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000
FXUS61 KPHI 200224
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
924 PM EST Sat Jan 19 2019

.SYNOPSIS...
An expansive area of low pressure will approach the region from the
west tonight and pass over our area overnight Saturday night and
early Sunday morning bringing a significant winter storm to the
region. Low pressure moves across southern New England then out to
sea late Sunday. Strong Arctic high pressure will build quickly into
the Mid-Atlantic through the early part of next week resulting in
very cold and dry conditions. Another area of low pressure will move
across the Great Lakes and into southeastern Canada late Tuesday
into Wednesday pushing a cold front into the region Wednesday.

&&

.NEAR TERM /THROUGH SUNDAY/...
Rain/snow line continues to creep to the north, and the
transition line is now along or north of a line from around
Reading to Doylestown to Trenton. Across the Lehigh Valley,
southern Poconos, and northern NJ, moderate to locally heavy
snow continues. The rain/snow line continues to lift to the
north, and shortly after midnight or so, expecting a wintry mix
of sleet and freezing rain, then a period of freezing rain
across Carbon, Monroe, and Warren counties. Max snow amounts in
the far northern areas will range from 6-8" (will bump up a bit
from earlier forecasts), along with up to 0.20" of ice. Winter
Storm Warnings remain in effect for the far northern zones, and
for now, will not make adjustments to the Winter Weather
Advisories, as there may still be some wintry precip as that
line lifts north.

Timing: The bulk of the precip falls tonight through Sunday
morning with this winding down as the cold front moves through
during the 15- 19z time frame Sunday.

Winds: Late tonight into Sunday morning, a very strong
southerly low level jet is expected to develop with 925/850 mb
winds progged to reach 70/90 knots over the area as the warm
sector moves in. There will be lots of moisture in play with
rain continuing at this time with some indications a convective
type line could develop even if it doesn`t actually produce
lightning. Nevertheless, this could potentially bring very
strong, even damaging winds, down to the surface. Not confident
in this though and this will need to be handled as a "short-
fused" type product situation, if needed. Then, following the
passage of the cold front, expect strong NW winds to develop
potentially gusting 30-40+ mph tomorrow afternoon into the
evening along with rapidly falling temperatures. This could
result in at least some scattered power outages with more
significant problems possible in the far north in the areas that
still may get more snow/ice.

Flash Freeze: As mentioned above, strong cold front moves
through NW to SE late morning into the early afternoon with
rapidly dropping temps to values well below freezing. This will
result in quick refreezing of wet/slushy surfaces causing very
ice conditions.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/...
The beginning of the week will feature deep winter arctic cold,
but dry conditions. Temperatures will continue the fall (from
Sunday) and drop into the single digits and low teens across
most areas. Mercury readings across the southern Poconos may
reach as low as -5 by dawn Monday. As bad as the cold is, wind
chills will be brutal with sub-zero readings in most areas and
readings around -20 to -25 across the Poconos. Proper
precautions against the cold will be required to be safely
outdoors Monday. Dry weather is expected Monday and into Tuesday
as high pressure builds in. Readings Tuesday morning will also
be very cold, but temperatures will moderate by days end back
into the low 30s S/E and low/mid 20s N/W.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
The midweek period looks unsettled as of now since another H5 trough
will be advancing from the Midwest and low pressure is expected to
form along it. Another wet/white storm is envisioned with
confidence on storm track and P-types low at this time. More
arctic cold looks to follow this system.

&&

.AVIATION /02Z SUNDAY THROUGH THURSDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.

Tonight...IFR and lower conditions as precipitation overspreads
the region from southwest to northeast. All rain expected at
MIV and ACY; precip has changed to rain at ILG, PHL/PNE, and
TTN; RDG and ABE start as snow then quickly go over to sleet and
freezing rain, then rain overnight. Main snow and ice
accumulations occur at RDG and ABE. Low confidence on the timing
of the precipitation type changes. Easterly winds around 10
knots, turning southeast or south toward morning (some gusts to
20-25 knots possible overnight mainly at ACY). A low- level
southerly jet around 2000 feet overnight into early Sunday of
40-50 knots results in low- level wind shear.

Sunday...MVFR/IFR conditions to start, then rapidly improving by
late morning or afternoon as the precipitation ends. An abrupt wind
shift to the northwest occurs by midday with winds increasing to 15-
25 knots with gusts to around 35 knots (highest during the
afternoon/evening). Low confidence on timing for improvement to
VFR.

Outlook...
Sunday night and Monday...VFR. Northwest winds 15-20
knots with gusts to around 30 knots, diminishing Monday night.

Tuesday...VFR. Northwest winds 10-20 knots, diminishing by late
afternoon.

Wednesday and Thursday...Sub-VFR conditions possible with the chance
for some snow to a rain/snow mix.

