Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 282046

Area Forecast Discussion
National Weather Service Mount Holly NJ
446 PM EDT Fri Apr 28 2017

A cold front over the upper Mississippi Valley will move east and
through our region Saturday night. This front will become stationary
near Delmarva on Sunday, then lift northward as a warm front on
Monday, as low pressure moving through the Great Lakes drags a
stronger cold front through our area Monday night. Another area
of pressure organizing over the Arklatex on Wednesday will move
northeastward toward the middle Atlantic coast by Friday.


Good weather will carry into the evening then increasing clouds and
increasing chcs for showers after midnight. A short wave interacting
with warm front across the Ohio valley will cause the showers which
will move East across PA/Nrn NJ overnight. We have increased the
pops in most areas, but the nrn areas of NJ and the Srn Poconos and
Lehigh valley still have the highest pops for the forecast area.
Instability is not the greatest, but still think that some tstms are
possible too. Tonight`s low will remain mild, mostly in the 60s.
Patchy fog may develop across Delmarva and srn NJ before the thicker
clouds arrive. Confid in fog development is low however.


A summer-like day expected across the area Saturday. After some
early morning showers and perhaps a tstm, skies will become partly
to mostly sunny by late morning. Temperatures will quickly rinse
into the mid/upper 80s across most areas. Humidity levels will
remain moderate as well, so there will be some discomfort during the
mid-day heat. Scattered showers and tstms will again develop west of
the area and move across the region later in the afternoon. We have
continued with the chc pops for the area attm.


The polar jet remains displaced well to our north in Canada, with an
active southern stream across the conus thru the period. A southern
stream closed low ejects northeast out of the four corners region on
Sunday and through the Great Lakes on Tuesday. A broader long wave
trough then sets up on Wednesday, extending from Atlantic Canada to
the Colorado Rockies. There is general model agreement that this
feature slowly progresses eastward, as a cutoff low develops across
the southeast states. Overall, this will maintain a southwest flow
regime with temperatures at or above normal. The two primary focuses
for precipitation will be with a cold frontal passage Monday night,
then within the overrunning area ahead of the southern stream cutoff
low from Thursday into Friday.

Some residual convection is possible through at least midnight on
Saturday night across Delmarva and southern NJ, as a cold front
moves slowly through this area, and stalls over central Delmarva
through Sunday. The GFS appears to be overdone with QPF north of
this boundary through Sunday, and have discounted it, given the
drier surface air to the north and slight ridging aloft as well. The
NAM and ECMWF are much drier, and the forecast reflects this, with
Delmarva the exception. As the boundary stalls, we expect renewed
showers and thunderstorms on Sunday. The high temperature forecast
will be challenging on Sunday, with a maritime air mass within the
easterly flow north of the front, while portions of Delmarva remains
south of the front within the warm sector. We expect low-70s to low-
80s across Delmarva, with low-60s to low-70s across the remainder of
the region. The exception will be some of the NJ barrier islands,
where highs will not make it out of the 50s!

The boundary is then expected to lift northward as a warm front on
Sunday night. There is not much support for precip, so PoPs were
kept in the slight chance category. Expect temperatures to remain
steady or rise overnight. With the cold front still over the Ohio
Valley on Monday, expect a mostly sunny and dry day. A brisk south-
west flow will develop, with wind gusts up to around 30 MPH in
the afternoon. Temperatures will be well above normal, with
highs in the low-mid 80s across the urban corridor. With the
cold frontal passage Monday night, showers and thunderstorms are
likely. While the timing is not ideal for severe weather and
instability is limited, the wind field is strong and
Precipitable Water values approach 2.0 inches, so gusty winds
and heavy downpours are likely with any thunderstorms, the
primary focus being northwest of the NJ Turnpike/I-95.

The post-frontal air mass will remain moist on Tuesday, with a
surface trough traversing the region under a cyclonic flow aloft.
Expect considerable cloudiness and a continued chance of showers,
especially during the afternoon, and northwest of the NJ Turnpike/
I95. It should be too stable for any thunder but winds may gust up
to around 30 MPH. Much cooler compared to Monday, but high temps
still at or slightly above normal. For Wednesday, slight ridging
builds in aloft and the column is dry, so fair weather is expected.

