Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 260730
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
330 AM EDT Fri May 26 2017

.SYNOPSIS...
Low pressure will move northeastward and away from our area today.
Meanwhile, a weak surface trough is expected to cross our region
this afternoon. A front will then remain to our south and west
Saturday and Sunday as weak low pressure tracks along it. Another
area of low pressure is forecast to track from the Great Lakes
Sunday and across southeastern Canada Sunday night and Monday. An
associated weakening cold front will move through our area later
Monday, then a secondary cold front arrives during Tuesday. High
pressure is forecast to build to our south Wednesday and
Thursday.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
The mid level low was off the northern part of the New Jersey coast
around 3:00 AM. It should progress northeastward today, passing over
southeastern New England this morning before approaching Nova Scotia
late in the day. The surface low will remain fairly well aligned
with the mid level feature.

Scattered showers were lingering in eastern Pennsylvania and New
Jersey early this morning. They should pull northeastward along with
the low and diminish during the morning hours. Another round of
showers is expected around midday, mainly in eastern Pennsylvania,
and northern and central New Jersey. An impulse rotating around the
departing low along with some marginal instability are forecast to
set off the shower activity at that time.

Low clouds should linger early this morning. Also, some patchy fog
is expected in our northern counties. While skies may remain mostly
cloudy over much of eastern Pennsylvania and northern New Jersey
today, we are expecting a substantial decrease in cloud cover over
the upper Delmarva and southern New Jersey as drying works its way
into our region.

A west northwest wind is anticipated to increase to 10 to 15 MPH
with gusts around 20 MPH. We have gone on the high end of the
temperature guidance for today. Highs are forecast to range from
around 70 in the Poconos to near 80 in southern Delaware.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SATURDAY/...
Weak high pressure is forecast to build into our region from the
west for tonight. We are anticipating dry weather conditions. The
sky is expected to become mostly clear during the evening with an
increase in high and perhaps some mid level clouds toward morning
ahead of our next weather system. There may be some localized fog
late tonight as the ground remains quite moist from the recent
rainfall.

A northwest wind around 10 MPH is expected to diminish. Minimum
temperatures should favor the 50s.

&&

.LONG TERM /SATURDAY THROUGH THURSDAY/...
Summary...Unsettled at times, however warming temperatures are
expected especially next week. The holiday weekend does not look to
be a washout, but some showers and thunderstorms cannot be ruled out
especially Sunday (cooler temperatures) into Memorial Day.

Synoptic Setup...While a weak ridge slides across the Northeast
Saturday into Sunday, a short wave trough is forecast to track from
the Ohio Valley to off the Mid Atlantic coast over the weekend. A
closed low in south-central Canada Saturday is forecast to amplify
south and eastward through the middle of next week. 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 series of fronts eastward. The exact timing of the
embedded features are less certain given an amplified pattern with a
closed low involved. We used a model/continuity blend for Saturday
through Sunday night, then blended in the 00z WPC Guidance
thereafter. Some adjustments were then made following additional
collaboration with our neighboring offices.

For Saturday and Sunday...Some generally weak ridging is forecast to
slide across the Northeast and Mid Atlantic later Saturday into
Sunday. However, the guidance continues to show a short wave trough
embedded within the faster flow during Saturday. While this occurs,
a frontal zone is to our south and west where a weak surface low may
track along. This may result in some showers and thunder especially
across the southern areas Saturday afternoon and evening. We kept
some chance PoPs for this potential with the highest PoPs across the
southern zones. It is less certain how much convection may develop
with a northern extent due to an onshore flow especially Sunday and
the instability axis should be farther south and west. Our attention
then turns to a closed low in south-central Canada, which gradually
slides south and east and amplifies some. This will drive low
pressure eastward and a front to our south will try and lift
northward as a warm front through Sunday. It appears the low-level
flow turns more onshore Sunday resulting in cooler temperatures. Low
pressure across the Great Lakes should be occluding and this adds
some uncertainty regarding the details for our area. A weak low may
develop along the frontal zone near Delmarva which may focus some
afternoon convection Sunday, or we wait for convection to our west
with the occlusion to arrive late in the day and at night. For now,
we kept PoPS in the chance range Sunday, however these increase some
at night with an initial weakening front and the idea of incoming
convection.

