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235
FXUS61 KPHI 150904
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
404 AM EST Wed Jan 15 2025

.SYNOPSIS...
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Cold and dry arctic high pressure will remain in place to our
southwest into tonight, keeping below normal temperatures and
dry conditions in place. A weak cold front will pass through on
Thursday, bringing potential for snow showers. A warm front will
lift north on Saturday, bringing a shot of widespread rainfall
and mild conditions. A strong arctic cold front will pass
through early Sunday, with much colder conditions and well below
normal temperatures expected into next week.
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&&

.NEAR TERM /THROUGH TONIGHT/...
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Skies have pretty much cleared across the region as WV imagery
shows subsidence aloft. The mid level 700mb trough is tracking
offshore as the 250mb jet has setup just to our south. With the
left entrance region expected to pass over the region we should
continue to expect generally sinking air aloft and little in the
way of sensible weather through tonight. This leads to a very
similar day today as Tuesday with temps generally sitting in the
20s to low 30s across the urban corridor. BUFKit soundings
suggest the PBL should end up mixing during peak heating to
between 875-900mb this afternoon leading to gusts on the order
of 25mph or so. Those gusts combine with chilly temps will
result in wind chills across the region sitting in the teens to
low 20s for most of the day before quickly starting to fall
heading into the evening hours. Minimum wind chills tonight are
forecast to fall into the single digits for most areas and below
zero for the higher elevations of Carbon/Monroe in PA and
Sussex in NJ.
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&&

.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
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The late week period Thursday through Friday night will start
out with continued below normal temperatures Thursday as a weak
frontal boundary and shortwave trough approach from the
northwest. This system is expected to bring potential for light
accumulating snowfall to portions of the region. The system will
move offshore Thursday night, then temperatures will finally
moderate back toward normal values on Friday following cessation
of cold advection and an upper ridge axis moving in throughout
the day.

A bit of a change to Thursday`s forecast with this update. Now
that we`re within range of higher resolution guidance,
confidence has increased that the period of light snow showers
could be a little more robust than originally forecast, although
not particularly impactful. A potent, but positively tilted
shortwave trough will approach quickly by midday. The dynamics
aloft support weak to modest forcing for ascent right around the
DGZ layer as the shortwave arrives, beginning into the
afternoon across our east to southeast PA areas. The forcing
then spreads ESE toward the Philly metro or so by late afternoon
and early evening, then beginning shifting offshore between the
7-10 PM hours. The limiting factor with this system is a lack
of any notable moisture advection ahead of it, and a rather dry
airmass in place at the surface. So whatever snow does develop
aloft will take some time to reach the ground, but once it does,
temperatures in the upper 20s to low 30s will be cold enough to
support some light dusting accumulations less than 1".

We have increased our PoPs to reflect the latest guidance
consensus of the system evolution. This includes up to 40-50%
for much of our Pennsylvania, New Jersey, and northern Delmarva
areas. While QPF remains very light (less than 0.05"), the high
snow to liquid ratios potentially as high as 20:1 or more should
support a dusting less than 1" for areas that receive a more
persistent, steady light snow. Some localized amounts around
Berks County, Lehigh Valley, or southern Poconos where snow
could persist longest could see around 1-2" at best. While
there is some concern with the snow falling around the evening
commute, the snow should be light and dry enough to not cause
any significant travel issues, especially in light of the
residual salt on many roads.

Following the system`s departure Thursday night, temperatures
will fall to the upper 10s to low 20s as skies clear out
overnight.

Temperatures will rebound closer to normal values for Friday,
with increasing heights aloft and an upper ridge axis passing
across the region into the night. Highs should be mainly in the
upper 30s to low 40s under mostly sunny skies. While not the
warmest of winter days, it will definitely be the nicest day for
any outdoor activities for the foreseeable future. Lows in the
mid to upper 20s Friday night with increasing clouds.
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&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
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For the long term period this weekend into next week, expecting
a rebound of temperatures to near or even slightly above normal
into the weekend thanks to increasing heights aloft. 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, mainly 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 some guidance remains much more suppressed
with this, keeping the system well offshore at our latitude.
Have maintained chance PoPs at this time, but am skeptical this
potential for light accumulating snowfall will pan out at this
point. These details should become a bit more clear within the
next day or two.

By Monday night into Tuesday, the coldest airmass so far this
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 he
middle of next week. This would mean highs near 20 degrees and
lows into the single digits. Wind chills potentially below zero
at night and in the single digits during the daytime. 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.
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&&

.AVIATION /09Z WEDNESDAY THROUGH SUNDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Rest of Tonight...VFR. Mostly clear. West- northwest winds
around 10- 15 kt. Gusts may occasional gust up to 25 kt. High
confidence.

Today...VFR with FEW/SCT afternoon clouds. West-northwest winds
around 10-20 kt with gusts 25 to 30 kt. High confidence.

Tonight...VFR. Winds decreasing around 5-10 kt. High
confidence.

Outlook...

Thursday...Mainly VFR, however a period of light snow possible
at all terminals between 18Z to 03Z with potential for MVFR
conditions. Southwest winds 5-10 kts.

Friday...VFR. No significant weather expected. Winds 10 kts or
less.

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

Sunday...VFR. No significant weather aside from breezy winds.
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&&

.MARINE...
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A Small Craft Advisory is in effect for all Atlantic coastal
waters and the Delaware Bay through today. A Freezing Spray
Advisory is in effect for all Atlantic coastal waters and the
Delaware Bay through early Wednesday afternoon.

Winds have been been fairly marginal and generally fell just
short of Gale criteria so with mixing not quite as efficient and
forecast to continue to weaken, the Gale Warning was ended
early and converted to an SCA. Northwest winds will generally be
15 to 20 kts with gusts up to 30 kt and seas of 4-6 feet.

Due to the combination of cold air/water temperatures, gusty
winds, and enhanced seas, moderate freezing spray accretion is
likely beginning tonight through early Wednesday afternoon.
While the winds should be slightly weaker Wednesday evening,
freezing spray is possible again as water temps should be
sufficiently colder thus allowing for more efficient ice
accretion.

Outlook...

Thursday 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, along with a
period of wind gusts near 25 kts and seas near 5 feet possible.
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&&

.PHI WATCHES/WARNINGS/ADVISORIES...
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PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...Small Craft Advisory until 7 PM EST this evening for ANZ430-
     431-450>455.
     Freezing Spray Advisory until 1 PM EST this afternoon for
     ANZ430-431-450>455.
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&&

$$

SYNOPSIS...Staarmann
NEAR TERM...Deal
SHORT TERM...Staarmann
LONG TERM...Staarmann
AVIATION...Deal/Staarmann
MARINE...Deal/Staarmann