Unsettled weather during the Thursday and Friday time frame. A broad
trough to our west will maintain a southwest flow aloft, along with
moisture of Gulf of Mexico origins moving up the eastern
seaboard, within an overrunning regime. Heavy rainfall is
certainly possible, with WPC guidance indicating the potential
for 1-2 inches across our region, but there is still inherent
uncertainty given it`s Day 6-7. Stay tuned.


The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.

The themes in the earlier tafs remain about the same with the
latest issuance. The biggest challenge will be in the after-midnight
pre-dawn period Sat. Until then, VFR conditions with mostly clear
skies expected. Winds will be mostly West or Southwest with a trend
towards more South by dusk. Winds at KACY will likely remain South
or turn Southeast with a meandering sea breeze nearby. Tonight,
clouds will increase and lower through the night. Some fog may
develop across KMIV/KACY since they will get the clouds last.
Showers and perhaps a tstm will move across the srn Poconos and nrn
NJ. We have included mention of showers even at KILG/KPHL in a
PROB30 group with what appears a better chc now than earlier today.
Kept mention of thunder out of the tafs, but I could see them being
added later if trends continue. VFR returning Sat in the 14z/15z
period with a brisk W/SW wind developing.

MVFR possible in any lingering showers and thunderstorms Saturday
night, especially ACY, MIV, and ILG. Predominantly VFR on Sunday,
with east wind gusts up to around 20 MPH at all TAF sites. MVFR is
likely at all TAF sites Sunday night into early Monday morning,
mainly attributable to low clouds. A return to VFR is expected by
late Monday morning, with southwest wind gusts up to around 25 kts
during the afternoon. MVFR possible in SHRA/TSRA Monday night.
Continued MVFR is possible in low clouds on Tuesday, with greatest
confidence at ABE and RDG. Winds will shift to the northwest by
Tuesday morning, with gusts up to around 25 kts possible during the
afternoon. Wednesday is expected to feature predominantly VFR at
this time.


Great conditions on the waters this afternoon should carry on into
the evening and then the early overnight periods. Sct showers and
perhaps a tstm may affect the NJ coastal waters and possibly into
Del bay after midnight. Overall, winds will be mostly SW or W with
speeds at or under 10 knots. Seas will remain mostly 3-4 FT on the
ocean a with a med period swell. Across Del Bay, seas will remain 1-
2 ft at most. Fair weather Sat after a few morning showers and sct
tstms. Increasing SW winds up to around 12-18 knots, looks like SCA
flag will probably not be needed.

SCA likely Monday through Tuesday. Southerly winds increase Monday,
with gusts up to 30 knots continuing into Monday night. Winds will
become northwest by Tuesday morning, with renewed gusts around 25
knots possible. Seas building to the 5-7 Ft range on Monday, and
then 7-9 FT Monday night, decreasing to around 5 FT late Tuesday.
Seas may remain elevated into Tuesday night on the ocean, which
would necessitate the extension of any Small craft Advisories.


**Record or number 2 warmest April on record expected**

Presuming our forecast temps these last 2 days of April are
accurate, we are assured of a top 2 warmest April on record in
much of our forecast area. Sunday is probably the critical day
for determining record or not.

Below: April projected within the top April average temps, the
normal for April and the period of record (POR).

This includes Friday`s (28th) high and low temperatures through
4 PM.

Sundays max temps may occur at 1 am and the min temps Sunday

PHL normal 54.0 POR 1874

59.5 2017 Projected warmest ever: still  could slip .2 degrees.
59.4 1994
58.5 1921
58.4 2010
57.9 1941

ABE normal 49.9 POR 1922

56.9 projecting record and almost cant miss a record.
56.4 1941
54.7 1994

ACY normal 51.7 POR 1874

57.6 projecting record and almost cant miss.
56.3 2010
56.1 2011

Record high temps listed tomorrow-Saturday where it is forecast
to be within 2 degrees of record.

PHL 90-1974

GED 88-1990




Near Term...O`Hara
Short Term...O`Hara
Long Term...Franck
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