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Area forecast discussion 
National Weather Service Mount Holly New Jersey
950 am EST sun Dec 28 2014

Synopsis...
low pressure moving across Quebec today will cause a cold front to
cross our area. The front will move well to the south tonight and
Monday...while a weak area of low pressure moves along it Monday and
Monday night. High pressure will ridge across the region Tuesday and
remain in control of the weather through Friday. A low pressure
system and front may advance toward our area next weekend.

&&

Near term /until 6 PM this evening/...
the showers are moving in/out faster than previously expected so
we have adjusted probability of precipitation accordingly. The last of the first surge is
moving through central and southern Jersey with drying behind
it...we carry categorical for a couple more hours in eastern New
Jersey and taper them to slight chance across our western zones.
There should be a decent break in the action later this morning
into the middle-afternoon hours before a weak wave of low pressure
slides just to the south of the region touching off more showers.
This second round of rain should stay mostly south of the philly
metropolitan area, with a few stray showers north of the city.

Otherwise, the WRF-nmmb initialization looked better than the GFS
at 500mb while at 850mb and 925mb both models were similar. With
the latter pair there was a cold initialization bias which was
taken into consideration for tonight. WRF-nmmb already had some
northwest biases. Because of the Monday night into Tuesday flips
that the GFS and WRF-nmmb have had, this package does lean more
heavily the ecmwf's way which has been the most consistent model.

The brief run of sunny weather has ended for our area. For today, we
see two impulses reflected in the model fields that will affect our
area. The first is pulling through the region as we type while the
second one is currently in southwest Virginia. This second impulse
is slated to arrive in the southeastern half of our County Warning Area this afternoon as
the cold front completes its pass through our County Warning Area. Highest probability of precipitation slide
southeastward as the day progresses and we end shower chances
northwest during the early afternoon. In reality precipitation starts
having an under-running look to it during the afternoon, but we
waited until tonight to convert the showers to rain to keep
formatted products a little less cluttered.

Maximum temperatures are a stat guidance blend. Given timing of precipitation we may be
too warm northwest and too cold southeast. Winds overall should be
on the light side, even in the Post cold frontal air mass.

&&

Short term /6 PM this evening through 6 am Monday/...
the next impulse to bring precipitation chances into our area is emanating
from the western Gulf of Mexico. Given its long trek to get here and
to factor in a bit of uncertainty, we compromised between the GFS
and European model (ecmwf) during this time period. So once precipitation associated with
impulse number two exits, a steady rain is most likely to occur
later at night in Delaware-Maryland-Virginia from impulse number three. Given the cold
bias initialization (also location/movement of the jet), we sided
with warmer thermal fields overnight. Ptype is all liquid and we
think the GFS hint of some sleet (advecting in sub zero 925mb air)
had too fast of a head start to occur. Skies should become clearer
(or at the least clouds higher) in the northern part of our County Warning Area. Min
temperatures are generally at or above stat guidance. Lowest
confidence northwest where some skies might clear.

&&

Long term /Monday through Saturday/...
the front from the near/short term parts of the forecast will have
settled well south of the area Monday. Most of the models show
some weak wave developing along it and cruising by to the south
Monday. The preferred ec/GFS models some some light quantitative precipitation forecast across the
Delaware-Maryland-Virginia Monday morning...so we have gone along with that...but
reduced probability of precipitation/quantitative precipitation forecast from yesterdays forecast. The trend in most models
has been to suppress the system. The 00z NAM remains north with the
quantitative precipitation forecast/higher probability of precipitation. The wpc considers the NAM an outlier solution...
so we are going to disregard that for now.

Tuesday through Friday...high pressure over the plains and Midwest brings
colder and dry air to the region. Temperatures will fall to a few
degrees below normal Tuesday and remain at or below normal through
Friday. A slight chance for a snow shower across the Delaware-Maryland-Virginia early
Tuesday...but other than that a dry forecast for the period.

Friday night/Sat...the op models showing another low deepening and
moving west of the area. Clouds will increase Friday and precipitation will
overspread the area Friday night and remain into Sat. Temperatures could be
cold enough for some snow/mixed precipitation Friday night...but readings
will probably warm enough for mostly rain Sat.

&&

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

12z tafs continue to contain MVFR conditions mainly during more
frequent showers.

This morning and afternoon...northern airports and terminals VFR
showers are ongoing terminals with ceilings lowering to MVFR later in
the morning. VFR ceiling improvement during the afternoon as showers
decrease and end.

Kphl area airports and terminals/airports to the south/southeast
expecting a VFR ceiling morning with spottier morning showers and
more widespread showers during the afternoon. MVFR ceilings appear
less likely than previously thought so we removed the tempo
groups.

All terminals visibility restrictions too brief to include, mainly VFR
visibilities. Winds will become west to northwest during the late morning
to early afternoon as the cold front moves through. Speeds should
be less than 10 knots.

Tonight, VFR middle level ceilings rising to cirrus levels at northern
airports. Northwest to north winds averaging 5 to 10 knots.
Southern terminals and Delaware-Maryland-Virginia airports might see a second surge
of mainly VFR rain late at evening and overnight.

Outlook...
Monday through early Tuesday...VFR north. Lower conditions possible
in precipitation and lower clouds south.

Tuesday afternoon through Thursday...VFR expected.

&&

Marine...
sub Small Craft Advisory conditions are predicted through tonight.
The surge of stronger southwest winds aloft this morning is not
mixing down as highest observed winds are around 15 knots. The air
temperature/water temperature differential is not going to improve
this morning for mixing and by this afternoon, the wind fields aloft
are lighter. Thus a cold frontal passage during the afternoon will bring
showers, but not stronger winds to the area waters.

Winds will veer to a northerly push behind the cold front tonight,
but the overall pressure gradient will remain relatively weak and
even with a better air/water temperature differential, sub Small
Craft Advisory conditions are predicted to continue.

Outlook...
Monday...mostly sub-Small Craft Advisory conditions.
Monday night/Tue...Small Craft Advisory conditions possible.
Tuesday night through Thursday...mostly sub-Small Craft Advisory conditions expected.

&&

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

&&

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

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