Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 181929
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
229 PM EST Sat Feb 18 2017

.SYNOPSIS...
A warm front will lift north of our area through today. A weak cold
front is expected to settle through our area late tonight and early
Sunday as low pressure tracks well to our north. Another cold front
is forecast to push through the area early Monday, then high
pressure moves in later Monday into Tuesday before shifting offshore
Tuesday night. A weakening cold front moves across the area early
Wednesday, then another frontal boundary approaches Thursday and
stalls near the area through Friday.

&&

.NEAR TERM /THROUGH TONIGHT/...
A quick update was sent to raise the high temperatures for many
areas, and adjust the hourly temperature grids to reflect an
even faster temperature increase this afternoon.

A spring-like afternoon in progress as low-level warm advection has
increased as a warm front continues to lift north of our area. The
12z Sterling, VA raob showed +14C at the top of a strong low-level
inversion (about 1500 feet). Some cooler temperatures are noted
right along the coast though with a more southerly wind component
off the chilly ocean water. Through tonight, our region is mostly
between systems. One tracks well to our north as the parent trough
slides from Hudson Bay toward the Canadian Maritimes. This will
however push a weak cold front into our area later tonight. The
second system is a closed low that will open up/weaken as it tracks
eastward from the Tennessee Valley to the southern Mid Atlantic
overnight.

Is is mostly the southern system that is driving an increase in
mostly high level cloudiness across our area this afternoon and
especially tonight. There is a low-level jet around 40 knots
forecast to develop close to our northern zones for a time tonight
before shifting into coastal New England. This will aid in some
moisture advection, however forcing with the incoming cold front is
weak and moisture looks rather limited. As a result, perhaps some
sprinkles across mostly our southern zones overnight. Given the
expected cloud cover on the increase tonight in combination with a
southwesterly wind, will result in milder temperatures. Low
temperatures are mostly an even blend of MOS and continuity.

&&

.SHORT TERM /SUNDAY/...
Surface low pressure will move into the Canadian Maritimes Sunday,
with a weakening upper-level trough sliding offshore of the southern
Mid Atlantic region. A weak cold front associated with the northern
surface low will settle across our area but then tend to stall or
even wash out. There is a secondary cold front that is forecast to
stay to our north during the day Sunday, and colder air is found
behind it. The initial front has little change in temperature with
it with just some weak cold air advection forecast in the afternoon,
however the boundary layer remains warm. The low-level flow turns
more from the west and northwest during the day which will add a
downslope component for the coastal plain. As a result, another warm
afternoon is expected although the far north should be a bit cooler
given the weak cool air advection settling in. Some spots, mainly
from Philadelphia on south and east, may be very close to their
record high temperature for the date.

An area of mainly mid level clouds associated with the southern
system will exit to the east in the morning, with an increase in
sunshine expected. High temperatures are a MOS blend, however these
were boosted a bit especially for the coastal plain (I-95 south and
east) given a downsloping component to the flow. It should be warmer
at the coast given enough of an offshore flow.

&&

.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
A back door front is forecast to push southward through the
area early on Monday before high pressure builds across the area
later Monday into Tuesday. Cooler conditions are expected
Monday and Tuesday as compared to Sunday, but will remain above
normal.

A warm front may pass across the area Tuesday into Tuesday
night as high pressure shifts offshore. Dry weather should
continue on into Tuesday.

A cold front is then expected to approach the area Tuesday night
and pass through during the day Wednesday. Precipitation may
start overnight Tuesday as a short wave/vorticity impulse slides
across the area. If precipitation starts early enough, there
could be a wintry mix across the far northern areas, mainly
along and north of I-80 corridor. Guidance indicates the
precipitation beginning to dissipate as it approaches the east
coast as the front moves through the area. So we`ll keep a
chance/slight chance for isolated showers across the area
Tuesday night into Wednesday.

Another front is forecast to approach the area Thursday, then
stall near the area through Friday. There is a chance that some
scattered showers could develop overnight Thursday into Friday
as a couple of short wave/vorticity impulses move across the
area. However, the best chance for precipitation looks like
Saturday as a stronger frontal boundary moves into the area.

&&

.AVIATION /20Z SATURDAY THROUGH THURSDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

This Afternoon...VFR with some increasing high level clouds.
Southwesterly winds around 10 knots, with some local gusts up to
20 knots.

Tonight...VFR with thickening clouds, and a ceiling lowering into
mainly the 7000-10000 feet range. Southwest winds less than 10
knots, becoming westerly.

Sunday...VFR. A ceiling between about 7000-10000 feet to start,
which then thins out. West to northwest winds increasing to around
10 knots.

OUTLOOK...
Sunday night-Tuesday...Generally VFR expected. CIGS may
approach MVFR at times Sunday night into Monday morning. Gusty
winds 15-20 knots during the day.

Tuesday night-Wednesday...Conditions lowering to MVFR or IFR
overnight into Wednesday morning with a chance of showers.

&&

.MARINE...
The conditions are expected to remain below Small Craft Advisory
criteria through Sunday. A southwesterly flow through tonight will
gust to around 20 knots at times, then turn west and northwest late
tonight and Sunday as a weakening cold front moves through.

OUTLOOK...
Sunday night-Monday...Generally sub Small Craft Advisory
conditions expected, although winds may approach advisory levels
across the northern New Jersey coastal waters overnight Sunday
into Monday morning.

Monday night-Wednesday...Sub Small Craft Advisory conditions
expected although winds may gust up to 20 knots at times.

&&

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

&&

$$
Synopsis...Gorse/Robertson
Near Term...Gorse
Short Term...Gorse
Long Term...Robertson
Aviation...Gorse/Robertson
Marine...Gorse/Robertson


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