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Area forecast discussion 
National Weather Service Mount Holly New Jersey
958 am EST Thursday Dec 25 2014

Synopsis...
the cold front has moved off shore. A high pressure system over
the Gulf Coast states will build northeast and reach the Virginia
coastal waters on Friday before receding farther offshore on
Saturday. A cold front is forecast to move through our area Sunday
and then slow its southward progress as a wave of low pressure
moves along it on Monday and Monday night. A strong high pressure
system from Canada should reach the northern plains on Tuesday and
then gradually build toward the Middle Atlantic States on Wednesday.

&&

Near term /until 6 PM this evening/...
the cold front pushed off shore a few hours ago and will continue
to move away from the region. The clearing line is just about to
the Delaware River valley and will continue to slide east. There
is another canopy of low clouds over central PA, but did not make
any changes to the forecast sky cover as dry air advection should
help to erode these clouds as they try to push east into our
region. Breezy westerly winds are expected to continue through the
day. However, the strongest winds may be in the next 2 to 3 hours
as after 18z, the low level jet dissipates and the pressure
gradient relaxes. With cold air advection all day, do not expect
much warming even when we clear out, but still should see daytime
highs in the 50s for most areas (higher terrain of the Poconos are
not likely to break out of the 40s.

&&

Short term /6 PM this evening through 6 am Friday/...
high pressure will expand across the area tonight. Fair weather and
seasonably cool temperatures are in the forecast. Lows will fall into
the 30 to 35 degree range in most areas. Winds will become light.

&&

Long term /Friday through Wednesday/...
the WRF-nmmb initialization looked better than the GFS at most
levels. Out west the gfs's trough appeared too strong, which is not
normally the modeling bias error. In spite of the start, the op
GFS run kind of flowed in the same direction as the other models.

All of the models respective to their own previous sounding runs
trended flatter with the weaves on the front early next week. The
biggest leap was by the UKMET which had been taking a vigorous low
northwest of our County Warning Area around Monday. Even the can ggem which is most
bullish with precipitation and snow trended flatter (still bullish though).
While the 00z run was flatter given how subtle differences with
each model sounding run has been causing County Warning Area size displacement of
precipitation fields, this forecast package has stayed close to continuity
until successive sounding runs start producing a trending and
consistent outcome. What we do know is that the long term will
start unseasonably mild and become colder than normal by Wednesday
as the pv settles around baffin island and the upper Hudson Bay.
Relative to normal what will occur on Friday and Saturday is more
off kilter than the end of the long term, even if it will feel
colder than it really is. Also during this transition period, the
chances for snow as a ptype will increase throughout our County Warning Area. The
question remains whether or not there will be enough moisture and
lift to have that ptype generate and reach the ground.

Anytime a high pressure system builds in from Texas, its not going
to be cold. Coupled with the current intense low pressure system
lifting more north than east doesnt make for a cold recipe. Skywise
this has been one depressingly cloudy month. But for once, the
forecast soundings are not indicating any trapped stratocu
underneath the inversion as well as giving US convective temperatures in
the 90s and low 100s. Dare we predict, a mostly sunny day? GFS MOS
maximum temperatures support the op nam's thermal fields more so than its own
MOS guidance. Maximum temperatures leaned strongly the former's way.

Friday night should be a decent radiational cooling night. We leaned
colder than stat guidance in outlying areas because of this.

As cautiously optimistic as we were above the lack of cloud cover on
Friday, we are not as much north for Saturday. Some models are
showing a weak warm front near the northern part of our County Warning Area as well
as the ubiquitous trapped low level moisture. We met this halfway for
now given that the predecessor air mass should be starting dry. There
is better model forecast sounding agreement about maximum temperatures. Here we
are closest to the stat guidance that suggested the same: an European model (ecmwf)
and GFS MOS blend.

