Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 210143

Area Forecast Discussion
National Weather Service Mount Holly NJ
843 PM EST Mon Feb 20 2017

High pressure will build over the Mid Atlantic states through
tonight, before shifting offshore. A warm front will slide through
our region Wednesday morning. A cold front may edge down into
eastern Pennsylvania and New Jersey early Friday before retreating
northward Friday night. Low pressure over the Great Lakes region
Saturday morning will send a cold front off the east coast Saturday
evening, as the storm heads across Quebec. High pressure follows
across the mid Atlantic states Sunday night.


Quiet night in progress with few changes needed in the fcst.
Temperatures and dew points running somewhat lower in a few
areas. All in all, tranquil pattern overnight.

As a sharp upper-level trough/closed low continues to exit the New
England coast through early this evening, a narrow but high
amplitude ridge will approach our area through tonight. This will
drive strong surface high pressure over our area during the course
of tonight, bringing with it subsidence.

The flow aloft will start to switch from north-northwest to
southwest toward daybreak as the aforementioned ridge axis nears our
region. This will result in increasing warm air advection up the
Ohio Valley. The ridge axis is very pronounced, which may limit the
amount of high level clouds making it to our area through the
overnight within the warm air advection pattern aloft to our west.
As a result, we slowed down the gradual increase in some of the high
clouds through the night.


A high amplitude ridge will slide across our area through early
afternoon Tuesday, before shifting offshore. This will push surface
high pressure offshore, allowing for a southeasterly surface flow to

Low pressure up near Hudson Bay will have a trailing cold front
southward to the Tennessee Valley, with a closed low tracking across
the Gulf Coast states. The flow turns more southwesterly aloft ahead
of these features across our region, which will contribute to some
increasing warm air advection aloft. An upper-level jet streak is
forecast to be moving across the Great Lakes Tuesday, which may help
contribute to some mid to high level clouds across our area through
the day. Overall, some increase in clouds are expected as we go
through the day ahead of a developing warm front. Despite some
warming aloft Tuesday, the low-level flow is expected to be out of
the southeast which will help keep temperatures cooler. This will
keep the immediate coastal locales even cooler given the wind off
the chilly ocean. High temperatures were mostly a blend of MOS and
continuity, with some tweaks especially along the coast.


500 MB: A ridge persists over the mid Atlantic states through
most of Saturday before a strong short wave departs the Great
Lakes for eastern Canada later in the weekend. The ridge
reemerges a little further south, off the mid Altantic coast,
early next week.

Temperatures: As our forecast area proceeds to a 1st or 2nd warmest
February on record and a top 10 warmest winter in the period of
record dating back to the late 19th century, calendar day averages
Wednesday are expected to be 10 to 15 degrees above normal, 17
to 22 degrees above normal Thursday, nearly 25 degrees above
normal again Friday (see yesterdays average temperatures in our
area), around 15 degrees above normal Saturday depending on the
cold air advection subsequent to the late Saturday CFP, still 2
to 7 degrees above normal Sunday and Monday.

Forecast basis: Unless otherwise noted, a 50 50 blend of the 12z/20
GFS/NAM MOS guidance Tuesday night; adjusted warmer guidance
Wednesday per the 4 Pm max`s on GGEM 2m temp and NAM boundary
layer temp; warmer adjusted mav/met guidance, then thereafter
close to the 15z/20 WPC guidance Thursday - Monday. The continuing
daily cool bias in the daytime max temperature guidance of the
last several days is probably related to the lack of snow cover
and the persistent and climatologically anomalously warm jet
stream pattern.

The dailies including any possible significant insight...

Tuesday night...Chance of light showers during the night ahead of a
warm front. Low probability there could be a touch of freezing rain
highest terrain above 1500 feet north of I-80. This ice risk isn`t
in the HWO or zones since confidence is below average and guidance
favors above freezing min temps during any rain. Confidence: average
or below average regarding the occurrence of any rain.

Wednesday...Considerable morning cloudiness, then becoming partly
sunny and warmer during the afternoon. Near record warmth still
(vulnerable records) possible though some of the cooler 2m temp
and MOS guidance does raise a cautionary flag. Our 330 PM forecast
temps may end up a degree or warmer than now predicted. This
fcst is above all available guidance and reflects the recent
cool bias in max temps the past several days... the warm regime
with a 550DM 1000-500mb thickness. Max temps probably occur
around 330 or 4 PM due to the warming southwest flow and
boundary layer temps reaching 13C at 21z. southwest wind but
much cooler coastal seabreezes. Confidence: less
than yesterday.

