049
FXUS61 KCTP 221817
AFDCTP

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

.SYNOPSIS...
* The first winter storm of the season will bring heavy snow to
  the higher terrain in north central Pennsylvania and the
  Laurel Highlands today into tonight
* Improving conditions over the weekend, followed by some rain
  on Monday
* Another bout of winter weather could impact Holiday travel
  heading into Thanksgiving Day

&&

.NEAR TERM /UNTIL 8 PM THIS EVENING/...
Elevation dependent snow storm continues over central PA. Reports
of 8-12 inches of snow in the higher terrain across Tioga and
Sullivan Counties with multiple trees/power lines down and
several roads closed. We were keen to adjust storm totals higher
for these zones (max around 15" in Sullivan Co) and be more
definitive (will not could) in regards to [weight of] snow
damage impacts. Heavy snow band continues to wrap westward
approaching the Endless Mtns per BGM radar.

Hires models suggests a weakening trend with the northeast PA
banding this afternoon with focus shifting to combined lake
enhanced+upslope snow continuing to impact the Laurel Highlands.
We added near blizzard conditions at times for this area with
prolonged visby between 1/2-1/4 mile at KJST/K2G9 and persistent
wind gusts between 25-35 mph.

As temps slowly rise and precip rates fade off with time, we
trimmed back the end time of the winter wx advisory to 4pm
across the NW Alleghenies and central ridges along the I80
corridor. The lower elevations/valley locations are seeing very
little to no additional accumulation, while ridgetops near or
above 14-1500ft could pick up a slushy coating up to 2 inches
before snow tapers off by this evening.

The only headline in effect after 4pm today will be the winter
storm warning for the Laurel Highlands.

&&

.SHORT TERM /8 PM THIS EVENING THROUGH 6 PM SATURDAY/...
Diminishing precipitation is expected in general late Friday
into Friday night, as the upper low lifts out. However,
lingering lake effect will affect the W Mtns. Forecast thermal
profiles moderate with the departure of the upper low to the
point that lake effect snow showers may mix with rain over the
Alleghenies Friday night.

&&

.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 advnace 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 /18Z FRIDAY THROUGH WEDNESDAY/...
Snow will continue to overspread the area this morning with
reduced visibility accompanying it and subsequent lowering of
ceilings to IFR areawide. The main uncertainty in the forecast
is in regard to precip type. Snow will be the predominant
precip type into early afternoon at all sites, but model
soundings suggest that rain will begin to mix in everywhere
except BFD and JST after 18Z. The exact timing of this
changeover will impact how long visibilities remain below 1
mile. Even if visibilities rise above IFR, ceilings are expected
to stay below 1000ft areawide through at least 00Z.

Wind gusts will increase this morning with gusts of 25 to 30
knots likely throughout the day. Gradual improvement is
expected tonight as the center of low pressure moves offshore.
Lingering upslope/lake enhanced clouds and occasional showers
will keep IFR or LIFR conditions at BFD and JST overnight, but
MVFR to VFR conditions are expected farther south and east.

Outlook...

Sat...Periodic restrictions in rain and snow showers, mainly
across the mountains (KBFD and KJST). MVFR much of the time for
KUNV/KIPT/KAOO. Mainly VFR at KLNS and KMDT. Continued breezy.

Sun-Mon...Lingering restrictions possible at KBFD and KJST,
otherwise mainly VFR.

Tues...MVFR cigs/isold SHSN NW, VFR SE.

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 4 PM EST this afternoon for
PAZ004-005-010>012-017>019-025-034-045-046-049-051-052.
Winter Storm Warning until 4 PM EST this afternoon for PAZ006-
037-041-042-053-058.
Winter Storm Warning until 7 AM EST Saturday for PAZ024-033.

&&

$$

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