Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 040943
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
443 AM EST Sun Dec 4 2016

.SYNOPSIS...
High pressure over the region today will progress offshore tonight.
A weak disturbance will pass  through the area tonight into early
Monday. High pressure builds back into the Mid-Atlantic states
Monday afternoon and night. An area of low pressure over the Gulf of
Mexico tracks northeastward  and toward the region Tuesday. This low
is forecast to pass to our south Tuesday afternoon and evening and
then move off the Mid-Atlantic coast late Tuesday night and
Wednesday. A strong cold front likely moves through our area
Thursday as another area of low pressure tracks across the
Northeast states. This low will strengthen over the Canadian
Maritimes Friday and Saturday while high pressure builds in from
the central U.S.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Low clouds are stubbornly hanging on this morning over the forecast
area in spite of model RH forecasts which indicates clouds should be
breaking up or dissipating. Anyway, the cloud cover is keeping temps
a few degrees above the forecast overnight mins in most areas. Winds
have diminished and become more northerly as the center of
surface high pressure approaches from the west.

For today, high pressure will continue to move across the area with
light NW to N winds continuing. The low clouds should tend to break
up during the morning but by afternoon high-level cirrus will be
spreading in from the SW ahead of the next approaching shortwave
trof. Afternoon max temps are forecast to be a few degrees cooler
than yesterday across the area.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM MONDAY/...
A fast moving shortwave trof and associated surface pres trof will
cross the area tonight. Winds become southerly with some decent low-
level warm advection and upward VV ahead of the trof. Some increased
moisture should be available as clouds are streaming NE from the NW
GulfMex already. Our forecast area should see a quick shot of fairly
light precip between midnight and dawn on Monday.

Based on the forecast temperature and moisture profiles, it looks
like p-type will be mostly snow in the Poconos and NW NJ, a mix of
rain and snow N/W of PHL and north-central NJ, and mostly rain
elsewhere. Some snow accumulation, up to around and inch, is
possible where the precip remains mostly snow.

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...
A northern-stream shortwave disturbance and associated surface
trough is forecast to quickly swing through the region early
Monday morning. Models have trended toward a more progressive
system, which would equate to a faster ending time of precipitation
Monday morning. This trend is good news for the Monday morning
commute in northeastern PA and northwestern NJ as any snowfall
accumulations after sunrise should be minor. We may still see up
to an additional half inch of snowfall in the higher elevations
along and north of I- 80 before it all ends later that morning.

High pressure briefly builds into the region Monday afternoon and
night. Expect skies to clear from southwest to northeast during the
afternoon. High temperatures Monday afternoon range from the upper
30s in the Poconos to the lower 50s from Philadelphia and points
south/east. A favorable radiational cooling pattern will initially
be in place Monday night with a break in clouds and calm winds
underneath the high. High clouds will start to overspread the area
from the southwest late tomorrow night as low pressure approaches
from the Gulf Coast states; which may curb cooling across the south.
Low temperatures near or slightly below freezing are forecast for
all of northeastern PA/northwestern NJ, and rural locations west of
the Phila metro in southeast PA and in the NJ Pine Barrens.

Low pressure lifts northeastward toward the Ohio Valley on Tuesday.
Models are in good agreement with a secondary low developing on the
lee side of the southern Appalachians Tuesday morning. This
secondary coastal low will then track up the Southeast coastline
Tuesday, passing to our south by Tuesday evening and offshore later
Tuesday night. Precipitation from this system will likely reach the
Delmarva by the morning rush, then spread farther north through the
day. Thermal profiles look warm enough for the ptype to be rain for
most of the region. However, precip at the onset may briefly start
out as snow or a rain/snow mix west of the Fall Line. Precip in
these northwestern zones should transition to liquid during the
afternoon as a warm nose aloft becomes established. Some of the
model guidance shows surface temperatures hovering in the mid 30s
in our coldest spots north of I-80 (southern Poconos in PA,
Sussex County in NJ). There is an outside chance of freezing rain
if temperatures in these coldest spots wind up being only a few
degrees lower than forecast. It will be important to monitor
trends/biases in wet-bulb temperatures for this event. Kept
snow/ice accumulations out of the forecast for Tuesday and
Tuesday night due to low confidence.

