Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 211008

Area Forecast Discussion
National Weather Service Mount Holly NJ
608 AM EDT Wed Mar 21 2018

A major Nor`easter just east of the Mid-Atlantic coast today will
track northeastward tonight, then will be located off the New
England coast Thursday morning. High pressure builds southward to
start the weekend, as low pressure slides to our south Saturday
night and Sunday. High pressure should then build back in for early
next week.


No major changes with this update. Although not as heavy as what
we are expecting later, we are starting to see snow bands across
the region. Based on the radar trends, expect to see the precip
fill in over the next few hours.

The main show of this developing coastal low will be unfolding
through the day time hours. The mid and upper level low to our
southwest should catch up to the surface low off the coast. Our
region, especially north central NJ down to the I95 corridor,
looks to be in a favored spot for mesoscale snow banding. The
storm total snow grid now includes this morning onward (thus,
does not take into account any snow, sleet or freezing rain that
has already fallen). The winter storm warning remains in effect
across the region.

No changes to the snow total forecast with this update. A large
portion of the coastal plains remains well above freezing. In
this area, models soundings and current temperatures suggest
that outside of heavy snow banding, we will likely see more of a
mix at least through the morning, cutting down on total snow.
However, under heavy snow bands, the temperatures at the surface
may not matter too much, and we should see all snow with these
heavy bands. The rest of the region should see mostly snow
through the remainder of the event. Regardless of snow amounts,
significant impacts, including power outages and additional tree
damage, are likely due to a combination of heavy wet snow and
strong winds.

As far as other aspects of the forecast, winds have
been slower to increase than previously expected overnight, but
expect this to change through the day as the surface low
intensifies. For temperatures, the MOS guidance continues to be
too warm (likely statistical or climo is throwing it off), so
have gone close to the operational models. Needless to say, with
all of the precipitation, do not expect a large diurnal
temperature swing today.


The low will begin to propagate northeast away from the region,
bringing a gradual end to the snow. For the most part, expect any
significant accumulations to be over with by midnight, though some
light snow showers may linger into the early morning hours,
especially across northern NJ. For low temperatures, have gone on
the lower side of guidance in anticipation of a widespread snow pack
by that time.


Summary...Brisk and chilly Thursday and Friday; low pressure should
slide to our south late Saturday and Sunday; some moderating
of the temperatures should occur during early next week.

Synoptic Overview...A significant closed low off the New England
coast Thursday will take the Nor`easter with it. A significant short
wave in the form of a closed mid level feature then drops
southeastward across the Northeast and northern Mid-Atlantic
Thursday night through Friday. The associated larger trough may
linger through the weekend across the Northeast, helping to force
low pressure to our south. There is some potential for an expansive
closed low to evolve somewhere off the East Coast early next week
while a ridge tries to shift eastward from the Great Lakes and
Tennessee Valley.

Given the major Nor`easter expected today, no major changes were
made to the long term and much of the following is from yesterday`s
day shift.

For Thursday and Friday...Blustery and cold with northwest winds
gusting to 35 mph during the day and a little less at night.
Blowing snow in open areas depending on the amount of melting of the
top layer of the expected snow pack. The snow pack could limit day
time heating, so went with the lower side of guidance for highs each
day. A southeastward moving mid level closed low crosses our area
and should produce some rain/snow showers and perhaps a heavier
snow shower.

For Saturday through Monday...The mid-level large scale features
include additional energy digging into the western states trough,
which amplifies a downstream ridge over the central U.S., while high
latitude blocking in the vicinity of the Davis Straits continues to
trend down. This continues to influence the axis and amplitude of
the trough across the Northeast U.S. and Southeast Canada, and the
short wave disturbances moving through this feature as it gradually
closes off well south of Nova Scotia early next week. There remains
disagreement in the deterministic and ensemble solutions regarding
low pressure tracking from the Great Planes on Saturday, with
redevelopment off the Mid-Atlantic coast Sunday.

The trend has been to suppress the low further to the south, yet the
extent of dry air associated with a high pressure located east of
the Appalachian Mountains remains in question, and therefore the
northward extent of overunning precipitation associated with this
system. While a focus for some precipitation would be across
portions of eastern Pennsylvania and Delmarva from late Saturday
into at least Sunday, it could certainly be more widespread across
the remainder of the area, however this is uncertain and PoPs remain
on the low side.

Northeasterly low-level flow sets up once again later in the weekend
and early next week, and we may have to monitor the potential for
some renewed coastal flooding however this will depend on the
strength and duration of the onshore flow.

