Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 220019

Area Forecast Discussion
National Weather Service Mount Holly NJ
819 PM EDT Wed Mar 21 2018

A major Nor`easter located just east of the Mid-Atlantic coast
this evening will track east out to sea later tonight.  High
pressure will attempt to build southward to start the weekend,
as cold air settles into the region. A system will move through
the eastern U.S. Saturday night and Sunday but may stay south of
the northern Mid- Atlantic. High pressure should then build
back in for early next week.


The storm remains at its height through about 10 PM and there
could be some 8 inch amounts for parts of coastal New Jersey
between from late this afternoon through 9 PM.

Strong snow bands continue along the NJ shore, and the heaviest
snow will be south and east of I-95 in NJ , but down towards
Atlantic City-Cape May, the strongest snow bands will be in the
vicinity of the Garden State Parkway.

The forecast is pattern recognition and blending 12z/21
models/WPC/adjacent office considerations.

The STS is from 2PM to 8AM Thursday with this storm essentially
done from west to east between midnight and 5 am. So our STS
does not include all the snow that occurred prior to 2 PM. We
have many reports of 10+ inches now.

Regardless of snow amounts, SUBSTANTIAL impacts, including
power outages and additional tree damage, are likely this
evening due to heavy snow.


Snow ends from west to east between midnight and 5 AM with not
much clearing. Temps may rise several degrees after the snow
quits wet bulbing. strong cold outbreak to follow but
still below normal for this time of year.


With the ongoing winter storm, very little time was spent on the
long-term forecast today. Main concerns include a chance of some
rain/snow showers with a northwest-flow vort max passage on Friday
and the ultimate track of a system moving through the eastern U.S.
this weekend. Few changes were made to the previous forecast overall.

The major coastal storm affecting our region today and tonight will
be pulling northeast away from the area tomorrow. The region should
be precip-free by 12Z, so a dry forecast is in place. Went below
guidance for highs given expected snow cover and albedo effects
tomorrow (and possibly somewhat persistent partial to considerable
cloud cover). Temps generally 10-15 degrees below seasonal averages.
Breezy conditions expected but nothing out of hand. Given the
dryness of the snow, may see a little bit of blowing snow in the
higher terrain, but winds look pretty marginal so did not feel the
need for inclusion in the grids anywhere. Skies may not completely
clear out Thursday night, so did not stray too far from guidance for
lows...only slightly below consensus at this point.

Friday`s forecast is tricky, as a potent northwest-flow vort max
moves into the Northeast during the day. Its passage will be during
the day, so timing is favorable for some instability showers,
especially in northern/eastern portions of the area (given the track
of the vort max). ECMWF is not enthused by the prospects, but
coarser models tend to underforecast this threat. Some indications
from GFS of this threat, and I think it is reasonable to keep slight
PoPs during the afternoon for areas northeast of Allentown to Philly
to Atlantic City. I did lower PoPs a little given insufficient
support from longer-range hi-res guidance. Temperatures again below
guidance given expected clouds and remaining snow cover (and once
again 10-15 degrees below climatology).

Another strong vort max moves southward from eastern Canada on
Saturday as a separate vort max moves west-to-east through the
central U.S. and interacts with the digging perturbation. Attendant
surface low in the central plains Saturday looks to be shunted
southward somewhat as it tracks into the Ohio/Tennessee Valleys.
Just how far south is a challenging question, with considerable
disagreement among the operational guidance. The GFS looks
especially suspicious, though, given its very progressive evolution
of the northern-stream vort max. The 12Z CMC/ECMWF are slower and
(as a result) have the track of the southern-stream system a little
farther north. This may give the Delmarva Peninsula a chance for
some precipitation Saturday night and Sunday. Additionally, there
are some indications that as the surface low intensifies off the
coast that wraparound (light) precipitation may affect the eastern
CWA on Sunday (aided by the passage of the main northern-stream vort
max). Cannot discount chances of rain and/or snow for much (if any)
of the area during this period, so kept slight-chance PoPs in the
grids. If the southward-deflection of the southern-stream system
occurs later than anticipated, this may bring somewhat heavier
precipitation into the area (especially Delmarva). A low-confidence
forecast exists for this period, to be sure.

