Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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836
FXUS61 KPHI 252211
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
611 PM EDT Wed Apr 25 2018

.SYNOPSIS...
An area of low pressure will move across our area this evening,
then move toward New England tonight as it combines with
another low pressure. Very weak high pressure tries to build
into the region late Thursday, before another low pressure moves
northward across the Mid Atlantic region Friday. This low will
combine with another low as it moves across New England Saturday
before moving into eastern Canada. A cold front is expected
Saturday, with additional surface troughs Sunday into Monday.
High pressure across the Great Lakes and Ohio Valley Sunday will
build to our south Monday, and remain to our south through
Wednesday.
&&

.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
6 PM Update...Based on current web cams and satellite, we have
extended the dense fog advisory along coastal NJ until midnight
after which time conditions should improve as a cold front moves
through. Otherwise, just some mostly minor adjustments to POP,
T/Td, and sky grids based on current conditions and trends.

Previous Discussion...Low pressure is currently located over
Delmarva and will continue to move to the north and east through
our area tonight. The associated upper trough will rotate
through the area through the overnight hours. A good amount of
energy associated with the upper trough will allow for the
continuation of showers late tonight with majority of the rain
ending between midnight and 2 AM. Even though the system will
move off to the north of the area overnight, low clouds and fog
will be slower to clear as plenty are likely to remain through
the early morning hours, especially across the northern parts of
our area.

Precipitation is spotty this afternoon. Some isolated heavier
showers, with embedded thunderstorms, remain possible across
southern Delaware and into southern New Jersey as the sun has
broken out across those areas this afternoon. We should lose the
convective potential as we continue to head towards sunset.
Some light rain was moving northward across northern New Jersey
with just some spotty showers or drizzle remaining. Areas to the
north and west of Philadelphia continue to see areas of fog
with varying visibilities.

We have taken down the Dense Fog Advisory for the Delaware
coast as the web cams show that things have cleared up nicely
there this afternoon. Dense Fog Advisory remains in place along
the New Jersey coast through 7PM. Areas along the New Jersey
coast show considerable fog this afternoon on area web cams.

Overnight lows will be mild and in the 40s to around 50 across
the region.

&&

.SHORT TERM /6 AM THURSDAY MORNING THROUGH 6 PM THURSDAY/...
Thursday brings a brief return to high pressure and fair
weather across our area.

The day may start off a little cloudy, especially across
northern areas, but we should see plenty of sunshine through the
day. Winds will be out of the west to northwest around 10 to 15
mph.

Temperatures are expected to rise into the mid to upper 60s
across the majority of the area with upper 50s across the higher
terrain of the Poconos and lower 70s across southern New Jersey
and southern Delaware.

&&

.LONG TERM /THURSDAY NIGHT THROUGH WEDNESDAY/...
After a brief period of possible unsettled weather at the
beginning of the period, dry weather takes hold of the forecast
for the rest of the long term forecast.

On Thursday night, an area of low pressure will be approaching
the area from the southwest, before moving across the area
during the day Friday. There remains some timing and locations
differences with the low between the guidance, however, there is
better agreement than there was yesterday. They all indicate an
increase in moisture while several short wave/vorticity
impulses slide across the area as well, especially during the
day Friday, which has the best chance of rainfall.

Once this low lifts to our northeast, it will combine with
another low pressure that will be moving out of the Great Lakes
region and across eastern Canada and northern New England. This
will pull a cold front across the area during the day Saturday.
Low-mid level lapse rates increase ahead of the front while
there will be an increase in low-mid level moisture. This could
bring another chance of showers during the day as the front
moves across the area. Not much in the way of instability is
forecast, so we are not including thunderstorms at this time.

Behind this front, drier conditions return to the forecast.

The low pressure across eastern Canada will stay near the
Canadian Maritimes through Monday, while high pressure across
the Great Lakes and Ohio Valley Sunday will build to our south
Monday. A couple of surface troughs will cross the area during
this time period, but are expected to remain dry. For Sunday and
Monday, there will be a pressure gradient in place between the
high to the south and low to the north, so a steady breeze with
gusts likely in the 20s is expected, with Sunday having the
strongest winds.

The high will remain to our south Tuesday into Wednesday,
keeping dry conditions in the forecast. Winds will remain out of
the west, and although a steady breeze is expected and slightly
gusty at times, winds are not forecast to be as gusty as Sunday
or Monday.

&&

.AVIATION /22Z WEDNESDAY THROUGH MONDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Tonight...Mainly IFR conditions in low clouds and fog across
the terminals. Periods of MVFR and/or VFR are possible through
this afternoon but are not expected to last very long.
Conditions are expected to deteriorate once again this evening
as winds start to go light. Scattered showers may briefly lower
conditions but primary concern is low clouds and fog through
tonight. Ceilings will lift between 06-09Z and start to become
VFR. An isolated thunderstorm is possible this
afternoon/evening, mainly towards KACY, but confidence is too
low to include in the current TAF. Easterly winds tonight will
lighten before turning to the northwest overnight.

Thursday...Mainly VFR conditions expected. Some lingering MVFR,
a little IFR possible, early in the day but clearing should be
quick as west to northwest winds pick up around 10-14Z. Winds
will be around 10 to 12 knots with a few higher gusts through
the afternoon.


OUTLOOK...

Thursday night...Generally VFR, although MVFR conditions may
begin late in the night across the southern areas as rain
approaches.

Friday...MVFR, possible IFR, with a chance of scattered
showers.

Friday night...MVFR conditions possible early with scattered
showers, becoming VFR during the evening and overnight.

Saturday...Mostly VFR. A chance of showers which may
temporarily lower conditions.

Saturday night-Monday...VFR. Gusty west to northwest winds
20-25 knots Sunday and Monday.
&&


.MARINE...

6 PM Update...Dense fog advisory has been extended until
midnight based on beach cams and satellite imagery.

Previous Discussion...Dense fog on the waters is slowly eroding
from south to north. However, beach cams continue to show fog
up and down the coastline, although there are some breaks
occurring at this time. Therefore, we will leave the Dense Fog
Advisory in place. The Dense Fog Advisory runs through 7pm.

Otherwise, the Delaware Bay looks fairly quiet through
Thursday. Winds may near 25 knots Thursday morning but are
currently forecast to remain below SCa criteria.

The SCA on the ocean will remain in place, mainly for seas,
through Thursday. Winds may gust to around 25 knots early on
Thursday.

OUTLOOK...

Thursday night...Small Craft Advisory continues due to elevated
seas.

Friday-Friday night...Elevated seas may linger into Friday and
Friday night.

Saturday night...Conditions expected to remain below advisory
levels.

Sunday-Monday...Winds may approach Small Craft Advisory levels
on Sunday.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...Dense Fog Advisory until midnight EDT tonight for NJZ014-
     024>026.
DE...None.
MD...None.
MARINE...Dense Fog Advisory until midnight EDT tonight for ANZ450>455.
     Small Craft Advisory until 6 AM EDT Friday for ANZ450>455.

&&

$$
Synopsis...Robertson
Near Term...Fitzsimmons/Meola
Short Term...Meola
Long Term...Robertson
Aviation...Robertson/Meola
Marine...Robertson/Meola/Fitzsimmons



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