By Wednesday morning, the southern low will have moved offshore and
will be east of the area. However, we may still be under the
influence of a surface trough associated with this low through the
day Wedensday into Wednesday night. As a couple of short
wave/vorticity impulses slide across the area, we could continue to
have low clouds and precipitation affect the area.

By early Thursday, the low pressure across southern Canada and
the low offshore weaken. They then combine to our north during the
day Thursday into Thursday night, before strengthening and slowly
lifting northward Friday into Saturday. A strong west to
northwest flow will develop across the area. With steep lapse
rates across the northern portions of the area and enhanced low-
mid level moisture forecast to remain, especially across the
northern portions of the area and farther north, we could continue
to see snow or rain showers Thursday through Friday, and possibly
continue into Saturday.

One thing for sure for the end of the week, regardless of
precipitation, is it will get cold and windy for the latter
portion of Thursday, but especially Friday and Saturday. Wind
chills will likely get into the single digits to lower teens for
many areas overnight each morning Thursday night through Saturday
morning when the temperatures are the lowest.

&&

.AVIATION /10Z SUNDAY THROUGH THURSDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

VFR conditions should continue at all the TAF site through today and
this evening. The low cloud cover with ceilings 4000 to 5000 ft has
been very persistent but some breaks should appear as the day
wears on. Winds today will be NW 10 kt or less as a ridge of high
pressure moves over the area.

Ceilings will begin to lower this evening ahead of low pressure
moving in from the west. MVFR conditions are expected to develop
overnight in light rain and fog. A mix of rain and snow is likely at
ABE and RDG so visibility may be further reduced there.

OUTLOOK...

Monday...Precip, mainly RA, ends by mid morning. RA may mix with
SN at northern terminals (RDG/ABE/TTN). MVFR or IFR around
daybreak will improve to VFR from SW to NE during the morning and
early afternoon.

Monday night...VFR.

Tuesday-Wednesday...Conditions lowering to MVFR/IFR during the
morning with periods of rain/fog/drizzle likely. Snow also
possible for northern areas. Winds likely become gusty 15-20
knots out of the northwest late in the day.

Wednesday night...Steady rain likely ends during the evening, but
lower clouds may linger into the night. Gusty northwest winds 20-25
knots possible.

Thursday...Generally VFR, but scattered showers are possible during
the day which may temporarily lower conditions. Gusty northwest
winds 25-30 knots.

&&

.MARINE...
Sub SCA conditions are expected through today and tonight. NW
winds should remain a bit gusty for a while today but will
diminish by this evening as a ridge of high pressure moves
overhead. Seas will gradually subside along with the wind. Winds
overnight will become light and variable, however visibility may
be reduces in areas of rain and fog after midnight.

Monday and Monday night...Winds and seas below SCA criteria.

Tuesday-Wednesday...Onshore flow strengthens on Tuesday. SCA may
be needed for winds by Tuesday afternoon. SCA for winds and seas
likely Tuesday night and Wednesday. Winds may reach gale force for
a period late in the day Tuesday, particularly across the coastal
waters of DE and southern NJ as well as the lower DE Bay.

Wednesday night...Winds likely drop below advisory levels, but seas
could remain above 5 feet.

Thursday and Thursday night...Northwest winds increase behind a
cold front. A SCA will likely be needed.

&&

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

&&

$$
Synopsis...Klein
Near Term...AMC
Short Term...AMC
Long Term...Klein/Robertson
Aviation...AMC/Klein/Robertson
Marine...AMC/Klein/Robertson



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