000
FXUS61 KPHI 252128
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
428 PM EST Sun Feb 25 2018

.SYNOPSIS...
A weak cold front slips southeast through our area overnight.
Strengthening high pressure is then forecast to build into the Mid-
Atlantic states Monday and Tuesday. A cold front will drop down into
the mid Atlantic states late Wednesday night while low pressure
develops over Illinois. That low slides to the Mid- Atlantic coast
by Friday morning, then intensifies into a strong storm over the
western Atlantic by Friday night before heading slowly out to sea
next weekend.

&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
Cold front across western PA as of 3 PM was gradually becoming
occluded as it continues moving eastward. Meanwhile, a warm front
was situated across Sussex County DE, and has been held at bay
much of the day as a wave of low pressure developed offshore.
In fact, this has shifted winds to a more westerly direction as of
late afternoon in southern NJ and Delmarva, with a light northeast
flow to the north. Meanwhile, the last area of showers was just east
of the NJ Turnpike at 3 PM. These showers will exit the coast in the
5-6 PM time frame, with a drying trend taking hold, as the cold/
occluded front moves across the area this evening.

As mentioned previously, winds have already shifted to the west
across southern NJ and Delmarva, so temperatures have reached their
maximums for the day, and will fall rather slowly this evening as
cold air advection is weak. With some clearing overnight, the moist
air mass in place, and weak winds, fog is expected to redevelop. The
fog could be dense in some areas, particularly across New Jersey,
and we have mentioned this in the Hazardous Weather Outlook.

Low temperatures will dip down to near freezing across portions of
northern NJ and northeast PA, generally north of the I-78 corridor.
If fog occurs in these locations, there is the potential for
freezing fog, albeit low. If freezing fog occurs, it could result in
localized areas of slippery travel on untreated surfaces.

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH 6 PM MONDAY/...
Sunshine will gradually increase on Monday from northwest to
southeast. Prior to that, patchy fog is possible until around 10 am,
and it could be dense in some areas. The exception will be far
southern New Jersey and Delmarva, where clouds remain much of the
day. At this time, and precip with the front to our south is
expected to remain there. Maximum temperatures will be in the 50s.
Northwest winds around 10 mph.

&&

.LONG TERM /MONDAY NIGHT THROUGH SUNDAY/...
We are adding a coastal flood section this afternoon as this
initially is the primary concern for Thursday-Saturday.

We are also commenting on the late week event in the hydro
section.

Hazards: None explicitly at this time but a few hazards are likely
with the potential for a powerful storm in the Thursday to Saturday
time frame. These potential hazards include a highly probable
coastal flood hazard, severity unknown but potential exists for
moderate coastal flooding along a portion of the Atlantic coast
with multiple high tide cycles of minor tidal inundation flooding
late Thursday into Sunday mornings high tide cycles; Friday-Saturday;
a small stream hydro hazard, mostly in NJ and PA, still a chance
vertical motion from an unusually strong storm can change rain
to a period of wet accumulative snow (WXA hazard) for the
elevations ne PA and nw NJ late Friday; a gale event, the first
2 hour or longer gale since Feb 5, is expected but the exact
time is not yet known. Storm force gusts are possible.

500 mb: east coast ridging follows the departing mid Atlantic
coast short wave Monday night and continues ridging into
Wednesday. Then a weakening closed low in the desert southwest
Tuesday night starts reenergizing in the Ohio Valley Thursday,
becoming a large and strong cyclonic circulation system along
the mid Atlantic coast Friday, and slowly weakening seaward next
weekend.

Temperatures: Please see the climate section for updated February
climate stats, which I`ll update further around 430 PM (pcpn
stats). Calendar day averages should be 5 to 10 degrees above
normal Tuesday, Wednesday and Thursday, then big differences
appear between the EC and GFS for Friday-Sunday. Have chosen to
run with the cooler blend of the 12z EC/15z WPC guidance and so
have 5 to 10F above normal Friday and generally less than 5F
warmer than normal for the weekend. This is decidedly cooler
than the the 12z/25 GFS OP cycle.

Forecast basis: Unless otherwise noted above a 50 50 blend of
the 12z/25 GFS/NAM was used for Monday night-Tuesday night, the
12z/25 MEXMOS for Wednesday, and the 15z/25 WPC 12 hr forecast
max/min temps and POP, as well as their 6 hourly sustained wind,
skycover and dewpoint from Thursday through Sunday. Did maintain
our prior higher pops for Wed night/Thu, and Friday night...
continuity.

