Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 182050

Area Forecast Discussion
National Weather Service Mount Holly NJ
350 PM EST Mon Dec 18 2017

A warm front will bring relatively mild temperatures through
Tuesday with a cold front bringing a return to seasonable
temperatures for midweek. Conditions will be mainly dry. A warm
frontal passage and associated low pressure system will bring a
return to milder conditions for late week through the weekend
along with periods of rain.

The warm front is expected to continue lifting north of the area
overnight. While an offshore flow is expected at the surface, a
zonal flow aloft will allow for near normal low temperatures
overnight ranging from the low to mid 30s north and upper 30s to low
40s south. Mostly cloudy skies are expected in the north, partly
cloudy skies in the south, all with no precipitation.

I am expecting this period to be dry. A few sprinkles are possible
ahead of a surface trough that digs southeast into the Great Lakes
region, but through the overnight hours, the latest models keep this
trough well to our west. There will be hardly any directional shear,
as flow from the boundary layer through the upper levels will be

Forecast lows are slightly below GFS MOS guidance given the light
winds which should promote radiational cooling. However, if low
clouds build in, as one model is depicting, lows may be several
degrees higher. This appears unlikely given the off shore flow.


Tuesday night through Thursday...

Cooler but fairly quiet for this part of the forecast with forecast
models in good agreement.

Early in the period, a deepening low will move through eastern
Canada with its associated cold front moving through the area
NW to SE Tuesday evening. Forecast model profiles continue to
indicate there won`t be much moisture with this feature so no
mention of precip. By Wednesday morning, lows look to range from
the upper 20s to low 30s across the southern Poconos to the mid
30s to low 40s elsewhere farther south.

For Wednesday, the pressure gradient between the low over
Atlantic Canada and a ridge of high pressure extending into the
Great Lakes will combine with enough diurnal instability in the
low and mid levels to result in a breezy and much cooler day as
cooler air is advected in. Downsloping NW winds will result in
skies being partly to mostly sunny but expect gusts of 15 to 25
mph. Highs range from the 30s in the southern Poconos with low
to mid 40s elsewhere.

Wednesday night, winds diminish as the ridge of high pressure to the
north noses southward into the region. This will result in a
pretty good set up for radiational cooling to so went slightly
colder than the consensus guidance....forecasting lows in the
upper teens to low 20s over the southern Poconos with mid 20s
elsewhere. The ridge crests over the area early Thursday before
slowly nudging just off to the east by late day well ahead of
the next approaching system. Other than some mid and high clouds
by afternoon ahead of this system skies will be mostly sunny
with highs in the 30s to near 40.

Thursday night through Monday...

In the big picture, the pattern amplifies as a surge of cold air
spills south targeting the central CONUS into the Great Lakes
over the weekend into early next week as a deep trough is carved
out. This will put the east coast in a deep layer SW flow with a
series of disturbances bringing periods of wet weather to the
area with generally quite mild conditions. That said, still some
differences in the forecast models regarding the day to day

Thursday night into Friday, high pressure moves off to the east
with an initial low moving north into the midwest resulting in a
warm advection pattern. Some initial light rain/showers will be
possible into Friday with the warm front moving in but most of
any heavier precip stays west through this period. Also, there
could be a little snow or ice at the onset over the southern
Poconos before a change to rain occurs.

Friday night into Saturday, the aformentioned low continues to
lift northward taking a track well west of the area bringing in
quite mild air by Saturday with highs in the 50s to near 60s. As
the system`s cold front approaches by late Saturday, rain is
likely and could even fall heavy at times as early indication
are for PWATs to surge to upwards of 1.5 inches. Differences in
forecast models increase by mid to late weekend as the GFS
drives through front through bringing in a period of cooler air
by Sunday while the ECMWF and GEM are less progressive with the
front tending to stall it over the area. Overall trend seems to
be toward this slower solution keeping the long range quite mild
with most precip falling as mainly rain. There may be a brief
break in precip behind the first low by early Sunday however
models still indicate a second system moving north along the
baroclinic zone by late Sunday into Monday. Though it`s early
forecast models and overall trend support a track near or west
of the area with mainly rain.

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

Today...VFR conditions are expected for the remainder of the
TAF period, with ceilings around or above 5000 ft AGL, along
with light and variable winds. High confidence.

Tonight...VFR conditions are expected. Winds will still be
light (less than 10 kt), but should settle out of the southwest
or west by early this evening. Moderate confidence.


Tuesday through Tuesday night:  Mainly VFR, A brief interval of
lower celings possible around sunrise. Wind gusts from the
southwest at 10 to 15 knots Tuesday afternoon, decreasing at
night. Moderate confidence.

Wednesday through Thursday: VFR. West to northwest wind gusts
around 20 knots Wednesday afternoon decreasing gradually into

Friday through Saturday...Ceiling restrictions likely by Friday
along a warm front lifting north into the region. Ceiling and
visibility restrictions likely by Saturday with cold front and
associated rain. Winds increase to 10 to 20 knots Saturday.

Winds and seas are expected to stay below small craft advisory
conditions today and tonight. Wind direction is expected to be
variable, eventually settling out of the west this evening, when a
few gusts near or above 20 kt will be possible.


Southwesterly gusts up to 25 knots likely beginning Tuesday
afternoon off the New Jersey coast and continuing through
Wednesday. There may be a brief lull in winds late Wednesday
with winds potentially increasing to near or above SCA levels
later Wednesday night into early Thursday. Seas look to stay
below SCA levels through the period. High confidence.

MARINE...Small Craft Advisory from 1 PM Tuesday to 7 PM EST Wednesday
     for ANZ450>452.


Near Term...Miketta
Short Term...Miketta
Long Term...Gaines/99
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