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FXUS61 KPHI 200811
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
411 AM EDT Thu Sep 20 2018

.SYNOPSIS...
High pressure will continue building in from the north through
Thursday before pushing off the New England coast through early
Friday. A cold front will approach from the north and west on
Friday before passing through the area Friday night and Saturday
morning. The front will then stall just south of our area
through the end of the weekend as high pressure builds to our
north. The high begins pushing offshore through the beginning of
next week.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
An area of light rain has developed overnight in northern New Jersey
in the vicinity of a decaying boundary.  Hi-res models take these
showers and gradually move them westward through this morning. Have
included a mention of isolated to scattered showers through the
morning, mainly for areas north and west of the I-95 corridor.

Moisture trapped below the inversion has allowed for a good deal of
clouds to remain across the region overnight. The cloudy start to
the day should gradually improve as high pressure starts to builds
into our area with drier air. We should start seeing the cloud bases
lift, with some sunshine breaking through towards late morning or
early afternoon. As the light winds start to pick up by mid-morning
across the region, we should see some mixing take place and drying
out will occur.

Temperatures will feel more comfortable with highs only reaching
into the lower 70s across the region. The southern Poconos and parts
of northwest New Jersey will struggle to reach 70 today, keeping
highs in the mid to upper 60s.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM FRIDAY/...
High pressure starts to move off to the north and east, moving
offshore of Newfoundland toward Friday morning. Some moistening in
the low/mid levels may allow for some light showers to develop in
the return flow around the back edge of the departing high later
tonight. Keep any mention of rain north and west of the I-78
corridor.

Otherwise, most areas will remain dry overnight. Lows will drop into
the upper 50s to low/mid 60s across the forecast area overnight.

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
Main challenge in the long-term period is the cold frontal passage
Friday night and Saturday and what happens to the front thereafter.

The 00Z operational model suite indicates a fairly strong shortwave
trough moving from the Great Lakes and adjacent southeast Canada on
Friday into the Canadian Maritimes on Saturday, with broadly zonal
flow in much of the northern U.S. for the weekend. A higher-
amplitude trough will begin to dig into the central U.S. late this
weekend, allowing for downstream ridging in the Great Lakes and Ohio
Valley by Monday moving into the Northeast on Tuesday. The large-
scale trough then progresses into the eastern U.S. by mid to late
week. Overall, model agreement is above average in the synoptic
scale, though there are noticeable differences regarding the
strength of the central U.S. troughing early next week, which leads
to some uncertainty with the ridging downstream and its effects on
surface boundaries in the eastern U.S. that will have rather large
implications on our sensible weather.

On Friday, the shortwave trough moving into/through the Great Lakes
region will have an attendant (rather strong) surface cyclone moving
through Ontario/Quebec during the day. A cold front will extend
south-southwestward into the Ohio Valley and should readily develop
a squall line given the strong large-scale and frontal lift.
However, the front will remain well west of the area Friday evening,
and convection will likely wane before reaching much of the area
(except perhaps the far northern/western CWA). Instability should be
quite low by this point, but the wind field aloft is strong, so even
the weakening squall line may produce sporadic strong wind gusts
until the line completely collapses overnight. For this reason,
cannot rule out some impacts in our region, but suspect the vast
majority of severe weather will be well north/west of the area.

Hi-res guidance does not maintain much precipitation associated with
the front in our area, so I generally lowered PoPs Friday and Friday
night across the area. Notably, a predecessor vort max will be
moving through New York/New England Friday morning, and this may
spawn a few showers as far south as the Poconos, so kept some low
PoPs to account for this during the day. Statistical guidance was
noticeably lower with max temperatures on Friday, about 4-8 degrees
lower than values suggested 24 hours ago. Followed suit, given
potential for some residual cool near-surface air to refuse to be
scoured, especially if flow maintains a modest onshore component.