&&

.MARINE...
East to southeast winds tonight will increase to advisory
levels, then become more southerly early Sunday morning. The
passage of low pressure and a strong cold front will result in
an abrupt wind shift to northwesterly during Sunday with a rapid
increase in the winds as bitterly cold air pours in across the
region. The gales may not fully take hold until the afternoon or
evening, however will maintain the Gale Warning as is although
did extend the end time to 23z/6pm Monday.

Outlook...
Sunday night and Monday...Gale Warning through 23z/7pm
Monday due to a bitterly cold airmass and deep mixing. The warning
may need to be extended into a portion of Monday night. Due to the
bitterly cold air and strong winds, freezing spray is expected
especially later Sunday night through Monday. As of now, looks like
moderate ice accretion rates will be achieved and therefore issued a
Freezing Spray Advisory.

Tuesday...The conditions (winds) are anticipated to be dropping
below Small Craft Advisory early.

Wednesday and Thursday...Winds may increase to Small Craft Advisory
criteria Wednesday then decrease through Thursday. Seas could remain
at 5 feet or higher on the ocean waters.

&&

.HYDROLOGY...
With the trend toward warmer solutions, models indicate that
the threat for heavy rain along the I-95 corridor has increased.
Consensus of operational model solutions suggests a swath of
1-2+ inches in this general area. These totals have been
observed to generate localized flooding on several occasions
during the past few months.

Additionally, there are indications that some of the rainfall
may result from convection, especially late tonight into early
Sunday morning. Should rainfall rates approach/exceed half an
inch per hour, urban and small stream flooding is likely to
occur, especially in the quickly responding basins within and
surrounding the Philadelphia metro.

River flooding is possible, but appears to be more likely if
QPF exceeds the current forecast (i.e., widespread totals of 2+
inches).

&&

.TIDES/COASTAL FLOODING...
Onshore continues across the region, and will increase tonight
and into Sunday morning. With the approaching full moon, the
threat of coastal flooding will increase by Sunday morning`s
high tide. However, winds are expected to become more southerly
late tonight, which should mitigate a more substantial coastal
flooding event. To this point, guidance continues to advertise
mainly minor flooding, though models do tend to exhibit a low
bias in these sorts of events. Notably, the Stevens Institute
ensemble guidance does suggest potential for spotty moderate
flooding, especially on the northern New Jersey coast. Also
noteworthy is the potential for heavy rainfall tonight and
Sunday morning, which may exacerbate coastal flooding owing to
contributions from freshwater runoff. At this point, however,
think widespread minor flooding is more likely on the New Jersey
and Delaware Atlantic coasts, along Delaware Bay, and the tidal
Delaware River, for Sunday morning`s high tide. Some locally
moderate coastal flooding remains possible.

As a result, we have issued a coastal flood advisory for the
above-mentioned areas. As flow will become strongly offshore by
Sunday afternoon, coastal flooding is not expected with high
tides following Sunday morning`s.

At this time, coastal flooding is not expected for the eastern
shores of Chesapeake Bay.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Winter Weather Advisory until 1 PM EST Sunday for PAZ060>062-
     103-105.
     Flood Watch through Sunday afternoon for PAZ070-071-101-102-
     104-106.
     Coastal Flood Advisory from 10 AM to 3 PM EST Sunday for
     PAZ070-071-106.
     Winter Storm Warning until 1 PM EST Sunday for PAZ054-055.
NJ...Winter Weather Advisory until 1 PM EST Sunday for NJZ007>010.
     Coastal Flood Advisory from 5 AM to 11 AM EST Sunday for
     NJZ012>014-020>027.
     Flood Watch through Sunday afternoon for NJZ012>019.
     Coastal Flood Advisory from 8 AM to noon EST Sunday for NJZ016.
     Coastal Flood Advisory from 10 AM to 3 PM EST Sunday for
     NJZ015-017>019.
     Winter Storm Warning until 1 PM EST Sunday for NJZ001.
DE...Coastal Flood Advisory from 5 AM to 11 AM EST Sunday for
     DEZ002>004.
     Flood Watch through Sunday afternoon for DEZ001.
     Coastal Flood Advisory from 8 AM to noon EST Sunday for DEZ001.
MD...Flood Watch through Sunday afternoon for MDZ008.
MARINE...Freezing Spray Advisory from 1 AM to 6 PM EST Monday for
     ANZ430-431-450>455.
     Gale Warning from 8 AM Sunday to 6 PM EST Monday for ANZ430-
     431-450>455.

&&

$$
Synopsis...Staarmann
Near Term...Fitzsimmons/Johnson/MPS
Short Term...Fitzsimmons/Johnson
Long Term...Fitzsimmons/Johnson
Aviation...Gorse/MPS/Staarmann
Marine...Gorse/MPS
Hydrology...
Tides/Coastal Flooding...