Models: The 12z/25 op GFS and UKMET look a little warm and
tracking too far north but they are part of the ensemble and
must be considered.

Please see this Sunday afternoons WPC D4-5 QPF and their D6
winter wx graphic to gain some appreciation of the potential
ahead.

The dailies...

Monday night...Clear. Northwest wind gusts 15 to possibly 20
MPH early as instability transfer deepens with cold air advection
aloft, tending to decouple late. Confidence: Well above average.

Tuesday...Sunny and beautiful! Light west wind becomes southwest
late in the day. Confidence: Well above average.

Wednesday...Partly sunny (lots of cirrus) and a few degrees warmer.
Southwest wind may gust 20 mph in the afternoon. Confidence:
Well above Average.

Wednesday night-Thursday night...In association with either a
cold frontal passage or a warm front extension east-
southeastward from the developing Midwest low pressure system,
rain will be developing either late Wednesday night or more
likely by midday Thursday. It may become heavy Thursday
afternoon and night. Winds becoming east and gusty 15-25 MPH in
the afternoon with rapidly falling pressure. Confidence: Above
average on scenario but nothing locked on storm track and
confidence below avg on any snowfall higher elevations of our
northern counties.


Friday into Saturday morning...Overall, probably gusty northerly
winds and periods of precipitation. As of now, rain most of
Friday and thereafter probably periods of showery rain, but
potential exists for some elevation snow. Confidence: average on
details, contending with a latitude tracking problem on what
looks to me to be a powerful (980-987MB) storm s of LI.

Sunday...Partly cloudy. North northeast wind gusty 15-25 MPH.

&&

.AVIATION /21Z SUNDAY THROUGH FRIDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.

This evening IFR conditions continue at all TAF sites. A
gradual return to VFR is expected later this evening, but that
may be short lived. Winds ranging from the northwest to northeast,
gradually becoming more westerly at all locations
Confidence: Low.

Tonight...For ILG, PHL, and PNE, some low clouds may work in
again around midnight, and we have included a tempo for this, as
there is some uncertainty. Elsewhere, there is the potential
for at least MVFR ceilings in fog later tonight, and we have
inserted a tempo at each of the following sites: ABE, RDG, TTN,
MIV. The only exception is ACY, where there is a better chance
of fog, so this is forecast as a prevailing condition after
midnight. Winds becoming light and variable. Confidence: Low.

Monday...Conditions improving to VFR at all TAF sites by 15Z as
both fog and low clouds dissipate. Winds northwest around 10 kts.
Confidence: Moderate.

Outlook...

Monday Night...VFR Clear. Northwest wind gusting 15 to possibly 20
kt early, diminishing late. Confidence: well above average.

Tuesday...VFR, virtually clear. Light west wind becomes southwest
late. Confidence: well above average.

Wednesday...VFR mostly mid and high cloud. Southwest winds may
gust 20 kt during the afternoon. Confidence: Above average.

Thursday...Conditions should deteriorate to MVFR or IFR in
rain. East to southeast wind and probably gusts 15-25 kt in the
afternoon. Confidence: Above Average.

Friday...Quite a bit of uncertainty with the latitude of a strong
western Atlantic low the determining factor on conditions. Conditions
can range from VFR cigs to IFR in rain/drizzle. Probably north
winds gusty 20-30 kt. Confidence: below average.

&&

.MARINE...
SCA will expire at 23Z this evening as seas continue a downward
trend, and should subside below 5 FT by that time. A Dense fog
advisory remains in effect for the Atlantic Waters of NJ from
Little Egg north through 00Z this evening. Once we get through this
evening, visibilities should improve across this area. Otherwise,
conditions are expected to remain below SCA criteria through Monday.
Winds shift from light and variable this evening to north tonight,
then northwest on Monday, generally less than 15 kts.

Outlook...

Monday night...We may need an SCA for nw wind gusts to 25 kt in the
northern NJ waters (ANZ450-51) early?. Confidence: below average.

Tuesday through Wednesday...Sub-advisory conditions are expected on
the area waters with light west winds Tuesday morning becoming
southwest Tuesday night and Wednesday, gusts under 20 kt.
Confidence: Average.

Thursday...An easterly SCA likely with a possible gale for the
NNJ waters. Confidence: Average.

Friday...Quite a bit of uncertainty with the latitude of a strong
western Atlantic low the determining factor on conditions. Certainly
SCA with potential for a northerly Gale , especially NNJ waters.
Confidence: below average.

