Special Marine Warning 115, NWS Philadelphia/Mount Holly

Area Forecast Discussion
National Weather Service Mount Holly NJ
936 PM EDT Mon Oct 15 2018

.SYNOPSIS...
A cold front extended from southwestern Quebec, across the
upper Ohio River Valley to the lower Mississippi River Valley
this afternoon. The boundary will progress to the southeast and
it should pass through our region tonight. Another cold front
approaching from the northwest is forecast to arrive on
Wednesday. High pressure is expected to build across our region
from the west on Thursday and Friday, followed by a cold front
late on Saturday.

&&

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
930 pm update: Made some minor edits to temperatures and edited
PoPs/Wx grids a little bit more to match radar trends. Forecast
thinking below remains unchanged at this point.

830 pm mesoscale update: I updated the PoPs/Wx grids substantially
based on the past two hours of radar trends. It is becoming
increasingly clear that a predecessor vort max has moved through
the northern Mid-Atlantic, and the cold front is now upstream
of it. When analyzing radar data over the past three hours, the
narrow band of showers along the front quickly fizzled after the
passage of the vort max (and attendant showers, generated from
the midlevels). I suspect weak/transient subsidence upstream of
the vort max combined with the nearly-nonexistent low-level
parcel buoyancy has (have) countered the lift generated by the
front. This process will likely continue until the next
perturbation reaches near/downstream of the front, and as the
23z HRRR suggests, this may not happen until the front is near
or even off the coast of New Jersey.

With the above in mind, greatly reduced PoPs this evening but
did keep them elevated near/east of the Delaware River 02z
onward (though somewhat lower than before). Also narrowed the
region at risk of lightning to the proximity of the front hour-
by-hour. Overall, though, think the risk of gusty showers/storms
along the front is lowering away from the coast and from
Delmarva.

700 pm mesoscale update: Front is quickly approaching the area
and will enter the northwestern CWA in the next hour or two. So
far, the strongly-forced showers along the front have not fared
well, losing some organization and intensity in the past hour or
so. However, as the front moves past the higher terrain of
central PA, it will begin to approach a modestly more favorable
environment to initiate and sustain stronger lift/updrafts.
Slab-like lift along the boundary is expected to resume the
strongly-forced narrow band of showers with increasing chances
of thunder as the front approaches the coast. Hi-res models
showing this process occurring between 02z and 04z generally
near and east of the I-95 corridor. The chances for stronger
convection increase closer to the coast, and with such strong
winds aloft, even low-topped convection with little or no
lightning will be capable of mixing down these stronger winds,
potentially producing gusts strong enough for sporadic wind
damage.

The main questions are if the above processes occur and when.
Hi-res models have been insistent on this occurring, but have
performed rather poorly with the predecessor (downstream) rain
generated from higher levels (likely associated with a weak vort
max). Per the 18Z NAM, the stronger vort max will be moving in
from the southwest between 00z and 03z and is quite evident on
moisture-channel imagery moving through the central Appalachians
at this time. The contributions from large-scale lift in
advance of this perturbation should aid in convective
regeneration, so confidence is fairly high on the "if" question.

The "when" question is more uncertain, and timing is everything
given the speed of the front. If the timing of the vort max is
slow even by an hour, chances are quite low of any substantive
convection developing north of the Mason-Dixon Line before the
front moves offshore. They remain higher in Delmarva given the
northeast-southwest orientation of the front. But, per the
HRRR/NAM Nest, the timing seems to favor development near or
just east of the I-95 corridor between 02z and 03z. We shall
see.

Previous discussion...

A strong upper-level trough will slide eastward from the Great
Lakes and across Ontario and Quebec Canada through tonight. This
will drive a deepening surface low eastward as it tracks well
to our north. An associated surface cold front however will
sweep across our area later tonight. Some showers will move
across parts of the area into this evening well ahead of the
cold front. These should be on the lighter side with the rain
falling mostly from a mid level cloud deck.

As this feature slides eastward an increase in the wind fields
are forecast. The 500 mb flow is forecast to increase to 70-95
knots tonight as the core of an intense mid level jet streak
tracks across much of New York State. As the flow, initially
southwesterly, increases and transports warmer and more humid
air northward, some instability is forecast to develop through
the evening into the overnight hours. The forecast soundings
vary to some degree on the amount of destabilization ahead of
the cold front, however generally up to 500 J/KG may be
realized. The setup looks to be of a high shear/low CAPE one,
and with the strong wind fields coupled with a band of enhanced
ascent near the cold front may result in a narrow band of forced
low-topped convection. Some of the guidance including the high-
res does show a line of showers organizing eastward across our
area by later this evening. There is a narrow line forming in
western Pennsylvania this afternoon and this should be the
feature to watch. It is not all that clear how much lightning
will be generated given the low instability forecast, however if
the line is organized enough locally strong to damaging winds
could occur briefly as the line moves through given the amount
of wind above the surface. This potentially looks to be after 8
PM overall for the area from west to east and is then over with
by 2 AM. This line may become better organized from about the
I-95 corridor on eastward.

