Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 180821

Area Forecast Discussion
National Weather Service Mount Holly NJ
321 AM EST Sun Feb 18 2018

High pressure briefly builds across our area today, then offshore
tonight. A strong warm front lifts northeast across our area early
Tuesday, followed by a cold front late Wednesday. That cold front
stalls to our south with waves of weak low pressure of moving
northeast along the front Thursday through Saturday. Eventually a
larger low pressure system should move across southeast Canada on


Watch for some slippery spots on untreated surfaces early this
morning due to residual moisture and/or slush.

A strong short wave trough with an associated robust short wave will
shift east of the New England coast this morning (a few snow showers
possible early this morning across the far northwest zones), with
the flow aloft going more zonal in its wake. As this occurs, a
strong ridge centered in the southwestern Atlantic Ocean extends
westward into the Gulf of Mexico. A sprawling area of high pressure
at the surface will quickly build over our region during today.

Some cold air advection occurs this morning, however this quickly
diminishes this afternoon. As drier air along with increasing
subsidence overspreads our area, the cloud cover is expected to
quickly erode early this morning. There could then be some
stratocumulus leftover for a time within a northwesterly wind which
diminishes this afternoon as high pressure arrives.

Temperatures could be a bit of a challenge today thanks to the
expansive area of 4+ inches of snow last evening. While temperatures
are expected to rise into the 40s for much of the area this
afternoon, these could be tempered some due to energy going into
melting the snow. We therefore went a little cooler especially north
and west of I-95 but not to much lower given lots of sunshine
expected. To the south and east of here, there is much less snow and
there will be a downslope component of the wind.


As a significant upper-level trough settles into the West, a ridge
begins to build across the East. Surface high pressure will
therefore shift offshore allowing a return surface flow to start
developing. In addition, the flow aloft backs to more southwesterly
through tonight along with an increase in warm air advection. There
are some weak short waves riding the northern side of the gradually
building ridge, and these along with an increase in warm air
advection could toss some clouds our way during the course of the
night especially late. This may have an impact on temperatures, as
winds will be light to calm at the surface with dew points low
enough to assist in radiational cooling. For now, we opted to go
somewhat colder across the northern areas assuming at least some
snow cover will remain.


**Record warmth possible Tue and expected Wed**

Monday through Wednesday....

For Monday, the high continues to push off to the east through
the day with a warm front approaching from the south and west
ahead of the next system. This will bring increasing clouds with
some showers likely by afternoon...mainly over eastern PA.
Highs will generally range from the mid 40s north to the 50s
across the Delmarva and southern NJ.

Some showers may continue into Monday evening before lifting
out overnight as the front moves through. Temperatures will be
quite mild with lows only dropping to the 40s to low 50s. This
will be followed by near record warmth on Tuesday as a strong SW
flow takes hold. We continue to forecast temperatures above the
model consensus and are generally looking at highs ranging from
the 60s in the north to the low 70s across SE PA as well as
much of the Delmarva and southern NJ. Areas right near the coast
will likely be cooler though.

For Tuesday night into Wednesday, temperatures continue to warm
with record warmth forecast by Wednesday...highs currently
forecast to reach the low to mid 70s over SE PA as well as much
of the Delmarva and NJ. Conditions should be dry for the most
part though by late Wednesday a cold front could bring some
showers in from the west...mainly for eastern PA.

Wednesday night through Saturday...

In the big picture, this period will be dominated by somewhat
cooler, though still well above average temperatures as a long
wave trough persists over the Rocky Mountains with the area in a
SW flow. Conditions will also trend more unsettled as a series
of waves move north and east along a wavering front that will
linger in the region.

For Wednesday night into Thursday, the aformentioned cold front
with some associated rain showers pushes south through the area
before stalling over the mid Atlantic. Forecast guidance then
indicates a wave trying to move north along the front though
there is uncertainty in how this all evolves as high pressure
will also be building in to our north. The high could suppress
precip mainly to our south into Thursday but again, these
details are uncertain so we keep chances for showers in the
forecast through Thursday. Beyond this time there may be a brief
break before a stronger low pressure system moves north along
the front by later Friday into next Saturday. Highs Thursday and
Friday will generally be in the 40s and 50s with 60s possible
again by next Saturday.


