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fxus61 kphi 221951 
afdphi

Area forecast discussion
National Weather Service Mount Holly New Jersey
351 PM EDT sun Sep 22 2019

Synopsis...
high pressure off the Carolina coast will drift out to sea tonight.
A cold front then approaches on Monday, and moves across the region
Monday night. High pressure returns for the mid-week period,
followed by another cold front late Thursday and Thursday night.
High pressure builds back into the northeast for the end of the week
and next weekend.

&&

Near term /until 6 am Monday morning/...
general midlevel southwesterly flow is in place this afternoon, with
a weak shortwave trough near the coast and a stronger perturbation
moving into the Great Lakes region downstream of a strong vortex in
the upper Midwest. Some weak showers were developing in central New
York and Pennsylvania along a diffuse surface trough, likely aided
by the advancing Great Lakes vort Max. The surface trough is
expected to move little through this evening, with the vort Max
lifting northeastward into southeast Canada and the northeast. As a
result, not expecting any showers to make it into our area before
dissipation (as nocturnal stabilization sets in).

This makes the main forecast challenge tonight fog development. With
subtly increasing near-surface moisture and another night of light
or calm winds, patchy fog is a good bet in the more susceptible
Rural/Valley locations northwest of the urban corridor. Have added
mention in these areas. Guidance is a little less aggressive in The
Pine Barrens and Delmarva, so have left mention out southeast of the
I-95 corridor from now (though this certainly cannot be ruled out).

A warm night is ahead, with lows in the 60s across the area. May see
some 70-degree readings in the urban corridor and near the
beaches.

&&

Short term /6 am Monday morning through 6 PM Monday/...
a surface trough will become established across the area tomorrow,
with a strong, positively-tilted shortwave trough progressing from
the Great Lakes to the northeast and adjacent portions of Canada. An
attendant cold front generally along the Appalachians will extend
southwest from a weak surface low in southeast Canada by Monday
afternoon. Some convection should develop along and ahead of the
front by afternoon, and may develop along the surface trough axis as
well. The latter is hinted at by the NAM nest and WRF-arw/nmm
simulations, as well as coarser guidance. Inherited pop forecast
looked reasonable and made few adjustments through the day. Chances
are generally highest northwest of I-95 and dwindle to unmentionable
near the coast and in most of Delmarva.

Model soundings indicate little instability will develop during the
day, even as diurnal heating maximizes, as midlevel temperatures
will be fairly warm owing to antecedent ridging. Nevertheless, given
the warm/humid conditions across the area, was hesitant to exclude
potential of thunderstorms entirely, so kept mention of slight
chances in during the late afternoon.

Monday will be unseasonably warm, with temperatures reaching to
around 90 degrees in the urban corridor and portions of Delmarva.
Most others will be in the 80s, with upper 70s possible in the
Poconos and at the beaches.

&&

Long term /Monday night through Sunday/...
a cold front will cross through the area Monday night. Flow looks to
be pretty progressive with the front working through the area Monday
night and then offshore by Tuesday morning, although the models have
slowed the arrival of the front a bit over the latest runs, which
has the main precipitation arriving late in the day. With enough
surface heating we will be able to have some instability but it will
be limited and with the sun setting earlier this time of year, it
won't hang around quite as long as it does during the Summer months.
Thunder looks isolated at best so will keep a slight chance in the
forecast. Thunder will wane through the late afternoon into the
evening, leaving just showers as we head into the overnight period.
Showers will mostly be right along the frontal boundary and will end
from northwest to southeast, with the bulk of the rain having exited
offshore by around daybreak.

Once the front moves through, high pressure starts to build back
into the region for Tuesday and Wednesday. Northwest flow on Tuesday
will help to rid US of the lingering moisture and will lend to nice
fall days across the area through Wednesday.

A weak cold front will cross through the area on Thursday. The
guidance shows that there there is limited moisture with the front
as it arrives in our forecast area. Some showers may hold together
as the front moves in and it looks like it may mostly be confined to
our northern areas and then possible continue slightly southeast as
the front pushes through, which correlates well with the passage of
the upper trough as well. Not a lot of confidence this far out so
will only include a slight change for showers at this time.

High pressure will then build across the mid-Atlantic on Thursday
night, sliding across our area on Friday, and then offshore late
Friday into Saturday. Expecting a return to dry conditions for
Friday through Saturday. Another weak front may approach our area
late Saturday into Sunday but once again it looks like it may remain
mostly dry as it crosses through our area.

&&

Aviation /20z Sunday through Friday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy and surrounding areas.

This afternoon...VFR with light south to southwest winds. High
confidence.

Tonight...mainly VFR. However, some patchy fog may develop late.
Winds light and variable. Low confidence on fog formation/timing.

Monday...any fog early in the day will dissipate rapidly. Mainly VFR
with winds increasing from the south/southwest around 10 kt,
possibly with some gusts 15-20 kt (especially at phl/acy).
Cannot rule out a few showers late in the day, especially at
rdg/Abe. High confidence.

Outlook...

Tuesday and Tuesday night...VFR. Northwest winds 10-15 knots during
the day, then around 5 knots or less overnight.

Wednesday and Wednesday night...VFR. Westerly winds around 5 knots
becoming southwesterly less than 5 knots.

Thursday...mostly VFR. Cold front expected to move across the area
during the afternoon, but likely to remain dry for most of the area
except northeast Pennsylvania and northern New Jersey. Wind shift
from southwest to west, then northwest behind the front and may gust
15-20 knots in the afternoon.

Thursday night...VFR conditions expected. Northwest winds 5-10 knots.

Friday-Friday night...VFR conditions expected. Light and variable
winds early, becoming south to southwest 5-10 knots late in the day
and overnight.

&&

Marine...
south to southwest winds 10 to 20 kt are expected to develop tonight
and continue through Monday. Some gusts may approach 25 kt by
afternoon on the Atlantic waters, with winds expected to be somewhat
lower on Delaware Bay.

In addition, seas will increase to around or slightly above 5 feet
by afternoon. As a result, have issued a Small Craft Advisory
beginning at 10 am Monday for the Atlantic waters.

Outlook...

Tuesday...Small Craft Advisory conditions through 10z with southwesterly wind gusts
to 20 knots and seas possibly exceeding 5 feet. Winds diminishing to
10 to 15 knots and turning westerly throughout the remainder of the
day with seas dropping to 2 to 4 feet.

Wednesday...sub-sca conditions expected with westerly winds from 10
to 15 knots turning southwesterly through the afternoon and seas
from 2 to 4 feet, though some 5 foot waves may be possible in the
afternoon.

Thursday...sub-sca conditions expected with southwesterly winds
continuing from 10 to 15 knots and gusts to 20 knots. Seas building
to 2 to 4 feet.

Friday...sub-sca conditions expected with northeasterly winds from 5
to 10 knots turning easterly by the afternoon. Seas to sit from 1 to
3 feet.

Rip currents...

There is a moderate risk for the development of dangerous rip
currents at New Jersey and Delaware beaches through this evening.
Winds and seas are expected to increase tomorrow, with conditions
anticipated to become sufficient for a high risk of rip currents.

&&

Phi watches/warnings/advisories...
PA...none.
New Jersey...none.
Delaware...none.
Maryland...none.
Marine...Small Craft Advisory from 10 am Monday to 6 am EDT Tuesday for
anz450>455.

&&

$$
Synopsis...mps
near term...cms

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