Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 180238
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
938 PM EST Tue Jan 17 2017

.SYNOPSIS...
Low pressure over the Great Lakes will track towards northern New
England tonight. Meanwhile, a secondary low will begin to develop
over the Mid-Atlantic, and that will approach southern Long Island
late tonight. This entire system will move offshore on Wednesday.
High pressure then briefly builds across the Eastern Seaboard
through the end of the work week. Weak low pressure will pass
through the region this weekend, and then a stronger system will
impact the area early in the new week.

&&

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
Temperatures at Mount Pocono, PA, and High Point, NJ, remain at or
below freezing with freezing drizzle and occasionally light
freezing rain being reported. As such, extended the freezing rain
advisory until 7 am for Monroe County, PA, and Sussex County, NJ.
Although most locations in these counties will remain above
freezing, elevations near or above 1500 feet will likely stay at
or below freezing through the night. Grids were updated to account
for current trends in these areas.

Primary band of showers is now mainly confined to central NJ, but
isolated showers persist in portions of central PA. Cannot rule
out a passing shower, especially north of the Mason-Dixon Line,
the rest of the night. Current PoPs suggest this reasonably well
and did not change.

Other concern tonight is patchy fog. So far, surface visibilities
remain well above criteria (outside of the freezing rain
advisory), so will hold off issuing a dense fog advisory for now.
However, this will continue to be monitored through the overnight
hours.

Rest of forecast is in good shape.

&&

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH 6 PM WEDNESDAY/...
Low level moisture is forecast to linger into Wednesday morning
with low clouds and some patchy fog. Also, there may be some
spotty light rain or drizzle for a while.

A mid level short wave trough that was located over Iowa and
vicinity this afternoon will progress to the east and it should
pass off the Middle Atlantic coast on Wednesday afternoon.

The enhanced mixing ahead of and with the short wave and drying
in its wake should result in some breaking of the cloud cover,
especially during the afternoon hours on Wednesday.

A northwest wind is anticipated to increase around 8 to 12 MPH.
Maximum temperatures are expected to range from the lower 40s in
the elevated terrain of the Poconos and northwestern New Jersey to
the upper 50s in southern Delaware.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/...
Overview: The long term period will feature a series of low
pressure systems that will bring unsettled weather to much of the
Northeast and Mid-Atlantic. This period also features a jet stream
that will keep the Arctic air bottled up to the north. Although a
series of storm systems will impact the area during this time,
they do not have origins from the Arctic, so any cold air that
funnels into the Northeast and Mid-Atlantic will generally return
temperatures closer to normal. With deep S-SW flow that will
dominate the time frame due to a Bermuda high that will set up
over the western Atlantic, temperatures will run well above
normal, with high temperatures generally 10 degrees above normal,
for this time of the year.

Although a bit beyond the time frame for this forecast period,
the Climate Prediction Center 6-10 day outlook starting on Monday
indicates a high probability, 60-70% for NJ and Delmarva and
70-80% for SE PA and the Poconos, of above normal temperatures
next week.

Low pressure over the western Atlantic will continue to drift
offshore Wednesday night as high pressure over the TN/OH Valleys
slowly presses east. Not anticipating much in the way of lingering
precip, so will carry a dry forecast for the CWA Wednesday
evening, and conditions will further clear through the night. The
high will continue to slowly press east on Thursday, and will be
nearly overhead along the East Coast late Thursday night, and then
will move offshore on Friday. Skies clear out during the day
Thursday, and generally expecting mild conditions with highs in
the low to mid 40s across the Poconos, and in the low to mid 50s
across the rest of NJ, SE PA, and into the Delmarva.

The next system is rather weak and disorganized, and is almost
falling apart as it tracks from the Southern Plains and into the
Great Lakes and OH Valley. Nonetheless, a weak warm front
approaches on Friday afternoon, and some light precip will develop
over extreme SW portions of the CWA, generally across SE PA, the
Delmarva, and southern NJ in the afternoon, and then light precip
spreads to the north and east Friday night as that system lifts
northeast through the region. High pressure briefly builds through
the region on Saturday, but moves offshore by Sunday as a weak
cold front passes through. Conditions should generally be dry, but
cannot rule out a few passing showers.

