Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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518
FXUS61 KPHI 181336
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
836 AM EST Thu Jan 18 2018

.SYNOPSIS...
High pressure will build across the Gulf coast through the end
of the week, then offshore over the weekend. An area of low
pressure will move across eastern Canada over the weekend as a
back door cold front approaches from the north. Another area of
low pressure will move through the Great Lakes Monday night into
Tuesday, pulling a cold front across the area. High pressure
will build toward the area late Wednesday into Thursday.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Adjusting hourly temps based on latest surface obs. Temps in
some spots in northwest NJ bottomed out, but temps in other
areas have risen as winds increased to 5-10 MPH. Temps should
steady off the next couple of hours, then rise after sunrise.

Otherwise, surface low pressure off the Mid-Atlantic coast
continues to lift out to sea today as surface high pressure over
the Lower Mississippi Valley slowly builds east. Meanwhile,
closed H5 low over the Carolina coast tracks east as upper
ridging builds into the Appalachians.

For the local area, can expect a mostly sunny day as subsidence
associated with the upper level ridging builds east. Pressure
gradient tightens in the afternoon, and W-NW winds will increase
to around 15 mph with 20-25 mph gusts.

Airmass moderates over the area as 850 mb temps rise to 0 to
+4C, resulting in highs in the mid 20s in the Poconos, and
otherwise mostly in the low to mid 30s. Highs in the southern
portion of the Delmarva will be near 40.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM FRIDAY/...
High pressure continues to build east tonight. Pressure
gradient slackens, and winds become light and variable. A weak
upper disturbance passes well north of the area tonight, and
this may bring some mid and upper clouds to the Poconos and NW
NJ. Otherwise, skies will be mostly clear. As a result, can
expect strong radiational cooling conditions for the Lehigh
Valley, northern NJ, and the Pine Barrens of southern NJ. Lows
tonight will range from the teens to lower 20s.

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
Quiet weather for the end of the week into the the weekend,
with a return of unsettled weather for early next week.

Dry conditions will continue for Friday into Saturday as high
pressure builds to our south across the Gulf coast states
through Friday, then offshore Saturday. Our area will remain on
the northern periphery of the high which will keep a dry, west
to southwest flow across the area.

On Sunday, a back door cold front will sag toward our area from
the north as an area of low pressure slides eastward across
eastern Canada. Sunday should remain dry, but as we move into
Sunday night and Monday, the back door frontal boundary is
forecast to make its way across a portion of the area. As it
does so, there will be some enhanced moisture and lift moving
overtop of the front. This may lead to some light rain
developing across the area Sunday night into Monday. It is
possible that temperatures could drop below freezing across
portions of northern New Jersey and northeastern Pennsylvania,
possibly leading to some light freezing rain.

Then Monday night into Tuesday morning, a cold front is
expected to sweep across the area as an area of low pressure
moves through the Great Lakes region. This will lead to a period
of rainfall overnight Monday into Tuesday. It is possible that
the rain could change over to snow across northern New Jersey
and northeastern Pennsylvania before the precipitation ends
Tuesday morning behind the cold frontal passage.

For Tuesday night into Wednesday, the low pressure system moves
across eastern Canada, while a secondary cold front moves
toward the area from the west, which may cross the area during
the day. Most of the area will remain dry, but there my be
enough moisture across the northern areas as a short
wave/vorticity impulse moves through for some snow showers to
get squeezed out across portions of northern New Jersey and
northeastern Pennsylvania.

&&

.AVIATION /14Z THURSDAY THROUGH MONDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Today...VFR/SKC. NW winds 10-15 KT with gusts up to 20 KT,
except for KPHL/KACY, where gusts up to 25 KT are possible.

Tonight...LGT/VRB winds. SKC.

OUTLOOK...

Thursday through Saturday night...VFR. West to southwest winds;
winds may gust 15-20 knots at time. High confidence.

Sunday night-Monday...Conditions may lower to MVFR overnight
Sunday into Monday, possibly IFR for northern areas, with a
chance of showers. Gusty southeast winds 15-20 knots. Moderate
confidence.

&&

.MARINE...
Today...Winds along the Delaware Bay and Delaware coastal waters
have dropped off. Therefore, have replaced the gale warning with
a small craft advisory. Expect SCA conditions on the Delaware
Bay to continue through mid day. For the coastal waters, wind
gusts may diminish a bit later this morning before picking up
again in the afternoon. Moderate freezing spray has been
reported at some near shore sites. However, this will likely be
short lived (only through late morning), before conditions
improve.

Tonight...SCA conditions end on the ocean this evening, and
gusts to 20 KT will continue. Seas will diminish to 2-4 feet. On
DE Bay, tranquil conditions.

OUTLOOK...

Friday-Friday night...Conditions expected to be below advisory
levels, but winds may periodically gust around 20 knots.

Saturday-Saturday night...Winds may approach Small Craft
Advisory levels across the northern half of the Atlantic coastal
waters.

Sunday-Monday...Conditions expected to be below advisory
levels, but winds may periodically gust around 20 knots.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...Small Craft Advisory until 1 AM EST Friday for ANZ450>455.
     Small Craft Advisory until 1 PM EST this afternoon for ANZ430-
     431.

&&

$$
Synopsis...Robertson
Near Term...MPS
Short Term...MPS
Long Term...Robertson
Aviation...Robertson/MPS
Marine...Johnson/Robertson/MPS



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