Area Forecast Discussion
Issued by NWS State College, PA

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000
FXUS61 KCTP 111211
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
711 AM EST Mon Dec 11 2017

.SYNOPSIS...
An alberta clipper will track just north of Pennsylvania
tonight, with a trailing arctic cold front sweeping through the
area 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.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
A moisture-starved shortwave is moving through central Pa early
this morning, accompanied by a few snow showers/flurries over
the northern mountains. The shortwave will be passing east of
the area by 12Z. However, will maintain mention of a few
lingering snow showers across the northwest mountains until late
morning in association with a dying cold front sagging south
from the Grt Lks.

For most of central Pa, expect a dry and slightly milder
Monday, as ridging briefly works into the region. Downsloping
subsidence should result in mostly sunny skies east of the
mountains, while stratocu lingers beneath subsidence inversion
over the northwest mountains. By late in the day, expect
increasing mid and high level cloudiness to arrive ahead of
clipper over the Grt Lks. Model soundings are well mixed to at
least 900mb, where temps of -4C to -6C should translate to max
temps from around 30F over the northwest mountains, to near 40F
across the Lower Susq Valley.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM TUESDAY/...
All model guidance tracks clipper north of Pa tonight, which
should keep the most substantial snow north of Pa. However,
blend of latest guidance still supports a period of light
overrunning snow across northern Pa, with accums generally in
the 1-3 inch range. An examination of model omega/temperature
time sections indicates bulk of lift occurring tonight will be
well beneath the DGZ, indicating snow/water ratios not much
above 10 to 1.

The coldest air of the season is forecast to arrive behind
trailing arctic cold front Tuesday with more lake effect snow
lasting through midweek. Between light clipper snow tonight and
Tue-Wed lake effect, WPC graphics indicate about a 50 pct chance
of exceeding winter storm criteria across the snowbelt of
Warren County, so have issued a wint storm watch up there.
Further east, all model guidance indicating limited potential of
reaching warning criteria. However, model blended qpf supports
a long duration advisory over Elk/Mckean counties.

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 00Z model CAPES are
nonexistent until front reaches the Lower Susq Valley, where
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.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
Model soundings suggest wind advisory criteria is possible
early Wed, as large scale subsidence and pressure fall/rise
couplet moves through. Have added blowing/drifting to the
forecast, where sig snow is expected over the northwest
mountains. Base of upper trough and coldest air will be over the
region Wed, with temps likely not reaching 20F over the
Allegheny Plateau and only reaching the upper 20s across the
LSV.

Lake effect snow is likely to abate late Wed, as weak surface
ridge builds in from the Grt Lks. Med range guidance indicates
another clipper is likely to affect the area Thursday with
another potential light snowfall. After that, ECENS and GEFS
both indicate upper trough will lift out, resulting in a marked
warm up next weekend. Latest EC ensemble MOS guidance indicating
temps returning to near or slightly above climo by next
weekend.

&&

.AVIATION /12Z MONDAY THROUGH FRIDAY/...
Lake flow will keep snow showers over the KBFD terminal off and
on through the mid morning hours. Restrictions there will remain
IFR through about 15z, then improve to MVFR. MVFR cigs will
persist at KJST into the early afternoon, and brief MVFR cigs
will be poss mid morning in parts of the central mountains. Mainly
VFR conditions are forecast elsewhere, with a scattered to
broken deck between 5000 and 12000 feet. Winds will be westerly
at 5 to 10 knots.

An alberta clipper will track just north of Pennsylvania
tonight, with a trailing arctic cold front sweeping through the
area Tuesday. Light snow will begin to impact NW mountains after
midnight, and spread into the NW half around 10-14z Tues. The
snow will be accompanied by cig/vsby reductions - again
primarily over the NW half of CWA. 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.


Outlook...

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.

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 7 PM this evening to 4 PM EST
Wednesday for PAZ005-010.
Winter Storm Watch from this evening through Wednesday
afternoon for PAZ004.

&&

$$
SYNOPSIS...Fitzgerald
NEAR TERM...Fitzgerald
SHORT TERM...Fitzgerald
LONG TERM...Fitzgerald
AVIATION...RXR



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