161
FXUS61 KCTP 082209
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
509 PM EST Mon Dec 8 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 6 AM TUESDAY MORNING/...
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 /6 AM TUESDAY MORNING THROUGH WEDNESDAY NIGHT/...
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 /21Z MONDAY THROUGH SATURDAY/...
Main change was to edge winds up later on Tuesday afternoon,
as now the TAFS go out to 00Z Wed.

Also took out the 3000 ft CIG at JST later tonight, hard to see
much support for this.

Some snow into BFD late Tuesday afternoon, but expect the snow
to be real light prior to 00Z Wed.

More information below.

High pressure will maintain VFR conds across Central PA
overnight, although a wave of low pressure passing to our south
will provide high clouds over at least the southern half of the
area for the at least the first part of the overnight period.

Skies will clear from northwest to southeast later tonight.

Tuesday will see clouds increase. CIGS could fall to MVFR by
late afternoon/evening across NW PA (BFD), where some light
snow is also possible, as a clipper system approaches from the
Great Lakes.

Much of the remainder of the week looks chilly and unsettled,
with occasional snow showers (possibly rain south) on Wednesday,
and occasional snow showers Thu-Sat as clipper systems
periodically impact the region.

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...NPB
SHORT TERM...Steinbugl/NPB
LONG TERM...Steinbugl/NPB
AVIATION...Martin/Evanego
CLIMATE...Steinbugl