Area Forecast Discussion
Issued by NWS State College, PA-- Highlight Changed Discussion --
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FXUS61 KCTP 061153
Area Forecast Discussion
National Weather Service State College PA
653 AM EST Tue Dec 6 2016
Low pressure over the Tennessee Valley will track northeast
through Pennsylvania late today and tonight. A cold front will
sweep southeast across the area Thursday. A low pressure system is
likely to track west of Pennsylvania through the Great Lakes
Sunday and Monday.
.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --Overrunning precip ahead of approaching sfc low is spreading into
northern Virginia and W Virginia as of 12Z and latest near term
models support arrival across the Laurels/SC Mtns by 14Z-15Z.
Model soundings indicate enough evaporational cooling potential at
onset to support a rain/snow/sleet mix across the southern valleys
during the late AM to early PM hours. However, with surface temps
mainly above freezing, don`t anticipate significant travel
issues across the Lower Susq Valley.
Main focus will be over the high terrain of the Laurels, where
model soundings indicate a light accum of freezing rain is likely.
Further north, model soundings, as well as SREF and NCAR ensemble,
all indicate a mainly snow event north of I-80. Surface high is in
ideal position over New Eng to hold in the relatively cold air
over Pa. Marginal surface temps could limit accums a bit in the
valleys. However, over the higher terrain of Northern Pa, model
blended QPF is supportive of snow totals around 3 inches by the
time precip tapers off late this evening. Based on coordination
with BUF/BGM, have lowered snow amts from WPC guidance and held
off on a winter wx advisory across Northern Pa, but will have to
revisit this possibility on the day shift. Will maintain the
advisory across the Laurel Highlands. However, current feeling is
that the freezing rain will be isolated to only the highest
terrain and thus the impact will be fairly low.
Deep moisture will exit the area with passage of mid level
shortwave late this evening. However, model soundings remain
nearly saturated below 850MB, indicating the likelihood of linger
drizzle late tonight. Superblend and high res NAM both indicate
temps creeping above freezing even across the N Mtns late tonight.
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.SHORT TERM /WEDNESDAY/...
Surface high pressure building into the region should supply a dry
Wednesday to Central Pa. However, low level moisture trapped
beneath inversion and weak mixing will likely result in stubborn
low clouds across the NW Mtns. A downsloping westerly breeze
should result in partly to mostly sunny skies east of the Mtns.
Temperatures there should respond by rising into the low-mid 40s,
while cloud cover holds readings to the mid 30s across the NW
.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
Broad and weak to moderate large scale lift/low to mid level warm
advection develops late Wednesday night across the mtns of Wrn PA,
and spreads across the remainder of Central PA Thursday ahead of
an approaching arctic front and beneath the thermally direct
segment of a 150kt 300mb jet moving by just to our north. Although
moisture will be lacking with this feature, the fairly impressive
large scale forcing, in conjunction with 00Z GEFS precip probs,
supports mention of SHSN (SHRASN Lower Susq) across the entire
The subsidence inversion base lifts rapidly up to 7-10 kft agl
Thursday afternoon, right through Friday night. The mean wind in
the 925-850mb layer veers from about 270 deg to 295-310 deg Friday
and Friday night creating the likelihood of a significant/heavy
Lake Effect/orographic snow event for the NW Mtns (i.e. mainly
the snowbelt of NW Warren county). Will highlight this potential
in the HWO.
Gusty NW winds could top 40 mph at times Friday.
A large area of high pressure and modified arctic airmass will
slide off the east coast Sat night and Sunday. The coldest temps
of the season so far will occur Sat night/early Sunday with lows
in the lower to mid teens across the snow covered ground of the
NW/Ncent Mtns...and upper teens to low 20s elsewhere.
00Z ECENS and NAEFS both track a surface low west of Pa through
the Grt Lks late Sunday into Monday. There could be a bit of light
snow in the WAA ahead of this feature, then milder/showery
conditions appear likely Monday before trailing cold front and
colder air arrive Mon night/Tues.
.AVIATION /12Z TUESDAY THROUGH SATURDAY/...
MVFR cigs over the northwest airspace should trend to VFR over
the next several hours. Elsewhere expect VFR with increasing/thickening
high clouds. Cigs will lower from south to north later this
morning with precip spreading over the airspace by the afternoon.
P-types should transition from frozen/freezing to rain/drizzle
across the western 2/3 of the airspace into Tuesday night. The
southeast airspace should see mostly rain with some sleet possible
at the onset. Confidence in ptypes is marginal given complex and
evolving thermal structure/evaporative cooling in the boundary
layer. Elevation and pcpn rates will also be a factor. A period of
LLWS is possible at BFD/JST from roughly 6/18z-7/03z. Overall,
expect flying conditions to deteriorate with high confidence in
sub-VFR Tuesday afternoon into Tuesday night.
Wed...A.M. low cigs becoming mainly VFR.
Thu-Fri...Becoming windy with periods of snow showers. Mainly
MVFR/IFR west to MVFR/VFR east.
Sat...Decreasing winds. Low cigs/-SHSN psbl NW. VFR east.
Winter Weather Advisory until midnight EST tonight for PAZ024-