Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 191912
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
212 PM EST Sun Feb 19 2017

.SYNOPSIS...
A cold front will move south across our region later tonight.
High pressure will build over the Mid Atlantic during Monday
into Tuesday before shifting offshore. A warm front arrives
early Wednesday, followed by another warm front on Friday. As a
surface low lifts across the Great Lakes region, a cold front
will sweep across our area on Saturday.

&&

.NEAR TERM /THROUGH TONIGHT/...
Yet another spring-like day across the entire area, with even some
new record high temperatures occurring.

An upper-level trough in eastern Canada is forecast to amplify
southward some especially across New England. This will push a cold
front down from the north, also known as a backdoor front, later
tonight. As this occurs, cold air advection will strengthen some
later tonight however this is more notable across the northern
zones. This will allow temperatures to drop much more later tonight.

As surface high pressure begins to build in from the west and
northwest overnight, a subsidence inversion is forecast to
strengthen with some moisture pooling beneath it. This moist layer
looks rather shallow, however some guidance indicates some low
clouds developing toward daybreak especially for portions of
northeastern Pennsylvania into northwestern New Jersey. Areas
farther to the south, the moist layer looks delayed and therefore no
low cloud development is expected. A north-northwest wind will be
light tonight despite some cold air advection on the increase, as
surface high pressure draws closer.

Low temperatures were mostly a blend of MOS and continuity. The
hourly temperature and dew point grids are being adjusted this
afternoon based on the latest obs, then the LAMP/LAV guidance was
blended with continuity through early this evening. A forecast
challenge through this evening could be just how quickly the
boundary layer cools.

&&

.SHORT TERM /MONDAY/...
A strong upper-level trough/closed low is forecast to exit New
England through about early afternoon on Monday. This will allow
surface high pressure to slide across our area, although it remains
centered well to our north. This will provide a northerly wind
across the entire region, although this should be on the light side
given a loose pressure gradient. Some cold air advection is forecast
to continue through much of the day, with the coldest air aloft
found over our northern zones. This all translates into a cooler
day, however highs will still be several degrees above where we
should be for this time of year.

A strong subsidence inversion to start the morning may trap in some
lower clouds across mainly portions of northeastern Pennsylvania and
northwestern New Jersey, otherwise this should weaken as the
boundary layer warms enough. Otherwise, plenty of sunshine should
become dominant as the forecast soundings indicate the column
overall dries out through the day. High temperatures are mostly a
continuity and MOS blend. The winds may turn a bit more
northeasterly along the coast to assist with cooling off the chilly
ocean waters.

&&

.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
In the wake of the back door cold front, temperatures Tuesday
will be about 10 to 15 degrees lower than today.

By the later half of Tuesday, the surface high will be shifting
off shore as a pre frontal trough approaches from the west. This
will set up southerly low level return flow by Tuesday
afternoon. As a result, expect an increasing chance for rain
showers across the region.

The next warm front is expected by late Tuesday night/Wednesday
morning. Stayed close to a blend of guidance at this time, but
as confidence increases for an early morning warm front arrival
time, may need to go above guidance for Wednesday highs as
guidance continues to underestimate warm air advection events.

For Thursday and Friday additional warm air advection is
expected, with Thursday possibly being the warmest day of the
week (assuming that the previously mentioned warm front doesn`t
slide back south into our region as a cold front early
Thursday). However, warming on Friday could be tempered by
overcast conditions and an area of rain expanding into our
region thanks to a closed surface low lifting over the Great
Lakes Region.

The associated cold front with this low should sweep through the
region early Saturday, though there is some uncertainty with the
timing. As it does so, it should bring an abrupt end to the
rain. Even with the forecast strong cold air advection,
temperatures over the weekend may still be slightly above
normal.

&&

.AVIATION /19Z SUNDAY THROUGH FRIDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.

Rest of this afternoon...VFR with some lingering high level clouds
across the area. Northwest winds around 10 knots with some localized
gusts up to 20 knots possible.

Tonight...VFR. However, some guidance shows few to scattered
stratocumulus around 2500 feet developing towards daybreak mainly to
the north and west of PHL. Winds will remain out of the north to
northwest at 10 knots or less.

Monday...Some clouds near 2500 feet possible early mainly north and
west of PHL, otherwise VFR. Light north-northwest winds increase to
10-15 knots between 15-18Z.

Outlook...
Monday night...VFR.

Tuesday...Ceilings could lower to MVFR with rain showers continuing
into Tuesday night.

Wednesday and Thursday...Mostly VFR conditions are expected.

&&

.MARINE...
High pressure will gradually build in from the west and northwest
later tonight and Monday. This will result in a northerly wind,
however an increase in cold air advection overnight and Monday
morning should result in some increase in the winds especially
across the northern coastal waters. It appears that any gusts to 25
knots mainly across the northern ocean zones look to be short in
duration, therefore we opted to hold off on a Small Craft Advisory.
Otherwise, the conditions are expected to remain below advisory
criteria through the day Monday.

Outlook...
Monday night...winds may gust near or above 20 kt at times, but
should stay just below 25 kt.

Tuesday through Thursday...winds and seas should stay below SCA
criteria.

&&

.CLIMATE...
Several places have either tied or set a new record high
temperature for today, as of 3 PM. Preliminary Record Event
Reports (RER) are being issued for the sites breaking their
record highs, and the final RER`s will be issued late this
afternoon.

Here are the record highs for today:

PHL 68-1948
ILG 67-1997
ABE 63-1997
TTN 68-1948
GED 74-1976
ACY 73-1961
RDG 67-1997
MPO 58-1981

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...None.

&&

$$
Synopsis...Gorse/Johnson
Near Term...Gorse
Short Term...Gorse
Long Term...Johnson
Aviation...Gorse/Johnson/Meola
Marine...Gorse/Johnson
Climate...


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