extended further into Friday night. At this time, we
opted to leave the expiration time as is, given model soundings
disagree on whether west-northwest winds will be at or just below
SCA criteria.

Friday...West-northwest winds expected to be predominantly below
SCA criteria, but cannot rule out a couple of gusts to 25 knots,
especially in the afternoon. This will need to be monitored, and
upgrade to SCA will be needed if more frequent 25 knot gusts are

Friday night and Saturday...Return of SCA conditions in a north-
westerly more likely during this period. A shortwave disturbance
will traverse the waters, leading to cold air advection/steeper
lapse rates, and more efficient momentum transfer. Thus, expect
frequent northwest wind gusts around 25 knots during this time-
frame over the ocean waters, with highest confidence northern
NJ waters (ANZ450-451).

Saturday night thru Monday...some residual SCA wind gusts over
the northern NJ waters possible early Saturday night. Otherwise,
sub-SCA conditions expected.


November based on the following calendar day max min temp.

PHL 64 55. Nov avg 50.0 or 2.4F above normal. Ranked 14th warmest
Nov in the PHL period of record (tied 14).

ABE 57 50. NOV avg 45.9 or 3.2F above normal. Ranked #16 warmest
in the ABE period of record.

ACY 66 54. NOV avg 48.3 or 1.5F above normal. Not ranked top 16.


MARINE...Dense Fog Advisory until 3 AM EST Thursday for ANZ431-450>455.
     Small Craft Advisory until 6 PM EST Thursday for ANZ450>455.
     Small Craft Advisory until 3 AM EST Thursday for ANZ430-431.


Near Term...Johnson/Meola
Short Term...Meola
Long Term...Franck
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