791
FXUS61 KCTP 090555
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
1255 AM EST Tue Dec 9 2025

.SYNOPSIS...
* Partly cloudy and bitterly cold/frigid tonight with some
  clearing across NW PA
* Not as cold Tuesday; quick shot of snow in the NW mtns
* Windy with snow/rain mix followed by lake effect snow through
  midweek; additional snow accumulation possible Friday-Sunday

&&

.NEAR TERM /UNTIL 8 AM THIS MORNING/...
11 PM Update...
Clearing has already allowed BFD to dip to -2F. They should go
a couple more degrees colder with Td currently -5F. They could
start to rise later tonight if the SE wind picks up at all. Have
tweaked the near term to make it colder on the whole.

Prev...
Recent surface analysis outlines high pressure at the surface
with high clouds gradually streaming northeast across the
forecast area as a 500mb trough continues to track south of the
region this afternoon. In terms of sensible weather, a fairly
quiet near-term period with the biggest concern being cold
temperatures overnight. Temperatures continuing to gradually
increase and could increase by another 2-3F over the next couple
of hours push high temperatures closer to the upper teens to
upper 20s across the area, ahead of an evening with radiational
cooling prospects across northwestern Pennsylvania where clouds
coverage is expected to decrease. Current low temperatures
overnight trend near-zero across NW PA; however, cannot rule out
negative single digit temperatures overnight under the
aforementioned radiational cooling. Fortunately, wind/gusts are
not expected to be too high overnight with the continued
presence of high pressure, thus wind chills are expected to be
near the low temperatures marks. It should be noted that some
daily record lows could be within reach particularly if the min
temps prints on 12/8 (before midnight) vs. 12/9 or after
midnight. (See climate section for 12/8 and 12/9 record mins).

&&

.SHORT TERM /8 AM THIS MORNING THROUGH WEDNESDAY NIGHT/...
11 PM Update...
Main worries would be for a little FZRA in the east Wed AM and
enough SN to make an advy in the far NW. Both look around 50-70%
likely at this point. NAM is very dry for the morning where
temps in the east might be allowed to warm up before precip hits
the ground. But, it is also a 3rd-4th period forecast at this
moment. Will allow the mid shift to further refine things with
the neighboring offices, as it will only be a 3rd period worry
for them.

Prev...
A complex short-term period begins as high pressure shifts east
of the region on Tuesday, allowing for a quick- moving mid-
level shortwave to bring a quick shot of snowfall across
northwestern Pennsylvania Tuesday afternoon. Model guidance does
have some disparity between the southern extent of the snowfall
footprint; however, recent 12Z HREF guidance has trended
upwards on probabilities of measurable snowfall across northern
McKean/Warren counties, thus have increased snowfall mentions in
these areas. Based on a consensus of model data, accumulations
still look likely to top out at ~1", with probabilities
generally below 30%. Some signals do continue to exist for an
isolated band of heavy snow to setup in the area and produce an
isolated swath of locally heavier snowfall that can exceed an
inch; however, low confidence on where this where set up at this
time. Those in NW PA during the evening commute hours on
Tuesday will need to continue to monitor the forecast in this
timeframe for near-term updates over the next couple of forecast
packages.

Upstream of the mid-level trough, an intense clipper low will
be racing through the Great Lake region Tuesday night 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.
Snowfall totals overnight will generally range between 1-2" for
NW PA with snowfall below 1" expanding further south into the
I-80/I-99 corridor. Snowfall continues and by Wednesday
afternoon, 24-hour snow totals are projected to reach 2-4" in
the NW mtns with C-1" fcst elsewhere in areas along and
north/west of I-80/I-99. Recent model guidance does indicate
some potential for an extended warm nose across the Lower
Susquehanna Valley 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, 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. Total snowfall in
this could reach into the 4-6" range across northwestern
Pennsylvania; however, given the uncertainty with the fast-
moving shortwave, clipper, and lake effect behind the system
there remains quite a bit of uncertainty with snowfall totals.
Given this remaining uncertainty in this timeframe, have
collaborated with neighboring offices and kept WWA decisions for
a future cycle given the uncertainty with this system although
we will continue to track this threat in the HWO.

&&

.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 /06Z 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...
None.

&&

$$

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