For Tuesday, the pattern is favoring a return to improved weather
with temperatures moderating to closer to average.


The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Today...Conditions are beginning to lower and expect that near
or shortly after 12Z, all TAF sites will be at MVFR or even IFR,
and will likely be prevailing IFR for much of the day due to
low ceilings and visibility restrictions in snow. Many sites,
especially the Delaware Valley sites, may see periods of 1/4SM
in heavy snow, but not sure when exactly that will occur, so
have left it out of the TAFs for now. Northeasterly winds will
gradually shift to northerly through the day. Gusts to 30 KT are
likely. At KACY, gusts to 40 KT are possible, but chance is too
low to include in the TAF at this time. Moderate confidence.

Tonight...Should see gradual improvement after 00Z as snow moves out
of the area, but do not expect to return to VFR conditions until
after 06Z. Northwesterly winds should gradually diminish as well
through the overnight hours. Moderate confidence, main source of
uncertainty is the timing of improving conditions.

Thursday and Friday...VFR overall, however a few rain or snow
showers possible Friday afternoon. Northwest winds near 15 knots
with gusts up to 30 knots, then diminishing some Thursday night and

Saturday and Sunday...VFR during the day Saturday, then possible
MVFR conditions Saturday night and Sunday with a chance rain/snow.
Northwest winds around 10 knots, becoming north to northeast 10-20
knots late Saturday into Sunday. Low confidence.


Winds should continue to increase through the morning hours. We
haven`t gotten to storm force yet, but think that remains likely, at
least through a few hour window during the day today, so have kept
the storm warning going for the coastal waters and lower Delaware
Bay. Along the upper Delaware Bay, gale conditions are expected.
Seas are already observed over 11 feet, and those should continue to
increase through at least the first half of the day. By early this
evening, expect winds to begin to diminish as the storm moves away
from the region. However, we may still see gale conditions for much
of the night especially on the coastal waters.

Thursday and Friday...Small Craft Advisory conditions expected
within a northwest flow.

Saturday and Sunday...Small Craft Advisory conditions expected
within a northwest flow Saturday, then continuing into Sunday as
winds becoming northeasterly.


A strong northeast wind continued along the coasts of New Jersey and
Delaware during the night. The surge around the nighttime high tide
was about 1.0 to 1.5 feet north of Barnegat Inlet and around 1.5 to
2.0 feet to the south. Minor flooding took place along the coast
from Long Beach Island, New Jersey down to Sussex County, Delaware
around the time of high tide.

We have not made much change to the total water level forecasts for
our tidal areas. We continue to favor the more robust ETSS due to
the strength of the coastal storm. The ETSS has remained rather
consistent from run to run over the past couple days.

The Coastal Flood Warning for the New Jersey counties of Ocean,
southeastern Burlington, Atlantic, Cape May and Cumberland, and for
the Delaware counties of Sussex and Kent remains in effect until
5:00 AM Thursday. It covers the next two high tide cycles.

The Coastal Flood Advisory for Monmouth County and Middlesex County
remains in effect from 9:00 AM today until 5:00 AM Thursday. The
surge will continue to lag a bit along the northern part of the New
Jersey coast. The across-water fetch there is limited by Long Island
and southern New England. Monmouth County and Middlesex County are
forecast to experience widespread minor flooding, falling short of
the warning threshold which is defined by moderate flooding.

The surge is forecast to push up Delaware Bay and into the far lower
Delaware River, impacting the high tides there this afternoon and
tonight. A Coastal Flood Advisory is in effect for New Castle County
and Salem County from noon today until 5:00 AM Thursday.

The surge along the coast for today`s high tide is forecast to be
around 2.0 feet in the far north and in the 2.5 to 3.0 foot range
elsewhere. It is expected to produce minor to moderate coastal
flooding along much of the New Jersey coast, the Delaware coast and
Delaware Bay. Also, minor flooding should reach the the far lower
part of the Delaware River.

The wind is forecast to transition from north to northwest tonight.
However, water is expected to remain trapped along our coast and we
are anticipating another round of surge levels in the 2.0 to 3.0
foot range. The degree of flooding is expected to be similar to that
of today.

At this point, only spotty minor flooding is anticipated for the
tidal Delaware River between the Commodore Barry Bridge and Trenton.
No tidal flooding is expected for the upper eastern shore of
Chesapeake Bay.


Record breaking March snowfall accumulation forecast at PHL.
The record is 12 inches on March 13-14, 1993. #9 is 8.8 inches
March 3-4, March 4-5 in 1981.