The combination of the strong wind field and then the cold air
advection in the wake of the cold front should result in a
period of gusty winds associated with the wind shift. The gusty
northwest winds are expected to diminish by daybreak as the
strongest winds shift offshore and the pressure gradient lessens
some. Temperatures may actually increase some through the
evening as the flow strengthens and the low-level warm air
advection occurs, then temperatures drop off with and following
the showers and cold frontal passage. The dew points will also
tumble overnight in the wake of the cold front. Low temperatures
are mainly a model/continuity blend.

&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH 6 PM TUESDAY/...
The flow aloft is forecast to be more zonal on Tuesday in the
wake of a strong upper-level trough early on that exits northern
New England. High pressure at the surface centered in the Ohio
Valley is forecast to gradually extend into our area, and this
will loosen the pressure gradient. A northwesterly breeze will
turn west or west- southwest during the afternoon.

As the cold front settles south and east of our area in the
morning, it may tend to stall to our south given the flow aloft
becoming more parallel to it. Some lingering showers are
possible across the far southern areas early, then given dry air
advection within the northwest flow should allow for a dry day.
The cloud cover should clear out quickly from north to south to
start the day, however mid to high level clouds may linger
longer mainly from the Philadelphia metro area on southward.

It will be a cool day with temperatures mainly in the 50s,
however dew points are forecast to drop into the 30s for much of
the area. The high temperatures are mostly a blend of guidance
and continuity.

&&

.LONG TERM /TUESDAY NIGHT THROUGH MONDAY/...
We should be well into a typical autumn weather pattern from
Tuesday night through Monday with the polar jet remaining over
the Great Lakes and the Northeast for much of the period.

A mid level short wave trough and its associated surface cold
front are expected to affect our region on Wednesday. The system
should bring limited moisture with it. As a result, we will
mention only a slight chance of afternoon showers across the
Poconos and far northern New Jersey.

Ridging at the surface and aloft are forecast to result in dry
and mostly sunny conditions for Thursday and Friday.

Another mid level trough is anticipated for the weekend. It
should bring a cold front through our region late on Saturday.
We will keep a chance of showers in the forecast for Friday
night and Saturday in the lift ahead of the system.

Dry weather is expected to return for Sunday and Monday.

Below normal temperatures are forecast through the period. The
chill will be most noticeable on the days following the cold
fronts.

Temperatures are expected to drop into the 30s in much of our
region on Wednesday night and Thursday night. A northwest wind
at 5 to 10 mph may preclude the development of much frost on
Wednesday night. However, the wind should become light and
variable on Thursday night and there may be widespread frost in
much of our area, away from urban locations and the immediate
coast.

&&

.AVIATION /02Z TUESDAY THROUGH SATURDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

This evening...Front will move through between 00z and 05z
across the terminals, likely with showers and a quick switch to
west-northwest winds at RDG/ABE around 01z-02z. Timing looks to
be 02z to 04z near the Philly terminals, and there is a slight
chance of lightning by this point. Confidence is too low for TAF
inclusion here. At MIV/ACY, timing looks to be 03z to 05z, and
the line of showers is expected to intensify to the point where
mention of TS in the TAFs is needed. The main terminal impact
will be the quick switch in wind direction, and it will be
likely accompanied by gusts (perhaps to 30+ kts near the showers
themselves). After frontal passage, any (brief) MVFR conditions
will become VFR quickly as winds become 270-320 degrees with
speeds 10-20 kts and higher gusts. Moderate confidence.

Overnight...Winds become more northwesterly with time and should
diminish to around 10 kts by daybreak. VFR. High confidence.

Tuesday...VFR with northwest winds around 10 kts becoming more
westerly during the mid to late afternoon. High confidence.

OUTLOOK...
Tuesday night...Mainly VFR. Southwest to west wind 8 knots or
less.

Wednesday...Mainly VFR. West to northwest wind 10 to 15 knots.

Wednesday night...Mainly VFR. Northwest wind 5 to 10 knots.

