Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000
FXUS61 KPHI 210226
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
926 PM EST Mon Nov 20 2017

.SYNOPSIS...
High pressure centered to our south will shift offshore during
tonight. A cold front approaches from the west Tuesday night as low
pressure passes south and east of our area Wednesday morning, then
the cold front shifts offshore late Wednesday. High pressure builds
in Thursday and Friday. A cold front moves through on Saturday, then
high pressure builds in from the west for the start of next week.

&&

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
For the 930 PM update, main adjustment was to the temperatures.
These vary across the region as some locales are cooling faster than
others, however the radiational cooling may not be as efficient as
it could be. A comparison of the 12z and 00z raobs from Sterling, VA
reveal a fair amount of warming aloft, especially in the 850 mb to
700 mb layer. The model guidance shows warm air advection continuing
through the overnight as the flow backs more to the southwest. This
may play a role in temperatures overnight despite the surface flow
being light. Dew points however should be slow to rise overnight and
this along with where the winds are calm and also no cirrus may
result in a better temperature drop near sunrise. In addition, a
short wave to the west along with warm air advection is tossing some
cirrus our way. This may actually thin some especially farther
north, however did indicate a bit higher cloud cover across our
southern zones for a time overnight (clear to partly cloudy).

&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH 6 PM TUESDAY/...
The area will be under the influence of weak shortwave ridging
aloft, with a cold front over the central Great Lakes and high
pressure well offshore, proving a southwest flow at the surface.
Expect some increase in mid and high level cloudiness during
the afternoon, mainly across Delmarva and south Jersey, as a
southern stream jet advects moisture northward. Otherwise,
mostly sunny. It will be brisk, with model soundings supporting
wind gusts up to 30 mph across the coastal plain, and 20 to 25
mph elsewhere. Temperature-wise, highs will be at least a couple
degrees above average as warm air advection continues.

&&

.LONG TERM /TUESDAY NIGHT THROUGH MONDAY/...
The extended period starts out Tuesday night a bit rainy and
above average in temperature, but the remainder of the period
tends toward seasonably cooler and mostly dry weather. The
larger scale pattern over the CONUS shows ridging aloft in the
East and more troughing in the East, with a couple of shortwave
trofs and associated frontal systems moving through the mid-
Atlantic region mid-week and again next weekend.

A cold front is forecast to approach from the west Tuesday evening
and cross the forecast area overnight. The fropa will trigger a few
showers N/W of PHL. A sfc low pressure is also forecast to develop
off the NC/SC coasts with moisture spreading north ahead of it along
the DE/NJ coastal areas. The highest PoPs are thus over south NJ and
Delmarva, counter to climo. Overnight temps should remain warm
enough so that all precip will be in liquid form. However a few
showers may linger past sunrise, and with cold advection behind
the front a few snow showers or flurries are possible in the
Poconos Wednesday morning.

The weather for Wed afternoon through Friday night should be
dominated by high pressure moving across the mid-Atlantic
region and a fairly dry airmass associated with it. Temperatures
will be a few degrees below normal on Thursday but should
return to near normal by Friday as the high shifts offshore and
a more swly flow develops. A cold front may push south in to NY
state and New England on Friday but probably will not affect our
area to the south,

Another fast-moving frontal system is forecast to push through our
area on Saturday. In part because of its fast movement it will
not be able to pick up much moisture. The current forecast has
chance PoPs, higher N/W of PHL, but even this may be overdone.
Again, temps on Saturday appear to be warm enough to avoid any
frozen precip. However, the airmass behind this front seems to
be colder than the one mid-week, with strong low level cold
advection beginning Saturday night and continuing through the
rest of the weekend. This pattern of NW flow will favor lake
effect snow with some streamers possibly reaching the Poconos
and vicinity.

&&

.AVIATION /03Z TUESDAY THROUGH SATURDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.

Tonight...VFR with some high clouds at times. Southwesterly winds
3-5 knots to locally light/variable or calm. High confidence.

Tuesday...VFR, with some high clouds especially in the afternoon.
Southwest winds increasing to 10-15 knots with gusts up to 25 knots
from late morning through mid-afternoon, especially from the PHL
area south and east. Moderate confidence.

Outlook...
Tuesday night and Wednesday...Mainly VFR. Rain possible south
and east of I-95 Tuesday night through Wednesday morning with
MVFR or lower conditions. SW winds 5-10 KT become NW Wednesday
afternoon and increase to 10-20 KT.

Wednesday night and Thursday...VFR. NW winds gradually diminishing.
A storm system is currently expected to remain offshore. Forecast
confidence: Medium to High.

Friday...VFR. NW winds 5-10 KT.

Saturday...VFR early...then MVFR or lower conditions possible in
rain showers later in the day. SW winds 10-15 KT.

&&

.MARINE...
SCA conditions prevailing across the NJ coastal waters through
Tuesday, with the combination of southwest winds and seas
meeting criteria.

Further south across the DE coastal waters, SCA conditions are
expected to return just before daybreak Tuesday morning and persist
through the day, with the combination of southwest winds and seas
meeting criteria.

The Delaware Bay waters are expected to remain below SCA criteria,
although the southern Bay will have to be watched for a possible
upgrade if winds strengthen a few more knots.

Outlook...
Tuesday night...SCA conditions should persist through Tuesday
evening but diminish overnight.

Wednesday...Lull in SCA conditions possible Wednesday morning.
Otherwise, winds shift to the NW and increase to 15-20 KT with 25-30
KT gusts.

Thursday through Friday...Sub-SCA conditions expected.

Saturday...SCA conditions are possible with a strong cold front
passage.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...Small Craft Advisory until 1 AM EST Wednesday for ANZ450>453.
     Small Craft Advisory from 5 AM to 7 PM EST Tuesday for ANZ454-
     455.

&&

$$
Synopsis...AMC
Near Term...Gorse
Short Term...Franck
Long Term...AMC
Aviation...AMC/Franck/Gorse
Marine...AMC/Franck


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