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

Today...MVFR/IFR ceilings are expected to improve to VFR by 12z.
Light west to northwest winds increasing to around 10 knots this
morning, then diminishing by late afternoon and becoming west-

Tonight...VFR. Light and variable or light southerly winds.

Monday...VFR early, lowering to MVFR or IFR during the
afternoon or evening with rain. South to southwest wind.
Confidence: above average.

Monday night...MVFR/IFR conditions continue with rain possible
in the evening, and low clouds/dense fog possible overnight.
Confidence: Above average.

Tuesday...MVFR/IFR conditions possible through midday in low
clouds/fog. Conditions improving to VFR during the afternoon.
Southwest winds may gust around 20-25 knots in the afternoon.
Confidence: average.

Tuesday night...VFR early, then possibly lowering to MVFR/IFR
as low clouds/fog may develop overnight. Confidence: average.

Wednesday...MVFR/IFR conditions possible early with low
clouds/fog. Conditions improving to VFR during the day. chance
of showers late in the day. Southwest winds may gust around
20-25 knots. Confidence: Average.

Wednesday night through Thursday...Chance of showers with
associated restrictions. Confidence: Below average.


A short surge in cold air advection should result in increased
mixing for a time this morning. As a result, we will maintain the
Small Craft Advisory through late morning with a round of wind gusts
to around 25 knots. Otherwise, the conditions are expected to be
below Small Craft Advisory criteria as high pressure builds in
through today then offshore tonight.

Monday...Sub Small Craft Advisory south winds. Confidence: Well
above average.

Monday night...Sub Small Craft Advisory conditions expected,
although southwest winds may gust around 20 knots. Confidence:
Above average.

Tuesday-Wednesday...Winds should stay below advisory levels,
but seas may increase to near 5 feet. Confidence: Average.

Wednesday night - Thursday...Winds should stay below SCA levels
with seas persisting in the 3 to 5 foot range.


Record high temperatures could be challenged on Tuesday,
February 20th and probably will be equaled or exceeded Wednesday
February 21st. These records are listed below.

February 20:

Atlantic City...70 in 1930

Philadelphia....70 in 1939

Wilmington......71 in 1930

Allentown.......68 in 1930

Trenton.........70 in 1930

Georgetown......68 in 2002

Mount Pocono....59 in 1930

Reading.........72 in 1930

February 21:

Atlantic City...74 in 1930

Philadelphia....72 in 1930

Wilmington......70 in 1953

Allentown.......67 in 1953

Trenton.........70 in 1930

Georgetown......71 in 2014

Mount Pocono....60 in 1930

Reading.........71 in 1930

We are not posting the monthly records at this time since our
forecast is 3 to 7 degrees below the monthly record. We`ll check
again Sunday and Monday to see if our forecast edges warmer.

The following are the record warm mins for Wednesday Feb 21.
Barring a sudden immediate cool down behind the cool front at
1159PM Wednesday, there is a good chance of record warm daily
minimum temperatures as well the previously referenced record

Record high mins for 2/21

ABE 46-1981
ACY 49-1954
PHL 49-2002
ILG 47-2002
RDG 48-1930
TTN 48-2002

Atlantic City rainfall already ranks 11th wettest in February
history with 6.50" in 2010 the wettest. By sunrise Sunday,
Atlantic City should rank about 8th wettest in its historical

The February average temp for PHL projects 41.0 or 5.3F above
normal or 8th warmest on record. This placement can change
anywhere from 3rd to 12th depending on a 1 degree change in the
eventual average. Bottom line...we`re likely on our way to a top
10 warmest February on record. The warmest was last year with a
44.2F average. Years 2002 and 2012 flank our currently
projected 8th warmest.


MARINE...Small Craft Advisory until 11 AM EST this morning for ANZ430-


Near Term...Gorse
Short Term...Gorse
Long Term...Fitzsimmons
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