Thursday...Mainly VFR. Northwest wind around 10 knots.

Thursday night...Mainly VFR. Variable wind 6 knots or less.

Friday...Mainly VFR. Southwest wind around 10 knots.

Friday night...Mainly VFR. A chance of showers. Southwest wind
5 to 10 knots.

Saturday...Mainly VFR. A chance of showers. Southwest to west
10 to 15 knots.

&&

.MARINE...
A cold front will cross the area later tonight. Strong winds
above the surface will result in gusty southwest winds ahead of
the front, with peak gusts in the 25-30 knot range. Along and
behind the front, a period of gale force northwesterly gusts are
anticipated for much of the area. As a result, the Gale Warning
continues for tonight. A Small Craft Advisory however continues
for the Upper Delaware Bay. A narrow band of heavier showers
and perhaps some embedded thunder may produce brief stronger
winds later this evening into the overnight.

For Tuesday, a Small Craft Advisory should be needed for the
morning following the Gale as winds and seas subside through the
day.

OUTLOOK...
Tuesday night...Westerly wind gusts may approach 25 knots on
our ocean waters north of Atlantic City.

Wednesday and Wednesday night...West to northwest gale force
wind gusts are expected.

Thursday...Northwest wind gusts of 25 to 30 knots are expected.

Thursday night and Friday...No marine headlines are
anticipated.

Friday night and Saturday...Southwest wind gusts around 25
knots are possible.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...Gale Warning until 6 AM EDT Tuesday for ANZ431-450>455.
     Small Craft Advisory until 6 AM EDT Tuesday for ANZ430.

&&

Synopsis...Iovino
Near Term...CMS
Short Term...Gorse
Long Term...Iovino
Aviation...CMS/Iovino
Marine...Gorse/Iovino

Hazardous Weather Outlook
National Weather Service Mount Holly NJ
344 PM EDT Mon Oct 15 2018

NJZ001-007>010-PAZ054-055-060>062-101-103-105-161945-
Sussex-Warren-Morris-Hunterdon-Somerset-Carbon-Monroe-Berks-Lehigh-
Northampton-Western Chester-Western Montgomery-Upper Bucks-
344 PM EDT Mon Oct 15 2018

This Hazardous Weather Outlook is for northern New Jersey,
northwest New Jersey, east central Pennsylvania, northeast
Pennsylvania and southeast Pennsylvania.

.DAY ONE...This afternoon and tonight.

The probability for widespread hazardous weather is low.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday.

Frost is possible from late Thursday night into early Friday
morning.

.SPOTTER INFORMATION STATEMENT...

Weather spotters are encouraged to report significant weather
conditions according to Standard Operating Procedures.

DEZ001>004-MDZ008-012-015-019-020-NJZ012>027-PAZ070-071-102-104-106-
161945-
New Castle-Kent-Inland Sussex-Delaware Beaches-Cecil-Kent MD-
Queen Annes-Talbot-Caroline-Middlesex-Western Monmouth-
Eastern Monmouth-Mercer-Salem-Gloucester-Camden-
Northwestern Burlington-Ocean-Cumberland-Atlantic-Cape May-
Atlantic Coastal Cape May-Coastal Atlantic-Coastal Ocean-
Southeastern Burlington-Delaware-Philadelphia-Eastern Chester-
Eastern Montgomery-Lower Bucks-
344 PM EDT Mon Oct 15 2018

This Hazardous Weather Outlook is for central Delaware, northern
Delaware, southern Delaware, northeast Maryland, central New
Jersey, northern New Jersey, southern New Jersey and southeast
Pennsylvania.

.DAY ONE...This afternoon and tonight.

The probability for widespread hazardous weather is low.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday.

The probability for widespread hazardous weather is low.

.SPOTTER INFORMATION STATEMENT...

Weather spotters are encouraged to report significant weather
conditions according to Standard Operating Procedures.

ANZ431-450>455-161945-
Delaware Bay waters south of East Point NJ to Slaughter Beach DE-
Coastal waters from Sandy Hook to Manasquan Inlet NJ out 20 nm-
Coastal waters from Manasquan Inlet to Little Egg Inlet NJ out 20 nm-
Coastal waters from Little Egg Inlet to Great Egg Inlet NJ out 20 nm-
Coastal waters from Great Egg Inlet to Cape May NJ out 20 nm-
Coastal waters from Cape May NJ to Cape Henlopen DE out 20 nm-
Coastal waters from Cape Henlopen to Fenwick Island DE out 20 nm-
344 PM EDT Mon Oct 15 2018

...GALE WARNING IN EFFECT UNTIL 6 AM EDT TUESDAY...