Clouds should start increasing on Saturday night, very low chance of
a shower sneaking into the Poconos before dawn, too low for now to
include. On Sunday, the precipitation associated with the cold front has less
of an anafront look to it, so we opted to call it showers. Forecast
soundings indicate that the sub 850mb layer is warm enough for rain
as a ptype.

From here the forecast starts lapsing into greater uncertainty
because of modeling handling of the troffing in the southwestern
Continental U.S.. the uncertainty is further complicated by the possibility of
convection in the far northwest Gulf and modeling handling of each
impulse correctly.

So while there is still decent consensus about an upper air impulse
for Sunday night, geographically it was sagged farther south. The
flow aloft over the eastern Continental U.S. Is confluent, so one would expect
the shearing and dampening of impulses. On the other hand, models
often weaken them too quickly. Highest probability of precipitation Monday night are south
of the Mason and Dixon line. Forecast soundings are indicating snow
as a possible ptype about as far south as the PA Turnpike/i195
corridor late. Soundings so far are not indicating much sleet or
freezing rain as there is no strong southerly push of cold air at
either 925mb or the surface.

It gets even more uncertain Monday into Monday night as the latest
European model (ecmwf) and GFS have trended much more subdued with the wave on the
front. As stated above until we see successive sounding runs
indicate similar solutions and with some gefs members wetter, we
kept the chance or slight chance for precipitation. While the chances for
snow increase farther north in our cwa, the chances for precipitation are
less.

On Tuesday dry or not, the models are predicting a channelized vorticity
maximum to move through. This was enough for the pgfs to generate precipitation
over our County Warning Area. We kept in slight chance probability of precipitation. Thermally were precipitation to occur
in our County Warning Area Tuesday, it would be cold enough for snow in most areas.
We kept Tuesday night and Wednesday dry.

With the return of the -epo ridge, the high pressure entering the
Continental U.S. Is originating in Siberia. Its first entering the Continental U.S. In the
northern plains, so it will lose some of its ferocity as it moves
east. Regardless below normal temperatures are expected as it comes
closer at the end of the long term.

&&

Aviation /15z Thursday through Monday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy and surrounding areas.

Here's something we haven't had much of a chance to say lately:
VFR conditions are expected through the taf period. Most places
should be breaking out of the clouds soon. Few to sct040 may move
in from the west, but dry air should help to erode them as they
do. Breezy westerly winds in the wake of this morning's cold front
should continue through most of the day, though the strongest
winds may be through 18z. After 18z, the pressure gradient
relaxes. By this evening, winds should be relatively light.

Outlook...
Friday and Saturday...VFR.

Saturday night...some MVFR ceilings possible northwest airports, VFR ceilings
elsewhere.

Sunday into Monday...MVFR, possibly IFR, conditions possible at
times as waves of precipitation move from north to south across the
area. The northern part of the precipitation shield could be snow.

&&

Marine...
westerly winds continue with a slight shift to northwesterly
possible by this afternoon. Wind speeds should remain in the Small Craft Advisory
gust range for the daytime hours at least, lingering into the
evening hours on the Atlantic coastal waters.

Outlook...
Friday through Monday...sub Small Craft Advisory conditions
expected. A weak cold frontal passage should occur on Sunday.

Lowest confidence is on Monday as a wave of low pressure is
predicted to form south of the area waters on the mentioned front.
Its possible that Small Craft Advisory conditions might occur if
this low intensifies faster than we are currently forecasting.

&&

Phi watches/warnings/advisories...
PA...none.
New Jersey...none.
Delaware...none.
Maryland...none.
Marine...Small Craft Advisory until 10 PM EST this evening for anz431-
450>455.
Small Craft Advisory until 6 PM EST this evening for anz430.

&&

$$
Synopsis...gigi/gorse
near term...Johnson/O'Hara
short term...O'Hara
long term...gigi
aviation...gigi/Johnson/O'Hara
marine...gigi/Johnson/O'Hara

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