Area Forecast Discussion
Issued by NWS State College, PA-- Remove Highlighting --
-- Discussion containing changed information from previous version are highlighted. --
FXUS61 KCTP 092121
Area Forecast Discussion
National Weather Service State College PA
421 PM EST Fri Dec 9 2016
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/...
An anomalously cold cross-lake flow will maintain a long-duration,
multi-band lake effect snow event across northwest PA...with bands
extending into the Central Mountains and Ridge and Valley regions
of central PA through this evening.
No big changes from previous thinking going on...as activity
persists in moderate northwest flow supporting multiple bands of
moderate to heavy snow showers. Shortwave traversing north central
PA is maintaining an intense band which is currently crossing
Interstate 80 between Beach Creek and Lewisburg producing
dangerous travel conditions there.
Elsewhere the main impacts are over the northwest mountains where
western portions of Warren County have likely exceeded a foot and
will add substantially to totals tonight. Will maintain the Lake
Effect Snow Warning (Warren County) and Lake Effect Snow Advisory
(Mckean County) through 17Z Saturday, before the llvl mean wind
gradually backs to about 250 Deg carrying the LES bands north of
the PA/NY border Saturday afternoon.
Little change to forecast storm total snow amounts as 12-18" with
locally 20"+ is expected over the NW third-half of Warren County
by Saturday. A light coating to one inch will occur in select
areas of the central Ridge and Valley Region of PA today...with
some spots receiving additional light accums tonight and Saturday.
Skies in this region of the state will stay mostly cloudy to
Across the Mid and Lower Susquehanna Valley Region, it will be
partly to mostly cloudy with generally just some scattered
flurries. But will need to watch the southeast extent of current
banding crossing I-80 which could bring a rush hour headache to
areas that don`t usually see heavier snowshowers/squalls.
Mins tonight will be fairly uniform...ranging from the upper teens
northwest to the mid 20s southeast. A brisk northwest wind will
gust between 20 mph and 30 mph...putting wind chills in the single
digits and teens.
.SHORT TERM /6 AM SATURDAY MORNING THROUGH 6 PM SATURDAY/...
Additional significant accumulation will occur across the 2 NW PA
counties into Saturday morning...while 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/...
-- Changed Discussion --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 both GFS and ECMWF better coming
together on timing for light precip moving into the area from the
west on Sunday. 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 Monday afternoon.
Potential with this event for advisories to be issued, but being a
4th/5th period event will hold off for now.
Another fairly short respite Mon night into Tue night, with
some lake effect snow showers over nw mtns. But progressive
pattern brings another wave through in the GFS for Wed with
chance for rain/snow, before westerly flow keeps mention of snow
showers over northern mtns after that.
After warm advection Sun night into Mon brings temps above
freezing across the SE, temps gradually fall back early next week.
Longer range models continue to indicate a significant cold front
passage Wed with noticeably below normal temps filtering in
starting Wed night and continuing for the rest of next week as
850MB temps fall to -20C.
-- End Changed Discussion --
.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.
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.
-- Changed Discussion --Lake Effect Snow Advisory until noon EST Saturday FOR PAZ005.
Lake Effect Snow Warning until noon EST Saturday FOR PAZ004.
-- End Changed Discussion --