Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 251615
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
1215 PM EDT Mon Mar 25 2019

.SYNOPSIS...
A cold front will settle to our south this morning. A weak area of
low pressure then tracks along the front and slides south of our
region tonight into early Tuesday. High pressure then builds into
the region Tuesday and remains in place through Thursday before
weakening some on Friday. A cold front approaches during Friday,
then moves through along with low pressure Saturday night into
Sunday.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...

1230 pm update: Some breaks in cloud cover primarily in the
southern portion of the forecast area resulted in temperatures
rising a bit more than expected, so update Temperature
trends/MaxTs based on this. Otherwise rest of forecast remains
on track.

930 update:No significant changes to previous forecast.
Expecting showers to move in from W-E this afternoon across
approximately the southern 2/3rds of the area. Main forcing will
be lift along the northern fringes of a shortwave currently
centered over SW Indiana which will induce sfc low development
over S Virginia this afternoon. Given cold advection and
abundant cloud cover temperatures will flatline for much of the
day, maybe rising a couple degrees from current readings.

Previous discussion below:
A cold front extended from New England, across Pennsylvania to
the Ohio River Valley early this morning. The boundary will sink
to the south, passing across the rest of the Keystone State, as
well as New Jersey, Delaware and northeastern Maryland by
midday.

Low pressure was located along the front in the lower Ohio River
Valley early this morning. It will progress eastward, reaching North
Carolina late in the day. The northern part of an area of rain
showers associated with the low will move into our region from the
west this afternoon. Light showers are likely in much of
southeastern Pennsylvania, northeastern Maryland, Delaware and
southern New Jersey. The potential for showers is expected to
decrease in areas to the north. We are anticipating little chance of
rain in the Poconos and in far northern New Jersey.

The sky will remain mostly cloudy for today. The wind should settle
into the north around 5 to 10 MPH. High temperatures are expected to
be mainly in the 50s in our forecast area. Readings should not get
above the 40s in the Pocono Region and in far northern New
Jersey.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM TUESDAY/...
The surface low is forecast to pass off the North Carolina coast
tonight. Meanwhile, high pressure will begin to build into our
region from the Great Lakes.

Light showers are expected to linger this evening in northeastern
Maryland, Delaware and southern New Jersey before they move away to
our southeast late tonight. A very sharp clearing line is
anticipated to drop over our region from the northwest overnight as
very dry air begins to arrive from that direction.

The northerly wind is expected to increase to 10 to 15 MPH. Lows
tonight should range from the upper teens in the elevated terrain of
the Poconos to the middle 30s in southern Delaware.

&&

.LONG TERM /TUESDAY THROUGH SUNDAY/...
Summary...Much cooler and drier Tuesday and Wednesday, then turning
much warmer Thursday and especially Friday into the weekend.

Synoptic Overview...A closed low initially centered just east of
Hudson Bay Canada will shift farther east through Wednesday. The
southern extension of this trough is forecast to shift off the East
Coast later Tuesday into Wednesday. Cyclonic flow aloft therefore
prevails into Wednesday before turning more zonal. A sprawling
surface high builds across our area before shifting north and east
Friday into Saturday, while a closed low is east of the Southeast
coast. An upper-level trough amplifies into the Plains late in the
week, however the extent of phasing will have an impact on the
timing of this feature shifting eastward. An initial cold front
looks to approach during Friday but it probably stalls before it
arrives due to some ridging, then the main cold front and surface
low moves through Saturday night or Sunday.

For Tuesday...The axis of an upper-level trough is forecast to swing
across our area during the afternoon, with weak low pressure exiting
early well to our south. An expansive area of high pressure centered
over the Great Lakes will gradually build eastward. This along with
weak low pressure well to our southeast will result in a
northeasterly surface wind, which will be gusty for a time
especially closer to the coast. Substantial drying of the airmass is
expected with dew points tumbling into the teens and single numbers
for most despite the northeast flow. It will be much cooler and with
the onshore wind component it will be even cooler along the coast.

For Wednesday through Friday...An area of tranquil weather is
situated across our region thanks to surface high pressure. This is
between an eventual trough that ejects out into the Plains toward
the end of the week, and low pressure in the Western Atlantic. The
trough out West eventually will send low pressure northeastward from
the Plains. An initial cold front looks to stall as it approaches
during Friday as it runs into some ridging. Ahead of this cold
front, southerly flow along with warm air advection will result in a
warming trend after a cold start Wednesday morning. The warming will
likely be tempered along the coast as the surface winds may retain
at least some onshore component. The airmass is forecast to be
rather dry Wednesday into Thursday, however a more southerly
component to the wind especially Friday should allow the dew points
to increase. A few warm air advection induced showers could occur
across the western zones Friday as the aforementioned cold front
approaches, however the main forcing looks to remain much farther to
the north and west.

For Saturday and Sunday...The pattern locally will depend on the
evolution of short wave energy over the western to central U.S. and
its interaction with an upper-level trough amplifying southward from
northern Canada. The general trend has been to further amplify the
short wave and phase it with part of the northern trough before
moving it through the East. The degree of amplification however will
impact the speed of the feature and its associated cold front. A
slower arrival of the cold front and low pressure system will be
likely if the trough amplification is stronger. Given the timing
uncertainty, kept the PoPs into the low chance range as both pre-
frontal convection and precipitation associated with the cold front
are possible.

&&

.AVIATION /16Z MONDAY THROUGH FRIDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.

Today...Mainly VFR under a mostly cloudy sky. Rain showers after
about 19Z may be accompanied by MVFR conditions. Variable wind 6
knots or less becoming north 4 to 8 knots this morning.

Tonight...Areas of MVFR conditions in showers through about 02Z,
then mainly VFR with decreasing cloud cover. North wind increasing
to 8 to 14 knots.

Outlook...
Tuesday...VFR. Northeast winds 10-15 knots with gusts up to 25 knots
with the highest at ACY, diminishing later in the afternoon and
especially at night.

Wednesday through Friday...VFR. Light and variable winds becoming
light east to southeast later Wednesday, then southerly Thursday and
Friday.

&&

.MARINE...
A cold front will drop across the waters of New Jersey and Delaware
from the northwest and north this morning. The wind is forecast to
settle into the northeast and it should increase to 10 to 15 knots
today. The northeast wind is expected to strengthen a bit for
tonight, with speeds of 15 to 20 knots and gusts of 25 to 30 knots
anticipated. There is a Small Craft Advisory in effect beginning
tonight for our ocean waters and for the lower part of Delaware
Bay.

Outlook...
Tuesday...Small Craft Advisory for the Atlantic coastal waters and
lower Delaware Bay with northeast winds gusting up to 30 knots. The
winds diminish from north to south later Tuesday (Delaware Bay by
midday). Seas on the ocean will remain elevated due to the onshore
flow.

Wednesday through Friday...Small Craft Advisory seas may linger
across the southern Atlantic coastal waters Wednesday morning,
otherwise the conditions should be below advisory criteria.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...Small Craft Advisory from 11 PM this evening to 8 AM EDT
     Wednesday for ANZ452>455.
     Small Craft Advisory from 3 AM to 4 PM EDT Tuesday for ANZ450-
     451.
     Small Craft Advisory from 3 AM to 10 AM EDT Tuesday for ANZ431.

&&

$$
Synopsis...Gorse
Near Term...Carr/Iovino
Short Term...Iovino
Long Term...Gorse
Aviation...Gorse/Iovino
Marine...Gorse/Iovino



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