Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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911
FXUS61 KPHI 250800
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
400 AM EDT Thu May 25 2017

.SYNOPSIS...
Low pressure will move from the Ohio Valley to the eastern Great
Lakes region today. Meanwhile, a warm front will lift northward into
parts of our region today into tonight while new low pressure develops
along it. This low pressure system then strengthens as it tracks
away from our area tonight and Friday. Weak high pressure may briefly
build in for Saturday, then low pressure and its associated fronts
move through later Sunday. A secondary cold front moves through during
Tuesday.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
A pair of mid level lows were located over the Ohio and Tennessee
River Valleys early this morning. The feature will progress eastward
with the two centers reaching western Pennsylvania and Virginia
early this evening.

There were two surface lows early this morning, as well. One was
located in western Ohio and the other in southwestern Virginia. A
warm front extended eastward from the Virginia low.  The two low
pressure systems are forecast to merge into a broad surface low over
Pennsylvania and Maryland early this evening. The warm front is
anticipated to lift slow northward into northeastern Maryland,
Delaware, extreme southeastern Pennsylvania and southern New Jersey
today.

The initial band of rain associated with the warm advection will
continue to lift northward through our region this morning. The back
edge of the steady rain is expected to work its way from south to
north through our forecast area between about 5:00 AM and 10:00 AM.
Rainfall amounts in the steady precipitation should range from about
a third to three quarters of an inch.

A mostly cloudy sky and showers are anticipated for the balance of
the day to the north of the warm front. As the front reaches our
southern counties there should be some substantial breaks in the
cloud cover as those location get into the warm sector.

We will continue to mention a chance of thunderstorms for this
afternoon. Locations in the warm sector will become unstable with
mixed layer CAPE values rising into the 600 to 1000 J/Kg range. The
approach of the mid level low and some elevated instability will
spread the potential for thunder to the north of the warm front. The
Storm Prediction Center has southeastern Pennsylvania, southern New
Jersey, Delaware and northeastern Maryland under a marginal risk for
severe weather for today.

Today`s temperature forecast is one of low confidence. The actual
temperatures will depend upon where the warm front settles and how
much clearing takes place over our southern counties. Generally,
highs should range from around 60 in the Poconos to near 80 in
southern Delaware.

The wind is forecast to remain from the east to the north of the
warm front. It should veer to the southeast and south once the front
passes. Speeds are expected to favor the 8 to 12 MPH range with some
gusts of 15 to 20 MPH possible.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM FRIDAY/...
The mid level low is forecast to pass over our region tonight,
reaching southern New England toward daybreak on Friday.  The
surface low will likely follow a similar pattern.

We are expecting a mostly cloudy sky and showers for tonight.
Thunderstorms may linger into the evening. The wind is anticipated
to become light and variable tonight in much of eastern Pennsylvania
and northern and central New Jersey before settling into the west
around 5 to 10 MPH. A southwest wind around 10 MPH is anticipated to
shift to the west on the upper Delmarva and in southern New Jersey.

Low temperatures are expected to favor the 50s for tonight.

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
Summary...Unsettled at times, however warmer temperatures are
expected.

Synoptic Setup...A significant closed low is forecast to shift up
into New England Friday then move out Friday night into Saturday.
Some brief weak ridging should slide into the east Saturday, however
the next trough amplifies from the Midwest and Great Lakes later
Saturday and Sunday. This trough looks to close off and be slow to
shift eastward through Wednesday, sending a slow moving low pressure
system well to our north while a series of cold fronts cross our
area. Timing and therefore the details are a bit less certain given
an amplified pattern with the idea of a closed low involved. We used
a model/continuity blend for Friday through Saturday night, then
blended in the 00z WPC Guidance thereafter. Some adjustments were
then made following additional collaboration with our neighboring
offices.

For Friday...Strengthening low pressure moves away during Friday,
and therefore after some possible low clouds and a shower to start
improving conditions are expected. However, cyclonic flow combined
with another short wave and a surface trough reflection should
result in some showers. The northern areas have a higher chance for
some showers than farther south, but overall coverage looks to be
isolated to scattered. A west-northwest wind will increase and
become gusty for a time as the pressure gradient tightens and
cooling occurs aloft allowing for better mixing. The winds diminish
at night along with any showers dissipating early, and lingering
clouds should thin out.

For Saturday and Sunday...The flow turns generally more zonal with a
weak but brief ridge in the east by later Saturday. The model
guidance overall shows a short wave within this flow although the
timing is a little uncertain, however this may ultimately track just
to our south where a frontal zone will be located. A closed low
centered north of the Great Lakes is forecast to amplify south and
eastward gradually by late in the weekend. This will drive a cold
front eastward and across our area later Sunday, however the model
guidance overall suggests low pressure develops along a triple point
as the main surface low to our west and north occludes. This may end
up enhancing the showers and some thunder during Sunday, especially
during the afternoon and evening. Backing up some, Saturday may end
up being dry as enough ridging is in place, and short wave energy
runs to our west and southwest. We will carry some more clouds
Saturday but keep it basically dry, and therefore Saturday looks
like the better of the two weekend days. The flow looks to turn more
southeasterly in the lower levels Sunday, and therefore while still
mild it will turn cooler along the coast.

