Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 210930
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
530 AM EDT THU JUL 21 2016

.SYNOPSIS...
High pressure builds south and east of the area today and tonight. A
frontal boundary is expected to into the area overnight Friday into
Saturday, and slowly sag south of the area through Sunday. Another
frontal boundary is expected late Monday into Tuesday. High pressure
should then briefly build back into the area Wednesday.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
As the high continues to shift further off shore, southwesterly
flow will start the warming trend that will continue right into
the weekend. For today however, the upper level ridge remains to
our west, keeping highs generally in the 80s and lower 90s for our
region today.

Today should be prime conditions for an afternoon sea breeze to
develop, keeping the shore a few degrees cooler than interior
locations. However, no showers are expected to develop along the sea
breeze as subsidence with the building ridge is expected.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM FRIDAY/...
Dew point temperatures will continue to increase thanks to
persistent low level southerly flow. Therefore, expect a warmer
night as compared to Wednesday night.

The other concern will be how quickly the pre frontal trough will
approach the region. We could see showers and thunderstorms
developing along or just ahead of this trough. The 00Z model runs
though for the most part depicted this trough staying well west of
our region through overnight period, keeping dry conditions again
tonight.

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
Hot and humid conditions are continued to be forecast for much of
the extended period, with Saturday, Sunday, and Monday expected to
be the warmest days. Thicknesses and 925/850 mb temperatures are
expected to continue to climb during this period. With the building
thicknesses and 925/850 mb temperatures, daytime highs are expected
to climb into the low to mid 90s Friday, followed by mid to upper
90s Saturday, Sunday, and Monday, followed by low to mid 90s again
by Tuesday. Heat index values will begin approaching the upper 90s
to 100 degrees by Friday, but the dangerously high heat index values
over 100 degrees are expected over the weekend into Monday, and
possibly into Tuesday. With several days of dangerously high heat
index values expected, we have issued an Excessive Heat Watch
starting Saturday and continuing into Sunday for all of our forecast
area except Carbon and Monroe counties in Pennsylvania and Sussex
county in New Jersey. This watch will likely need to be extended
into Monday, and possibly Tuesday.

Rain chances through the extended will be centered around a couple
of frontal boundary passages. The first is late Friday into Friday
night, and the second period being Monday into Monday night.

On Friday, a pre-frontal trough will be to our west, with a frontal
boundary approaching the area late in the day as well. As these
features move eastward, along with the associated short wave aloft,
scattered showers/thunderstorms could begin moving into the area
late in the day Friday into Friday night. There is a fair amount of
instability forecast with the heat and humidity, and there will be
some weak shear present as well. If any thunderstorms do develop,
the could produce a brief period of heavy rainfall and gusty winds.

A similar situation is forecast to occur on Monday as a frontal
boundary is forecast to approach late in the day into Monday night.
Instability increases during the day into the evening, and as the
frontal boundary and associated short wave move into the area,
showers and thunderstorms may develop and move across the area.

The rest of the extended forecast is expected to be dry.

&&

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

Patchy MVFR and IFR visibility restrictions are possible,
primarily for more rural TAF sites (especially KMIV and KACY),
with BR between Through 13Z both this morning and between 09 and
12Z Friday morning. Otherwise, VFR conditions are expected
through the TAF period.

Winds will be mostly light (10 kts or less) and southwesterly. The
one exception to this is the sea breeze which should develop early
this afternoon and affect at least KACY and KMIV (and may propagate
as far inland as the Delaware Valley TAF sites). Behind the sea
breeze, southerly winds near 10 kt, with higher gusts will be
possible.

OUTLOOK...

Friday-Friday night...Generally VFR. A chance of showers and
thunderstorms which may briefly lead to lower conditions. Gusty
southwest winds 15-20 knots.

Saturday-Sunday...VFR.

Monday-Monday night...Generally VFR. A chance of showers and
thunderstorms which may briefly lead to lower conditions.
Gusty southwest winds 15-20 knots.

&&

.MARINE...
Southerly winds may gust just above 20 kt this afternoon and evening
along the northern NJ coastal waters, but are expected to remain
below SCA criteria at this time. Seas should generally be 3 ft or
less.

OUTLOOK...

Friday-Friday night...Small Craft Advisory conditions possible with
increasing winds ahead of an approaching cold front later Friday
into Friday night.

Saturday-Sunday...Sub-Small Craft Advisory conditions expected.

Monday-Monday night...Near Small Craft Advisory conditions
possible with increasing winds ahead of an approaching cold front.

RIP CURRENTS...there is a moderate risk for the formation of
dangerous rip currents along the central and northern NJ shore
today.

The probable risk for the formation of dangerous rip currents
Friday is moderate along the NJ shore and low for the Delaware
Beaches.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Excessive Heat Watch from Saturday morning through Sunday
     afternoon for PAZ060>062-070-071-101>106.
NJ...Excessive Heat Watch from Saturday morning through Sunday
     afternoon for NJZ007>010-012>027.
DE...Excessive Heat Watch from Saturday morning through Sunday
     afternoon for DEZ001>004.
MD...Excessive Heat Watch from Saturday morning through Sunday
     afternoon for MDZ008-012-015-019-020.
MARINE...None.

&&

$$
Synopsis...Robertson
Near Term...Johnson
Short Term...Johnson
Long Term...Robertson
Aviation...Johnson/Robertson
Marine...Johnson/Robertson


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