Things get interesting for the start of the new work week. A
trough moves into the Western U.S. early in the weekend, and then
a strong closed H5 low moves into the Southern Plains/Gulf Coast
states on Sunday, where a storm system become more organized and
developed. This system will lift to the north and east, towards
the TN/OH Valleys, Sunday night and Monday, and will slowly work
its way through the East Coast Monday through Tuesday. Latest
GFS/ECMWF in decent agreement with the overall setup, so feel
reasonably confident going with high-end likely PoPs for Sunday
night through Monday night, with western portions of the CWA
bumped up to low-end categorical. With strong onshore flow ahead
of this system, can expect abundant low-level moisture to spread
into the region. GFS indicating PWATs around 1.5" during this
time, so can expect locally heavy rain from time to time. In
addition, GFS indicating an environment with CAPE (less than 100
J/kg) and 850-700MB wind speed 60-65 KT. Cannot rule out a rumble
of thunder Monday afternoon, especially south of I-76, but given
that it is mid-late January, may be a bit too far to include a
mention of thunder on Day 7. But will keep an eye out on it.

Lower confidence in the forecast by Tuesday. Models indicating
secondary low will develop off the Mid-Atlantic coast, and it
remains to be seen how that will impact the Northeast/Mid-
Atlantic. Will carry chance PoPs for most of the region, with
higher PoPs along the coast.

Monday looks to be the warmest, but wettest, day of the period
with highs ranging from the 40s across the Poconos to near 60 in
the Delmarva. Otherwise, as mentioned above, temperatures will be
warm.

&&

.AVIATION /03Z WEDNESDAY THROUGH SUNDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Light to moderate showers are generally moving away from the TAF
sites at this time, though isolated showers remain possible
through the overnight hours. Ceilings are generally IFR to LIFR
across the region and are expected to hold in these categories
through the night. Visibilities are generally 1-3 SM and am
anticipating these to deteriorate to around a mile, perhaps less
in isolated spots, through the rest of the night.

Expecting improvement to MVFR by the late morning hours and VFR by
the afternoon. Northwest winds should increase, potentially with
gusts 15-20 kts in the afternoon. However, latest forecast
soundings suggest ceilings could remain near upper-end MVFR
thresholds through much of the day in most of the area, perhaps
even lowering again by late afternoon or early evening. Forecast
confidence is below average during the day tomorrow.

OUTLOOK...
Wednesday night through Friday morning...VFR. Wind speeds should
be 10 KT or less during this time.

Friday afternoon through Friday night...Sub-VFR conditions in
-RA.

Saturday through Sunday. Mainly VFR. Few passing showers with
brief sub-VFR conditions possible.

&&

.MARINE...
Weak low pressure is forecast to develop off the coasts of New
Jersey and Long Island tonight before it moves out to sea on
Wednesday. The system is not expected to become particularly
strong so wind speeds and wave heights should remain below the
Small Craft Advisory criteria.

The wind is anticipated to veer from the southeast and south this
evening to the west and northwest for Wednesday with speeds
increasing around 15 knots. Wave heights are forecast to build
only to around 2 to 3 feet on our ocean waters.

OUTLOOK...
Wednesday night through Sunday...Sub-SCA conditions expected. Few
passing showers possible on Friday/Friday night.

Sunday night through Monday night...Easterly flow 20-30 KT. SCA
conditions likely, with gale force winds possible on Monday,
mainly on the ocean waters. Rain, possibly heavy at times.
Isolated thunderstorms possible Monday afternoon.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Freezing Rain Advisory until 7 AM EST Wednesday for PAZ055.
NJ...Freezing Rain Advisory until 7 AM EST Wednesday for NJZ001.
DE...None.
MD...None.
MARINE...None.

&&

$$
Synopsis...MPS
Near Term...CMS
Short Term...Iovino
Long Term...MPS
Aviation...CMS/Iovino/MPS
Marine...Iovino/MPS



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