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FXUS61 KPHI 271022
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
622 AM EDT Sat May 27 2017

.SYNOPSIS...
As a front remains draped to our south today and tonight, weak
low pressure will track along it and exit off the Mid Atlantic
coast tonight into Sunday. Another low pressure system is
forecast to consolidate just north of the Great Lakes Monday and
then gradually shift eastward through Wednesday. An associated
cold front moves through our area later Monday, then a secondary
cold front arrives during Tuesday. High pressure builds from
the Midwest to the Carolinas Wednesday and Thursday, then closer
to our area Friday.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
A mid level short wave located over Lake Erie and vicinity
early this morning will progress east southeastward and it is
forecast to pass over our region during the late afternoon and
early evening hours. We are anticipating an increase in cloud
cover this morning in advance of the system.

The short wave was producing a fair amount of shower activity
in the upper Ohio River Valley early this morning along with
isolated thunder. The precipitation is expected to diminish a
bit this morning as it moves to the east southeast. The showers
may become reinvigorated this afternoon as they encounter
marginal instability to the southwest of our forecast area.

We are anticipating only isolated to scattered rain showers in
eastern Pennsylvania and New Jersey for this afternoon. There
appears to be a better chance for scattered showers and
thunderstorms in northeastern Maryland and Delaware.

A light west wind is expected for this morning. The direction
should become variable in the afternoon. Highs should be within
a couple degrees of normal for today, ranging from the upper 60s
in the elevated terrain to the middle 70s on the coastal plain.
Maximum temperatures are forecast to be in the middle and upper
60s right along the coast.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SUNDAY/...
Lingering showers and thunderstorms are possible on the upper
Delmarva this evening, then we are not expecting any additional
precipitation overnight. Partial clearing is anticipated, mainly
over eastern Pennsylvania, and northern and central New Jersey.

Another mid level short wave trough is expected to move from
the Ozarks vicinity this morning to North Carolina late tonight.
A weak surface low associated with the mid level trough is
forecast to pass off the coast between the Virginia Capes and
Cape Hatteras late tonight. It is not anticipated to have much
impact on our region.

The wind should be light tonight, with its direction favoring
southeast to northeast. Lows are expected to be mainly in the
50s.

&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...
Summary...Unsettled at times through early next week. After a
cooler Sunday especially closer to the coast, warmer
temperatures (close to where they should be this time of year)
are expected next week.

Synoptic Setup...While a weak ridge slides across the Northeast
Sunday, a closed low in south-central Canada is forecast to
amplify south and eastward through the middle of next week
before weakening some Thursday and Friday. It is forecast to
remain centered well to our north, however cyclonic flow will be
in place along with several short waves revolving around it.
This will drive a couple of fronts eastward. The exact timing of
the embedded features are less certain given an amplified
pattern with a closed low involved, however a model consensus
now indicates that Sunday is drier than Monday. We used a
model/continuity blend for Sunday through Monday night, then
blended in the 00z WPC Guidance thereafter. Some adjustments
were then made following additional collaboration with our
neighboring offices.

For Sunday...A weak ridge is forecast to slide across the East,
however it should quickly move off the coast in the afternoon.
This will take weak surface high pressure to off the coast of
New England through the afternoon, meanwhile a front remains
draped to our south with weak low pressure slowly moving
offshore of the Mid Atlantic coast. A closed low centered just
north of the Great Lakes is forecast to expand south and east
some through Sunday. This will drive weak surface low pressure
up across the eastern Great Lakes, then it should consolidate
eventually north of the Great Lakes at night. The frontal zone
to our south should lift northward some, however weak surface
high pressure wedged southwestward will keep an onshore flow in
place and probably hold back the surface front. What appeared to
be an unsettled day may end up being dry, at least for the
daylight hours. A cold front or occluded front looks to arrive
later at night, and enough lift and moisture should result in
some showers and perhaps thunderstorms mainly at night as we
wait for convection to our west to arrive. The onshore flow
should result in a fair amount of clouds (perhaps low
clouds/drizzle to start Sunday), and therefore temperatures are
anticipated to be held down at least some especially closer to
the coast.

For Monday and Tuesday...The center of a closed low is forecast
to slowly move across southeastern Canada, mostly near James
Bay. A short wave trough with an embedded stronger short wave
lifts up across the Northeast Monday. This will be accompanied
by a weakening front, however enough lift and instability should
be present to result in some showers and thunderstorms Monday.
The greatest deep- layer shear is forecast to be to our south
Monday, however if enough instability can develop then an
isolated strong/severe thunderstorm is possible across our
southern zones. The initial front may dissipate as it shifts
east Monday night into Tuesday, however a secondary front is
forecast to arrive during Tuesday. The forcing looks weaker for
Tuesday with the incoming secondary front, however cyclonic flow
combined with some height falls may allow for limited
convective development in the afternoon especially near the
higher terrain. We therefore have the highest PoPs on Monday,
then lower on Tuesday when isolated to perhaps scattered
convection is possible. We are anticipating warmer temperatures
ahead of the weak fronts.

