Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 211506

Area Forecast Discussion
National Weather Service Mount Holly NJ
1106 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.


1030AM update: Increased snow amts N central NJ through ptns of
e central and se PA down thru e MD and srn-central DE, and then
tonight coastal NJ Atlc nwd. WSW is out. 1030 AM STS is posted
and reminder...only 8A today to 8A Thursday. We know its struggling
to snow snow north of I80 and we haven`t changed amts there and
sweat it out as models insist it will snow pretty good there
this aftn/early tonight. We have not changed PHl amt at all
until we know the reality at 230 PM.

930 AM checkin. STS snow grid as posted on PHI web site and in
briefing pkgs conts as is and is from 8AM today through 8 AM
Thursday and does NOT include what occurred between 8 AM ydy and
8AM this morning. No change yet but once we see the 12z NAM
trends we will probably make an adjustment higher to the w and n
of PHL. We need time to digest multiple sources of ongoing info
and hourly updated model guidance. Hopefully most folks I95
nwwd know the storm is ON! to the east, we hear wheres the snow
but we think its coming. Need more time to assess.

Max snowfall so far 4.5" in Lehigh County and ABE officially at
8AM 2.1" snowfall rates in the e PA NNJ band now mostly 1-almost

Cold sub freezing air pouring swwd into the snow area ... see
Sandy Hook 31F!

No change in the following pgh updates from 8 AM:

No further briefing pkgs today but we will update the STS as it
becomes apparent to us that amounts will differ more 2 inches
from our fcst. Will we get 10-12" in PHL? Possibly not but its
going to be quite a mess. We already have a widening areas of
MDT snow developing eastern PA and nw NJ just west of the I95
corridor and its only 12z with many reports coming in now of 2"
snowfall in the last several hours.

Also fwiw...temps rose into the upper 30s overnight in the I95
corridor when pcpn quit and still the ice/snow mix held strong.
Ground has been cooled.

We will be issuing LSR`s only for 1/hr snowfall accumulations
and glaze reports elsewhere that totaled 0.1 or greater. Lets
continue sending those reports to us via our skywarn or social
media accts. Both the glaze overnight and the storm total snow
and lets us know how the roads are doing and if any power

Collapsing thicknesses as pcpn now is changing to sleet and then
snow most of our I95 area except the coast this morning.

Synoptically: no chg from pattern recognition. A big event is
unfolding and we just need to be patient. Significant nearly
stationary banding now evident N central MD to eastern Berks
western Bucks County to near NYC. EVERYONE will share in snow
but the main axis of the S+ should be vcnty MQS-CKZ-SMQ. Higher
amts than forecast are possible in the NNJ part of our fcst,
particularly Northampton, Warren, Hunterdon, Morris, Somerset
but we`re not raising at this time until we know for sure what
we already have at 230 PM. If we will be STS only
and posted to our office winter wx web page and also SM.

Inverted trough developing from the developing primary coastal
low through through Ches Bay and that can aid lift to its
northeast. Monitoring.

Regardless of snow amounts, SUBSTANTIAL impacts, including
power outages and additional tree damage, are likely due to a
combination of heavy snow, strong winds, blowing and drifting

Mesoscale wise: please note we are aware of a typical Berks
county downslope shadow in western Berks. I can see storm totals
ranging 7" western Berks to 15" near Huffs Church in the high
terrain far eastern Berks. No changes yet but we are aware of
the potential.

Snow ratios: in 3 hr increments 12z tdy-07z tonight.
PHL 9,10,11,12,12,12 to 1 using snow ratio blender.

In the cldr ptn of storm e PA/NNJ vcnty I78 10,12,12,12,12,12
to 1 with Poconos slightly higher snow ratio. So even if qpf
were to decrease this aftn, snow ratios will permit greater
hourly accums.


The low will begin to move northeast away from the region,
bringing a gradual end to the snow but still expect an easy 1-3"
after 8 PM. For the most part, expect any significant
accumulations to be over with around 2 AM. 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


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...IFR/LIFR developing in snow, some of it heavy at times
with 1/4S+ VV003. The chg has occurred now to MIV and ACY.

Plowing ops will be needed at all TAF sites this aftn and tonight.
Drifting snow will develop at most if not all TAF sites by late
this aftn. NE wind with occasional gusts 20-30 kt except gust
35-40 kt possible KACY. Winds trend N late today.

Tonight...IFR conds in snow 00z-03z/22 becoming VFR as nw winds
gust 20-30 with drifting snow and blowing snow at some of the
TAF sites.

Storm total accums 8 AM today through 5AM Thursday as of our
current fcst. Amounts should be accurate to within 3".

RDG 6-8"
ABE 10-13"
TTN 13
PNE 11
PHL 11
ILG 10
ACY 8 Probably hammers there late aftn/evening.
GED 4 Still 4 but might be under done there by 4"

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 haven`t gotten to storm force yet, but think that remains
a possibility through 3Pm. If not we downgrade to gale all
STW`s. Seas are already observed over 12-15` 44091 to 44009,
and those should continue to increase through at least the
afternoon. Winds to begin to diminish as the storm moves away
from the region tonight but still gale conditions for much of
the night.

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.


Tide fcst still looks to be close to target at 940 AM!

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.


NEAR 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. 1.1" so far at PHL mstly

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. 2.1" as of
12z and all this morning.

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. 1.4 so far at ILG, mostly ydy.

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 today 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-
     Coastal Flood Warning until 5 AM EDT Thursday for NJZ020>027.
     Coastal Flood Advisory until 5 AM EDT Thursday for NJZ016.
     Coastal Flood Advisory until 5 AM EDT Thursday for NJZ012>014.
DE...Winter Storm Warning until 2 AM EDT Thursday for DEZ001>004.
     Coastal Flood Warning until 5 AM EDT Thursday for DEZ002>004.
     Coastal Flood Advisory until 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...Drag/Johnson  1106
Short Term...Drag/Johnson 1106
Long Term...Drag/Gorse
Aviation...Drag/Gorse/Johnson 1106
Marine...Drag/Gorse/Johnson 1106
Tides/Coastal Flooding...1106
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