Area Forecast Discussion
Issued by NWS State College, PA

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FXUS61 KCTP 130718

Area Forecast Discussion
National Weather Service State College PA
318 AM EDT Tue Mar 13 2018

A storm moving off the coast will clip the south and east with
some light snow this evening and tonight. The storm will deepen
as it moves into New England, turning our wind to the northwest
as it does so. These northwest winds and a slow moving upper
level trough swinging through over the next two days will
create lake effect snows across northwest PA and the Laurel


Latest HRRR and MRMS RALA loop shows the western edge of steady
light snow associated with the deepening coastal storm
extending from Tioga County southward to Dauphin Counties. The
southern portion of this over the Lower Susquehanna River Valley
has been and will continue to slowly erode early this morning
as subsidence on the NW quadrant of the deepening offshore low
strengthens. A narrow band of deformation snow showers is slowly
working through the central and north central mountains as
well, producing a coating as it slowly propagates eastward.
This area of snow will meet the same fate as it encounters
increasing subsidence in favor of the offshore deepening nor-
easter over the next few hours.

A blend of latest HRRR and earlier NAM/HREFV2 support overnight
accums of a coating to locally 1 inch along and east of the
Susq River, with locally 3 inch amounts over the high terrain
of Sullivan County. Expect the light snow to push east of the
forecast area by dawn, as the inverted surface trough and
associated ribbon of higher PWATS push east of the area.

Over the Alleghenies, the upper trough axis will combine with
orographic forcing to produce scattered to numerous snow
showers, producing a fresh coating overnight in many locations.


Upper low crossing the lakes will be the star of the show for
the short term. Tuesday seems like a typical NW flow SHSN day,
with just a few SHSN making it past the Allegheny Front
(roughly I-99). Although little activity is expected early in
the day, coverage and intensity of diurnally-driven snow showers
should peak during the afternoon, then begin to wane towards
evening. Steep lower tropospheric lapse rates indicated in the
model data across western Pa, indicating some locally heavy
squalls are possible over the Alleghenies during the afternoon.
However, the cellular nature of the convection will result in
very brief episodes of heavier snow and model qpf only supports
accums across the Allegheny Plateau of a coating to an inch

NBM/Superblend indicating max temps Tuesday ranging from the low
30s over the Alleghenies, to the low 40s across the Lower Susq
Valley. A tight pressure gradient west of intensifying low over
New England will result in gusty winds, making it feel even
colder. Bufkit soundings support gusts between 20-25kts, with
the highest gusts in the southern half of the state.


A large upper level low dropping south from the Great Lakes will
keep periodic scattered SHSN over the western high terrain
through mid-week. No period looks particularly worse than any
other so not looking at any advisory necessary. The blustery
persistent northwesterly flow will keep cold air advection
moving into the region through mod week. This will allow for
well below normal temperatures. Couple this with the gusty winds
and wind chills every morning will be in the teens through mid
week. Conditions will improve through the latter half of the
week to around normal this weekend. Temperatures should begin to
moderate by the upcoming weekend as upper-level ridging across
the middle of the country builds eastward.


Snow over the eastern 1/3 of the airspace trended downward in
intensity after midnight, with visibility improving from IFR to
MVFR/VFR. Pattern is transitioning to a northwest flow regime
with gusty downslope winds from 270-320 degrees supporting
mainly low VFR ceilings and occasional light snow showers and
flurries over the central and eastern 2/3 of the airspace into
late week. The western 1/3 of the airspace will be a different
story with persistent snow showers and prolonged MVFR to IFR
conditions. A few localized snow squalls are also possible over
the western 1/3 of the airspace Tuesday afternoon and included
TEMPO group at KJST/KBFD to show vsby dropping below 1SM.
Expect wind gusts 20-25kts during the day Tuesday through


Tue-Thu...MVFR-IFR in snow showers wrn 1/3; mainly VFR with
occasional MVFR possible in brief snow showers/flurries central
and eastern 2/3.

Fri-Sat...VFR. No sig wx.




NEAR TERM...DeVoir/Fitzgerald
SHORT TERM...Dangelo/Fitzgerald
LONG TERM...Lambert/Ceru
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