Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 270504
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
104 AM EDT Tue Oct 27 2020

.SYNOPSIS...
A cold front will pass through our region late tonight. Weak high
pressure builds in through mid week. Broad low pressure, including
the remnants of Tropical Cyclone Zeta, is anticipated to cross off
the Middle Atlantic coast on Thursday night. High pressure is
expected to build over the region Friday and Saturday. Another cold
front may approach from the northwest late Sunday.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
Patchy dense fog developed across portions of southeast
Pennsylvania, northern Delaware, and portions of New Jersey.
Since dense fog is not widespread, and is occasionally lifting,
will not issue a Dense Fog Advisory at this time, but will opt
for a Special Weather Statement. Some low clouds are spreading
into the region, and that should cut back on fog with VSBY less
than 1 mile.

Cloud cover will remain pretty thick through the night which
should keep the temperatures on the mild side. Overnight lows
will only drop slightly down into the 50s with some 40s across
the higher elevations of northwestern New Jersey and the
southern Poconos.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM WEDNESDAY/...
High pressure will build in from the west on Tuesday and that
should keep us dry through the day. With more of a north to
northwest flow across the area, temperatures will be slightly
cooler than they were today, remaining the upper 50s to lower
60s. It will be more noticeable though as the dew points drop
down into the 40s/low 50s as opposed to the mid 50s to 60s they
have been of late.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
Overview: Will be keeping a close eye on the Thursday and Friday
time period as the combination of the remnants of Zeta and a cold
front could bring heavy rain to our region (and possibly some snow
to the higher terrain in NW NJ and E Central PA). Outside of that,
the long term looks relatively quiet.

Details:

Tuesday night through Wednesday night: A weak low level short wave
trough could spark some very light showers Tuesday night into
Wednesday morning. However, the trough will be very progressive, so
do not expect a long period or widespread opportunity for
precipitation.

Thursday and Friday: The remnants of Zeta and the secondary low
pressure system are not expected to cross our region until Thursday
night into Friday. However, a slow moving E-W oriented front (likely
staying just south of our area or getting as far north as Delmarva/S
Jersey) and isentropic lift along and north of it, will allow rain
to begin in our area early in the day on Thursday. The prime window
for precipitation looks to be Thursday afternoon through early
Friday morning. As for the hazards:

Heavy rain: Precipitable water values should be well above normal
(1.5 inches or higher) and if the front gets into our region, areas
south of the front should have a deep warm cloud layer, this will
raise the risk for heavy rain. However, there is uncertainty as to
where the axis of heaviest rain will be, and it could be falling
over a long enough period to limit the flash flood threat. None the
less, think there is enough of a risk to include a mention in the
HWO with this issuance.

Snow/mixed precip: If the cold front arrives early enough and if
cold air filters in fast enough behind it on Thursday night,
precipitation could switch to snow in the higher terrain of the
southern Poconos and NW NJ. At this point it is too early to
forecast any other details (including amounts). However, it appears
at this point that it should be a low impact event, if it occurs, as
lows Thursday night are expected to barely expected to drop to
freezing and earlier rain and warm ground should limit accumulation
potential.

Saturday through Monday: High pressure should be the dominant
feature through much of the weekend, resulting in tranquil, but cool
conditions on Saturday. By Sunday, southwesterly winds could kick
start a brief warming trend. Another cold front could approach the
region late Sunday or Monday, but there is still considerable
uncertainty in the timing of this front, and it is unclear if we
will have enough moisture advection in between the two fronts to see
significant precipitation with this second front.

&&

.AVIATION /05Z TUESDAY THROUGH SATURDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.

Tonight...Mainly IFR/LIFR conditions are expected through the
night as low clouds and fog prevail at the terminals. Winds
remain light and variable through the overnight. Slight
improvement with periods of MVFR entirely possible after 09Z as
drier air does work its way southward, but confidence remains
low. Generally moderate confidence with lower confidence on
timing of category changes.

Tuesday...Mainly VFR conditions expected though a few lingering MVFR
ceilings are possible through 15Z. North to northwest winds less
than 10 knots. Moderate confidence.

Outlook...

Tuesday night and Wednesday...Mainly VFR. Northwest wind up to 10
knots, becoming southwest late Wednesday. Moderate confidence.

Thursday and Thursday night...MVFR/IFR conditions in rain. The rain
may be heavy at times resulting in visibility restrictions. Winds
could start light and variable, but should settle out of the
northeast by Thursday evening at 10 to 20 kt with gusts up to 25 kt
possible, primarily at KACY. Moderate confidence on the overall
pattern, but low confidence on the details.

Friday...Conditions should gradually improve to VFR by late in the
day. Northerly winds 10 to 20 knots with gusts to 25 kt. Moderate
confidence on the overall pattern, but low confidence on the details.

Saturday...Mostly VFR conditions expected. Northerly winds becoming
northeasterly at 5 to 10 kt. Moderate confidence.

&&

.MARINE...
Seas continue to subside to less than 5 feet, so will allow
Small Craft Advisory to expire at 1 am.

Sub-Small Craft Advisory conditions are expected to continue on
the Delaware Bay through Tuesday.

Outlook...

Tuesday night through Thursday...Winds and seas should stay below
SCA criteria through this time.

Thursday night and Friday...Winds and seas are expected to build as
a low approaches the region. Gale force gusts are possible
especially during the day on Friday.

Saturday...Winds and seas will gradually decrease, but we will
likely have SCA conditions continuing at least on the ocean waters
for most, if not all of Saturday.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...None.

&&

$$
Synopsis...Johnson
Near Term...Davis/Meola/MPS
Short Term...Meola
Long Term...Johnson
Aviation...Davis/Johnson/Meola
Marine...Davis/Johnson/Meola/MPS



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