The front moves through the area Friday night and Saturday, but in
the same old story we have had for months, gets hung up south of the
area from the strong ridging in the Southeast and adjacent western
Atlantic. Operational models are not producing much precipitation in
the southern CWA on Saturday, so kept fairly low PoPs during the day
(with the northern CWA most likely to be dry). Some cloudiness may
remain near/north of the front as another vort max approaches the
area during the day (aiding in large-scale midlevel lift), and steep
boundary-layer lapse rates may produce stubborn low clouds. Should
this occur, maximum temperatures (currently similar to Friday's) may
be too high.

As surface flow acquires a more onshore component on Sunday (a
result of the surface high to the north of the front progressing
eastward), low clouds may develop on Sunday (though cold/dry
advection may impede this process, as suggested by GFS model
soundings). Combination of cold advection and cloud cover will
result in a cooler day across the area, with highs generally near or
below 70 (and possibly not above 60 in the Poconos).

Meanwhile, the proximity of the front to Delmarva and southern New
Jersey suggests that precipitation chances will not go away this
weekend. Several vorticity maxima will be moving along the front and
will likely generate periods of showers in the central Mid-Atlantic,
which may affect our southern CWA from time to time Saturday through
Monday.

Early next week, the central U.S. trough will allow large-scale
ridging to develop in the eastern U.S., and this should permit the
stalled front to the south to begin its retreat northward. As usual,
suspect the models are too aggressive in doing this, so I have
slowed the return of higher PoPs northward slightly Monday and
Monday night. However, by late Monday night and Tuesday, models are
fairly consistent in showing increasing precipitation chances in a
regime of warm advection and increasing elevated instability (north
of the front) followed by entry into the warm sector Tuesday and
Tuesday night. Maintained chance PoPs across the CWA by this time
frame, and included thunder chances beginning Tuesday. Model QPF is
generally quite decent across the area, with widespread 0.5-1.5 inch
totals. Locally higher totals should be expected if stronger
convection can develop in this regime. As can be expected,
temperature forecasts are very low-confidence during this period.

The strong central U.S. trough approaches the eastern U.S. mid to
late week, with an attendant cold front bringing another chance of
convection. Given uncertainty with timing by this point in the
forecast, maintained chance PoPs through the end of the forecast.
Temperatures should be at least slightly above seasonal averages
before frontal passage.

&&

.AVIATION /08Z THURSDAY THROUGH MONDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Today...Conditions vary from MVFR to VFR early this morning as an
area of stratus has slowly been overspreading the region from east
to west overnight. Light winds this morning will pick up out of the
east southeast around 14-16Z at 5 to 10 knots through this
afternoon. Winds will turn slightly more to the south southeast
through the day.

Tonight...Mainly VFR conditions are expected but some lowering
of the ceilings to MVFR at KRDG/KABE possible after midnight.
Winds will decrease after sunset and become light and variable
overnight.

OUTLOOK...
Friday...CIGs may linger/develop near MVFR levels during the day,
but VFR conditions are more likely. Southeast winds becoming
southwest 5 to 15 kts (stronger near the coast). Moderate confidence.

Friday night and Saturday morning...A slight chance of storms with
some potential for locally sub-VFR conditions near any precipitation
and near a cold front that will be moving through the region during
this time. Southwest winds switching to north/northwest after
frontal passage, generally 5 to 15 kts. Moderate confidence.

Saturday afternoon through Monday...Periods of showers possible
generally south of PHL with potential for sub-VFR conditions at
times. Low clouds may also develop to the north, especially Sunday
night and Monday. However, VFR conditions may be the primary
condition at the TAF sites through this period. Winds generally
north to northeast 5 to 10 kts (somewhat stronger on Monday,
especially near the coast). Fairly low confidence during this
period.

&&

.MARINE...
Small Craft Advisories are in effect for the ocean waters of New
Jersey and Delaware.