Strong ridging develops early next week as the strong cyclonic
vortex meanders eastward off the Atlantic coast. This should bring a
prolonged dry period to the area along with a warming trend. A
system may affect the region by mid to late week, but models have
large timing differences. Generally included slight-chance to low-
chance PoPs on Wednesday for now, but temperatures fortunately look
more seasonal by then.


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

Tonight...Conditions slowly improve to VFR at KRDG/KABE by 06Z.
Otherwise, IFR/LIFR conditions in snow will continue at
KTTN/KPNE/KPHL/KILG through 08Z, and for KMIV/KACY until 10-12Z
Thursday. NW winds 10-15 kt.

Thursday...VFR. NW winds 10-15 kt with gusts up to 20 kt.


Thursday night: VFR with northwest winds 5 to 15 kts. High

Friday: Potential for MVFR or low VFR CIGs and rain/snow showers,
especially northeast of ABE-PHL-MIV. Northwest winds 5 to 15 kts
with potential for gusts to 20 kts or so. Moderate confidence.

Friday night and Saturday: VFR with northwest winds 5 to 15 kts,
potentially lighter during the night. High confidence.

Saturday night and Sunday: Some potential for sub-VFR conditions
with light rain and/or snow. Winds north to northeast under 10 kts
Saturday night and 10 to 20 kts on Sunday. Very low confidence.


Gale force winds through tonight with elevated seas.

Thursday: Remnant gale-force northwest gusts becoming small-craft
advisory criteria during the day. Seas slowly subsiding.

Thursday night: Small-craft advisory northwest winds continue.

Friday and Friday night: May see a lull in winds on Friday morning,
but they should increase again by afternoon evening to advisory

Saturday and Saturday night: Sub-advisory winds/seas expected. A
slight chance of rain and/or snow late, especially near/south of
Delaware Bay.

Sunday: Advisory-level northeast winds expected, with some potential
for gales (though this is low confidence). Some potential for rain
and/or snow.


Winds have shifted to the northwest, and have begun to diminish
t0 10-20 mph.

Although tides remain elevated tonight, they should not be as
high as previously expected given that winds will not be quite
as strong as forecasted. In general, expecting departures around
2 feet for northern and central NJ, 2 to 2.5 feet for southern
NJ and DE zones, including land adjacent to Lower DE Bay, 1.5 to
2 feet for northern NJ, and around 1.5 feet for land adjacent
to Upper DE Bay and the Tidal DE River.

Coastal Flood Advisory remains in effect for northern NJ and parts
of NJ and northern DE adjacent to Upper DE Bay and DE River as minor
coastal flooding is expected with the upcoming high tides.

The Coastal Flood Warning remains in effect for all other areas,
though now anticipating widespread minor coastal flooding with areas
of moderate coastal flooding, as opposed to widespread moderate
coastal flooding.

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.

Between this evening and early Thursday morning, these should be the
last rounds of coastal flooding for this storm.


This section will be updated later this evening.

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.

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 VERY 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
good chance of cracking top 10.

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 5 to 10
inches...this would put northern NJ by Thursday morning 8 AM as
one of the highest ever in our recorded history. Right now the
average is 18.9 there and we expect it to rise to ~25 by 8AM
Thursday (this has yet to happen), which would propel us to the
top 3 snowiest March on record in NNJ. Its going to take awhile
before we know for sure.

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, to near those records. We just
wont know for sure until the final values post midday Thursday.

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

All climate sites will probably have record daily snowfall for
March 21! See the records below. We wont know until early
Thursday morning regarding specifics of the records. Our staff
will post the appropriate RER at that time. Please dont call us.
Our staff will still be very busy. Thank you.

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


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 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...Gale Warning until noon EDT Thursday for ANZ450>455.
     Gale Warning until 4 AM EDT Thursday for ANZ430-431.


Near Term...Drag/MPS
Short Term...Drag
Long Term...CMS
Tides/Coastal Flooding...
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