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fxus61 kphi 290122 
afdphi

Area forecast discussion
National Weather Service Mount Holly New Jersey
922 PM EDT Fri Apr 28 2017

Synopsis...
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.

&&

Near term /until 6 am Saturday morning/...
with loss of diurnal heating along with the combination of
clear skies and light winds, radiational cooling is allowing
temperatures to drop down into the 60s away from the major
urban centers along the I-95 corridor.

No significant changes will be made to the forecast, other than
to adjust hourly grids based on the latest surface obs. Precip
remains on track to approach the region well after midnight, so
no changes to the pop grids were made.

Cold front has moved into eastern New York/PA and northern NJ, and
will continue to track east late tonight through Saturday
morning. Ahead of the front, surface dewpoints are rising into
the 50s and low 60s.

That mesoscale convective system over Indiana has moved into Ohio. So far, few storm
reports have been issued, but radar indicates widespread heavy
rain, and numerous lightning strikes have been detected.

Going through the overnight, this mesoscale convective system and the aforementioned
cold front will continue to approach. Models indicate the bulk
of the instability across the Delmarva, correlating to the
higher dewpoints. However, the forcing will mainly be aligned
with the approach of the front itself, over northern zones. Will
keep a swath of likely pops in the forecast for northern zones
late tonight, but will keep thunder potential capped at chance.
Slight chance/low chance pops should cover southern NJ, the
Delmarva, and extreme southeast PA.

A warm night on tap with lows in the upper 50s and 60s.

&&

Short term /6 am Saturday morning through 6 PM Saturday/...
any lingering showers and thunderstorms will taper off Saturday
morning. West winds develop behind the front, and will increase
to 10-15 mph with afternoon gusts up to 20 mph. Skies become
mostly sunny by late morning/early afternoon, and temperatures
will quickly rise 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.

&&

Long term /Saturday night through Friday/...
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 quantitative precipitation forecast 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 European model (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 New Jersey 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 miles per hour 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 New Jersey 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 New Jersey Turnpike/
i95. It should be too stable for any thunder but winds may gust up
to around 30 miles per hour. 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.

&&

Aviation /01z Saturday through Wednesday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy and surrounding areas.

Tonight...patchy IFR visibility in fog, mainly at kmiv/kacy late
tonight. Otherwise, mainly VFR through around 08-10z. Rain showers and
sct thunderstorms and rain will move into the terminals during that time with
localized MVFR conditions. Light winds become SW 5-10 knots late
tonight.

Saturday...any lingering rain showers/thunderstorms and rain tapers off in the morning.
VFR for most of the day. West winds increase to 10-15 kt with
gusts as high as 20 kt in the afternoon. Scattered late
day/early evening rain showers/thunderstorms and rain possible.

Outlook...
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 miles per hour 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 rain showers/thunderstorms and rain Monday night.
Continued MVFR is possible in low clouds on Tuesday, with greatest
confidence at Abe and ridge. 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.

&&

Marine...
great conditions on the waters this evening and then the early
overnight periods. Sct showers and perhaps a tstm may affect the
New Jersey coastal waters and possibly into del Bay after midnight.
Overall, winds will be mostly SW or west with speeds at or under 10
knots. Seas will remain mostly 3-4 feet 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 Small Craft Advisory
flag will probably not be needed.

Outlook...
Small Craft Advisory 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 feet Monday night, decreasing to around 5 feet late Tuesday.
Seas may remain elevated into Tuesday night on the ocean, which
would necessitate the extension of any small craft advisories.

&&

Climate...
**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
evening.



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

&&

Phi watches/warnings/advisories...
PA...none.
New Jersey...none.
Delaware...none.
Maryland...none.
Marine...none.

&&

$$
Synopsis...franck
near term...mps/O'Hara
short term...O'Hara

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