Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 221243
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
843 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 /THROUGH TONIGHT/...
930 AM ESTF: No major changes to temps/dews, in part because of
cirrus blowoff capping potential advy day. Still monitoring and
may need to make last minute upward adjustments and associated
advisory for the TTN-PHL-ILG metro corridor. We may need to issue
SPS/SVR this afternoon e Pa and N 2/3rds NJ.

From the mid shift:

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 (although
interestingly, as of 6 AM EDT, there is considerably more coverage
of convection along the trough which is currently over Lake Erie
than what high res models previously depicted). 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.

Tonight...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).

&&

.SHORT TERM /SATURDAY/...
Will update from below by 330 am.

&&

.LONG TERM /SATURDAY NIGHT 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 /12Z FRIDAY THROUGH TUESDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.

Today...VFR sct-bkn aoa 5000 ft with a sw wind gusting 15-20 kt
this afternoon. Considerable cirrus late this morning-midday as
blowoff from sewd moving-initially decaying convection in nw pa,
then sct- bkn clouds develop near 5000 ft. Anticipating redevelopment
of convection 17z-20z near and N of Krdg-KABE-KTTN. nnw wind
gusts to 40 kt possible in tstms.

Tonight...VFR with possible MVFR haze/fog late at night, especially
wherever it rain after 21z/22 (today). there may still be some
leftover decaying evening convection vcnty PHL-ACY as it runs into
the capped mid lvl thermal profile. southwest wind with gusts to
15 kt early shifting to light northwest late.

Saturday...VFR sct-bkn aoa 5000 ft. Potential for convection may
still exist vcnty KPHL/KILG/KACY/KRDG. Light northwest wind in
the morning turning westerly in the afternoon with gusts 15 to 20
kt.

OUTLOOK...

Saturday night-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...
Today...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.

Tonight...Winds and seas should subside before daybreak Saturday.

Saturday...Sub small craft advisory conditions anticipated.

OUTLOOK...

Saturday night-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 probable risk for the formation of dangerous
rip currents should be low this weekend.

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...
Barring afternoon convective cloud debris, Monday is likely to
experience record breaking heat .. vulnerably low records. Our
330 am gridded fcst is for record values of 97 at Philadelphia
and Wilmington Monday, 96 Allentown and a record equaling 96 at
Reading.

Other near record (within 2f) or record warmth can occur on other
days, especially the 24th and 26th.

Based on 12z guidance we may extend the records to the 28th... if
we still are showing rather high modeled 2m temps. There may be a
slight warm bias on these modeled 2m temps at extended ranges...so
we are cautious about adding any additional days.

        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...Drag 844
Short Term...Drag 844
Long Term...Robertson
Aviation...Drag/Robertson 844
Marine...Drag/Robertson 844
Climate...844


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