Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 231411

Area Forecast Discussion
National Weather Service Mount Holly NJ
1011 AM EDT Fri Mar 23 2018

Low pressure will linger today in the vicinity of the Canadian
Maritimes. Strong high pressure builds to our north over the
weekend, then extends southward over our area early next week.
Meanwhile, a weak low pressure system slides well to our south
Saturday night into Sunday. A cold front is then forecast to arrive
toward later next week.


Mid morning water vapor satellite imagery shows an upper low
near Lake Erie-Lake Ontario. This disturbance is forecast to
dive southeastward thru the northern Mid-Atlantic region late
this afternoon and early evening. There is a very weak surface
reflection marked by a surface trough (wind shift) over the
eastern Great Lakes-Adirondacks-northern New England. This
surface trough will progress southward through eastern PA and NJ
this afternoon and evening.

Daytime mixing combined combined with lift ahead of the
shortwave disturbance will lead to the development of high-
based stratocu and increase in mid-level cloud deck from
northwest to southeast across the region this afternoon. Hourly
sky grids were updated to account for timing. Hourly PoPs were
also updated with 20-30 PoPs pushed back about 2-3 hours later
compared to previous forecast (matched up better with
anticipated timing of lift ahead of the trough and with the
latest hi-res CAM reflectivity guidance). 18Z is the first
mention of showers along and north of I-80. Convection should
be isolated later this afternoon and early this evening
(perhaps widely scattered in the southern Poconos and northern
NJ). With highs in the 40s across most of the region this
afternoon, thermal profiles are warm enough for mainly rain.
However, given the significant dry layer beneath the LCL, strong
evaporative cooling could allow for temps to briefly drop into
the 30s and for some snow to mix in (assuming we have ice

For the higher elevations (above 700 ft) in the NE PA and NW
NJ, where temperatures will only be in the 30s this afternoon,
snow would be the preferred ptype given that ice crystals will
be available for snow growth (it may not be). For these higher
elevations, BTV snow squall parameter (per GFS, NAM, RAP)
indicates a marginally supportive environment for squalls in the
southern Poconos this afternoon, possibly in far NW NJ and
Lehigh Valley toward sunset. A deeper look at the forecast
soundings, reveals a lack of of robust lift, moisture, and
stronger winds in the boundary layer. Accordingly, the setup
does not appear to be favorable for heavier snow showers or
squalls today.

Convection should wane after sunset with the loss of daytime
instability but isolated sprinkles/flurries were kept in the
forecast after dark this evening for southeastern PA,
southern/central NJ, and northern Delmarva as the activity
pushes southward.


As the mid and upper level low propagates off shore, should see
clouds clear out late this evening and overnight. This,
combined with relatively light winds, will set the stage for
efficient radiative cooling. Therefore, expect temperatures to
be 5 to 10 degrees below normal, with lows generally in the 20s
across the region.


Summary...Weak low pressure slides well to our south over the
weekend with chilly air in place, then warming is forecast to
arrive as next week progresses.

Synoptic Overview...A highly amplified pattern over the weekend and
to start next week, with a closed low in the western Atlantic while
a ridge builds into the East. An upper-level trough is forecast to
become established from central Canada to the southern Plains next
week, and a cutoff low in the western Atlantic may slow the eastward
movement of the Plains trough. This should result in a ridge aloft
into the East, which probably narrows with time and also surface
high pressure that gradually weakens. A cold front is forecast to
gradually approach from the west late Thursday.

For Saturday and Sunday...A potent upper-level trough, at least the
western portion of it, slides across the Northeast and Mid-Atlantic
region Saturday night and Sunday. This along with strong high
pressure that builds across portions of eastern Canada will steer a
weakening surface low well to our south Saturday night into Sunday.
While no precipitation is anticipated with the southern system,
potent short wave energy moving across the area with some enhanced
low/mid level moisture and low/mid level lapse rates steepening
during Sunday, may lead to some rain/snow showers. This does not
look all that widespread if it were to occur, therefore kept PoPs on
the low side across portions of the area. Otherwise, it will be
chilly and breezy at times especially Sunday as strong high pressure
well to our north has more influence and strengthens a northeast
wind. Therefore, much more of a breeze and even cooler conditions
along the coast as opposed to farther inland.

For Monday and Tuesday...High pressure builds southwestward across
much of the East Coast, while a potential storm is located well
offshore. This will maintain a northeasterly flow which should
weaken during Tuesday. Given some ridging aloft and stronger high
pressure building southwestward at the surface, dry conditions are
anticipated across the area. Temperatures remain on the chilly side,
although some warming is expected on Tuesday as the northeast flow
wanes. It will likely still be cooler though at the coast.

