Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 152043
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
343 PM EST Sun Jan 15 2017

.SYNOPSIS...
High pressure will crest over our region tonight and move
offshore on Monday. Low pressure trekking through the Mississippi
Valley and Great Lakes will lift a warm front through our area on
Tuesday followed by a cold front on Wednesday. In the wake of the
frontal passage, high pressure over Atlantic Canada will build
southward into our region late in the week and into the weekend.

&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
High pres has built over the region and nwly flow has brought dry wx
and not nothing more than high clouds.  The high will shift ewd
tonight.  Expect a chilly night with light wind over the area.  It
should be a decent radiational cooling night, so temps will have to
be monitored.

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH 6 PM MONDAY/...
Dry wx is again in store for Mon as high pres moves away from the
area.  There will be an increase in clouds durg the day as a wmfnt,
assocd with low pres in the cntrl plains, moves thru.  Temps shud be
a few degrees warm than on Sun, and guid looked reasonable and was
genly accepted.

&&

.LONG TERM /MONDAY NIGHT THROUGH SUNDAY/...
A split flow pattern continues across North America. In the southern
stream, a disturbance ejects northeastward out of the four corners
region, and interacts with a northern stream shortwave as it reaches
the Ohio Valley on Tuesday night. This leads to some model spread in
terms of shortwave amplitude and timing, and thus uncertainty in the
Tuesday-Wednesday time frame, leading to lower confidence in
outcomes. There will be transitory ridging over the region Thursday
into Friday, in advance of the next southern stream disturbance
ejecting out of the four corners region, in response to a vigorous
shortwave entering the Pacific coast. There is general model
agreement on the placement of this feature, but significant
differences in amplitude, as it traverses our area Friday night into
Saturday. This is partly due to a northern stream ridge building
over eastern Canada, which tends to attenuate the aforementioned
shortwave. Moving into the weekend, phasing between the northern and
southern streams takes place, resulting in a more amplified pattern
across North America with a ridge modeled along the east coast.

A warm front will approach our region Monday night into Tuesday.
While it will be sub-freezing generally northwest of the NJ and PA
Turnpikes Monday night, the question is whether any precipitation
can be generated in this region. While the atmosphere gradually
saturates in the mid to upper levels, there will be a dry layer of
air in the lower 5 to 10 kFT, as high pressure recedes offshore.
Warm air advection aloft is also fairly slow, resulting in weak
isentropic ascent over the cooler low level air mass. There is also
some spread in the 12Z/15 model suite regarding the onset time of
precipitation. The general model consensus brings at least
measurable precip to much of our area by 12Z Tuesday, while the NAM
holds off until 00Z Wednesday.

For the most part, areas generally north of I-78 look to have the
greatest chance of mixed precip Monday night. Model soundings
indicate thermal profiles favorable for a very brief period of snow
and sleet, then favoring predominantly freezing rain. Keep in mind
that precip should be intermittent and light, so would not expect
more than 0.10" of ice glaze. With the uncertainty in this portion
of the forecast, confidence is low.

The consensus of the 12Z/15 models is more progressive by 6 to 12
hours over the NAM with this system. The NAM solution would hold off
most of the precip until Tuesday afternoon, overspreading the entire
region during Tuesday evening. This forecast reflects the model
consensus, with measurable precip having overspread the entire
region around sunrise Tuesday. As the redevelopment of low pressure
takes place near the NY/NJ Bight, in addition to low pressure over
the Great Lakes, this puts the breaks on a northward advancing warm
front, which looks to stall somewhere near the PA Turnpike and I-195.

Although the ultimate location of where the warm front becomes
stationary is far from certain, there is strong model agreement for
in-situ cold air damming just to the north. With the warm front near
the PA Turnpike and I-195, the deepest moisture and strongest lift
would coincide just north of this area, resulting in the highest
precip amounts, generally up to around one-half inch. Fortunately,
the thermal profile warms Tuesday into Wednesday, so expect
predominantly rain by Tuesday afternoon across the entire region.

Overall, we expect a dusting of snow close to I-80, with up to 0.10"
ice glaze north of I-78.

Fog and drizzle are likely Tuesday into Tuesday night, especially
north of the warm front, where dense fog is possible. Lingering
showers are possible Wednesday morning with the cold front moving
through the area, otherwise fair weather is anticipated by the
afternoon, when Northwest winds will gust 20 to 25 mph. It will be
relatively warm, with high temperatures around 15 degrees above
normal.

Fair weather is expected to continue into Thursday, with a chance of
showers returning for Friday and Saturday, possibly lingering into
Sunday. At this time, indications are that it will be warm enough
for precip to be predominantly in the form of liquid. Daily high
temperatures during the Thursday thru Sunday time frame are expected
to continue around 10 degrees above average.

&&

.AVIATION /21Z SUNDAY THROUGH FRIDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

VFR conds are expected thru the TAF pd.  High pres is in control
thru Mon.  It will be over the region tonight before moving ewd on
Mon.  NW flow durg the remainder of today will go light ne or calm
overnight and then become more swly on Monday.  Wind speeds should
stay around 10 kts through eve today, and be genly 5 kts or less on
Mon.  Clouds will thicken and lower durg the day Mon.

OUTLOOK...

Monday night...Ceiling will lower to at least 5 to 10 kFT across the
area. Scattered MVFR ceilings likely for the I-95 terminals,
especially after midnight, with more solid MVFR developing at ABE
and RDG. For MIV and ACY, predominantly VFR. South to southeast
winds less than 10 knots.

Tuesday and Wednesday...Strong signal for a period of widespread
MVFR across the region in terms of ceilings, especially at TTN, ABE,
and RDG (near and to the north of a warm front), where IFR is
possible. In addition, fog could also lead to MVFR or even IFR
conditions at times across the area, especially the aforementioned
terminals. Conditions gradually improving to VFR during the day
Wednesday. Southeast flow on Tuesday veering to southwest Tuesday
night, generally at or below 10 knots. On Wednesday, a cold frontal
passage veers winds to the northwest during the day, increasing 10
to 15 knots with gusts of 20 to 25 knots.

Thursday..Predominantly VFR conditions. Northwest winds 10 to 15
knots.

Friday...VFR ceilings may deteriorate to MVFR from south to north
across the terminals. Northwest winds may back to the east, but are
expected to be light.

&&

.MARINE...
No marine headlines are expected thru the near and short term pds.
Seas will genly be in the 1-2 foot range.  Win, which could gust
around 20 kts today will decrease and genly be 10 kts or less for
the remainder of the pd.

OUTLOOK...

There is a low probability of southerly Winds approaching Small
Craft Advisory criteria Tuesday night into Wednesday ahead of a cold
front. There is a moderate probability of northwest winds
approaching Small Craft Advisory criteria behind the cold front
Wednesday and Wednesday night. Seas may also approach 5FT during
these time frames.

With a warm and moist air mass moving over the cooler maritime
waters in association with a warm front Tuesday afternoon into
Wednesday moring, we expect areas of fog to develop during this
period.

For the remainder of the period, winds and seas are anticipated to
remain below SCA thresholds.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...None.

&&

$$
Synopsis...Franck
Near Term...Nierenberg
Short Term...Nierenberg
Long Term...Franck
Aviation...Franck/Nierenberg
Marine...Franck/Nierenberg



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