Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 221044

Area Forecast Discussion
National Weather Service Mount Holly NJ
644 AM EDT Thu Mar 22 2018

In the wake of the departing Nor`easter, high pressure in Canada
will slowly build south towards our region through the end of
the week. A low pressure system propagating from the southern
Plains to the southeastern U.S. should remain south of our
region late this weekend. High pressure builds over our region
early next week.


Some flurries generally along and east of the Delaware River
continue early this morning, but even those are starting to
dissipate. Thus, expect dry conditions through the daylight

In the wake of the departing low, should have a relatively
tranquil, albeit cold day. Thanks to the northwesterly flow,
cold air advection, and fresh snow pack, temperatures will be
10 to 15 degrees below normal, with highs forecasted between the
lower 30s in the Poconos and mid 40s elsewhere. This is slightly
below MOS guidance as that tends to have a warm bias immediately
following a snow event. While there will be some melting thanks
to the temperatures above freezing, expect much of the region
will keep a substantial snowpack going into this evening.


Thanks to clearing skies, temperatures tonight are expected to
be lower than what we saw this morning, with lows tonight
forecasted to be generally in the 20s across the region. As a
result, any water on the roads from snow melt during the day
could freeze leading to slippery conditions on area roads
tonight into early Friday morning.


Friday...clearing skies on Thursday night will be short lived as
a mid and upper level low, digs quickly southeast over the
region through the day. This will result not only in increasing
clouds, but also possibly some rain and snow showers, especially
along and north of the I-78 corridor through the day. As noted
in the previous forecast, the ECMWF continues to show dry
conditions this day, and moisture could be very limited with
little chance for moisture advection before this event. However,
lower resolution models tend to underforecast precip with these
types of clipper systems, so kept PoPs close to the previous

Did not spend much time on the forecast beyond Friday to focus
on wrapping up the winter storm event. From the previous
discussion...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.

Today...VFR conditions expected. NW winds 10-15 kt with gusts
up to 20 kt. High confidence.

Tonight...VFR conditions expected with only high clouds (15000
AGL or higher). Northwesterly winds near or below 10 KT. High


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

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.


Today and tonight...winds and seas will continue to subside,
but expect SCA conditions to continue on the coastal waters for
much of this period. Gale force conditions will continue through
mid morning on the lower Delaware Bay and right at the mouth of
the Bay. On the upper Delaware bay, winds and waves will likely
subside below SCA criteria later this morning.

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

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.


There were several record daily maximum snowfalls set yesterday,
March 21st. This occurred at Philadelphia, Wilmington and Allentown
(which smashed their daily record). Atlantic City just missed the
daily snowfall record.

Location        Record for 3/21     Actual Snowfall 3/21/18
--------        ---------------     -----------------------

PHL             4.7" (1932)          6.7"
ACY             5.9" (1889)          5.7"
ILG             5.4" (1964)          6.7"
ABE             4.3" (1964)         13.2"


MARINE...Small Craft Advisory until 6 AM EDT Friday for ANZ450>452.
     Gale Warning until noon EDT today for ANZ453>455.
     Small Craft Advisory until 8 AM EDT this morning for ANZ430.
     Gale Warning until 10 AM EDT this morning for ANZ431.


Near Term...Johnson
Short Term...Johnson
Long Term...CMS/Johnson
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