Allentown record March two day storm total snow 19.9 inches
March 19-20 1958 (close to a 60 year anniversary). # 10 is the
10.2" event of 3/29-30/1970. We have a very good chance of top
10 at ABE, barring any last minute model surprises.

Wilmington record March two day storm total snow is 17.9 inches
3/19-20/1958. # 10 is 7.9" 3/2-3/1960. We have a good chance of
cracking top 10 list.

Atlantic City record March two day storm total is 11.6 inches
3/1-2/69 and #7 is 7 inches 3/4-5/15 and 3/6-7/53. There is a
chance of cracking top 10.

We`ll update again at 5 PM Wednesday once we know whats occurred
and whats coming.

Also from Rutgers-Dave Robinson and Mat Gerbish at our request

Since we think northern NJ per the Rutgers areal definition will
exceed 5 inches of snow (areal average), probably end up closer
to 15 inches or more... this would put northern NJ by Thursday
morning 8 AM as the highest ever in our recorded history. Right
now the average is 18.9 there and we expect it to rise to ~25 or
30" by 8AM Thursday (this has yet to happen), which would
propel us to the snowiest March on record in NNJ.

The monthly MARCH record for a single station in NJ to our
knowledge via Rutgers is 43.0 in March 1958 at Canistear
Reservoir. Oak Ridge had 42.0 and Greenwood Lake 36.8 also in

This storm may drive the current Jefferson Township and Rockaway
values which are near 33 inches, above those records...we just
dont know yet but by this time! We`ll let the reality determine
the outcome.

This is all stated to place some perspective on what we think
this upcoming event can produce for us.

Daily Record Snowfall

Site  3/20          3/21          3/22
----  ----          ----          ----
PHL   9.6"  (1958)  4.7" (1932)   3.0" (1914)
ACY   5.0"  (1914)  5.9" (1889)   2.4" (1964)
ILG   10.3" (1958)  5.4" (1964)   3.0" (1943)
ABE   16.5" (1958)  4.3" (1964)   2.6" (1992)

Snowfall as of (3/18/18)

Site  March `18  Rank   Since 7/1  Rank
----  ---------  ----   ---------  ----
PHL   7.6"       26     22.2"      56
ACY   3.5"       17     28.0"      13
ILG   6.1"       24     19.9"      48
ABE   7.5"       26     32.8"      39

Daily Record Rainfall

Site  3/20          3/21          3/22
----  ----          ----          ----
PHL   1.76" (1958)  2.24" (2000)  1.90" (1977)
ACY   2.56" (1958)  1.98" (2000)  1.54" (1903)
ILG   1.99" (1913)  3.21" (2000)  2.22" (1977)
ABE   2.12" (1958)  1.42" (1983)  2.49" (1977)
RDG   3.03" (1958)  1.57" (1890)  2.70" (2000)
TTN   1.74" (1958)  2.02" (1980)  2.25" (1977)
GED   2.12" (1975)  1.94" (2001)  1.20" (1964)
MPO   2.13" (1975)  1.28" (1950)  2.74" (1980)


PA...Winter Storm Warning until 2 AM EDT Thursday for PAZ070-071-
     Winter Storm Warning until 11 PM EDT this evening for PAZ054-
NJ...Winter Storm Warning until 2 AM EDT Thursday for NJZ001-007-
     Winter Storm Warning until 2 AM EDT Thursday for NJZ009-010-
     Coastal Flood Warning until 5 AM EDT Thursday for NJZ020>027.
     Coastal Flood Advisory from noon today to 5 AM EDT Thursday
     for NJZ016.
     Coastal Flood Advisory from 9 AM this morning to 5 AM EDT
     Thursday for NJZ012>014.
DE...Winter Storm Warning until 2 AM EDT Thursday for DEZ003-004.
     Winter Storm Warning until 2 AM EDT Thursday for DEZ001-002.
     Coastal Flood Warning until 5 AM EDT Thursday for DEZ002>004.
     Coastal Flood Advisory from noon today to 5 AM EDT Thursday
     for DEZ001.
MD...Winter Storm Warning until 2 AM EDT Thursday for MDZ008-012-
MARINE...Storm Warning until 6 PM EDT this evening for ANZ431-451>455.
     Storm Warning until 7 PM EDT this evening for ANZ450.
     Gale Warning until midnight EDT tonight for ANZ430.


Near Term...Johnson
Short Term...Johnson
Long Term...Drag/Gorse
Tides/Coastal Flooding...
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