Area Forecast Discussion
Issued by NWS State College, PA

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FXUS61 KCTP 092129
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
429 PM EST Fri Dec 9 2016

.SYNOPSIS...
A broad and very cold upper level trough over the Great Lakes
and southeastern Canada will remain in place for the next few
days. This weather feature and a well-aligned westerly low level
flow off the lower Great Lakes will bring a prolonged period of
lake effect snowfall and significant snow accumulations to
northwest PA today through Saturday. High pressure will briefly
build across the commonwealth late Saturday and Saturday night
causing the Lake Effect snow bands to lift north of the region
with a brief period of clearing elsewhere. Then, a weak low
pressure system is likely to track east from the Ohio Valley and
impact Pennsylvania with another bout of wintry weather Sunday
into Monday. Unsettled weather will persist next week with
additional storm chances during the mid...and late week periods.

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
Updated the forecasts with mainly minor changes.

Primary short term issues include the snow and wind. Radar still
shows a significant lake effect snow (LES) event. Some reports
northeast of Warren had 11 inches and 9 inches in Chandlers
Valley. These reports are several hours old and the snow
continues.

There is one elongated band that extends from Lake Erie down
across Clinton County into Union and Snyder counties. Impressive
length to the band. The band crosses I80 so it could produce
periods of snow and blowing snow on I80 in southern Clinton County this
afternoon and evening.

The 3km HRRR shows the long band but it forecasts it to weaken
over the next 2-8 hours. The HRRR shows snow and periods of
moderate snow in Warren County through at least 8 AM Saturday. At
least light snow in McKean county through the same period.

All guidance focus the accumulating snow in our northwestern
counties and limits snow; outside the one elongated band we
currently have; to the northwestern 4 counties.

Overnight lows in the teens and twenties but the wind will make
it feel a good 10F colder at times. Most central areas and the
southwest mountains will have flurries overnight with little or no
accumulation to a dusting.

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH 6 PM SATURDAY/...
The HRRR and 15Z SREF continue to support additional snow accumulation
across the 2 NW PA counties into Saturday morning, some areas of
light additional accumulation is possible across the west-central
mtns and Laurel Highlands.

Gradually improving conditions will take place later in the
morning and afternoon as lake effect snow bands become more
scattered and slowly wind down. Despite decreasing in intensity...
WSW fetch off the lakes should continue to produce snow showers
until Sat evening across the N Mtns. Skies should be clear
across southern PA Saturday thanks to 1032 mb surface high
building into the region.

&&

.LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/...
High pressure will bring a brief period of tranquility Sat
evening. However, a developing overrunning scenario is expected
Sunday into Monday, as weak low pressure lifts into the Eastern
Grt Lks and high pressure remains lodged over northern New Eng.
Enough cold air is in place to support a light snowfall across
much of area by Monday AM, with GFS bringing light precip into the
area on Sunday earlier than the ECMWF. Model consensus low track
west of PA should bring in enough warm air to cause snow to change
to rain (or a period of more problematic freezing rain) across
Southern PA, and esp the Lower Susq Valley, a before precip tapers
off later Monday.

A bit cooler than normal temps indicated early next week, but
longer range models indicate a significant cold front passage
Wed with noticeably below normal temps filtering in for the rest
of next week.

&&

.AVIATION /21Z FRIDAY THROUGH WEDNESDAY/...
Cold W-NW flow pattern downwind of the Great Lakes will continue
to support a prolonged period of MVFR/IFR conditions over the
western 1/3 of the airspace into the weekend, with frequent lake
effect/upslope snow showers at KBFD/JST. MVFR cigs and ocnl vsby
reductions in -shsn are possible over the central terminals with
VFR prevailing across the eastern sites. Expect sfc wind gusts
20-25+kt from 270-300 degrees for most of today before winds
subside after 10/00z. Lake effect snow showers should decrease in
coverage and intensity by later Saturday as area of high pressure
briefly slides over the airspace. Low pressure tracking from the
lee of the Rockies to the Ohio Valley will bring a broad area of
snow/rain to the area Sunday into early Monday.

Outlook...

Sat...MVFR/IFR western 1/3 with snow showers decreasing.

Sun-Mon...Widespread MVFR/IFR in snow/rain. Becoming breezy Monday
night with snow showers over the wrn 1/3.

Tue...VFR to MVFR cigs. Snow showers ending.

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
Lake Effect Snow Advisory until noon EST Saturday for PAZ005.
Lake Effect Snow Warning until noon EST Saturday for PAZ004.

&&

$$
SYNOPSIS...DeVoir
NEAR TERM...Grumm
SHORT TERM...Jung/DeVoir
LONG TERM...Lambert/RXR
AVIATION...DeVoir/Steinbugl



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