East northeast winds around 10 to 15 knots today with gusts around
20 knots across the area waters. Winds will turn more to the
southeast later today.

Seas on the ocean are around 5 feet this morning and will linger
around 5 feet throughout the day. Seas will start to decrease from
north to south this afternoon through evening.

Tonight, conditions should remain below Small Craft Advisory
criteria. Seas may linger near 5 feet, especially on the eastern
edges of the ocean zones, but are expected to remain below advisory
criteria tonight.

Outlook...

Friday:  Sub-advisory winds/seas expected, though south winds will
be increasing to near advisory criteria by late in the day.

Friday night and Saturday: Marginal advisory conditions possible,
especially off the New Jersey coast, as winds become northwesterly
after frontal passage. Seas may approach 5 feet as well. A slight
chance of showers/storms.

Saturday night through Sunday night: Sub-advisory winds/seas
expected, with a chance of occasional showers off the Delaware and
southern NJ coast.

Monday: Onshore winds increase with seas likely rising above
advisory levels. A chance of showers.

Rip Currents...

There is a moderate risk for the development of dangerous and life
threatening rip currents at NJ and DE beaches today, due to a
continued easterly flow with a medium-period easterly or
southeasterly swell.

&&

.TIDES/COASTAL FLOODING...
During this past evening's high tide, levels along the tidal
Delaware River reached flood stage (but not to advisory levels).
The current forecast suggests this may occur again with
tonight's high tide, but only spotty minor flooding is
considered possible at this time. Advisory conditions are
unlikely.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...Small Craft Advisory until 1 PM EDT this afternoon for
     ANZ450>452.
     Small Craft Advisory until 6 PM EDT this evening for ANZ453.
     Small Craft Advisory until 6 PM EDT this evening for ANZ454-
     455.

&&

$$
Synopsis...CMS
Near Term...Meola
Short Term...Meola
Long Term...CMS
Aviation...CMS/Meola
Marine...CMS/Meola
Tides/Coastal Flooding...CMS

FXUS61 KPHI 200811
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
411 AM EDT Thu Sep 20 2018

.SYNOPSIS...
High pressure will continue building in from the north through
Thursday before pushing off the New England coast through early
Friday. A cold front will approach from the north and west on
Friday before passing through the area Friday night and Saturday
morning. The front will then stall just south of our area
through the end of the weekend as high pressure builds to our
north. The high begins pushing offshore through the beginning of
next week.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
An area of light rain has developed overnight in northern New Jersey
in the vicinity of a decaying boundary.  Hi-res models take these
showers and gradually move them westward through this morning. Have
included a mention of isolated to scattered showers through the
morning, mainly for areas north and west of the I-95 corridor.

Moisture trapped below the inversion has allowed for a good deal of
clouds to remain across the region overnight. The cloudy start to
the day should gradually improve as high pressure starts to builds
into our area with drier air. We should start seeing the cloud bases
lift, with some sunshine breaking through towards late morning or
early afternoon. As the light winds start to pick up by mid-morning
across the region, we should see some mixing take place and drying
out will occur.

Temperatures will feel more comfortable with highs only reaching
into the lower 70s across the region. The southern Poconos and parts
of northwest New Jersey will struggle to reach 70 today, keeping
highs in the mid to upper 60s.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM FRIDAY/...
High pressure starts to move off to the north and east, moving
offshore of Newfoundland toward Friday morning. Some moistening in
the low/mid levels may allow for some light showers to develop in
the return flow around the back edge of the departing high later
tonight. Keep any mention of rain north and west of the I-78
corridor.

Otherwise, most areas will remain dry overnight. Lows will drop into
the upper 50s to low/mid 60s across the forecast area overnight.

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
Main challenge in the long-term period is the cold frontal passage
Friday night and Saturday and what happens to the front thereafter.