For Wednesday and Thursday...An upper-level ridge along the East
Coast Wednesday is forecast to narrow and weaken with time as a
trough amplifies across the Midwest and Plains. The eastward
progression of the trough may be slowed due to a cutoff low in the
western Atlantic. This will have an impact on the timing of an
incoming cold front. As of now, looks like the frontal zone slows
Wednesday and especially Thursday as the trough sharpens some more.
There should be some waves of low pressure developing along the
front as additional short wave energy swings through the base of the
amplifying trough and interacts with the baroclinic zone. Given a
more southwesterly flow ahead of the main trough aloft and surface
cold front, warm air advection should start to boost the
temperatures during this time frame. We even have temperatures
around 60 degrees forecast for parts of the area Thursday afternoon.
The degree of warming will depend on cloud cover and the timing of
the cold front and any showers with it. For now given the warming,
kept the precipitation type as rain for much of the region along
with low PoPs as the front may end up being slower.


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

Today...Mostly VFR conditions expected. There is a slightly chance
of rain/snow showers along and north of a KRDG to KPNE line.
However, the chance is too low to include in the TAFs at this time,
and even if showers develop near these TAF sites, it is unlikely
that conditions will lower below VFR. Northwesterly wind will
continue around 10KT, gusts could approach 20 KT between 15 and 21Z,
primarily for KPHL, KILG, and KACY. High confidence on the flight
category, moderate confidence that the entire period will be dry.

Tonight...VFR conditions with only high clouds (at or above 15000 ft
AGL). Winds will remain northwesterly but wind speeds should drop
below 10 KT. High confidence on all aspects of the forecast in this

Saturday...VFR, with a ceiling between about 3000-5000 feet possible
late at night especially for ACY and MIV. Northwest winds around 10
knots, becoming north-northeast at night.

Sunday...Mostly VFR. Isolated snow/rain showers possible during the
day. Northeast winds 10-18 knots with gusts up to 25 knots, with the
highest winds closer to the coast.

Monday and Tuesday...VFR overall. Northeast winds around 10 knots
with gusts up to 20 knots Monday especially closer to the coast,
then becoming light east or southeast during Tuesday.


Winds and seas on the coastal waters have dropped below small craft
advisory criteria. Therefore, we have cancelled the remaining SCA.
For today and tonight, winds and seas are likely to stay below SCA
criteria on all the waters. Gusts near or above 20 KT are expected
late this evening and overnight. There is a small chance of gusts at
or above 25 KT in that same period on the coastal waters, but chance
is too low to issue another SCA at this time.

Saturday...The conditions are anticipated to be below Small Craft
Advisory criteria.

Sunday and Monday...Small Craft Advisory conditions are anticipated
due to gusty northeast winds (around 30 knots) and building seas.
The winds should start diminishing during Monday, however seas look
to remain elevated.

Tuesday...Winds are expected to be below Small Craft Advisory
criteria, however seas on the ocean may remain elevated especially
due to a storm well offshore.


It has been a snowy March this year, and the four climate sites with
snowfall data are now in their top 5 snowiest March`s on record.

Snowiest March`s on Record...

Philadelphia - Currently tied for second.

1) 17.7" in 1941
2) 15.2" in 2018
2) 15.2" in 1914
4) 13.4" in 1958
5) 12.4" in 1993

Allentown - Currently at fourth.

1) 30.5" in 1958
2) 21.6" in 1993
3) 21.3" in 1960
4) 20.7" in 2018
5) 18.3" in 2017

Wilmington - Currently at second.

1) 20.3" in 1958
2) 14.2" in 2018
3) 13.9" in 1993
4) 13.4" in 1960
5) 13.3" in 1914

Atlantic City - Currently at fifth.

1) 17.6" in 1969
2) 15.6" in 2014
3) 13.4" in 1960
4) 12.7" in 1956
5)  9.6" in 2018

1-Day Snowfall Records in March...

Atlantic City, 5.7 inches on 3/21/18 is the 7th highest.

Wilmington, 6.7 inches on 3/21/18 is the 6th highest (2-day total of
8.1 inches is tied for the 7th highest).

Allentown, 13.2 inches on 3/21/18 is the 4th highest behind 16.7
inches on 3/13/93, 16.5 inches on 3/20/58 and 13.8 inches on




Near Term...Klein
Short Term...Johnson
Long Term...Gorse
Marine...Gorse/Johnson Climate... is the U.S. government's official web portal to all federal, state and local government web resources and services.