This Hazardous Weather Outlook is for Atlantic coastal waters and
Delaware Bay Waters.

.DAY ONE...This afternoon and tonight.

Please listen to NOAA Weather Radio or go to weather.gov on the
Internet for more information about the following hazards.

   Gale Warning.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday.

Gale force wind gusts from the west and northwest are possible on
Wednesday and Wednesday night.

.SPOTTER INFORMATION STATEMENT...

Weather spotters are encouraged to report significant weather
conditions according to Standard Operating Procedures.

ANZ430-161945-
Delaware Bay waters north of East Point NJ to Slaughter Beach DE-
344 PM EDT Mon Oct 15 2018

This Hazardous Weather Outlook is for Delaware Bay Waters.

.DAY ONE...This afternoon and tonight.

There is a low probability for widespread hazardous weather.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday.

There is a low probability for widespread hazardous weather.

.SPOTTER INFORMATION STATEMENT...

Weather spotters are encouraged to report significant weather
conditions according to Standard Operating Procedures.

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Special Weather Statement
National Weather Service Mount Holly NJ
1119 PM EDT MON OCT 15 2018

NJZ012>015-018>020-026-PAZ070-071-104-106-160415-
Northwestern Burlington-Eastern Monmouth-Camden-Coastal
Ocean-Ocean-Western Monmouth-Middlesex-Mercer-Lower Bucks-Eastern
Montgomery-Delaware-Philadelphia-
1119 PM EDT MON OCT 15 2018

...A LINE OF SHOWERS WILL AFFECT NORTHERN OCEAN...NORTHWESTERN
CAMDEN...MERCER...NORTHERN BURLINGTON...MIDDLESEX...MONMOUTH...
SOUTHEASTERN MONTGOMERY...SOUTHEASTERN BUCKS...PHILADELPHIA AND EAST
CENTRAL DELAWARE COUNTIES...

At 1118 PM EDT, radar indicated showers were located along a line
extending from Plainsboro Center to Roxborough. Movement was east at
45 mph.

Winds up to 40 mph are possible with these showers.

Locations impacted include...
Philadelphia, Toms River, Trenton, Camden, Perth Amboy, Long Branch,
Asbury Park, Sandy Hook, Lakewood, Middletown, Old Bridge, Bensalem,
Jackson, Howell, East Brunswick, South Brunswick, Sayreville,
Marlboro, Manalapan and Ewing.

LAT...LON 4010 7403 3993 7434 3997 7538 4052 7431
      4052 7426 4050 7428 4047 7427 4044 7420
      4046 7418 4045 7413 4041 7402 4044 7399
      4048 7402 4044 7398 4042 7400 4042 7398
      4039 7398 4039 7401 4038 7397 4036 7397
TIME...MOT...LOC 0318Z 267DEG 40KT 4034 7459 4002 7523

SJ

Special Weather Statement
National Weather Service Mount Holly NJ
1139 PM EDT MON OCT 15 2018

DEZ001-002-MDZ008-012-015-NJZ016-017-021-160415-
Kent-New Castle-Queen Anne's-Cecil-Kent-Salem-Cumberland-Gloucester-
1139 PM EDT MON OCT 15 2018

...A LINE OF SHOWERS WILL AFFECT NEW CASTLE...NORTHWESTERN KENT...
NORTHEASTERN QUEEN ANNE'S...KENT...SOUTHEASTERN CECIL...NORTHWESTERN
CUMBERLAND...SALEM AND CENTRAL GLOUCESTER COUNTIES...

At 1139 PM EDT, radar indicated showers were located along a line
extending from near Wilmington Manor to Newtown. Movement was east at
35 mph.

Winds up to 40 mph are possible with these showers.

Locations impacted include...
Wilmington, Middletown, Elkton, Glassboro, Pennsville, Smyrna,
Carneys Point, New Castle, Chestertown, Salem, Woodstown, Alloway,
Clayton, Quinton, Delaware City, Elmer, Newport, Cecilton, Millington
and Shiloh.

LAT...LON 3929 7617 3932 7618 3934 7616 3933 7614
      3937 7611 3937 7606 3942 7600 3948 7600
      3972 7561 3971 7552 3967 7555 3966 7553
      3971 7550 3968 7495 3915 7579 3926 7622
TIME...MOT...LOC 0339Z 280DEG 31KT 3967 7563 3932 7618

SFJ