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775
FXUS61 KPHI 241959
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
359 PM EDT Mon Jul 24 2017

.SYNOPSIS...
A cold front will move slowly south across our region this evening
and offshore tonight. A broad high pressure system extending from
the Great Lakes into eastern Canada will gradually build southeast
into our area through Wednesday. As this high slides offshore late
Wednesday, a warm front will move through our region on Thursday,
followed by another slow moving cold front on Friday. High pressure
is expected to make a return this weekend into the beginning of the
work week.

&&

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
Significant thunderstorm wind damage occurred overnight in the
Stevensville area of Kent Island in Queen Anne`s County,
Maryland. A survey team is on their way to assess the damage and
we should have more information on this event later this
afternoon.

A front will lift across the region and the rains has ended.
The back of the boundary will bring more sct tstms to the area
later this afternoon. Temperatures today will be very warm with
upper 80s and low 90s over the region. Clouds will gradually
thin later this morning and into the afternoon. Winds will be
mostly S/SE early, then turn SW/W this afternoon.

&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH 6 PM TUESDAY/...
System begins to move away and the showers associated with the cold
front will end from W to E early tonight. Drier air will begin to
arrive N/W and will spread over the rest of the area later Tuesday.
Lows will be in the low 70s S/E and low 60s N/W.

&&

.LONG TERM /TUESDAY NIGHT THROUGH MONDAY/...
One mid-level trough exits the east coast Tuesday night, with a
brief zonal flow and some short wave ridging for Wednesday, followed
by continued troughiness through the end of the long term period.
A frontal system in the Thursday thru Friday time frame features the
greatest chance of sensible weather, in terms of increased humidity,
and the chance for showers and thunderstorms. This front will slow
as it moves offshore, and stall to our south through the weekend
into early next week, as waves of low pressure traverse it. All of
the available guidance keeps our region dry in the Saturday thru
Monday period, but lingering cloudiness is possible, especially
south Jersey into Delmarva. In addition, if the guidance slows the
southward progress of this feature, this could result in a more
pessimistic forecast for the aforementioned area.

Showers and thunderstorms with heavy downpours and gusty winds are
possible Thursday into Friday. It`s still too early to nail down the
spatial and temporal details, as the GFS is much more progressive
with the front compared to the Euro, so there is low confidence due
to the uncertainty. In fact, the GFS event window would be Thursday
into Thursday night, with the Euro window is centered on Friday.
Nevertheless, effective bulk shear values rise to near 40 knots,
while surface-based cape is in excess of 2.0 kJ across portions of
the area. In addition, the front slows as it moves trough or area,
while Precipitable Water values rise to around 2.0 inches. These
indicators point to some potential for strong thunderstorms and
heavy rainfall in the Thursday and Friday period, and we have
mentioned this in the Hazardous Weather Outlook.

Temperature-wise, slightly below normal temperatures on Wednesday
rebound to at or slightly above average from Thursday thru Friday.
Average to slightly below average temperatures are expected in the
post-frontal air mass on Saturday, with a moderation to near normal
in the Sunday thru Monday time frame. In fact, Thursday and Friday
are shaping up to be the warmest days, with temperatures well into
the 80s to near 90. The only exception may be closer to the coast,
where a prolonged onshore flow may develop over the weekend into
early next week, keeping temperatures cooler.

Finally, depending on the extent of the aforementioned onshore flow,
astronomical tides are much lower over the weekend into early next
week as we move away from the new moon. This should limit the
potential for coastal flooding.

&&

.AVIATION /20Z MONDAY THROUGH SATURDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Challenging fcsts for the morning with widespread poor flying
conditions across the area and sct showers/downpours and a few tstms
too. Overall, expect improvement this morning, but timing in the
tafs is low confid with a variety of mesoscale factors affecting
conditions. Winds will be mostly SE early, then turn SW/W by late
morning. There will probably be more showers/sct tstms this
afternoon across the area, again low confid in timing, basically
used PROB30s from guidance. Frequent Amds expected.

OUTLOOK....
There is some potential for MVFR in low clouds associated with
a frontal system from Thursday into Friday. This potential may
linger into Saturday in ACY and MIV as the southward progression
of the front slows. In addition, any showers or thunderstorms
during this time frame may briefly reduce ceilings and
visibility`s to IFR. Otherwise, VFR for the remainder of the
period.

&&

.MARINE...
Small Craft Advisory for hazardous seas is in effect for our
northern New Jersey coastal waters through 4PM. Seas are at 5
feet and will start to drop through this afternoon. The SCA has
been dropped elsewhere.

Wind directions have mostly been E or SE on the north side of
the front. The front will move northward today and winds will
become S or SW behind that. Scattered showers and tstms with
locally higher winds and seas around tstms. Showers coverage
will diminish later this morning, be a few more tstms possible
later this afternoon and into the evening.

OUTLOOK...
Wednesday through Saturday...A Small Craft advisory may be
needed on Thursday and Friday.

RIP CURRENTS...
A moderate risk for rip currents remains in effect through this
evening for the Delaware and New Jersey beaches.

A low risk of rip currents is currently expected for the
Delaware and New Jersey beaches on Tuesday.

&&

.TIDES/COASTAL FLOODING...
There is Coastal Flood Advisory in effect for this evening`s
high tide along the New Jersey and Delaware coasts. We do not
anticipate minor flooding in Delaware Bay.

While surface wind turned offshore during on Monday, it is
expected to become onshore again this evening, especially
along the New Jersey coast. Conditions may be a bit marginal
for Delaware.

&&

.EQUIPMENT...
Dew point readings at KDOV continue to measure too high
compared to surrounding locations and should be treated as
unrepresentative of the area.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...Coastal Flood Advisory from 9 PM this evening to 2 AM EDT
     Tuesday for NJZ012>014-020-022>027.
DE...Coastal Flood Advisory from 9 PM this evening to 2 AM EDT
     Tuesday for DEZ003-004.
MD...None.
MARINE...Small Craft Advisory for hazardous seas until 6 PM EDT this
     evening for ANZ450.

&&

$$
Synopsis...Meola
Near Term...Meola
Short Term...Meola
Long Term...Franck
Aviation...Franck/Meola
Marine...Franck/Meola
Tides/Coastal Flooding...Franck
Equipment...Staff