000
FXUS61 KCTP 060026
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
726 PM EST Tue Dec 5 2023

.SYNOPSIS...
A weak clipper system will spread light snow, mixed with rain in
the valleys, across the area this evening through Wednesday
morning. Another period of light rain and snow is possible
across the northern tier of PA on Thursday ahead of a
noticeable warmup into the weekend. The mild spell Friday into
Saturday will precede a late weekend storm with the potential to
bring heavy rainfall and strong wind gusts on Sunday.

&&

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
Upper level trough with 2-3 embedded Meso-B shortwaves and an
associated weak sfc low(s) will move ESE across the Ohio Valley
and Central Appalachians late this afternoon and tonight.

The upper level trough is slightly positive the tilt of its axis
with a few spokes of enhanced small scale DPVA and FGEN forcing
generating enough UVVEL to create brief periods of moderate
snowfall rates (with ~1/2SM vsby). This supports our forecast
1-2 inches of snow across the Laurels (with perhaps around 3
inches on the ridges above 2500 msl) by late Wed morning.

That being said, the larger-scale jet structure (with the
unfavorable, thermally direct/descending branch of the jet
brushing the region and its primary axis well south of the CWA)
will act to limit snowfall amounts from exceeding values noted
above. The broader lift generating the enhanced higher/layer and
textured clouds as seen on regional vis and IR satellite imagery
was essentially wasted on deep dry air, producing mainly virga
and perhaps some intermittent very light rain/snow.

A look at the regional radar mosaic loop across the Ohio Valley
supports this analysis and short range forecast of periods of
light to briefly moderate snow associated with small scale jet
maxes and bands of enhanced FGEN forcing. This is also supported
by the spattering of several small areas of slightly anomalous
LLVL -U component to the LLVL flow via the latest GEFS.

18Z temps are just a deg or two shy of their forecast maxes,
which range from the mid 30s across the Northern and Western
Mtns to the mid 40s throughout the Mid and Lower Susq Valley.

As the clipper weakens late tonight into Wednesday morning with
jet energy jumping over the Appalachians to the main baroclinic
zone along the Carolina Coast, a secondary low will develop
offshore the OBX of NC.

The impact for our area will be that increasingly colder NNW
flow could generate up to an inch of additional/lake enhanced
snow over the NW mtns.

Elsewhere, any light snow/flurries should produce nothing more
than a dusting to 0.5" of snow over most of Central PA. Across
parts of the Lower Susq Valley, model soundings indicate any
very light precip could fall as either snow or rain, but surface
temps should remain too warm for even a coating.

&&

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH THURSDAY NIGHT/...
The main, large scale mid/upper level trough axis reaches the
East Coast by 15Z Wed with some lingering light snow ending by
noon over and to the east of the Susq Valley, while areas of
primarily snow showers falls over the Alleghenies of Wrn PA
through Wednesday afternoon as cold air deepens/lapse rates
steepen following passage of the upper trough.

Wednesday will turn out to be the coldest day the week with
highs averaging 5 to 10F below normal for early December or in
the 30-40F range.

A narrow sfc ridge axis should spell a brief break in the snow
showers (decreasing POPs) by Wednesday evening. However, surge
of warm advection preceding a warm front lifting through the Grt
Lks could potentially produce a brief period of light snow and
rain across mainly northeast and eastern PA late Wednesday night
into AM Thursday. A coating to an inch of accumulation is
possible.

Despite warming aloft, a good deal of cloudiness should hold
max temps to near or a bit below seasonal normals Thursday,
with highs ranging from the mid 30s to low 40s. Lows Thursday
night will vary from west (warmer) to east (cooler) thanks to
elevation/gradient WSW flow and boundary layer decoupling. Some
sites in the western part of the CWA may even see a non- diurnal
temp trend develop late Thu night into early Friday morning.

&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...
Medium range guidance supports fair and increasingly mild
conditions late this week, as upper level ridging builds along
the east coast. The bulk of guidance tracks a deepening surface
low west of PA late next weekend. Without a blocking high to
the northeast of PA, expect well above normal temps to continue
until the arrival of a trailing cold front Sunday PM or Monday
AM.

A deep plume of GOMEX moisture and strong upper level divergence
ahead of an upstream trough should produce a period of moderate
to heavy rain ahead of the front Sunday. Latest ensemble plumes
indicate most likely rainfall will fall between 0.75 and 1.50
inches. Strong/gusty southerly winds are possible if the region
can break into the warm sector Sunday PM. However, climatology
suggests the strongest winds will come in the cold advection
regime behind the cold front Sunday night into Monday. Latest
ECENS plumes indicate a possibility of wind gusts in excess of
40kts during this time frame. A return to cooler weather appears
likely Monday, as upper level trough shifts into the region,
accompanied by lingering orographic rain/snow showers over the W
Mtns. Wind gusts will be on the decrease by Tuesday as the deep
cyclone pulls away.

&&

.AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
Clipper system has pushed light snow and rain across the
airspace though coverage is spotty as precip is encountering
dry air. Associated sfc low should track south of the state
tonight. Periods of enhanced lift will produce light to briefly
moderate snowfall rates will lead to widespread IFR to LIFR
CIGS and MVFR to IFR vsbys across the western mtn airfields
(KJST and KBFD) with mainly MVFR cigs and vsbys through 12Z at
the the central PA airfields. VFR cigs in the Susq Valley may
dip to the mid and upper MVFR range at times in occasional very
light snow overnight.

The constant light snow could get moderate (1/2SM) at JST but
lighten up in the wee hours of the morning. A thin coating to an
inch of snow accum is poss at valley locations by the time
precip ends early Wed, with more on the ridge tops of the
Laurels (JST), where locally 2+ inches can`t be ruled out.

De-icing is going to be necessary at JST and BFD, and probable
at UNV/AOO/IPT before ops shut down overnight tonight.

Improvements on Wed as a high pressure ridge moves in from the
west. The high will be centered to our south, but have a narrow
neck stick northward over us and into Canada. The subsidence
should help break up the clouds downwind of the mountains. But,
the low clouds will hang tough for much of the rest of the
area. Warm air starts to flow in aloft from the west on
Thursday, and some snow will likely fall along and east of the
warm front which will cross the area.

Outlook...

Thu...Light snow, mainly N. Restrictions likely.

Fri...Mainly VFR.

Sat...VFR early. Showers late.

Sun...Widespread reductions in rain/snow.

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

SYNOPSIS...Lambert
NEAR TERM...Lambert
SHORT TERM...Lambert/Fitzgerald/Steinbugl
LONG TERM...Fitzgerald/Colbert
AVIATION...Lambert/Gartner