Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000
FXUS61 KPHI 280736
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
336 AM EDT Wed Jun 28 2017

.SYNOPSIS...
High pressure over our region today will shift offshore this
evening, then remain there through Friday. A weak cold front is
forecast to arrive later Sunday, however this boundary may then
stall across our region early next week.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Early this morning...Mostly clear. Light northwest winds.

Today...Sunny or mostly sunny and comfortably cool for summer
with few or sct sc 16z- 21z aoa 5000 ft, mainly northwest of
I-95. west northwest wind gusting 15-20 mph this morning
becoming more westerly this afternoon and diminishing slightly.
Dewpoints in the 40s while max temps 2 to 7 degrees below
normal. One of the nicest days we`ll see for quite a while.

Forecast basis: a 50 50 blend of the 00z/28 GFS/NAM MOS.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM THURSDAY/...
Tonight...Mostly clear with some cirrus after midnight, especially
northwest of I-95. Lowered 50 50 blended 00z/28 mos gfs/nam temps
a degree or two from that guidance due to light wind. These
temps 1 to 4 degrees below normal.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
Summary...Increasing heat and humidity Friday into Sunday, then the
humidity should lower some early next week for much of the area. The
details though will depend on the timing and location of a weak cold
front that may end up stalling across our region.

Synoptic Overview...A more zonal flow aloft Thursday will give way
to some amplification across the Northeast. This change will be due
to a strong short wave carving out a trough in the Midwest and Great
Lakes Friday and Saturday, which then gradually shifts eastward
later in the weekend and early next week. There may be several
stronger short waves within this trough, which will impact the
sharpness and timing eastward. At the surface, high pressure remains
anchored offshore which will result in a hot and humid southwest
flow for a time. The main feature is a weak cold front that will
settle into our area later Sunday, however it may then stall in our
vicinity through early next week. The presence of the incoming front
and trough nearby will result in some convection. We used a
model/continuity blend for Thursday through Friday night, then
blended in the 00z WPC Guidance thereafter. Some adjustments were
then made following additional collaboration with our neighboring
offices.

For Thursday and Friday...High pressure anchored offshore will drive
an increasing southwesterly wind across our area. The flow aloft is
mainly zonal, with the main short wave energy tracking to our north
Thursday. There is increasing low-level warm air advection forecast
during Thursday, which will boost temperatures well into the 80s.
The southwesterly flow will also start to transport increasing low-
level moisture our way especially as a 40-50 knot low-level jet
moves through Thursday night. This moisture increase should be
gradual during the day Thursday resulting in a not so humid feel
overall. This will change however Thursday night and Friday as dew
points are forecast to increase into the 60s. As the low-level warm
air advection continues in addition to perhaps some subsidence on
the northwest side of offshore high pressure, daytime highs on
Friday will edge into the lower 90s for several areas. This combined
with higher dew points will result in heat indices into the mid 90s
during peak heating. There will be a southwesterly breeze, and as
mixing deepens the dew points may locally lower some during peak
heating which in this case would keep the heat indices a bit lower.
Thursday looks to be a dry day for much of the region, although some
upstream convection may get into our northwestern zones later in the
day and in the evening. A lead short wave crossing the northern
areas Friday afternoon may allow for some convection. This looks to
be focused near the higher terrain areas of our northwestern zones.
We will continue to carry slight chance to low chance PoPs
especially Friday afternoon and evening.

For Saturday and Sunday...Low pressure is forecast to track from the
Great Lakes Saturday morning to just east of James Bay Canada by
later Sunday. This will pull a cold front slowly eastward, and it
currently is not forecast to arrive into our area until later
Sunday. The synoptic setup would suggest though that a lee-side
trough will be in place, with this potentially being located near
the I-95 corridor both days. There will be a hot and humid airmass
in place, especially Saturday where the humidity should peak. The
main upper-level trough is forecast to hang back over the Great
Lakes for Saturday, then more eastward progress occurs Sunday. This
will settle a weak cold front into our area later Sunday. The bulk
of the convection Saturday may reside to our west closer to the
frontal zone, however some convection is anticipated tied to the lee-
side trough. Given the higher heat and humidity on Saturday a heat
advisory may be needed, especially for the urban corridor from
Wilmington to Philadelphia/Camden to Trenton, as heat indices may
approach 100 degrees during peak heating. The convective evolution
during this time frame is less certain, as the timing of the front
will be key and also how much can develop near or along the lee-side
trough. There is some potential that upstream organized convection
moves across much of our area Saturday night. Given less certainty,
held PoPs no higher than the chance range.

For Monday and Tuesday...The main part of an upper-level trough may
lift into Northern New England during this time frame, therefore the
flow is more parallel to a surface front in the vicinity. As a
result, our sensible weather will be dependent on the location of
this front as it stalls out. Some lingering low-level convergence
combined with instability and some short waves aloft may result in
some convection especially each afternoon and evening. The overall
timing though and especially coverage is less certain. While it will
still be rather warm, a bit of cooling is anticipated based on the
front in the area and the dew points should be a little lower as
well.

&&

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

Through today....VFR. few or sct clouds aoa 6000 ft. west northwest
wind gust around 15 kts.

Tonight...VFR. Broken cirrus probably arrives toward dawn Thursday.
Light southwest wind.

OUTLOOK...
Thursday and Friday...VFR overall. A shower or thunderstorm is
possible Thursday afternoon and evening mainly north and west of
KABE, then this may spread south and east some through Friday.
Southwest winds increase each day to 10-15 knots, with local gusts
up to 20 knots each afternoon.

Saturday and Sunday...Times of lower conditions possible due to some
showers and thunderstorms, especially each afternoon and evening.

&&

.MARINE...
SCA issued around 140 AM for DE Bay early this morning where
widespread gusts 25-30 kt. These gusts should diminish toward
dawn.

Otherwise, no headlines through tonight. Northwest wind gust
15-20 kt at times during the daylight hours becomes south to
southwest late this afternoon and continues tonight. Gusts to 25
kt possible late this afternoon NNJ waters.

OUTLOOK...
Thursday and Friday...A low-level jet is forecast to move across the
area Thursday night into Friday, however the forecast soundings show
vertical mixing is not all that efficient due to a very warm airmass
in place. However, stronger winds are not that far above the
surface. As a result, wind gusts up to 30 knots are possible for a
time especially on the ocean zones. This stronger southwesterly flow
will also build the seas. A Small Craft Advisory therefore may be
needed starting Thursday afternoon and continuing into Friday. The
winds and seas should diminish Friday night.

Saturday and Sunday...The winds and seas are forecast to be mostly
below Small Craft Advisory criteria.

RIP CURRENTS...
The forecast is for a low risk of rip currents for today.
However, southwest winds will increase to around 15 kts with
higher gusts by late afternoon. With a 9-second period from a
southeasterly direction, this may increase the rip current risk
level, especially on the New Jersey coast.

&&

.CLIMATE...
At 5 AM: we will finish off the marginally warmer than normal
month of June temperature assessment (except KMPO).

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...Small Craft Advisory until 6 AM EDT early this morning for
     ANZ431.

&&

$$
Synopsis...Gorse
Near Term...Drag
Short Term...Drag
Long Term...Gorse
Aviation...Drag/Gorse
Marine...Drag/Gorse
Climate...Drag



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