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Area forecast discussion 
National Weather Service Mount Holly New Jersey
628 PM EST Friday Dec 19 2014

Synopsis...
high pressure just north of Lake Superior will gradually move
eastward into northern New England through Monday. A wave of low
pressure will form along the middle-Atlantic coastline on Monday
and move northeastward just offshore on Tuesday. Meanwhile...
a strong area of low-pressure will form over the Mississippi
Valley and move through the Great Lakes region during the middle
of the week...bringing a strong cold front through the region
by Thursday. High pressure is projected to build in on Friday.

&&

Near term /through Saturday/...
with this estf update we adjusted sky cover going more pessimistic
north based on current posning of clouds and the 18z models
bringing an 850mb short wave through the northern part of our County Warning Area. We
upped temperatures slightly north, left the rest as is. With light winds,
confidence about temperatures due to cloud cover uncertainty is lower
than average.

For tonight...northwest winds will continue but will become lighter as
Canadian low pressure moves away and high pressure moves closed with
resulting relaxed pressure gradient.

&&

Short term /Saturday night through 6 PM Saturday/...
for Saturday...high pressure centered over Canada shifts eastward from
Ontario into Quebec. A ridge axis is forecast to extend southward through the
middle-Atlantic region resulting in only light northerly winds. Some low-level
moisture should remain trapped below the large-scale subsidence
inversion but hard to say how extensive any low clouds may be. The
12-km NAM shows a thin low cloud layer developing during the day but
higher-res arw/nmm and the GFS do not. There will be some higher
clouds also associated with the shortwave now moving east-northeastward out of the Southern
Plains...however probability of precipitation remain near zero.

&&

Long term /Saturday night through Friday/...
highlights...

* slight chance of snow showers Sunday morning mainly north.
* Snow possible northwest of the I-95 corridor late Monday
through early Tuesday.
* Potential for heavy rain increasing on Christmas evening day.

Overview...

Middle-level blocking pattern over noam begins to dislodge in response
jet energy moving into the Pacific northwest this weekend...carving
out a deep trough over the MS valley early early next week...which
leads to inclement weather in the Tuesday through Wednesday time frame.

Details...

Sunday...
shortwave lifting through the region early in the day may generate
enough lift along with marginal moisture in the column to produce
some light snow showers...mainly during the pre-dawn hours. Little
if any accumulation expected as moisture is very limited. Ridging
then builds in so fair weather is expected the remainder of the day.

Monday and Tuesday...
high pressure anchors along the Lee of the Appalachians. A southern
stream shortwave will induce low-pressure of the middle-Atlantic coast.
Models bring quantitative precipitation forecast northward into the area on Monday night into early
Tuesday. Thermal profiles are cold enough for snow to the northwest
of the I-95 corridor...but the best lift is focused just southeast
of this area...and the system could track further to the south per
12z UKMET model. Still a lot of uncertainty with ultimate track.

Wednesday...
a middle-level ridge will move through the region Tuesday night into
early Wednesday leading to a brief respite between weather systems.
Then a middle-level trough is projected to become negatively tilted
over the Ohio Valley on Wednesday...leading to a meridional flow along
the East Coast...with the entire column expected to be well above
freezing across the County Warning Area favoring a rain event. There are several
ingredients coming together for heavy rain. In particular...deep
Gulf moisture...low-level isentropic lift...mid-level positive vorticity advection...and
the right-rear quadrant of a 140 knot upper-level jet just north.
The system should be fairly progressive but will have to monitor
potential for flooding.

Thursday and Friday...
low-pressure moves northward into Quebec and high-pressure begins
to build in. Temperatures will return to seasonable levels and
there could be snow showers in the blustery northwest flow.

&&

Aviation /23z Friday through Wednesday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy and surrounding areas.

The 00z tafs take ceilings down to MVFR levels tonight from the kphl
area airports northwestward with improvement on Saturday. Its been
tough to shake this stratocu level cloudiness pattern.

For tonight. Low clouds advancing in from the higher terrain
airports are still heading into the terminals. We bring MVFR ceiling
potential from the get go at kabe and krdg (hier confidence
overnight) and bring it down to the kphl metropolitan airports after 05z.
We leave kacy and kmiv VFR. Winds will be light from the
northwest. No visibility restrictions expected.

On Saturday, predicting the MVFR ceiling to become scattered during
the morning from the kphl metropolitan airports nwwd with a cirrus ceiling
above. Kacy and kmiv not expecting a MVFR ceiling. It will be a weak
pressure pattern and winds will be light. A northerly direction
is favored, but speeds are expected to remain below 10 knots,
probably predominately less than 6 knots at some of the more
rural airports and terminals.

Outlook...
Saturday night and Sunday...VFR conditions expected.
Monday and Tuesday...IFR possible in rain showers and shsn.
Wednesday...IFR possible in rain and fog.

&&

Marine...
sub-Small Craft Advisory conds are expected for the next 24 hours at least. Somewhat
gust northwest winds this evening will gradually diminish tonight through
Saturday as a ridge of high pressure moves overhead. Seas are
currently running 2 to 3 feet but they should gradually diminish
also.

Outlook...
Sunday and Monday...sub-sca conditions expected.
Tuesday...Small Craft Advisory may be needed for building seas.
Wednesday...Gale Warning may be needed.

&&

Phi watches/warnings/advisories...
PA...none.
New Jersey...none.
Delaware...none.
Maryland...none.
Marine...none.

&&

$$
Synopsis...franck
near term...amc/gigi
short term...amc
long term...franck
aviation...franck/gigi
marine...amc/franck

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