Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 270138
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
938 PM EDT Wed Jul 26 2017

.SYNOPSIS...
High pressure across the northeast will move offshore tonight.
A cold front will approach the region on Thursday before
dissipating. A warm front will move northward into the region
late Thursday. Low pressure will form along the frontal
boundary, moving through our area on Friday and Saturday. High
pressure will then return later Saturday and persist through
Tuesday. Another cold front will approach the region on Tuesday
or Wednesday.

&&

.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
High pressure located off the New England coast this evening
will continue to gradually lose its influence over our weather.

The light east to southeast surface flow is forecast to veer
toward the south and southwest overnight. Increasing moisture
should result in the development of a cloud deck with bases in
the 1500 to 2500 foot range over much of eastern Pennsylvania,
northeastern Maryland, Delaware and New Jersey.

We will continue to mention patchy fog due to the recent heavy
rainfall.

Low temperatures will favor the 60s.

&&

.SHORT TERM /6 AM THURSDAY MORNING THROUGH 6 PM THURSDAY/...
Low pressure moves into the Ohio Valley on Thursday. The warm
front out ahead of the low will lift into the Lehigh Valley and
Pocono Mountains Thursday morning, and there may be just enough
lift to touch off a few showers with its approach. Will cap PoPs
at slight chance for areas west of the Fall Line. Any showers
that develop should taper off by late Thursday morning.

Otherwise, warm front continues its eastward approach
throughout the day, and seems to get hung up across southern NJ
by late afternoon. Latest models are fairly consistent in
holding off on bulk of precip until late in the day, so will
adjust hourly PoP grids to hold off on the higher PoPs until
after 4pm-5pm. With SB CAPE values of 1000- 1500 J/kg expected
across the region, there should be enough instability for
convection. The question will be if any convection will be
strong enough to overcome any capping inversions shown on BUFKIT
sounding profiles at 800-700 mb. Will keep PoPs and thunder
chances capped at chance through 7pm.

A warm and increasingly humid day on tap with higher generally
in the low to mid 80s and dewpoints rising into the 60s/low 70s.

&&

.LONG TERM /THURSDAY NIGHT THROUGH WEDNESDAY/...
Unsettled, wet weather will affect the region from Thursday
night through much of Saturday before we see a couple of dry
days from Sunday through the early part of next week.

Thursday night starts with a strong upper level shortwave
moving through the region. At the surface, a weak cold front
dissipates as it moves into the area while a warm front start to
push northward into the region. Limited instability does exist
as the shortwave crosses the region so there is the potential
for thunderstorms to develop and some may become severe. SPC has
lowered the severe risk for Thursday night to marginal.

Friday will be the day when the rains move into the area. Low
pressure will form along the frontal boundary and travels along
it and into our area on Friday. PWATS will increase in the
southerly flow and

The biggest threat from Thursday night through Saturday looks
to be mainly from heavy rain. Antecedent conditions are
extremely wet and the ground is not able to do much more than
create runoff in many areas across our forecast area.
Precipitable water values will once again rise to 1.5-2.0 inches
and it is becoming much clearer that parts of the area will see
decent rainfall through Saturday. Models continue to show a
solid swath of 2-4 inches of rain around the I- 195 corridor to
I-95 and points to the south and east, with 1 to 2 inches
possible across the northern and western areas. Held off on
issuing any kind of flash flood or flood watch at this time due
to timing and location uncertainties but one will need to be
considered, mainly for Friday into Saturday. Not as sold on
convection for Friday but again, some instability is present and
some thunderstorms may develop across the region. Increased
rainfall totals will be possible wherever thunderstorms develop.

The low deepens and picks up speed as it moves to the northeast
on Saturday. Strong, gusty winds, especially along the coast,
will be possible. However, we should see conditions improve by
the afternoon hours as high pressure spreads into the region.
With a decent northerly flow, temperatures will remain cooler
across the region, struggling to reach 80 across much of the
region.

Quiet weather will continue for Sunday through Wednesday as the
high remains in control. A cold front may approach the region
on Tuesday or Wednesday but it looks like we might have limited
moisture with it and have kept the forecast dry for now.

&&

.AVIATION /02Z THURSDAY THROUGH MONDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

VFR conditions were being reported this evening. There were
scattered to broken clouds with bases around 3500 to 4000 feet
along with cirrus drifting overhead from the west.

A deck of clouds with bases in the 1500 to 2500 foot range is
forecast to develop over our region late tonight and it should
linger into Thursday morning. VFR conditions are anticipated to
return for Thursday afternoon. Scattered showers and
thunderstorms may approach from the west late in the day.

A light and variable wind overnight should settle into the
south and southwest on Thursday around 5 to 10 knots.

OUTLOOK...
Thursday night thru Saturday...Periods of MVFR/IFR conditions
in showers and thunderstorms. Strong northeast winds on Saturday
with gusts up to 25 knots possible, especially at KACY.

Saturday night thru Monday...Mainly VFR conditions expected.

&&

.MARINE...
Winds and seas will remain below SCA thresholds tonight through
Thursday. Seas are around 2 to 3 feet on the ocean with onshore
winds around 10 to 15 knots on Thursday.

OUTLOOK...
Thursday thru Friday...Sub-SCA conditions expected. Locally
higher seas and gusty winds in the vicinity of thunderstorms
through Friday night.

Saturday and Sunday...both seas and winds will increase as low
pressure deepens along the Mid-Atlantic coast. A Small Craft
Advisory will likely be needed. Gale force gusts possible on
Saturday.

Sunday night through Monday...Sub-SCA conditions are expected.


RIP CURRENTS...
There is a low risk for the development of dangerous rip
currents on Thursday as the surface flow veers from the east and
southeast to the south and southwest.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...None.

&&

$$

Synopsis...Meola
Near Term...Iovino
Short Term...MPS
Long Term...Meola
Aviation...Iovino/Meola
Marine...Meola/MPS


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