Area Forecast Discussion
Issued by NWS State College, PA-- Highlight Changed Discussion --
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FXUS61 KCTP 081203
Area Forecast Discussion
National Weather Service State College PA
703 AM EST Thu Dec 8 2016
A upper level trough over the Great Lakes will pivot eastward
across the region over the next couple of days. High pressure will
briefly build into Pennsylvania late Saturday, then a weak low
pressure system is likely to track west of Pennsylvania through
the Great Lakes Sunday into Monday.
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
-- Changed Discussion --Regional radar mosaic at 10Z showing some weak returns aloft assoc
with lift along jet streak, which extends from the Ohio Valley
through Pa. Dry air in the lowest 5kft, should continue to
preclude precip from reaching the ground in most places, but
can`t completely rule out a flurry in spots this morning.
Shortwave and assoc batch of mid level cloudiness should push east
of the region by around midday. In it`s wake, arrival of colder
air will result in developing lake effect snow downwind of Lake
Erie today. All model data currently indicating the boundary
layer flow will remain WSW for much of the day, keeping the bulk
of the accumulating snow north of the border. However, a gradual
veering of the flow is anticipated by late afternoon, bringing
snow into Warren/Mckean counties. A lake effect snow warning/advisory
goes into effect at 18Z across Warren/Mckean Co, where a light
coating appears likely by early evening.
Model soundings support skies becoming msunny across Eastern Pa by
this afternoon, helping to push temps into the low 40s across the
Susq Valley. Further west, skies are likely to remain mainly
overcast today due to developing lake effect over the NW Mtns and
orographic forcing over the Laurels.
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.SHORT TERM /6 PM THIS EVENING THROUGH SATURDAY/...
A fairly long-duration lake effect snow event will play out across
the NW Mtns tonight through Saturday, as anomalously cold WNW flow
follows the passage of upper trough axis this evening. Cross lake
flow will result in multiband le snow across the northwest Pa, with
the heaviest accums in the favored snowbelt of NW Warren Co. Model
soundings showing a deep, moist boundary layer with an inversion
height around 700MB and although the 850mb temps of around -13C
aren`t exceptional, relatively warm lake waters of around 50F will
result strong instability/moisture flux.
The passage of a shortwave around midday Friday could briefly support
lake effect snow extending well downwind of the lakes, with a
quick coating likely in the ridge/valley region of Central Pa and
possibly even into parts of the Susq Valley.
The boundary layer flow is progged to remain close to 270 degrees
across Southern Pa, excluding the Laurel Highlands from a direst
link to lake moisture. However, persistent upslope flow should
yield occasional light snow with accumulations of 1-2 inches
between Friday and Sat morning.
An examination of model time sections shows the greatest lift
occurring just below the DGZ, which in combination with fairly
gusty winds should hold snow/water ratios to no better than 20/1.
Based on a blend of available high res model and WPC QPF, have
come up with 48-hour event snow totals of 12-18 inches over
extreme northwest Warren Co, with rapidly decreasing amounts
Although not an exceptionally cold air mass for this time of the
year, this will be the coldest air mass so far this season with
temps 5-10F below normal Friday/Saturday. A gusty wind will make
it feel even colder. Expect relenting wind and clearing skies
across Southern Pa Saturday, as high pressure builds in from the
Ohio Valley. However, WSW fetch off the lakes should continue to
produce le snow showers until Sat evening across the N Mtns.
.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
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. Model consensus low track west of Pa
could cause snow to change to rain across Southern Pa before
precip tapers off later Monday.
Seasonable temps indicated early next week, but both the 00Z
ECENS and NAEFS indicate a significant cold front passage late
Tue/early Wed with below normal temps likely the rest of next
.AVIATION /12Z THURSDAY THROUGH MONDAY/...
A developing cold W-NW flow pattern in the wake of a low moving
across Quebec into Atlantic Canada will support a prolonged period
of MVFR/IFR conditions over the western 1/3 airspace into the
weekend, with frequent lake effect/upslope snow showers. MVFR
cigs and ocnl visby reductions are possible over the central
terminals with VFR prevailing across the eastern sites. Expect
frequent sfc wind gusts 20-25+kt by this afternoon resulting in
low level mechanical turbulence during takeoff and final approach.
Lake effect snow showers should decrease in coverage/intensity by
later Saturday as area of high pressure briefly slides over the
Sun-Mon...MVFR/IFR with mixed rain/snow likely.
Lake Effect Snow Advisory from noon today to noon EST Saturday
Lake Effect Snow Warning from noon today to noon EST Saturday