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Area forecast discussion 
National Weather Service Mount Holly New Jersey
935 am EST Friday Dec 26 2014

Synopsis...
a high pressure system over North Carolina will slowly move east
today through Saturday and be well offshore by Saturday night. A
cold front is forecast to move through our area Sunday before
slowing its southward progression as a wave of low pressure moves
along it on Monday. A strong Canadian high pressure system will
slowly sink south and reach the northern plains on Tuesday and the
Gulf Coast states on Thursday.

&&

Near term /until 6 PM this evening/...
930 am update...no major changes in the near term. Though a few
places were colder this morning than expected, with clear skies
and downsloping winds, temperatures should have no trouble climbing into
the 40s and 50s.

Previous near term discussion...great weather expected across the
middle Atlantic region today. High pressure across the southeast
states will ridge across the area as upper heights slowly build.
This will result in mostly sunny skies and more above normal temperatures
for the region. Highs will range from the upper 40s to low 50s
across most areas. Winds will be light from the west/northwest this
morning...then west/SW by sunset.

&&

Short term /6 PM this evening through 6 am Saturday/...
more fair weather tonight with the surface high moving off the coast.
Skies will remain mostly clear and temperatures will continue above normal.
Lows tonight will be in the low/middle 30s in most areas. Winds will be
light.

&&

Long term /Saturday through Thursday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy and surrounding areas.

The long term period will bring colder weather back into our County Warning Area
with a transitional precipitation event Sunday into Monday. The GFS
initialization at 500mb looks better than it did last night and
was on par with the European model (ecmwf) and WRF-nmmb. Domestically the WRF-nmmb
looked better at 850mb and both models comparable at 925mb. While
the models have come closer, there are still timing and intensity
differences that only subtle changes initiated. While we thought
we had the diurnal bias of flatter solutions night sounding runs,
more robust solutions day sounding runs, the European model (ecmwf) flipped on US
tonight because its decay of its southwestern trough is slower.

The European model (ecmwf) ensembles infer a slightly northwest and warmer track.
Greatest uncertainty is smack at the base of the short wave trough.
There were about 5 gefs members that were wetter than the op and
the can gefs, two members were stronger, two comparable and about
16 weaker than the op model.

No weather issues on Saturday as the high pressure system should be
off the North Carolina coast and the approaching cold front still
well to our west. The predicted convective temperatures off the
soundings are still in the 90s and low 100s and low level moisture
even on the WRF-nmmb is not that plentiful. We are expecting a
mosunny day with maximum temperatures a couple of degrees higher
than today. Once again the full sun macros off the WRF-nmmb model
support GFS MOS more than its own NAM MOS (which was not
utilized).

Saturday night cloudiness associated with the cold front's
precipitation should start arriving in the area. Min temperature confidence
is lower than average because of this and actual mins might occur
earlier at night with a bump up in temperatures as clouds arrive. Far
northwest County Warning Area only area that gets predicted Omega and location of
liquid probability of precipitation late.

The cold front is predicted to pass through our County Warning Area on Sunday and Sunday
evening. Models not overly enthused about shower/precipitation potential. We
do see the best predicted middle level qvec convergence with the precipitation
potential occurring during the day and hiest relatively speaking
instability. Not much DPVA or reflected Omega, so we kept probability of precipitation as
chance and mention of precipitation as scattered showers. We did not sway
much from stat guidance for maximum temperatures.

There are forcing similarities with the wave on the front. Since its
predicted to be relatively weak we are not seeing much middle level warm air advection
past 12z Monday and not much predicted isentropic lift. But, our County Warning Area
will be in an excellent entrance region of a 180kt 250mb jet and the
700mb jet also is predicted to pass across the southern part of our
County Warning Area. Middle level qvec convergence gets replaced by middle level fgen
forcing as a precipitation processor (again leaning south). Differences come
around with timing and how strong these processes will be. The added
element is that colder air will be advecting into this system and a
change to non liquid ptype is expected to occur. But like last
night, the most likely places to see a transition to sleet (added it
per WRF forecast soundings) and snow (generally northwest of the fall
line/i95 corridor and west of 287 in nj) are expected to see the
lowest amounts of precipitation. In addition warm weather leading into
this event and supposive light precipitation intensity should reduce
accumulation efficiency. On the other hand, precipitation transition
occurring at night will not Hurt. Right now any accums dont look
to be much, but might coincide with the Monday morning commute.
We will add a mention in the severe weather potential statement given there are still
uncertainties to the strength of the system and do not want to
sell it short. Timing we are closest to the parallel GFS. Thermal
fields with the GFS and European model (ecmwf) were fairly close and 925s and 850s
temperatures were used as the demarcation of non-liquid. As precipitation
intensity decreases as Monday continues, a backward change or mix
to some rain might occur.

Given the faster trend, we decided to remove the mention of probability of precipitation for
Monday night. The short wave on Tuesday is predicted to be so
channelized and relatively weaker, we only kept the mention of
flurries in northwest. We did add flurries in as a starter for
Wednesday as a much stronger and more orthogonal short wave trough is
predicted to move through. By Tuesday and new years evening
temperatures should become colder than normal. No change to Thursday
(new years day) forecast was made as 2015 is expected to commence
relatively quietly.

&&

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

Wonderful flying conditions today and tonight as high pressure rules
the weather picture. Skies will feature just some high cloudiness at
times today. Winds will be wrly/nwrly around 5 knots early today and
then winds will shift more southwesterly at 5 to 10 knots later this
afternoon. Tonight sky clear and calm or very light SW winds.

Outlook...
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.

Monday night and Tuesday...VFR.

&&

Marine...
high pressure off to the south will build across the waters today
and then move to the east tonight. Winds and seas will remain sub-
Small Craft Advisory conditions through the period. Winds will be west or northwest this
morning and then back to more of a west or SW direction tonight.
Speeds will be around 10 knots today and closer to 5 knots
tonight. Seas on the ocean 2 to 3 feet and 1 to 2 feet over del Bay.

Outlook...
Saturday and Saturday evening...sub Small Craft Advisory conditions
expected.

Saturday night into Sunday morning...a slightly stronger southwest
flow preceding a cold front will bring wind gusts closer to Small
Craft Advisory criteria on the ocean.

Sunday afternoon and night...sub Small Craft Advisory conditions
expected.

Monday and Monday night...sub Small Craft Advisory conditions expected.
Lower confidence 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.

Tuesday...sub Small Craft Advisory conditions expected.

&&

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

&&

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

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