For Wednesday and Thursday...As the center of the closed low
gradually shifts east more across eastern Canada, it amplifies
across the Northeast and northern Mid Atlantic for at least a
time. At least some guidance shows a pronounced short wave
rotating around the closed low late Wednesday into Thursday as
it crosses the eastern Great Lakes then slides across interior
New England. This may be accompanied by a surface trough
especially during Wednesday with potentially some convection
with it. There is still some resemblance of a surface trough on
Thursday, however much of the forcing is forecast to shift into
New England. Meanwhile, surface high pressure is forecast to
build from the Midwest to the Carolinas during this time frame.
Due to the cyclonic flow, daytime temperatures will be in the
70s to about 80 degrees each day. The Pops were kept at low
chance or less.

For Friday...As the closed low gradually weakens and heads
toward the Canadian Maritimes, a lobe of vorticity may sharpen
the western part of the upper-level trough as is swings across
the Great Lakes and Northeast. Weak high pressure is forecast to
be building much closer to our area from the west and south,
however another weak front or surface trough slides across our
area. Depending on the moisture available along with the
sharpness of the trough, some convection cannot be ruled out
especially in the afternoon and early evening. As of now, kept
slight chance PoPs.

&&

.AVIATION /10Z SATURDAY THROUGH WEDNESDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

VFR conditions are expected to prevail through the TAF period.
We are anticipating an increase in cloud cover for today and
partial clearing for tonight.

There is a chance of showers from this afternoon into the early
evening. The showers are expected to be isolated to scattered
around KRDG, KABE, KTTN, KPHL, KPNE and KACY. There is a
slightly better chance for showers around KILG and KMIV along
with a small potential for thunder. The impact of the showers is
anticipated to be limited.

A light west wind this morning is forecast to become variable
for this afternoon. The wind should favor the southeast to
northeast tonight at 8 knots or less.

OUTLOOK...
Sunday...MVFR/IFR possible to start due to low clouds and/or
some fog, otherwise mainly VFR during the remainder of the day.
Lower confidence regarding low clouds/fog in the morning.
Ceilings should then lower to MVFR or IFR at night as some
showers and perhaps a thunderstorm moves through.

Monday...MVFR/IFR conditions with some showers and
thunderstorms. Some improvement may occur in the afternoon and
at night as a cold front moves through. Some fog is possible
later at night. Lower confidence regarding timing of improving
conditions and timing/coverage of showers/thunder.

Tuesday and Wednesday...Some fog possible to start Tuesday,
otherwise generally VFR through Wednesday. Some showers and
thunderstorms still possible mainly Tuesday afternoon and
evening.

&&

.MARINE...
The wind is forecast to back from the northwest and west to the
south and southeast today at speeds of 5 to 10 knots. The wind
should become east to northeast tonight around 10 knots.

Wave heights on our ocean waters will be mainly in the 2 to 3
foot range. Waves on Delaware Bay will be 2 feet or less.

RIP CURRENTS...
A light northwest to west wind this morning is expected to
become south to southeast this afternoon. Wave heights off the
coast should be 2 to 3 feet. As a result, we are anticipating a
low risk for the development of dangerous rip currents for
today.

For Sunday, an onshore flow is forecast to strengthen some and
this may result in the rip current risk approaching moderate
especially for the coast of New Jersey.

OUTLOOK...
Sunday through Wednesday...The conditions are anticipated to be
below Small Craft Advisory criteria. East to southeast winds
however should increase Sunday with some gusts to around 20
knots at times. The seas are currently expected to be 4 feet or
less.

Some showers and thunderstorms are expected, especially later
Sunday night and Monday.

&&

.TIDES/COASTAL FLOODING...
No coastal flooding is anticipated with this morning's high
tide. However, we will issue another Coastal Flood Advisory for
tonight's high tide. It will be in effect for the coastal
counties of New Jersey and Delaware, and for the counties along
Delaware Bay and the lower Delaware River up to near the
Commodore Barry Bridge.

The guidance is suggesting the tonight's coastal flooding will
be greater than that on Friday evening and a bit less than what
occurred on Thursday evening. The loss of the offshore wind
should allow some water to return back toward the coast, so the
guidance seems reasonable.

We will continue to keep an eye on Sunday evening's high tide
as well since the surface wind is expected to be onshore at that
time and the astronomical tides will remain high.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...Coastal Flood Advisory from 8 PM this evening to 2 AM EDT
Sunday for NJZ012>014-020>027.
Coastal Flood Advisory from 11 PM this evening to 3 AM EDT
Sunday for NJZ016.
DE...Coastal Flood Advisory from 8 PM this evening to 2 AM EDT
Sunday for DEZ002>004.
Coastal Flood Advisory from 11 PM this evening to 3 AM EDT
Sunday for DEZ001.
MD...None.
MARINE...None.

&&

$$

Synopsis...Gorse
Near Term...Iovino
Short Term...Iovino
Long Term...Gorse
Aviation...Gorse/Iovino
Marine...Gorse/Iovino
Tides/Coastal Flooding...Iovino
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