Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Mount Holly New Jersey
912 am EDT sun Aug 30 2015
a weakening cold front will arrive tonight, otherwise high
pressure will remain mostly centered near the middle Atlantic region
through much of this week. However, a weak cold front may slide
into our region on Thursday. An offshore low and high pressure to
our northeast may provide some cooler conditions for next weekend.
Near term /until 6 PM this evening/...
a short wave trough will arrive into the northeast later today, and
as it does it should tend to weaken. A weak cold front at the
surface is tied to this feature, and with some moisture on the
increase there are some showers currently with it to our west. There
is some instability during the day, with this probably best across
the western zones. However, the forecast soundings mostly show a
skinny cape profile which tends to keep updrafts on the weaker side.
The bulk of the lift associated with the trough axis is forecast to
be to our west during peak heating with the actual short wave and
the right entrance region of an upper-level jet. However, terrain
influences and a weak surface trough could come into play and
therefore we kept a slight chance pop during the afternoon across the
northwestern zones. Some increase in the clouds is expected
especially across the western zones in advance of the aforementioned
It will be rather warm to hot across much of the County Warning Area this afternoon,
however dew points may lower a little bit this afternoon in some
areas due to significant heating of the boundary layer. The pressure
gradient is not forecast to be all that tight, therefore light
enough flow should result in a sea breeze once again this afternoon.
The hourly grids were adjusted based on the latest observations,
then the lamp/lav guidance was blended in to assist. No major
changes were made to the high temperatures at this time.
Short term /6 PM this evening through 6 am Monday/...
any isolated showers or thunderstorms will come to an end and then
expect just a pcldy sky with gradually increasing dew pts, as the
high remains the dominant weather feature as we close out August and
Long term /Monday through Saturday/...
some shifts in tracks and timing with the latest model runs, but
the main story remains the high sliding over the region for much
of the work week.
Monday through Wednesday...may see a few lingering showers or
thunderstorms Monday morning as an upper level short wave trough
moves further away from the region, but otherwise precipitation
chances through this period are very slim. Should see a modest
warming trend from Monday into Tuesday as the ridge axis slides
overhead, thus leading to increasing 1000-500 mb thicknesses for
the region. Even with this high amplitude ridge though, highs
should stay well below records, and heat index values should stay
in the lower to middle 90s.
Thursday...a bit more uncertainty in this period, specifically
with the evolution of the weak cold front. Some models are now
stalling this front well north of the region, or showing the
temperature gradient almost disappear completely by the time it
reaches our region. For now though, have stayed close to the
previous forecast for both temperatures and precipitation chances,
as the upper level short wave trough could provide enough lift and
focus for convection even without the front, and still think there
is a chance the front will reach the area given that the models
tend to underestimate how far south fronts will propagate in the
Friday through Saturday...stayed relatively close to the previous
forecast as there are some large differences among the long range
models in this period. The GFS shows steady on shore flow as a
surface high develops to our northwest. Meanwhile, the European model (ecmwf) shows
a vertically stacked, and nearly stationary, low to our southeast.
Either solution though does look to bring a cooling trend through
Aviation /13z Sunday through Thursday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg,
kilg, kmiv, kacy and surrounding areas.
Rest of today...VFR with some cumulus developing around 5000 feet.
Light southwesterly winds increasing up to 10 knots, which should
turn more southerly at kacy and perhaps kilg due to a sea/Bay
breeze. There is a low chance a shower or thunderstorm approach the
kabe to krdg areas toward evening.
Tonight...VFR overall. A weakening cold front should allow a shower
or thunderstorm to arrive near the kabe and krdg areas this evening,
however coverage is expected to be very low. Southwesterly winds 5-
10 knots, becoming light and variable at many of the terminals.
Monday through Wednesday...VFR conditions expected though
localized MVFR conditions with fog possible each morning.
Thursday...mostly VFR conditions. Isolated thunderstorms
no marine flags are anticipated through the near and short term
periods. Seas will generally be in the 2 to 4 feet range. Wind will generally be
SW in the 10 to 15 knots range with gusts as high as 20 knots.
Monday through Thursday...winds and seas should stay well below
Small Craft Advisory criteria. Water temperatures are above
a long period east to southeast swell, 10-11 seconds, continues to
roll in along the coast. This combined with winds turning more
southerly and increasing some through the day will result in tricky
conditions at times within the surf zone especially during tide
changes. As a result there is a moderate risk for the development of
dangerous rip currents through this evening, and the Delaware
beaches are now also included in this.