Special note: This big western Atlantic storm is likely to drive an
increasing northeast swell of 10 to 15 ft toward the NJ and DE coasts
this weekend, exception 5 to 10 FT off Monmouth County sheltered a
bit by Long Island. This could affect marine operations next
weekend, especially at the entrance to Delaware Bay.

&&

.HYDROLOGY...
Small streams including the Perkiomen Creek at East Greenville
in Montgomery County Pennsylvania and the Neshanic at Reaville
in Hunterdon County New Jersey were in action stage this morning
but no action since they have generally crested or are within
bankful and anticipated to remain so.

Of note will be how much rain falls over the Susquehanna, as
there is the potential for inconvenience flooding below the
Conowingo Dam on Monday but no statements anticipated from our
office today.

A large and strong storm will affect our area Thursday into
Saturday. The bulk of the rain is anticipated Thursday into
Friday with widespread 1-2" amts expected in e PA and NJ,
particularly near and north of I78. If the track of the low
permits, there could be significant backlash pcpn late Friday
but at this time, we are not forecasting that option. Therefore,
we may need to deal with some small stream flooding in nNJ and
and e central-ne PA later Friday if we receive basin average
rainfall of nearly 2 inches. No action is needed at this time
and we`ll see if the models remain similar through the week. Its
easily possible that we`ll be able to escape any significant
small stream flooding, especially if the storm tracks further
north than now forecast. So, while the MMEFS outlook is
significant,we are opting for lower than these outcomes,
especially based on recent performance history, in part due to a
slight high bias to the qpf.

Suggest all interests monitor future forecasts issued Monday-
Thursday for information trends and any office briefing
packages.

&&

.TIDES/COASTAL FLOODING...
Low pressure is forecast to approach from the west and it should
pass off the Middle Atlantic coast around Thursday night. The system
is expected to strengthen as it moves slowly out to sea on Friday
and over the weekend. It is anticipated to have some impact on the
coasts of New Jersey and Delaware at that time.

Tides will already be running high due to the full moon that will
occur on Thursday. Heavy surf and the potential for a developing
strong northeast wind may result in some coastal flooding along with
beach erosion.

Based on the latest forecast guidance, it appears as though there
may be some minor coastal flooding on Thursday evening, mainly along
the northern and central parts of the New Jersey coast. The
potential for widespread minor flooding exists from late Friday into
early Sunday along the entire New Jersey and Delaware coast and into
Delaware Bay and the tidal Delaware River. Depending on the system`s
development, some moderate flooding could occur. However, the event
is several days away and the forecast details are subject to change.

If you live along the coast or along Delaware Bay, please pay close
attention to the forecast over the coming days.

&&

.CLIMATE...
**Top 3 warmest February on record and top 10 wettest February
on record.**

February projected climate ranking as of 7 am today-Sunday Feb
25, based on our mid shift fcst through the 28th and mins this
Sunday morning; and for rainfall, amounts 7 AM today. RDG and TTN
not included due to too much missing data.

ABE #3 warmest 38.0 or 7.3F warmer than the 30.7 norm.
39.2-2017
38.6-1998
38.0-2018
36.8-1954

ACY #1 warmest 42.8 or 7.5F warmer than the 35.3 norm.
43.0 -2017
42.8 -2018
40.6 -1954

ILG #3 warmest 41.2 or 6.2F warmer than the 35.0 norm.
43.1-2017
42.3-1903
41.2-2018
41.2-1976

PHL #3 warmest 42.3 or 6.6F warmer than the 35.7 norm.
44.2-2017
42.3-2018
42.2-1925
41.8-1998
41.4-1890

Water equivalent February pcpn as of 4PM today. These rankings
below are the lowest they will be for the month and possibly the
final rankings for February.

PHL ranked #5 with 6.02". All time 6.87-1896

ILG ranked tied #4 with 6.00". All time 7.02-1979

ABE ranked #4 with 5.50". All time 7.62-2008

ACY ranked #2 with 6.43". Wettest is 6.50-2010.

MPO 4.71
RDG 5.53
TTN 5.52
GED 3.97

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...Dense Fog Advisory until 7 PM EST this evening for ANZ450-451.
     Small Craft Advisory until 6 PM EST this evening for ANZ450-
     451.

&&

$$
Synopsis...Drag
Near Term...CMS/Franck
Short Term...CMS/Franck
Long Term...Drag 427
Aviation...Drag/Franck
Marine...Drag/Franck
Hydrology...Drag
Tides/Coastal Flooding...Iovino
Climate...Drag 427

NWS PHI Office Area Forecast Discussion