556
FXUS61 KCTP 091014
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
514 AM EST Tue Dec 9 2025

.SYNOPSIS...
* Not as cold today; quick shot of PM snow today across the NW
  Mtns with light Accumulation
* Windy with several inches of snow, locally up to 5-6 inches
  across Northern PA with a snow/rain mix across southern PA.
* Lake Effect snow follows for Thu/Thu night; Additional snow
  accumulation possible Sat-Sun from another area of low
  pressure moving by just to the south and east of PA


&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
A frigid morning grips the entire region early this morning
thanks to clear skies, light/variable wind and dry air
associated with a large area of sfc high pressure extending from
the Adirondack Region of NY to Southern VA. Temps ranged from
the single digits to mid teens across the south to between zero
and 10 below across the Northern Mtns of PA. A slight wind of 5
kts appears to have snagged a pool of even colder air from the
SE part of the airfield and dipped the temp to -11F there at
10Z. This technicall places that localized part of McKean Cty
within Extreme Cold Warning criteria, but the rest of the county
has little or no wind and higher temps not even in the Cold
Weather Advisory values.

Increasing Southerly LLVL flow in the wake of this ridge will
transport a layer of bkn-ovc stratocu NNE from the Laurel
Highlands through the Central Mtns this morning, while a shield
of mid and high clouds streams east into the Commonwealth later
this morning and this afternoon.

A quick shot of weak low-mid level warm advection, compact and
transient 850-700 FGEN and a glancing blow by the nose
(thermally indirect cell of a 100 kt, 300 mb nwrly jet max) will
bring up to a several hour period of light snow across the NW
Mtns of PA this afternoon and evening with accums up to around 1
inch.


&&

.SHORT TERM /6 PM THIS EVENING THROUGH WEDNESDAY NIGHT/...
An intense clipper low will be racing through the Great Lake
region tonight into Wednesday morning. Warm air will filter
into the region ahead of this anomalously deep Alberta Clipper
(one of the strongest for this time of year by
historical/climatological MSLP standards) and is expected to
spread accumulating light to moderate snow across the NW 1/2 of
the CWA for the Wednesday morning commute.

Thus, any break in the snow across the NW Mtns will be very
short- lived as dual jet segments (with the southern jet
strengthening to over 140 kts) arrive from the Ohio Valley on
Wednesday.

Latest high res models and their EFS (along with a host of
larger scale, operational models) focus the primary area of
UVVEL and snow from the NW Mtns to Sullivan County in the NE
part of our CWA. Coordinated with surrounding WFO to post a Wint
Weather Advisory for all of our NRN Mtns late tonight early
Wednesday evening. NBM Probs for 2.5 to 3 inches of snow - ending
at 7 PM Wed ranged from 80-100 pct across the Northern Mtns.

The strength of the swrly llvl jet (55-65 kts) and the
collocation with the coupled jet region and focused deep-layer
UVVEL have all the markings of a few to several hour period of
MDT to HVY (aka thumping of) snow later Wed morning and early
afternoon with several or more inches likely across the Advisory
area with a few locations seeing up to around 6 inches. We can
see that layer lifting/cooling by the decrease in the MAX Tw in
the 1000-700 mb layer dip by 1-2 deg C during the late morning
hours Wed as the nose of the strengthening LLJ moves into Ncent
PA.

Across the Central and Southern Ridge and Valley region of the
state and the Laurel Highlands, snow accums should be in the 1-2
inch range with locally around 3 inches on the ridges near the
I-80 corridor.

Another concern would be for a little FZRA in the east (esp
across the higher terrain of Schuylkill Cty) Wed AM.

NAM is very dry for the morning across the SE (in the lowest
5-6 kft AGL) where temps might be allowed to warm up before
precip hits the ground. But, it is also a 3rd period forecast
at this moment. Will allow the day shift to examine the details
of upcoming model cycles to better assess the threat for light
icing Wed morning and further refine things with the
neighboring offices, as it will only be an early 3rd period
worry for them.