The 00Z operational model suite indicates a fairly strong shortwave
trough moving from the Great Lakes and adjacent southeast Canada on
Friday into the Canadian Maritimes on Saturday, with broadly zonal
flow in much of the northern U.S. for the weekend. A higher-
amplitude trough will begin to dig into the central U.S. late this
weekend, allowing for downstream ridging in the Great Lakes and Ohio
Valley by Monday moving into the Northeast on Tuesday. The large-
scale trough then progresses into the eastern U.S. by mid to late
week. Overall, model agreement is above average in the synoptic
scale, though there are noticeable differences regarding the
strength of the central U.S. troughing early next week, which leads
to some uncertainty with the ridging downstream and its effects on
surface boundaries in the eastern U.S. that will have rather large
implications on our sensible weather.

On Friday, the shortwave trough moving into/through the Great Lakes
region will have an attendant (rather strong) surface cyclone moving
through Ontario/Quebec during the day. A cold front will extend
south-southwestward into the Ohio Valley and should readily develop
a squall line given the strong large-scale and frontal lift.
However, the front will remain well west of the area Friday evening,
and convection will likely wane before reaching much of the area
(except perhaps the far northern/western CWA). Instability should be
quite low by this point, but the wind field aloft is strong, so even
the weakening squall line may produce sporadic strong wind gusts
until the line completely collapses overnight. For this reason,
cannot rule out some impacts in our region, but suspect the vast
majority of severe weather will be well north/west of the area.

Hi-res guidance does not maintain much precipitation associated with
the front in our area, so I generally lowered PoPs Friday and Friday
night across the area. Notably, a predecessor vort max will be
moving through New York/New England Friday morning, and this may
spawn a few showers as far south as the Poconos, so kept some low
PoPs to account for this during the day. Statistical guidance was
noticeably lower with max temperatures on Friday, about 4-8 degrees
lower than values suggested 24 hours ago. Followed suit, given
potential for some residual cool near-surface air to refuse to be
scoured, especially if flow maintains a modest onshore component.

The front moves through the area Friday night and Saturday, but in
the same old story we have had for months, gets hung up south of the
area from the strong ridging in the Southeast and adjacent western
Atlantic. Operational models are not producing much precipitation in
the southern CWA on Saturday, so kept fairly low PoPs during the day
(with the northern CWA most likely to be dry). Some cloudiness may
remain near/north of the front as another vort max approaches the
area during the day (aiding in large-scale midlevel lift), and steep
boundary-layer lapse rates may produce stubborn low clouds. Should
this occur, maximum temperatures (currently similar to Friday's) may
be too high.

As surface flow acquires a more onshore component on Sunday (a
result of the surface high to the north of the front progressing
eastward), low clouds may develop on Sunday (though cold/dry
advection may impede this process, as suggested by GFS model
soundings). Combination of cold advection and cloud cover will
result in a cooler day across the area, with highs generally near or
below 70 (and possibly not above 60 in the Poconos).

Meanwhile, the proximity of the front to Delmarva and southern New
Jersey suggests that precipitation chances will not go away this
weekend. Several vorticity maxima will be moving along the front and
will likely generate periods of showers in the central Mid-Atlantic,
which may affect our southern CWA from time to time Saturday through
Monday.

Early next week, the central U.S. trough will allow large-scale
ridging to develop in the eastern U.S., and this should permit the
stalled front to the south to begin its retreat northward. As usual,
suspect the models are too aggressive in doing this, so I have
slowed the return of higher PoPs northward slightly Monday and
Monday night. However, by late Monday night and Tuesday, models are
fairly consistent in showing increasing precipitation chances in a
regime of warm advection and increasing elevated instability (north
of the front) followed by entry into the warm sector Tuesday and
Tuesday night. Maintained chance PoPs across the CWA by this time
frame, and included thunder chances beginning Tuesday. Model QPF is
generally quite decent across the area, with widespread 0.5-1.5 inch
totals. Locally higher totals should be expected if stronger
convection can develop in this regime. As can be expected,
temperature forecasts are very low-confidence during this period.

