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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KPHI 282332
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
732 PM EDT Wed Oct 28 2020

.SYNOPSIS...
The remnants of Hurricane Zeta will move through the Mid-Atlantic
Thursday into Friday. High pressure will build across the region on
Saturday, exiting to the northeast Saturday night. A cold front will
move through our area on Sunday night. High pressure will build
across the southeastern states, influencing our weather through the
middle of the new week.

&&

.NEAR TERM /THROUGH THURSDAY/...
The remnants of Zeta will be approaching our region through the day
tomorrow, and the center should be off shore by late tomorrow. As we
have been mentioning for the past several days, there are several
risk factors for heavy rain, including a deep warm cloud layer and
high precipitable water values. In a change from previous days, the
forecast axis of heaviest precip has shifted south, now mostly south
of the PA turnpike and I-195 corridor. More information on the
hydrology concerns are discussed in the hydro section below.

With the remnants of Zeta quickly approaching during the day, winds
will increase quickly during the second half of the day. However, at
this point, it still looks like winds should stay below wind
advisory criteria.

Thanks to the persistent cloud cover, we won`t see a big swing in
temperatures from tonight into tomorrow. Lows will likely be within
10 degrees of the highs.

&&

.SHORT TERM /THURSDAY NIGHT/...
Rain will continue, even with the remnants of Zeta already offshore,
as a low and mid level short wave trough will be digging in quickly
behind it. However, by tomorrow night, our moisture advection will
be limited. Thus, expect the intensity of the rain to decrease
starting as early as tomorrow evening.

We will start to see some significant cold air advection through the
night. Consequently, some snow could mix with the rain in the higher
terrain of the Poconos and NW NJ. Still think there will be little
if any accumulation thanks to relatively warm ground and rain ahead
of the snow.

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
The remnants of Zeta and the trailing secondary low pressure should
be offshore by Friday morning, continuing to pull away to the east.
Some rain will still be around the region but should be on the
lighter side and will start to exit the region from west to east,
finally ending most locations by Friday afternoon. Skies will remain
cloudy through much of the day with some clearing possible as we
head towards the evening.

High pressure will slide across the Great Lakes region and into the
Mid-Atlantic Friday night. Skies really clear as the flow turns more
to the north-northwest. With clear skies in place, we radiate
efficiently and temperatures should drop well into the 20s north and
west of the I-95 corridor. Along the I-95 corridor and points to the
south and east, temperatures will fall into the lower to mid 30s.
The exception is along the immediate coast of New Jersey and
Delaware where temperatures are more likely to stay in the mid/upper
30s. Additionally, winds should drop off and become light through
the overnight period. This will allow for frost to develop and with
the temperatures dropping down near freezing, we will likely need
some form of frost/freeze headlines for late Friday night/early
Saturday morning.

The high will cross over our area on Saturday, quickly pushing off
to the northeast as another low pressure system moves through
Ontario and, with its cold front, makes its way eastward. Being
between the departing high and the approaching cold front, we should
have a very nice fall day in place with highs in the 40s to low 50s.
Skies should be mostly clear through the day but we will start to
see them creep back in from the east as the return flow brings some
moisture back into our area Saturday night. A few light showers may
occur, mainly along the coast late Saturday night but not confident
enough to include in the forecast at this time. Overnight lows will
warmer than the night before and mostly in the 30s to lower 40s.

Low pressure will cross through Ontario and into Quebec on Sunday.
Its attendant cold front will move through central Pennsylvania on
Sunday, crossing through our forecast area Sunday evening. We should
see some warming ahead of the front in the southwest flow and
daytime highs will be into the 50s to lower 60s. The front will also
bring a round of rain to the region and some fairly gusty winds as
the gradient tightens up. The rain should taper off late Sunday
night as the front exits offshore. A deep upper trough will also
cross the region Sunday night and this will help to usher in some
much colder air aloft. The timing of when the cold air arrives and
the final showers exit the region will be important as it means we
could see some mixed ptypes, especially across the southern Poconos
and far northwestern New Jersey. For now, models show the precip
exiting well before the cold air arrives so we leave out the mention
of any mixed precipitation at this time. Behind the front, in the
northwest flow, we should dry out and see skies clear once again.
Another strong radiational cooling night is likely to take place and
overnight lows will drop down into the 30s, with some upper 20s
across the higher terrain of the southern Poconos.

High pressure will move from the central plains to the southeastern
states Monday through Tuesday, moving off the Atlantic coast on
Wednesday. The deep upper trough cross the area on Monday and exits
to our east Monday evening. We should be dry through the first half
of the week with mostly clear skies. Temperatures will start off
cool on Monday as the trough crosses the region, generally in the
40s, but as the high starts to take hold of our weather the airmass
will modify and temperatures should be able to warm into the upper
40s/ lower 50s on Tuesday and then upper 50s to lower 60s by
Wednesday.

&&

.AVIATION /00Z THURSDAY THROUGH MONDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.

Through 06Z...Ceilings will likely be waffling between MVFR and VFR
for much of this period, though a few sites may have transient IFR
conditions through this time. Mostly light southwesterly winds.
Moderate confidence.

Late tonight...Ceilings should lower quickly back to IFR or even
LIFR. Winds will become light and variable, with the direction
beginning to flip to northeasterly. Moderate confidence on the
pattern, but low confidence on the timing details.

Thursday...IFR conditions expected for most, if not all day.
Ceiling should be the primary controlling factor, but visibility
restrictions are possible too, especially in bands of heavy rain. If
there is a long enough lull, there may be brief windows of
improvement to MVFR, but this is unlikely. Northeasterly winds of 10
to 15 kt with gusts up to 20kt. Moderate confidence.