For Monday and Tuesday...A closed low is forecast to gradually
expand into the Northeast. This will drive surface low pressure
eastward 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 weakening cold front is forecast to
move across our area Tuesday and shift offshore Tuesday night. The
afternoon of either Monday and/or Tuesday may become convectively
active, 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 (highest in the afternoon and early evening), then slight
chance to chance PoPs on Tuesday. We are anticipating warmer
temperatures ahead of the weak cold fronts.

For Wednesday and Thursday...As the center of the closed low
gradually shifts across eastern Canada, the overall trough becomes
more established across the Northeast into the Mid Atlantic. The
main surface low is forecast to be shifting 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 portions of the
northern and western areas Wednesday. Given the core of the closed
low well to our north, keeping the coldest air aloft there, daytime
temperatures look to be mostly in the 70-80 degree range. High
pressure is currently forecast to build to our south during this
time frame.

&&

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

Variable conditions are expected early this morning. They should
range mainly between MVFR and VFR with brief periods of IFR
possible. Dry air will build into our region from the west northwest
today and conditions should improve to VFR during the morning hours
and they should remain there through the balance of the TAF period.

Scattered showers are forecast to be on the decrease early this
morning with another potential for scattered rain showers around
midday. The second round of showers is expected to have limited
impact on our TAF sites.

A west northwest wind is anticipated to increase to 10 to 15 knots
with gusts around 20 knots for the mid morning to early evening
hours. Wind speeds are forecast to diminish for tonight.

OUTLOOK...
Saturday...VFR during the day, then ceilings should lower to MVFR or
IFR late at night. A few showers and thunderstorms possible,
especially south and west of KPHL. Confidence on the low side
regarding timing and coverage of showers/thunder.

Sunday...MVFR/IFR ceilings possible with some showers and
thunderstorms especially in the afternoon and at night.

Monday and Tuesday...Conditions should improve to VFR during Monday
morning and continue through Tuesday. However, some showers and
thunderstorms cannot be ruled out each day.

&&

.MARINE...
Low pressure will continue to move to the northeast and away from
our region today. The wind is expected to settle into the west
northwest at 10 to 20 knots. Wind speeds are forecast to decrease to
5 to 10 knots tonight.

We will keep the Small Craft Advisory in effect for our ocean waters
until 6:00 PM. Wave heights remained in the 5 to 6 foot range early
this morning and it should take the better part of the day for them
to subside below 5 feet. Wave heights will continue to decrease
tonight.

RIP CURRENTS...
A west wind is expected to develop today. However, wave heights off
the coast will likely remain in the 5 to 6 foot range for much of
the day. Also, the tidal range remains amplified due to the new
moon. As a result, we will keep the moderate risk for the development
of dangerous rip currents for today.

OUTLOOK...
Saturday and Sunday...The conditions are expected to be below Small
Craft Advisory criteria. A sea/bay breeze Saturday afternoon should
enhance the wind along the coast for a time, then a more pronounced
onshore flow Sunday may result in wind gusts to around 20 knots. The
seas are currently anticipated to remain below 5 feet.

Monday and Tuesday...The conditions are expected to be below Small
Craft Advisory criteria.

Some showers and thunderstorms are possible each day, however timing
and coverage is of lower confidence.

&&

.TIDES/COASTAL FLOODING...
Widespread minor flooding occurred on Thursday evening along the
coasts of New Jersey and Delaware and into Raritan Bay, the back
bays and Delaware Bay. There was some locally moderate flooding
along the New Jersey shore.

We will take a closer look at trends to determine whether another
advisory will be needed for this evening. The wind will be from the
west northwest today allowing water to drain away from the coast.
However, the astronomical tides remain quite high.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...Small Craft Advisory until 6 PM EDT this evening 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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