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-- Discussion containing changed information from previous version are highlighted. --
133
FXUS61 KPHI 132049
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
349 PM EST Fri Dec 13 2019

.SYNOPSIS...
Low pressure across the southeast states will strengthen while
moving across the Middle Atlantic region later tonight and Saturday.
The low will then move up across New England and into eastern Canada
through Sunday. High pressure will build over the area later Sunday
before moving away Monday. Another low and its associated fronts
will affect the area Monday afternoon through Tuesday. More high
pressure will follow for the middle and end of next week.

&&

.NEAR TERM /UNTIL 6 PM SATURDAY/...
Mother Nature is cooperating with a freaky Friday forecast for
your Friday the 13th. A strong area of low pressure continues to
develop to our south over the Carolinas this afternoon. This
low will continue to intensify and move towards the northeast
and into our region through the overnight hours, bringing a
whole slew of excitement as it does so. Strong WAA and PVA ahead
of the surface low will continue to promote surface
cyclogenesis and height falls ahead of the system as an
energetic and strongly negatively tilted mid-level trough lifts
out of the lower Mississippi River Valley and into the mid-
Atlantic. A strong 150-kt 300 mb jet streak developing directly
over the Delaware Valley will also provide forcing for ascent,
and there is and will be plenty of moisture available with
strong southerly flow off the Atlantic ahead of this system.


PWATs from 1-1.5 inches will begin to advect into the region, thus,
a widespread moderate to heavy rain event is in store for tonight.
Light to moderate rain is currently overspreading the region, and
will continue to fill in and increase in intensity through the
evening. At this point, the heaviest rainfall is likely to fall just
ahead of the surface low through 8 AM Saturday. The progressive
nature of this storm will be the one saving grace, as the current
track of the surface low takes it right across much of the Garden
State. As the low moves overhead, rainfall rates will likely taper
off a tad as we head into the later morning hours. Current hi-res
models are suggesting another line of heavier rainfall will develop
into the early afternoon. There is some CAPE associated with this
line, thus we cannot rule out a clap or two of thunder. After this,
we will begin to dry out, save for a few wrap around showers into
the evening and early overnight hours. This could mix with some
wintry precip for a brief time in the Poconos and Sussex County, NJ,
but no significant impacts are expected at this time.

Total rainfall accumulations are forecast to range from 1 to 1.5
inches across the region, with the potential for localized amounts
to near two inches. Given the already sodden ground across Central
and Northern NJ, this may lead to some flood concerns, which are
outlined in the hydro section below.

Otherwise, a warmer than average overnight tonight with lows in the
mid to upper 40s across much of the area and above average highs in
the mid to upper 50s Saturday.


&&

.SHORT TERM /6 PM SATURDAY THROUGH SUNDAY NIGHT/...

Quieter conditions Sunday and Sunday night as the low pulls off to
the northeast and high pressure continues to build into the region.
As low pressure lifts to our northeast, the pressure gradient behind
it will tighten quite significantly. Winds above the surface
increase as well and could mix down to the surface. This could
potentially lead to wind gusts of at least 25-35 mph, with
occasional higher gusts of near 40 mph late Saturday afternoon,
Saturday night into early Sunday. High temperatures will be cooler
in the low to mid 40s. Lows in the upper 30s Saturday night as
the low pulls out of the area.

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
Monday thru Tuesday night...

An area of low pressure will form across the lower Mississippi
Valley Monday and then move NE into the Middle Atlantic area by
Tuesday. The system is not strong as it nears, but much like
the present system, it will deepen as it moves through. A shield
of precipitation will develop and run ahead of the system,
arriving across our area Monday. The precipitation will
continue into Tuesday before tapering off. Right now, much of
the precip will be rain, but the onset may contain some mixed or
frozen precip, especially if it begins early enough Monday.
Right now the rain/snow/rain-snow mix/ wording will be used, but
as we get closer to the event, some sleet or perhaps some
freezing rain may be added to the fcst.

Highs Monday will be a little below normal, but by Tuesday, readings
should climb above normal with low/mid 50s for the Delaware Valley
(S/E) and mid/upper 40s for the Lehigh valley, Berks County and nrn
NJ. A cold front will follow for Tue night, ending the milder
temperatures.

Wednesday thru Friday...

Colder and drier air arrive across the area Wednesday and lasts into
the end of the week. As high pressure noses in, fair weather is
expected, so we will keep the fcst dry for Wed thru Fri attm.

&&

.AVIATION /20Z FRIDAY THROUGH WEDNESDAY/...
Rest of Today...Ceilings have lowered to IFR this afternoon and
visibilities will also lower as rainfall moves into the area.
East to northeast winds around 5 to 10 knots. --High confidence.

Tonight...IFR conditions expected to continue through the
overnight ours with periods of LIFR possible as rain moves
across the area. Periods of moderate to heavy rain will occur at
times helping to reduce visibilities. Light east to northeast
winds around 5 knots may become light and variable for some
areas. --High confidence on IFR occuring, with lower confidence
on how low conditions will get.