For Monday and Tuesday...A closed low is forecast to expand across
the Great Lakes, Midwest to the Ohio Valley and gradually into the
Northeast. This will drive surface low pressure eastward mainly
north of the Great Lakes. An initial surface low should be moving
away from the Mid Atlantic coast early Monday as a frontal zone sits
offshore. The main cold front is forecast to move across our area
Tuesday and shift offshore Tuesday night. The second half of Tuesday
may be convectively active as a cold front arrives, however this
will depend on short wave timing and potential convective
development to our west. The timing overall is less certain given
the scope of the closed low to our north-northwest and plenty of
short wave energy revolving around it. Kept chance PoPs for Monday
then slight chance to chance PoPs on Tuesday. We are anticipating
warmer temperatures ahead of the cold front.

For Wednesday...As the center of the closed low gradually shifts
across eastern Canada, the overall trough becomes more established
across the Northeast and into the Mid Atlantic. The main surface low
is forecast to be east of James Bay Canada with its trailing cold
front east of our coast to start Wednesday. A cyclonic flow will be
in place and a surface trough should be sliding across the Great
Lakes region. While less likely at this time, a few showers still
cannot be ruled out given the synoptic setup. For now, kept some
slight chance PoPs across the northern and western areas. Given the
core of the closed low well to our north, keeping the colder air
aloft there, daytime temperatures look to be on the warmer side.

&&

.AVIATION /08Z THURSDAY THROUGH MONDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Deteriorating conditions are expected for early this morning in
rain. IFR conditions are likely to prevail. The main band of rain
should lift to the north of our TAF sites this morning. However,
conditions should improve only into the low end of the MVFR category
with showers. KMIV and KACY could improve to VFR but it is a low
confidence forecast. There is a chance of thunderstorms for this
afternoon and evening.

Conditions are forecast to remain in the MVFR and perhaps the IFR
range for tonight with additional showers. An improvement to VFR is
possible at KACY, KMIV, KILG and perhaps at KPHL and KPNE.

An east wind around 8 to 12 knots this morning is expected to veer
toward the southeast and south at KACY, KMIV, KILG, KPHL and KPNE as
the day progresses. The wind may become light and variable for a
time tonight before settling into the west at 5 to 10 knots.

OUTLOOK...
Friday...Possible MVFR/IFR ceilings early, otherwise improving to
VFR. Isolated to scattered showers should develop during the day
before dissipating in the evening. West-northwest winds increase
with gusts up to 25 knots, then diminishing in the evening.

Saturday...VFR overall. Light northwest winds turning southerly
toward evening. Clouds increase at night and possibly lower.

Sunday...MVFR/IFR conditions possible with showers and some possible
thunderstorms, especially in the afternoon and evening.

Monday...Sub-VFR conditions possible at times with a chance of
showers and afternoon/evening thunderstorms.

&&

.MARINE...
A warm front is expected to lift slowly over the waters of Delaware
and New Jersey today. Low pressure from the west and southwest
should pass across the waters tonight.

Wave heights on our ocean waters are expected to remain in the 4 to
7 foot range for today and tonight. As a result, the Small Craft
Advisory will stay in effect. The wind is anticipated to work its
way gradually around from the east to the south to the west during
the period. Speeds should favor the 10 to 20 knot range with some
gusts around 25 knots on our ocean waters.

RIP CURRENTS...
The flow is expected to veer from the east to the south today
along the coasts of Delaware and New Jersey with wind speeds
mainly in the 10 to 20 knot range. As a result, we will keep the
moderate risk for the development of dangerous rip currents.

OUTLOOK...
Friday...Small Craft Advisory extended through 22z for the ocean
zones as elevated seas gradually subside with an offshore flow. Some
wind gusts may reach 25 knots during the day especially nearshore,
however confidence is not high enough to issue an advisory for
Delaware Bay.

Saturday through Monday...Conditions are forecast to be below
advisory criteria, however winds may gust to around 20 knots at
times especially on Sunday.

&&

.TIDES/COASTAL FLOODING...
The astronomical tides with the new moon are particularly high with
the evening high tide cycle. Positive tidal departures near 1 foot
are anticipated again for today. As a result, we may see some spotty
minor coastal flooding this morning with more widespread coastal
flooding expected with this evening`s high tide. We will continue
the Coastal Flood Advisory for this evening in the coastal counties
of New Jersey and Delaware, as well as for the counties along
Delaware Bay and Raritan Bay.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...Coastal Flood Advisory from 7 PM this evening to 1 AM EDT
     Friday for NJZ012>014-020>027.
DE...Coastal Flood Advisory from 7 PM this evening to 1 AM EDT
     Friday for DEZ002>004.
MD...None.
MARINE...Small Craft Advisory until 6 PM EDT Friday for ANZ450>455.

&&

$$
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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