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Area forecast discussion 
National Weather Service Mount Holly New Jersey
611 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/...
this estf update we upped probability of precipitation for faster movement of the first
surge in our area. We lowered probability of precipitation close to middle day to account for
a possible break and then raised them again during the afternoon for
the second surge.

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. Through 06z the GFS seemed to be
verifying the closest with precipitation placement and amounts, with the
European model (ecmwf) second and others lagging further. 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. One was initially in the Ohio Valley last evening, the second
currently in western Kentucky. That first impulse will mainly affect the
northwestern part of our County Warning Area through the first half of today. Here
we are seeing the best confluence of relative instability, precipitable water and
prox to the entrance region of the jet. So this locale has the
highest chance relative to guidance of seeing some heavier amounts.
The second impulse over Kentucky 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. (11z it is nearing pittsburgh) highest probability of precipitation
slide southeastward as the day progresses and we end shower
chances northwest during the 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 /11z 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 are
possible during the afternoon.

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
short term...gigi
long term...O'Hara
aviation...gigi/O'Hara
marine...gigi/O'Hara

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