Area Forecast Discussion
Issued by NWS State College, PA

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FXUS61 KCTP 120511

Area Forecast Discussion
National Weather Service State College PA
1211 AM EST Tue Dec 12 2017

An alberta clipper will track over northwestern PA late
tonight, with a trailing arctic cold front sweeping through the
area early Tuesday. A deep upper level trough will remain over
the eastern conus through the rest of this week with another
weak clipper likely affecting the area Thursday. The upper
trough will likely lift out by next weekend. A low pressure
system lifting northeast from the Great Plains will bring a
southwest flow of milder air for the weekend.


Only very light snow/flurries S of Route 6 right now and the
expected pivot to the best lift is about to start as the low
pressure center gets close to KCLE. Have lowered POPs some in
the srn half of the area for the overnight as most near-term
guidance makes little or no QPF south of Route 22.

Low pressure over IN attm. Good band of snow stretches from Erie
back through Rock City to Valpo. Mid clouds from WAA ahead of
this is generating a few flurries for the NW, but most of the
area will remain only mo/cloudy for the first 2/3rds of the
night. As the low center passes over BFD, the wind will pivot
and drag a line of snow showers through late tonight/almost to
sunrise (per latest CAMs). Little in the way of instability when
this first volley is slated to arrive. In fact, the temps may
be mild enough that the first volley could be a mix instead of
straight snow south of I-80.

Dry and milder conditions prevailing this afternoon thanks to
high pressure building into the region. Downsloping subsidence
resulting in clear skies across the south central mountains and
now working through the southeast while stratocu lingers beneath
subsidence inversion over the northwest mountains. Increasing
mid and high level cloudiness arriving ahead of clipper over the
Great Lakes on schedule, and will continue to thicken late this
afternoon and evening as clouds increase farther east and south
as well.

Model consensus brings a batch of warm advection snowfall to
western and northern sections this evening through overnight
with a coating to 1 to 3 inches from I80 northward to the NY
border respectively. Main impacts from this system will come as
the cold front ushers in the coldest air of the season into PA
later Tuesday, after FROPA Tue morning.

As per collaboration with PBZ and BUF, Winter Storm Watch was
already upgraded to Lake Effect Snow Warning for Warren County.
Also expanded Winter Weather Advisory southward to include the
rest of the Laurels (Clearfield, Cambria and Somerset Counties).


The coldest air of the season is forecast to arrive behind
trailing arctic cold front Tuesday with more lake effect snow
lasting through midweek. Northwest Warren County should get into
some of the more robust lake effect banding later Tuesday and
continuing into Wednesday. Lake Effect Snow Warning in effect for
this, per collaboration with BGM, for widespread 10 to 15
inches, with local amounts up to 18 inches over extreme
northwest Warren County. Model blended qpf supports a long
duration advisory over Elk/Mckean counties, as well as
Clearfield/Cambria/Somerset Counties where 4 to 8 inches are
expected from 12z Tuesday through 18z Wednesday.

Still some concern about snow squalls accompanying cold front
passage between 12Z-18Z Tuesday. However, lower tropospheric
lapse rates look less impressive than would be expected for a
significant snow squall event and are actually separated from
the best frontal/isallobaric forcing. Still isolated snow bursts
and a few squalls are possible on Tuesday. It appears the Lower
Susq River Valley will be spared from any snow squall threat
Tuesday since boundary layer temps appear borderline for shra
vs shsn and surface temps are likely to be near 40F.

Gusty wnw winds will develop Tuesday behind the cold front with
bufkit soundings supporting frequent gusts of 30kts+ by late
in the day.


Gusty northwest winds and snow showers will be the main issue
Tuesday Night into Wed. Warnings and advisories in effect until
18Z Wed.

Models show another system for Thursday. This system looks weak
and EC a little further south, as been the case. Thus just have
very light amts in. Maybe more of an impact for the far
southeast, than system for Tue into Wed.

After this the pattern supports a deep low tracking northeast
from the Great Plains for the weekend, which will result in
milder conditions. As been the case, the Gulf of Mexico is not
really open, so looking at a mainly dry weekend.

Complex pattern for Monday, perhaps a little light snow, but
nothing major.

Minor changes to the extended package.



Some feeder bands have moved through out ahead of an alberta
clipper that will track just north of Pennsylvania tonight.
These feeder bands are fairly light and low level stratocu has
set up over the region. Brief IFR conditions are possible
between 06Z to 08Z. More widespread IFR cigs and vsbys will
occur as a trailing arctic cold front sweeps through the area
early Tuesday around 06Z at BFD. Between 06Z to 15Z the front
will spread from the NW across the state though the worst cigs
and vsbys will primarily be over the NW half of CWA. There is
some concern about snow squalls accompanying cold front passage
between 12Z- 18Z Tuesday. Then gusty WNW winds develop with
frequent gusts of 30kts+ by late in the day.

 Reducing conditions will continue for the western and central
TAF sites through most of Tuesday and will slowly improve
into Tuesday night, though reducing cigs and vsbys could linger
at BFD and JST into Wednesday.


Late tonight and Tuesday...Periods of light snow - mainly NW
half. Widespread MVFR likely, with periods of IFR and brief
LIFR cigs and vsbys NW.

Wed...Snow showers with IFR NW Mtns. Sct snow showers with MVFR
NW half. Otherwise VFR.

Thu-Fri...Sct snow showers. Reductions west.

Sat...Mainly VFR. Perhaps a snow shower north early.


Winter Weather Advisory from 7 AM Tuesday to 1 PM EST
Wednesday for PAZ005-010-017-024-033.
Lake Effect Snow Warning from 7 AM Tuesday to 1 PM EST
Wednesday for PAZ004.


NEAR TERM...Dangelo/DeVoir/Fitzgerald
SHORT TERM...DeVoir/Fitzgerald
LONG TERM...Martin
AVIATION...DeVoir/Ceru is the U.S. government's official web portal to all federal, state and local government web resources and services.