633
FXUS61 KCTP 230150
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
850 PM EST Fri Nov 22 2024

.SYNOPSIS...
* Snow shifts into the Laurel Highlands this evening; otherwise
  cloudy and breezy with a spotty rain or snow shower tonight
* Breezy with showers over the western Alleghenies to start the
  weekend, followed by improving conditions on Sunday
* Windy with rain and snow showers Monday night into Tuesday;
  another potential bout of winter weather possible for
  Thanksgiving Day

&&

.NEAR TERM /UNTIL 7 AM SATURDAY MORNING/...
01Z radar loop shows the back edge of the steady precipitation
associated with TROWAL/frontogenetic forcing pushing southwest
through Cambria, Bedford, Fulton and Franklin counties. The
latest HRRR, which is depicting the back edge well, indicates
steady precipitation will exit Southern Somerset County by
around midnight. Near term model qpf this evening ranges from
0.2 to 0.4 inches over Somerset County. Warming boundary layer
temps should change precip to rain in many valley locations down
there this evening. However, the ridgetops of Somerset County
still stand to see another 1-2 inches of snow before it tapers
off around midnight. Will likely be able to cancel the Winter
Storm Warnings over the Laurel Highlands earlier than the 12Z
expiration time.

Across the rest of the forecast area, a few light rain/snow
showers remain over the area this evening associated with low
level instability under the upper low, which is over Eastern PA.
As the upper low weakens and drifts east of the state, expect
the risk of additional showers to wane overnight.

Large scale subsidence arriving behind the exiting upper low,
combined with a downsloping northwest flow should yield
breaking clouds late tonight east of the Alleghenies. However, model
soundings indicate upsloping flow will result in persistent low
clouds across the W Mtns. Weak low level cold advection late
tonight should translate to slowly falling temps with readings
at dawn likely in the low to mid 30s.

&&

.SHORT TERM /7 AM SATURDAY MORNING THROUGH 6 PM SATURDAY/...
The northwest flow behind the departing upper low is just cold
enough to support lake effect Saturday. Model soundings show
inversion heights peaking late morning through the afternoon
hours, coincident with the passage of a weak upper level
shortwave. Have ramped POPs upward toward the HREF values due to
nearly saturated model soundings in the 0-2km layer, which
should support light precip in most spots across the Allegheny
Plateau. A few wet snowflakes are possible on the higher
ridgetops of the Laurel Highlands Sat morning. Otherwise,
progged thermal profiles are too warm for anything but rain
showers.

Model RH profiles support a partly to mostly sunny start to
Saturday east (downwind) of the Alleghenies. However, warm
advection ahead of the approaching shortwave should result in
increasing clouds by afternoon.

A fairly tight gradient west of intense low pressure over Nova
Scotia will result in gusty northwest winds across the area
Saturday. Bufkit soundings indicate frequent gusts of 20-25kts
are likely. GEFS 2m temp anomalies support near seasonable high
temps Saturday, ranging from the low 40s over the highest
elevations of the Alleghenies, to the low 50s in the Lower Susq
Valley.

&&

.LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/...
* Winter Weather may impact travel on Thanksgiving Day across
  Central PA

Sct-nmrs SHSN linger over the Alleghenies Sat night with only
minor addtnl accums. Then the temp advection turns positive on
Sunday and should lift any remaining SHSN up into NY. High
pressure doesn`t last long with a progressive storm affecting
the state late mon into Tues morning. Milder conditions (+5F vs
Sun) look likely for Monday in advance of the storm. Temps
should stay mild enough to be only rain for all of the area.
Latest guidance supports minT in the 40s area-wide Mon night.
CFROPA in the late night/early morning time-frame will probably
keep the chc for thunder low, but would not be surprised to hear
a rumble or two since the front is potent and 8H temps drop 15C
over 12 hrs at UNV. Could be a gusty passage, too (potential
NCFRB) due to 8H winds from 240deg at >=50kt per GFS. Tues looks
mainly dry under high pressure. Perhaps a SHSN NW.

Wed now looks fairly good for travel across PA with most models
converging on a Thursday/Thanksgiving Day arrival for the next
precip event. However, they are not in lock-step. Cold llvl air
residing north of the Mason/Dixon line combined with a zonal
WSW jet aloft across the ern 2/3rds of the CONUS will likely
lead to a fast, progressive flow.

The front that pushes S of the commonwealth Tues will stretch
out West to East to the south of our latitude, and moisture
should start to return and pool up along it on return flow from
the GOMEX. How far south will it be on Thursday is the tricky
part to the forecast. 00Z ECMWF generates a widespread QPF of
0.5" across most of the CWA. 12Z operational GFS has the sfc
ridge stronger and farther south on Wed. The result is that it
would take most of the precip from a much weaker and quicker
wave to the south of PA. Thus, the confidence level has not
increased all that much over the past 24hrs. Continuing with
PoPs maxed at about 70pct on Thanksgiving Day.

That said...The thermal profile for the start of any precip
late Wed or Thurs would likely be cold enough over some (nrn)
portion of the CWA to make frozen or freezing precip. Temps in
the lower elevations may be warm enough for only rain there.
But, arrival timing (before/after sunrise) and depth of cold air
in llvls will have a big influence on p-types. At this point,
the prudent answer to the question about Thanksgiving`s weather
reads:
"The probability for measurable snow is highest in the northern
tier and lowest in the lower elevations of the southern tier.
There is also a non-zero chance of freezing rain across Central
PA, but something less than 20pct at this point. Continue to
monitor the forecast as confidence is expected to increase over
the next 2 to 3 days. Be prepared for slippery/poor travel
during this upcoming long holiday travel time."

Current timing and placement of mass features should allow for
gusty winds and drying on Friday except in the northern
Alleghenies where the cold air and WNW flow will generate
lake effect SHSN which may linger thru much of next weekend
(days 7-9). A shot of even colder air comes along late in the
weekend, and looks like a pattern favorable for snow squalls.

&&

.AVIATION /01Z SATURDAY THROUGH WEDNESDAY/...
The main area of rain and snow continues to push southwest this
evening and steady rain and snow is mainly confined to areas
near and southwest of JST and AOO. Ceilings have risen over the
past few hours to MVFR for areas east of the Allegheny Front and
further improvement to VFR is possible towards daybreak
(especially at MDT and LNS). Moderate to heavy snow continues at
JST as of 00Z and is leading LIFR restrictions. This will
continue for a few more hours before drier air moves in
overnight and brings an end to steady snowfall. While
visibilities will improve, ceilings will remain IFR. Gusty winds
20-30kt from 280-320 degrees will continue through Saturday.
Showers will develop once again Saturday afternoon near BFD and
JST and could reach as far east as AOO and UNV.

Outlook...

Sun...MVFR cigs NW 1/2 impacting KBFD and KJST. VFR elsewhere.

Mon-Tue...Strong CFROPA Monday night with rain and potential
LLWS followed by strong winds and snow showers.

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

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
Winter Storm Warning until 7 AM EST Saturday for PAZ024-033.

&&

$$

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