Wednesday night...Fair (thin high clouds). patchy fog possible in a
few countryside locations.

Thursday...Mixed clouds and sun. Near record warmth still possible
though some of the cooler 2m temp and MOS guidance does raise a
cautionary flag. Models may be rain contaminated. So there is
uncertainty. Much cooler coastal sea breezes embedded within the
southwest gradient wind. BL temp right now only fcst to 14C PHl
but 18C Delmarva...all this because of modeled showers which if
occurred would reduce max temps to the 60s. Confidence: less than yesterday and throwing caution to the
wind because of a shower risk.

Friday...early morning stratus/fog possible along a cool front that
may settled into the Nj and PA portion of our area? Maybe a shower
north of the boundary during the afternoon or maybe the boundary
doesn`t make it down into our forecast area? otherwise considerable
clouds. Wind probably southeast turning south to southwest.
Confidence: below average on the scenario.

Saturday...Models slowing down and warming. It should shower
for a few hours along and head of the cold front with a chance
for a gusty thunderstorm. Wind fields pretty strong, weak cape
but unstable with swi near -2 and tt 50. Dewpoints probably
close to 60 in a sliver ahead of the cold front. Could have a
squall line and embedded isolated severe thunderstorms if the
strong wind field instability maintains. Confidence: average.

Sunday...Becoming mostly sunny and cooler but still above normal
temps as the sfc low moves northeast into Canada taking the primary
chunk of colder air east northeast with it, making it difficult
to import too much of the cold air here, from the midwest. Still
it will be cold. Breezy. Westerly Gusts to 25 or 30 mph.
Confidence: average.

Monday...increasing clouds ahead of the next Midwest toward the
Great Lakes low pressure system. WAA precipitation may arrive
late in the day or at night.  Confidence: below average.


The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.

Tonight...VFR. North to northeast winds 5 knots or less, or becoming
locally light and variable.

Tuesday...VFR with some increase in clouds mainly above 15000 feet.
Winds becoming southeasterly during the morning at 10 knots or

Tuesday night...VFR with a small chance of shower. light south

Wednesday and Thursday...Mostly VFR conditions with ocnl cigs
aoa 5000 ft. There could be a little MVFR fog late each night.
south to southwest wind .

Friday...VFR but north of a possible quasi stnry front it might
become MVFR in a shower. east southeast wind ahead of the warm
front and southerly gusty 20 kt south of it and this front
should edge north during the afternoon and at night.

Saturday...VFR cigs with a period MVFR conds and gusty southwest
winds to 30 kt in showers and a possible tstm ahead of a CFP.


The conditions are expected to remain below Small Craft Advisory
criteria through Tuesday. High pressure will slide across our area
tonight before moving offshore during Tuesday morning. This will
result in northwest to north winds with gusts up to 20 knots to
diminish, and turn northeast to east before becoming southeasterly
Tuesday. There could be somewhat of an enhancement to the southeast
flow Tuesday nearshore and up Delaware Bay, however winds are
expected to remain under 20 knots.

Tuesday night through Friday...Winds and seas should stay below SCA
criteria. A gradual shift from southeasterly to southwesterly is
expected Tuesday night. By Thursday night, winds could be light and
variable shifting to southeasterly on Friday in response to a weak
cool front briefly settling southward into our area.

Saturday...SCA south to southwest wind conditions likely ahead of a
late day or nighttime cold frontal passage.


Records for later this coming week.

Most of these records will probably remain intact as is, but
there appears to be opportunity for approaching within 2 degrees
at PHL/ABE/TTN/MPO on 1 to 3 days.

Wednesday 2/22    Thursday 2/23   Friday 2/24

ACY 68-1991       72-1985         75-1985

PHL 68-1997/1974  75-1874         74-1985

ILG 69-1997/1974  72-1985         78-1985

ABE 68-1974       71-1985         76-1985

TTN 66-1997       74-1874         74-1985

GED 72-1997       no data          no data

RDG 70-1974       72/1932/1922    77-1985

MPO 56-1997       60-1977         60-1984




Near Term...Gorse/PO
Short Term...Gorse
Long Term...Drag
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