Model guidance continues to show some potential for an extended
warm nose across the Lower Susquehanna Valley (with max Tws of
1.5 to 2.5C in the 900-800 mb layer by around 15Z Wed) that
does indicate some freezing rain potential and light ice
accumulation if precipitation manages a quick enough eastward
expansion, mainly in the 7am-1pm timeframe. Recent model
soundings do outline some discrepancies with respect to how warm
the lower- levels will get at this time, so there is quite a
bit of uncertainty with regards to if ice accumulation will
occur, so have continued with NBM model guidance and will
highlight this potential in the HWO rather than issuing a low
confidence Advisory with some time to iron out the forecast
uncertainties in future packages. As the precipitation expands
eastward into Wednesday afternoon, marginal temperatures/thermal
profiles will favor a snow/rain mix across north/western
Pennsylvania as temperatures reach into the mid-30s with plain
rain from the central ridges eastward into the Susquehanna
Valley.

As the storm tracks through the St. Lawrence River Valley
Wednesday night through Thursday, colder northwesterly flow is
expected to trigger lake effect snow with minor snow
accumuations over the typical northwestern Pennsylvania snow
belts and favored upslope areas along the Allegheny Front and
Laurels.

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
Lake effect snow and breezy northwesterly winds continue on
Thursday with additional snow accums expected over the
northwestern mountains and Laurel Highlands. A cold frontal
passage early Thursday will promote some snow squall threat as
outline in more recent Snow Squall Parameter guidance. The main
deterrent for snow squalls will be that instability is largely
expected to be limited given that the front is passing on early
in the day. At this times, no mentions in even the HWO given the
low confidence at this juncture and longer time horizon until
the event is on our doorstep.

The next winter weather system is progged to arrive later
Friday into Friday night, although models are showing some
variance with the evolution and track. Lake effect snow/snow
showers continue over the weekend with temperatures staying
below the historical average heading into mid-December.

&&

.AVIATION /09Z TUESDAY THROUGH SATURDAY/...
Skies have cleared out and VFR conditions will continue through
the night for most central PA airfields with light winds. The
exceptions are JST and AOO where an area of stratus should
develop by 11Z as winds take on more of a southerly component.
This will lead to a few hours of MVFR ceilings at those two
sites.

High clouds increase into the afternoon ahead of an approaching
upper level trough, and will gradually lower through the
evening. This system will bring light snow to northwest PA, with
the snow expected to reach BFD by 20Z. The snow should remain
very light, but could result in brief reductions in visibility.
All other TAF sites likely remain dry. Winds during the day will
be out of the south at 10 to 15 knots with gusts of 20 to 25
knots possible.

Ceilings continue to lower through the rest of the night, with
MVFR ceilings likely extending as far south as JST and AOO, and
as far east as IPT. A 40 to 45 knot west-southwesterly low-level
jet moves into western PA after 00Z Wednesday ahead of the next
low pressure system that will impact PA. A period of LLWS will
be possible at BFD and JST as surface winds decrease to 5 to 10
knots. This system will bring periods of moderate to heavy snow
to the region on Wednesday morning and into the afternoon,
initially moving into BFD in the 06-08Z timeframe. Snow will
reach the eastern airfields by 12-14Z, possibly mixed with rain
or freezing rain south of UNV.

Outlook...

Wed...Restrictions possible with snow north/west and wet
snow or rain showers south/east.

Wed night-Thu...Snow showers continue, mainly N/W PA. Westerly
wind gusts of 15-30 kts (possibly higher in the Laurels) are
expected.

Fri-Fri night...A round of light snow possible later Fri into
Fri night, with a clipper system.

Sat...Improving conds expected.

&&

.CLIMATE...
Astronomical winter (solstice) begins at 10:03 a.m. on Sunday,
December 21st

Record lows for 12/8:
MDT  12 in 2002
IPT  3  in 1901
AOO  7  in 2005
BFD -2  in 1970

Record lows for 12/9:
MDT  7   in 1989
IPT  3   in 2002
AOO -3   in 1989
BFD -12  in 2002

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 1 AM to 10 PM EST Wednesday for
PAZ004>006-010>012-017-018.
Winter Weather Advisory from 3 AM to 10 PM EST Wednesday for
PAZ037-041-042.

&&

$$

SYNOPSIS...Lambert
NEAR TERM...Lambert
SHORT TERM...Lambert/Dangelo
LONG TERM...Lambert/Steinbugl
AVIATION...Bauco
CLIMATE...Steinbugl