Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Mount Holly New Jersey
357 am EDT Thursday Jul 30 2015
a weak cold front will move through our region tonight, then stalls
to our south and east. The next weak cold front should cross our
area late Saturday before stalling offshore Sunday. A few weak waves
of low pressure may track along the front and possibly move closer
to our coast Monday as high pressure tries to arrive. A stronger
cold front is then forecast to arrive during Tuesday, before also
stalling nearby on Wednesday.
Near term /until 6 PM this evening/...
excessive heat warning remains in effect for today for the
Philadelphia metropolitan and surrounding areas.
Some scattered showers have started to pop up across the region this
morning and are moving fairly quickly to the northeast.
Clouds will filter into the region as a cold front approaches from
the west. However, there will still be plenty of sunshine to be had
for much of the region through today. The cold front will track from
western Pennsylvania to our area today, reaching our western zones
around late morning/early afternoon. As the front crosses the
region, there will showers and thunderstorms associated with it as
it pushes towards the coast.
Storms look most likely to arrive to the region after noon, with a
gradual shift to the south and east. With a ripe atmosphere and
plenty of moisture around heavy rain will be possible with any storm
In addition, the Storm Prediction Center has much of our area in
a marginal risk for severe storms. The greatest threat from
stronger storms will be gusty to potentially damaging winds.
Another humid day on tap as we see temperatures continue to rise
near 90 across much of the area. Heat index values will be in the
middle to upper 90s, approaching 100. Therefore, we have continued
the excessive heat warning for the urban areas in and around
Short term /6 PM this evening through 6 am Friday/...
the aforementioned cold front will continue its trek toward the coast
and should move offshore tonight. The showers and thunderstorms will
continue into tonight and will end from northwest to southeast as
the front pushes off the coast and then further offshore. As the
front pushes away, we will also see some clearing behind it and
areas to the north and west of philly will be able to cool off a bit
and drop down into the lower to middle 60s overnight. Areas to the
south and east of philly will hold onto the cloud cover a bit longer
and will likely remain in the upper 60s to lower 70s for overnight
lows. Even with the clearing, low level moisture may hang around for
a bit and patchy fog will remain possible.
Long term /Friday through Wednesday/...
the synoptic setup is comprised of an upper-level trough from the
Great Lakes to the northeast Friday with some amplification into the
weekend. Despite a warm to hot airmass in place, a substantial
reduction in the dew points is expected Friday and even for the
weekend overall for the County Warning Area. A weak front moves through late
Saturday with some potentially tricky convective chcs, then the next
one arrives during Tuesday before stalling nearby Wednesday. There
is more uncertainty in the details especially next week as the
amplitude of the trough and the positioning of frontal boundaries
will impact our sensible weather. We used a model blend Friday
through Sunday, then went with mostly a wpc/continuity blend
For Friday...an initial front is stalled offshore as it becomes
trapped between a ridge in the western Atlantic and a trough from
the Great Lakes to the northeast. Any remaining frontal forcing and
associated convection should remain well offshore, meanwhile a
noticeable drier airmass settles into our area. Despite it still
being warm to hot across the cwa, the lower dew points will result
in a much less humid feel /even cooler at night/. The aforementioned
upper-level trough amplifies some especially to our northwest
through northeast, and some upstream convection may try to make a
run at our northwest zones very late at night. Overall, this looks
like a very small chance plus with the initial drier airmass in place
and therefore we opted to leave the night time frame dry.
For Saturday and Sunday...an upper-level trough remains across the
northeast although it may weaken some Sunday as a ridge in the
western Atlantic tries to expand northwestward. This keeps a stalled
frontal boundary offshore however it appears that weak ripples of
energy along it remains to our east. A secondary frontal zone is
forecast to move through late Saturday into Sunday, and the greatest
lift and shear is mostly from near our northern zones on northward
into New England. The dew points should start to inch back upward
again later Saturday, however enough drying may limit much
convective development. Some guidance does initiate more convection
by late Saturday from northeastern Pennsylvania to northern New
Jersey then slides it southeastward. There may be enough shear with
increasing instability to allow for a gusty thunderstorm, however
this is dependent on the airmass moistening up sufficiently as the
upper-level trough remains in place. For now, we continued some low
end chance probability of precipitation across the far north Saturday afternoon.
The front looks to stall just offshore given weaker flow with a
southeastern extent, however some weak impulses may track along it.
It appears that any convection leftover with the front is offshore,
therefore we have a dry Sunday. It will continue to be warm given a
similar pattern and the dew points will probably increase a bit
mainly Sunday night across the southern and eastern areas.
For Monday and Tuesday...as the upper-level trough reloads from the
west, it may support weak impulses traversing the offshore front. If
this occurs and with the upper-level flow turning more southwesterly
for a time, the front may inch back into our area to help focus some
convection Monday. This looks weak overall with the main forcing
remaining mostly across the Great Lakes region Monday. Tied to this
forcing, another cold front arrives during Tuesday with the
potential for some convection although the stronger shear may again
slide to our north. We opted to go close to the 00z wpc guidance
which carries probability of precipitation of low end chance or less.
For Wednesday...as the upper-level trough starts to weaken in the
northeast, the frontal boundary from Tuesday should slow or even
stall in our vicinity. This could help focus some convective
development especially during peak heating, with possible
convectively induced impulses arriving from the west. There is much
more uncertainty this far out as the positioning of the upper-level
trough will govern the frontal zone placement and subsequent
Aviation /08z Thursday through Monday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg,
kilg, kmiv, kacy and surrounding areas.
A couple of light showers have developed near krdg this morning.
These showers are fairly light and are moving quickly off to the
northeast. Some additional showers may develop through the early
morning, fully exiting the region by late morning. Majority of the
region remains dry with showers having little to no impact to the
terminals this morning.
Mainly middle level cloudiness is expected at the terminals through
this morning with some MVFR decks impacting krdg and possibly kabe
through around 12-13z.
Showers and thunderstorms, associated with an approaching cold
front, are expected to reach the area between 16-18z. The front will
push to through the terminals from the northwest to the southeast,
exiting offshore late tonight. Timing is still an issue but expect
the front to push through kacy between 22-01z. Clearing is expected
to occur behind the frontal passage.
South to southwest winds around 5 to 10 are expected through today,
becoming northwest behind the frontal passage.
Friday...a chance of some fog early mainly at kmiv and kacy,
otherwise VFR. Northwest winds around 10 knots, then diminishing to
near 5 knots at night and becoming southwesterly.
Saturday...VFR overall. A shower or thunderstorm possible in the
afternoon and evening mainly north and west of kphl. Southwest winds
Sunday and Monday...VFR is anticipated.
a south to southwest flow of around 10 to 15 knots with gusts up to
20 knots is expected on the area waters through tonight. Seas will
remain around 2 to 4 feet.
A cold front will approach from the west and reach the area waters
late tonight. Showers and thunderstorms are expected to accompany
the frontal passage.
Friday through Monday...the conditions are anticipated to be below
Small Craft Advisory criteria overall. A lingering front offshore
Friday into Saturday, then another front moves through late Saturday
and possibly stalls nearby into Monday.
a moderate risk of dangerous rip currents is forecast for
today, with increasing south to southwest flow ahead of a cold
front and the full moon on Friday.
PA...excessive heat warning until 6 PM EDT this evening for paz070-
New Jersey...excessive heat warning until 6 PM EDT this evening for njz015-
Delaware...excessive heat warning until 6 PM EDT this evening for dez001.