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803
FXUS61 KPHI 141459
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
959 AM EST Tue Jan 14 2025

.SYNOPSIS...
Cold and dry arctic high pressure will remain in place to our
west through the middle of the week, keeping below normal
temperatures and dry conditions in place. A weak cold front will
pass through on Thursday. A warm front will lift north on
Saturday, bringing a shot of widespread precipitation. A strong
arctic cold front will pass through early Sunday, with much
colder conditions expected into next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
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The main story of the near term forecast remains the cold
Canadian high pressure that is beginning to slow inch its way
towards the Mid-Atlantic region out of the High Plains.

As of 9:45am...temperatures this morning have risen into the
20s for most locations. However, temps will struggle to reach
the freezing mark this afternoon with many locations topping
out in the upper 20s to low 30s for highs under partly to mostly
cloudy skies with another stratocumulus deck developing by late
afternoon. A shortwave aloft will also be passing through in
the evening, which could result in a few snow showers. Latest
CAM guidance is a bit less optimistic on how far south the snow
showers make it so, have largely confined the mention of the
slight chance (15-20%) for snow showers to near and north of the
I-80 corridor. In any case, no significant accumulations are
expected. In addition to the cold temps, a modest pressure
gradient will setup over the region. So, today will be quite
breezy with wind gusts up to 30-35 mph possible. This should
result in wind chills remaining in the teens this afternoon.

Heading into tonight, the pressure gradient over the region
continues to strengthen with model soundings indicating only a
weak inversion developing. As a result, gusty conditions are
expected to continue into the overnight hours, with wind gusts
around 25-30 mph possible. Temps look to fall into the upper
teens across most of the region, under clearing skies following
the departure of the passing wave. Adding in the winds will
result in single digit wind chills for many locations (feeling
up to 5 degrees below zero in the Poconos).
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&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
For the midweek period Wednesday through Thursday night, the
cold advection of an artic airmass will begin to wane as high
pressure across the Ohio Valley weakens. By Thursday, another
trough axis arrives from the northwest, keeping heights and
thicknesses anomalously low. This will keep temperatures below
normal despite the lack of cold advection. A weak cold front
will pass through late Thursday associated with the passing
upper trough.

Generally expect dry conditions through this period. A few
light snow showers or flurries are possible with the trough and
frontal passage late Thursday mainly northwest of I-95, but this
won`t amount to much other than potentially a dusting in the
Poconos. Remaining breezy on Wednesday with a northwest wind
10-20 mph, and gusts up to 30 mph. Winds lessening and shifting
southwest for Thursday. Diurnal stratocumulus possible each day,
especially Thursday as some better low level moisture will be
present in the southwest flow.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
For the long term period Friday into early next week, expecting
a rebound of temperatures to near or even slightly above normal
into the weekend as heights increase aloft and an upper ridge
axis passes across the region Friday night. A warm front should
lift north through the area on Saturday, with south to southwest
flow and warm advection pushing temperatures into the low to
mid 40s across much of the area. While the mild temperatures
will provide brief reprieve from the prolonged frigid
temperatures, the milder weather will be accompanied by periods
of rain showers, especially by Saturday afternoon. Any
precipitation will diminish into late Saturday night.

A strong arctic front is expected to arrive sometime Sunday,
with a much colder airmass advecting in behind it. Some guidance
suggests potential for a coastal system late Sunday into early
Monday, although much of the latest guidance is much more
suppressed with this, keeping the system well offshore at our
latitude. Have maintained chance PoPs at this time, but suspect
these will need to be lowered or removed in future updates if
the current trends hold.

By Monday night into Tuesday, the coldest airmass of the season
is expected to be in place across a large portion of the CONUS
from the Midwest eastward across much of the Northeast. 850 mb
temperatures in the -20C to -25C range will likely spell
temperatures upwards of 15 to 20 degrees below normal through
the middle of next week. This would mean highs near 20 degrees
and lows into the single digits. A period of a few days of well
below freezing temperatures could lead to some cold weather
impacts to infrastructure, including freezing water pipes and
high demand for heating energy.

&&

.AVIATION /15Z TUESDAY THROUGH SATURDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Today...VFR. Mostly clear skies early with SCT/BKN ceilings in
the afternoon/evening. West-northwest winds around 10-20 kt
with gusts up to 25-30 kt. High confidence.

Tonight...VFR. Gusts gradually weakening as the night goes on,
though still will be around 20-25 kt out of the west/northwest.
High confidence.

Outlook...

Wednesday through Friday...VFR. No significant weather
expected. Breezy Wednesday with gusts up to 25 kts, then winds
10 kts or less.

Saturday...Ceiling and visibility restrictions likely with
periods of rain showers. LLWS possible.
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&&

.MARINE...
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A Small Craft Advisory is in effect for all Atlantic coastal
waters including the Delaware Bay through today. A Gale Warning
is in effect for all Atlantic coastal waters including the
Delaware Bay tonight. A Freezing Spray Advisory has also been
issued for all Atlantic coastal waters including the Delaware
Bay for tonight.

West-northwest winds around 15-25 kt with gusts up to 30 kt are
expected through the day today with seas around 4-6 feet. Due
to the combination of cold air/water temperatures, gusty winds
and enhanced seas, light freezing spray will be likely on both
the Atlantic coastal waters and Delaware Bay this morning.

Heading into tonight, winds will turn more northwesterly and
increase to 20-30 kt with gusts up to 35-40 kt. Seas of 4-6
feet continue. Due to the increasing winds and decreasing air
temperatures, along with continued enhanced seas and cold water
temperatures, freezing spray accumulation is expected to
increase to moderate. Thus, the Freezing Spray Advisory was
issued for all coastal waters.

Outlook...

Wednesday...Small Craft Advisory conditions with northwest
winds 15-20 kts gusting up to 30 kts. Freezing spray possible
early.

Wednesday night through Saturday...No marine hazards expected.
Winds 10-15 kts with gusts up to 20 kts possible at times. Seas
mostly 1-3 feet. Rain showers developing late Saturday.
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&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...Small Craft Advisory until 6 PM EST this evening for ANZ430-
     431-450>455.
     Gale Warning from 6 PM this evening to 6 AM EST Wednesday for
     ANZ430-431-450>455.
     Freezing Spray Advisory from 8 PM this evening to 1 PM EST
     Wednesday for ANZ430-431-450>455.

&&

$$

SYNOPSIS...Staarmann
NEAR TERM...AKL/DeSilva
SHORT TERM...Staarmann
LONG TERM...Staarmann
AVIATION...AKL/DeSilva/Staarmann
MARINE...AKL/DeSilva/Staarmann