The strong central U.S. trough approaches the eastern U.S. mid to
late week, with an attendant cold front bringing another chance of
convection. Given uncertainty with timing by this point in the
forecast, maintained chance PoPs through the end of the forecast.
Temperatures should be at least slightly above seasonal averages
before frontal passage.

&&

.AVIATION /08Z THURSDAY THROUGH MONDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Today...Conditions vary from MVFR to VFR early this morning as an
area of stratus has slowly been overspreading the region from east
to west overnight. Light winds this morning will pick up out of the
east southeast around 14-16Z at 5 to 10 knots through this
afternoon. Winds will turn slightly more to the south southeast
through the day.

Tonight...Mainly VFR conditions are expected but some lowering
of the ceilings to MVFR at KRDG/KABE possible after midnight.
Winds will decrease after sunset and become light and variable
overnight.

OUTLOOK...
Friday...CIGs may linger/develop near MVFR levels during the day,
but VFR conditions are more likely. Southeast winds becoming
southwest 5 to 15 kts (stronger near the coast). Moderate confidence.

Friday night and Saturday morning...A slight chance of storms with
some potential for locally sub-VFR conditions near any precipitation
and near a cold front that will be moving through the region during
this time. Southwest winds switching to north/northwest after
frontal passage, generally 5 to 15 kts. Moderate confidence.

Saturday afternoon through Monday...Periods of showers possible
generally south of PHL with potential for sub-VFR conditions at
times. Low clouds may also develop to the north, especially Sunday
night and Monday. However, VFR conditions may be the primary
condition at the TAF sites through this period. Winds generally
north to northeast 5 to 10 kts (somewhat stronger on Monday,
especially near the coast). Fairly low confidence during this
period.

&&

.MARINE...
Small Craft Advisories are in effect for the ocean waters of New
Jersey and Delaware.

East northeast winds around 10 to 15 knots today with gusts around
20 knots across the area waters. Winds will turn more to the
southeast later today.

Seas on the ocean are around 5 feet this morning and will linger
around 5 feet throughout the day. Seas will start to decrease from
north to south this afternoon through evening.

Tonight, conditions should remain below Small Craft Advisory
criteria. Seas may linger near 5 feet, especially on the eastern
edges of the ocean zones, but are expected to remain below advisory
criteria tonight.

Outlook...

Friday:  Sub-advisory winds/seas expected, though south winds will
be increasing to near advisory criteria by late in the day.

Friday night and Saturday: Marginal advisory conditions possible,
especially off the New Jersey coast, as winds become northwesterly
after frontal passage. Seas may approach 5 feet as well. A slight
chance of showers/storms.

Saturday night through Sunday night: Sub-advisory winds/seas
expected, with a chance of occasional showers off the Delaware and
southern NJ coast.

Monday: Onshore winds increase with seas likely rising above
advisory levels. A chance of showers.

Rip Currents...

There is a moderate risk for the development of dangerous and life
threatening rip currents at NJ and DE beaches today, due to a
continued easterly flow with a medium-period easterly or
southeasterly swell.

&&

.TIDES/COASTAL FLOODING...
During this past evening's high tide, levels along the tidal
Delaware River reached flood stage (but not to advisory levels).
The current forecast suggests this may occur again with
tonight's high tide, but only spotty minor flooding is
considered possible at this time. Advisory conditions are
unlikely.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...Small Craft Advisory until 1 PM EDT this afternoon for
     ANZ450>452.
     Small Craft Advisory until 6 PM EDT this evening for ANZ453.
     Small Craft Advisory until 6 PM EDT this evening for ANZ454-
     455.

&&

$$
Synopsis...CMS
Near Term...Meola
Short Term...Meola
Long Term...CMS
Aviation...CMS/Meola
Marine...CMS/Meola
Tides/Coastal Flooding...CMS