Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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040
FXUS61 KPHI 220738
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
338 AM EDT FRI JUL 22 2016

.SYNOPSIS...
A frontal boundary is expected to move into the area overnight
tonight into Saturday, and slowly sag south of the area through
Sunday. High pressure will briefly affect the area Sunday. Another
frontal boundary is expected late Monday into Tuesday and stall to
our south through Wednesday and Thursday. High pressure should
briefly affect the area Wednesday.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Southwesterly flow ahead of the weak cold front tonight will lead
to the continuation of the warming trend. Expect highs to be
around 5 degrees higher than Thursday, but we should still fall
short of heat advisory criteria, with maximum heat index values
generally in the mid to upper 90s.

A pre frontal trough is expected to slide over our region by this
afternoon. Along this trough, expect surface and low level
convergence. With the heating, expect mixed layer CAPE values to
be above 1000 J/kg across the northern half of our region. Bulk
shear values are modest, and there is limited mid and upper level
support which should limit the coverage of storms. However, with a
dry mid level layer (around or just above 700 mb), any storms that
are able to sustain an updraft to that level will have potential
for downbursts. Thus, will mention the threat for strong winds
(especially across the north) in the HWO. Hail threat looks to be
limited thanks to a very high melting layer (between 14 and 15k ft
AGL). Also not that concerned about heavy rain as storm motions
should be near 20 kt and precipitable water values are just
slightly above normal.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SATURDAY/...
The pre frontal trough should still be over the region at least
through the evening hours continuing the risk for thunderstorms
with strong winds. Very late in the night though, the cold front
should slide into the Poconos and NW NJ. Given the timing of the
front, and continued mid level drying, do not expect any storms
with the front (expect nearly all the convection to develop near
the trough).

&&

.LONG TERM /SATURDAY THROUGH THURSDAY/...
Hot and humid conditions are continued to be forecast for much of
the extended period, with Saturday, Monday and possibly Tuesday
expected to be the warmest days. It is possible that Sunday may be
slightly "cooler" and have lower dewpoints, leading to lower heat
index values, but it will still be quite hot. With 925 mb
temperatures forecast to be around 25/26 degrees, this would yield
highs into the mid/upper 90s Saturday, Monday and Tuesday. The
combination of the heat and humidity will lead to dangerously high
heat index values over the weekend into Monday, and possibly into
Tuesday. With several days of dangerously high heat index values
expected, we continue with the Excessive Heat Watch for all of our
forecast area except Carbon and Monroe counties in Pennsylvania
and Sussex county in New Jersey and have extended it into Monday.

There could be some isolated showers/thunderstorms late Sunday
into Sunday night across the far southern areas as a couple of
short wave/vorticity impulses move across the area. However, most
areas will remain dry.

On Monday, a pre-frontal trough will be in place across the east
coast, with a frontal boundary approaching the area late in the
day and overnight. 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 Monday into Monday
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.

There will be a chance of showers/thunderstorms each day from
Tuesday, Wednesday, and Thursday as several short wave/vorticity
impulses move across the area. The strongest of these short waves
may move across the area later on Thursday, leading to a greater
chance of showers/thunderstorms.

&&

.AVIATION /07Z FRIDAY THROUGH TUESDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.

Scattered thunderstorms are possible this afternoon and evening.
Coverage will be quite limited, so have only mentioned a PROB30 at
KABE and KTTN for now. However, if any storms do move over TAF
sites, downbursts leading to variable and gusty winds will be
possible, along with brief IFR visibilities.

Aside from the storms, VFR conditions are expected today and
tonight. Winds will be southwesterly and will be around 10g18kt
between 15 and 00Z (excluding in the vicinity of storms, where
winds could be stronger).

OUTLOOK...

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.

Tuesday-Tuesday night...VFR.

&&

.MARINE...
Southwesterly winds will continue through the day today,
increasing this afternoon. For the New Jersey coastal waters,
expect gusts above 25 kt to develop by mid afternoon, with seas
expected to subsequently increase to 5 feet by this evening. For
the Delaware coastal waters and the Delaware Bay, wind gusts above
20 kts are possible, but should stay below SCA criteria.

Winds and seas should subside before daybreak Saturday.

OUTLOOK...

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.

Tuesday-Tuesday night...Sub-Small Craft Advisory conditions expected.

RIP CURRENTS...The risk for the formation of dangerous rip
currents today is moderate along the NJ shore from Atlantic
County northward and low for the Delaware Beaches and Cape May
county. Confidence on how much southerly component is a little
below average so the moderate risk may end up low enhanced.

Looking further ahead, with the Atlantic Basin still devoid of
tropical storms, the risk for the formation of dangerous rip
currents should be Low.

Next Monday the 25th, we might have enough wave height to around
4 feet and water buildup due to southerly winds, to have a more
widespread low enhanced or even moderate risk but confidence on
seas building that high is below average.

Water temperatures have rebounded after the massive upwelling
event associated with the squall line passage late Monday. Water
temps today were in the low to mid 70s, above normal for this time
of year and quite a rebound from the lower 60s of Tuesday. Colder
upwelling might develop again late Friday or Saturday.

&&

.CLIMATE...
Near record (within 2f) or record warmth is anticipated for many
sites on 1 or 2 days of the following listed.

        23rd    24th    25th     26th
PHL 101-2011 98-2011 96-1899 101-1892
ABE  99-1955 95-1999 95-1999  98-1940
ACY 105-2011 100-2011 99-2010 96-2011, 1963
ILG  100-2011 98-2011 96-1987 99-1894
TTN  104-2011 98-1910 97-1999 99-1892
GED  104-2011 99-2011 99-2010 97-2012
RDG  100-2011 96-2010 96-1999 99-1940
MPO   91-1955 91-1914 90-1999 89-1949

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Excessive Heat Watch from Saturday morning through Monday
     afternoon for PAZ060>062-070-071-101>106.
NJ...Excessive Heat Watch from Saturday morning through Monday
     afternoon for NJZ007>010-012>027.
DE...Excessive Heat Watch from Saturday morning through Monday
     afternoon for DEZ001>004.
MD...Excessive Heat Watch from Saturday morning through Monday
     afternoon for MDZ008-012-015-019-020.
MARINE...Small Craft Advisory from 2 PM this afternoon to 5 AM EDT
     Saturday for ANZ450>453.

&&

$$

Synopsis...Robertson
Near Term...Johnson
Short Term...Johnson
Long Term...Robertson
Aviation...Johnson/Robertson
Marine...Johnson/Robertson
Climate...Staff



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