018
FXUS61 KCTP 250423
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
1123 PM EST Sun Nov 24 2024

.SYNOPSIS...
* Periods of rain Monday night followed by gusty winds and lake
  effect rain and snow showers into Tuesday
* Potential travel disruptions for Thanksgiving Day followed by
  cold temperatures and lake effect snow through the holiday
  weekend

&&

.NEAR TERM /UNTIL 7 AM MONDAY MORNING/...
Satellite loop at 04Z shows some lingering low clouds over the N
Mtns, while the bulk of Central PA has become mostly clear.
Expect the lingering northern clouds to break up late tonight, as
surface ridging builds over the state and inversion heights
fall.

Clearing skies, a light wind and relatively low dewpoint
depressions going into the evening support the development of
patchy valley fog later tonight. We have adjusted min temps
slightly below NBM guidance due to conditions favorable for
efficient radiational cooling. Expect daybreak readings to
range from the upper 20s in the normally colder rural valleys,
to the mid 30s in the more urbanized spots across the Lower Susq
Valley.

&&

.SHORT TERM /7 AM MONDAY MORNING THROUGH WEDNESDAY NIGHT/...
Partly to mostly sunny skies through the first half of Monday,
combined with strong WAA and southerly flow ahead of an
approaching frontal system, should support max temps +5-10F
above climo with highs ranging from the mid to upper 40s in the
Endless Mtns to the mid 50s in the south central valleys near
the MD line.

Models in good agreement spreading rain showers into the
western part of the forecast area Monday afternoon, as a 30kt
southwesterly low level jet and associated plume of anomalous
pwats work into the state ahead of an upstream trough. Strong
large scale forcing and a decent plume of pre-frontal pwats
supports high POPs Monday night into early Tuesday associated
with the cold front passage. Most likely rain totals based on
latest HREF/EPS/GEFS QPF range from 0.10-0.30" with the highest
totals likely over the Laurel Highlands. Thickening cloud cover
and warm advection ahead of the approaching cold front should
result in a mild Monday night with fcst lows adjusted higher to
the 40-45F range, or +10-20F above the historical average for
late November.

The cold front and any associated rain showers should exit the
eastern edge of the forecast area by midday Tuesday. Large
scale subsidence behind the front should result in blustery
conditions with breaking clouds over most of Central PA. A
progged west-southwest boundary layer flow should keep
developing lake effect snow showers north of the border.

Pressure rises/isallobaric couplet and CAA behind the front
will result in windy conditions Tuesday with fcst soundings
supporting peak gusts 30-40 mph. Diurnal temps may go neutral to
even falling during the day across the western mtns through
Tuesday afternoon. Surface high pressure building east from the
Ohio Valley should supply fair and seasonable conditions with
diminishing winds Tuesday night. Latest guidance indicates a
west-southwest flow will continue to keep lake effect snow
showers north of the border.

Fair weather and light winds look likely Wed, as surface
high pressure slides just south of PA. However, thickening high
clouds are possible in the PM hours ahead of an area of low
pressure approaching from the Miss Valley. 24/12Z model spread
(GFS/CMC vs. ECMWF) has increased in a big way Wednesday night
into Thanksgiving - more to come in the long term section.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
The latest guidance cycle presents similar themes as before.
These include good agreement on the large scale pattern
evolution toward an amplified eastern trough late week into the
first week of December. However, there remains uncertainty
inherent in a day 4 forecast regarding the exact track of a
surface low tracking along or just south of the Mason Dixon Line
Thanksgiving Day.

A large majority of ensemble members support a moderate
precipitation event late Wed night through Thursday with mean
qpf close to a half inch. Lack of a blocking high suggests any
snow will likely be confined to a relatively narrow corridor on
the northern edge of the precip shield. Model thermal profiles
at this point indicate the best chance of a light snow
accumulation will be over the N Mtns, with all rain likely over
Southern PA.

WPC noted that most machine learning models show a more
suppressed low track than the EPS, aligned closer to the
operational GFS/CMC with development occurring much farther
offshore and leading to reduced impacts (drier on balance) over
Central PA.

There is much greater confidence in blustery and cold weather
conditions (stretch of below average temperatures) developing
behind the late week system with lake effect snow over the NW
Mtns remaining very likely Friday into the weekend.

I did up POPS some across the west and north Friday into Saturday,
given the tendency for a large scale pattern change to a colder
northwest flow pattern, as the western states trend toward a
large scale upper level ridge. There is increasing model
consensus in an Alberta Clipper affecting PA Sat night or
Sunday, which could potentially produce a more widespread light
snowfall, even east of the Alleghenies.

&&

.AVIATION /04Z MONDAY THROUGH FRIDAY/...
Northwest flow will persist overnight with some, but only slow
improvement to cig situ. KMDT and KLNS are VFR and should
remain that way into Monday. Remaining isolated light rain
showers, confined to northwest corner of the airspace will
continue to diminish in coverage

Late Monday afternoon, we will see increasing mid and high
clouds, before rain moves into the area ahead of a cold front
after 00Z Tue.

Outlook...

Tue...Strong CFROPA Monday night with widespread rain and
potential LLWS followed by strong winds and snow showers over
the western half of the airspace.

Wed...Not as windy with pcpn ending and MVFR to VFR cigs; mixed
precip could reach the southwest airspace by 12Z Thu.

Thu...Increasing likelihood of widespread IFR in rain across
the southern half of PA. Snow possible across the northwest.

Fri...Becoming windy. Snow showers across the north and west.

&&

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

&&

$$

SYNOPSIS...Steinbugl
NEAR TERM...Fitzgerald
SHORT TERM...Fitzgerald/Steinbugl
LONG TERM...Fitzgerald/Steinbugl
AVIATION...Martin/Gartner