Outlook...

Thursday night...IFR or even LIFR ceilings are expected for much of
the night. Northeasterly winds of 10 to 20 kt with gusts up to 30
kt, with the strongest winds at KACY. Non-convective low level wind
shear is possible. Moderate confidence on pattern, but low
confidence on timing of category changes.

Friday...MVFR/IFR conditions possible through the morning with
improvement to VFR expected by the afternoon. Northwest winds around
10 to 20 knots with gusts up 30 knots possible. Higher gusts
possible, especially at KACY. Moderate confidence.

Saturday...VFR conditions expected. Northeast winds in the morning
will veer to the east and then southeast by Saturday night with
speeds less than 10 knots. Moderate confidence.

Sunday...Mainly VFR conditions but periods of MVFR are possible in
rain, mainly in the afternoon/evening as a cold front crosses the
terminals. Southwesterly winds 5 to 15 knots. Moderate confidence.

Monday...VFR conditions expected. Northwest winds 15 to 20 knots
with gusts up to 30 knots possible. High confidence.

&&

.MARINE...
Marine impacts likely from the remnants of Zeta late Thursday
through Friday.

For tonight, sub-advisory conditions are expected with an offshore
wind around 5-10 kts and seas 1-3 feet. Winds and seas will begin to
increase throughout the day Thursday. The strongest winds will be
across the southern ocean waters by late Thursday afternoon and into
the evening as the remnant low passes offshore along with heavy
rain. Wind gusts of 35-40+ kts are expected mainly south of Atlantic
City during this period. Seas in these areas will build up to 8
feet. The Gale Watch has been upgraded to a Gale Warning starting
late Thursday afternoon. Additionally, a Gale Watch has been issued
for the lower Delaware Bay as the aforementioned gale conditions
could impact this area, but confidence is still too low for a
warning at this time. A Small Craft Advisory has been issued for the
upper Delaware Bay.

Outlook...

Thursday night through Friday...Northerly winds will continue to
build after the remnant low of Zeta pulls away from the coast
Thursday night with winds of gale force expected through at least
the first half of Friday across the ocean waters. Seas will build to
6-9 feet with winds gusting up to 40 kts by around daybreak Friday
across the ocean waters. Small craft advisory conditions are
expected to persist across Delaware Bay during this time as well.

Friday night through Saturday...Winds and seas will continue to
decrease to below advisory criteria by the overnight period Friday
night. Saturday will also be below advisory criteria with easterly
winds 5-10 kts and seas 2-4 feet.

Sunday through Monday...Winds and seas will increase throughout the
day Sunday to advisory criteria. Expect offshore winds gusting 25-35
kts into the overnight period Sunday night with seas of 3-5 feet.
Gale force wind gusts of 35-40 kts are possible, especially into
Monday.

&&

.HYDROLOGY...
The remnants of Zeta will be moving through our region, bringing a
few waves of heavy rain from Thursday morning through Thursday
evening. At this point, we expect the heavy rain to be confined to
the period from tomorrow morning through early tomorrow evening.
However, light rain could linger Thursday night into Friday morning.

Confidence is increasing that the axis of heaviest rain will be
south of the PA Turnpike and Interstate 195 corridor, where a flood
watch has been issued. Storm total rain of 2 to 4 inches is possible
across the watch area. Elsewhere, storm total rain amounts of 1 to 3
inches is possible.

Within the watch area, overland and road flooding as well as small
stream flooding are possible. However, at this point, we are not
expecting any flooding on main stem rivers.

&&

.TIDES/COASTAL FLOODING...
The combination of the remnants of Hurricane Zeta and a full
moon Friday will lead to the potential for minor coastal
flooding across portions of New Jersey, Delaware, and
potentially the northern Chesapeake Bay. Astronomical tides will
already be running high for the blue moon before accounting for
surge from what will be a deepening low pressure system off our
coastline. This will lead to easterly flow for the NJ coastline
during the day on Thursday followed but strong northeasterly
flow overnight on Thursday.

This will push water into the back bays and will likely cause
some minor tidal flooding especially across coastal NJ. Using
guidance from the Stevens Institute there are hints that the
tide gages could reach moderate flood stage however I`ve opted
to keep the forecast currently minor. Per NHC, typically in
these type storms the ETSS guidance typically under performs on
the tidal surge so I`ve gone with a blend of the median of the
Stevens ensemble guidance and a bias corrected ETSS/ESTOFS blend
which worked out quite well running slightly higher than the
raw ETSS guidance.

Currently tidal flooding is not expected on the tidal Delaware
river.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Flood Watch from 6 AM EDT Thursday through Thursday evening
     for PAZ070-071-101>104.
NJ...Flood Watch from 6 AM EDT Thursday through Thursday evening
     for NJZ016>027.
DE...Flood Watch from 6 AM EDT Thursday through Thursday evening
     for DEZ001>004.
MD...Flood Watch from 6 AM EDT Thursday through Thursday evening
     for MDZ008-012-015-019-020.
MARINE...Gale Warning from 6 PM Thursday to 2 PM EDT Friday for
     ANZ450>455.
     Small Craft Advisory from 6 PM Thursday to 2 PM EDT Friday for
     ANZ430.
     Gale Watch from Thursday evening through Friday afternoon for
     ANZ431.

&&

$$
Synopsis...Meola
Near Term...Johnson
Short Term...Johnson
Long Term...Meola
Aviation...Johnson/Meola
Marine...Staarmann
Hydrology...WFO PHI
Tides/Coastal Flooding...Deal