Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 151754
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
1254 PM EST Mon Jan 15 2018

.SYNOPSIS...
High pressure centered in Quebec early this morning will
continue to influence our weather today. Low pressure is
forecast pass across the southern and eastern Great Lakes
tonight and Tuesday. A secondary low is expected to develop off
the Middle Atlantic coast on Tuesday night before moving
northeast toward Canada`s Maritime Provinces on Wednesday. High
pressure from the west is forecast to build across the
southeastern and Middle Atlantic states on Thursday and Friday
before moving out to sea over the weekend.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Some ocean-effect snow has developed in eastern Sussex County,
DE, late this morning and continues at this time. Needed to
boost PoPs in lower portions of our Delmarva CWA for this
threat. Though impacts generally should be minimal, area webcams
showed a coating of snow was occurring on untreated surfaces,
whereas more traveled and/or treated surfaces were generally
wet. Basically kept this threat through the afternoon, using
the latest HRRR as a guide for timing (for now).

Did make some more upward adjustments to dew points and
temperatures as well based on latest trends, with models
generally a little too low in most spots with both variables
this morning.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM TUESDAY/...
The influence of the high will continue to relax while a weak
trough develops across the area. It will remain rather cold, but
warmer than this (present) night. The trough may result in some
light snow developing across wrn/nrn areas towards dawn. The
airmass is still rather dry and this leads me to question how
much will occur. The low confid in whether accums will occur
leads me to only keep the ongoing chc pops in these areas for
now. Lows tonight will be in the teens north/west and low/mid
20s elsewhere.

&&

.LONG TERM /TUESDAY THROUGH SUNDAY/...
A long wave trough is expected to settle over the eastern
states for the middle part of the week. The trough should lift
to our northeast late in the week, allowing ridging to build
overhead from the west for the weekend. The pattern will
maintain cold conditions in our region through Thursday with a
warming trend anticipated after that time.

It continues to appear as though weak low pressure will move
across the eastern Great Lakes on Tuesday and it should pull a
cold front into our region from the west on Tuesday night. We
still anticipate snow on Tuesday and Tuesday night in much of
eastern Pennsylvania and northern New Jersey with accumulations
of 1 to 2 inches in areas to the northwest of the Interstate 95
corridor and 2 to 4 inches in the elevated terrain of the
Poconos and northern New Jersey.

There remains the potential for light snow from the Interstate
95 corridor southeastward. Enough warming may take place on
Tuesday afternoon in advance of the cold front to cause the snow
to change to rain for a time in that area. Little or no snow
accumulation is anticipated for the coastal plain of New Jersey
and the Delmarva with a light coating possible along the
Interstate 95 corridor.

The secondary low development off the Middle Atlantic coast on
Tuesday night appears as though it will be too late to have any
significant impact on our region. However, we will continue to
keep an eye on the system in case the details regarding its
development change. The low is not expected to begin deepening
much until it reaches our latitude late on Tuesday night. It
should lift quickly toward the waters off New England and
Canada`s Maritime Provinces on Wednesday.

High pressure is expected to build across the southeastern and
Middle Atlantic states late in the week before moving over the
western North Atlantic during the weekend. The high is forecast
to bring dry weather conditions and a warming trend.

&&

.AVIATION /18Z MONDAY THROUGH SATURDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Today...Generally MVFR to low VFR CIGs through the afternoon
with northeast winds around 10 kts. High confidence.

Tonight...CIGs will likely lower through the night, with light
snow developing in the Lehigh Valley and southern Poconos by
daybreak. Sub-VFR CIGs should be present in most locations by
daybreak, with sub-VFR VSBYs likely at RDG/ABE once the light
snow begins. Light winds, which should be generally east or
northeast, though speeds may become light enough to be somewhat
variable after midnight. Medium confidence.

Tuesday...Sub-VFR CIGs should continue through the day, with
most precipitation (snow) remaining confined northwest of I-95.
Kept any precip mention out of Philly terminals, though there is
some chance of precipitation occurring by late afternoon. Where
snow occurs, sub-VFR VSBYs should occur. Winds generally light
and variable, with perhaps a southeast component becoming
dominant by late in the day. Medium confidence.


OUTLOOK...
Tuesday night and Wednesday morning...A chance of light snow
with low ceilings and reduced visibility possible.

Wednesday afternoon through Friday...Mainly VFR.

&&

.MARINE...
930 am update: Freezing spray is winding down on the lower
portions of Delaware Bay, so will let the advisory expire as
scheduled. No changes made to the forecast at this time.

Previous discussion...

High pressure northeast of the waters will move away today and
tonight. A weak trough will develop across the area tonight.
These systems will keep a light-moderate NE flow across the
waters. The SCA flag will be extended tonight with low end gusts
around 25 knots at times and seas near 5 ft. Freezing spray
this morning. Fair weather with perhaps a brief flurry this
morning psbl.

OUTLOOK...
Tuesday through Wednesday...No marine headlines are
anticipated.

Wednesday night through Thursday night...A northwest wind
gusting to 25 to 30 knots. Light to moderate freezing spray is
expected.

Friday...No marine headlines are anticipated.

&&

.HYDROLOGY...
An ice jam has developed along the Delaware River at Trenton,
and flooding has been reported adjacent to the river in Bucks
and Mercer Counties. Several road closures are in place between
Morrisville and Yardley in PA and along NJ State Highway 29 in
Trenton.

The ice is having an impact on the ability to accurately
forecast the river level in the Trenton vicinity. Please use any
forecast levels with caution.

If you live near the Delaware River in the Trenton and Yardley
vicinity, pay special attention to any additional information
that is issued regarding the Delaware River.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...Small Craft Advisory until 6 AM EST Tuesday for ANZ450>455.

&&

$$
Synopsis...Iovino
Near Term...CMS
Short Term...Robertson/Meola/O`Hara
Long Term...Iovino
Aviation...CMS/Iovino
Marine...CMS/Iovino/O`Hara
Hydrology...CMS/Iovino



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