Saturday...IFR conditions will continue through much of the day
Saturday. A break in the steady rainfall will transition to drizzle
around daybreak for several hours, before another period of moderate
to heavy rainfall briefly moves across the area round midday. Light
and variable winds will increase out of the east to southeast around
5 to 10 knots. Winds will shift to the south to southwest and
increase to 10 to 15 knots with gusts around 20 knots to 25 knots
during the afternoon. --Moderate confidence.

Outlook...

Saturday night...An improvement to MVFR is possible during the
evening hours and may improve to VFR overnight. Winds become
westerly around 10-15 knots with gusts of 20-30 knots possible at
times. --Moderate confidence.

Sunday...MVFR ceilings may develop after sunrise for a few hours,
before lifting to VFR by late morning into the afternoon. West winds
15-20 knots, with gusts 20-30 knots. --Moderate confidence.

Sunday night...VFR conditions expected.  West winds early, become
light and variable overnight. --Moderate confidence

Monday thru Tuesday night...MVFR or IFR expected with low CIGS.
Rain/snow and fog expected.

Wednesday...VFR returning to the area.

&&

.MARINE...
Seas have increased already today and have reached 5-7 feet.
Therefore, we have started the Small Craft Advisory as of now. Winds
will remain around 10 to 15 knots out of the east with gusts around
20 knots.

Winds will turn more to the south and then southwest on Saturday
increasing to 15 to 20 knots with gusts around 25 to 30 knots
starting late afternoon/early evening. Seas will remain elevated
through Saturday.


OUTLOOK...

Saturday night...Gale Watch in effect for all waters, including
Delaware Bay as 35-40 knot wind gusts could develop behind a
departing low pressure system.

Sunday...Gale Watch continues for the Atlantic coastal waters as
wind gusts could continue to reach 35 knots through midday before
diminishing to advisory levels during the afternoon.

Sunday night...Winds lower below advisory levels overnight and seas
subside below 5 feet as well.

Monday thru Tuesday night...SCA expected. Rain and fog expected.

&&

.HYDROLOGY...

Rainfall amounts will range from 0.50-1.00 inches for portions of
eastern Pennsylvania, northwestern New Jersey, and northern
Delmarva. This rainfall amounts will not cause more than some
ponding on roadways and nuisance type flooding. However, farther
east, rainfall amounts are forecast to range from 1.00-1.50 inches,
with some spots potential reaching 2 inches, especially across
northeastern New Jersey, portions of coastal New Jersey, and
southern Delaware. Again, ponding on roadways and poor drainage type
flooding will be likely in these areas. However, for portions of
northern and central New Jersey, as well as Bucks county have the
potential for more widespread flooding impacts, including some river
and creek/stream flooding. Therefore a Flood Watch has been issued
for Bucks County in Pennsylvania, as well as portions of northeast
and central New Jersey. The majority of the rainfall will occur
tonight and the faster responding creeks and roadway flooding would
occur tonight into early Saturday morning. However, some larger
rivers, like the Passaic and Millstone, would not flood until later
Saturday into Saturday night.

&&

.TIDES/COASTAL FLOODING...
Confidence has increased that we will see minor tidal flooding on
the Atlantic oceanfront, south shores of the Raritan Bay and
adjacent back bays.

Astronomical tides remain high thanks to the full moon which just
occurred on Thursday. We will have persistent onshore flow through
much of the day tomorrow. A coastal flood advisory has been issued
for the Atlantic oceanfront and the south shores of the Raritan Bay.
For the Delaware Bay and tidal portions of the Delaware River,
spotty minor flooding is likely, but there is less confidence there
will be widespread minor flooding, so have held off on any advisory
in these areas for now.

We will see an abrupt shift to offshore flow by Saturday night.
Therefore, not expecting the coastal flooding to continue into
subsequent high tide cycles.

With only a brief period of southerly flow, tidal flooding is not
expected on the northeastern shores of the Chesapeake Bay.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Flood Watch from 9 PM EST this evening through Saturday
     morning for PAZ105-106.
NJ...Flood Watch from 9 PM EST this evening through Saturday
     morning for NJZ008>010-015.
     Flood Watch from 9 PM EST this evening through late tonight
     for NJZ012>014-019-020-026-027.
     Coastal Flood Advisory from 7 AM to 1 PM EST Saturday for
     NJZ012>014-020-022>027.
DE...Coastal Flood Advisory from 7 AM to 1 PM EST Saturday for
     DEZ003-004.
MD...None.
MARINE...Gale Watch from Saturday evening through late Saturday night
     for ANZ450>455.
     Small Craft Advisory until 6 PM EST Saturday for ANZ450>455.
     Gale Watch from Saturday evening through Sunday morning for
     ANZ430-431.
     Small Craft Advisory from 1 PM to 6 PM EST Saturday for ANZ430-
     431.

&&

$$
Synopsis...O`Hara
Near Term...Davis
Short Term...Davis
Long Term...O`Hara
Aviation...Davis/Robertson/O`Hara
Marine...Davis/Robertson/O`Hara
Hydrology...Robertson/Kruzdlo
Tides/Coastal Flooding...Johnson