Area Forecast Discussion
Issued by NWS State College, PA

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FXUS61 KCTP 101709
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
1209 PM EST Sat Dec 10 2016

.SYNOPSIS...
Lake effect snow will continue today with total accumulations
around 2 feet across the perennial Northwest Snowbelt. A new
frontal system will approach for Sunday and Monday. It will turn
sharply colder behind a cold front on Tuesday, with a shot of
arctic air and frigid temperatures expected through the end of the
week.

&&

.NEAR TERM /THROUGH TONIGHT/...

Have allowed the lake effect headlines to expire.

The long-duration lake effect event will continue to gradually
wind down with only light additional accums expected across the
NWRN lake snow belt.

Outside of the lake effect area, expect a partly to mostly cloudy
day with little more than a stray light snow shower or a flurry
spilling southeast over the Alleghenies into the Central Ridge
and Valley region.

Skies may actually scatter out for a few hours later today and
this evening, just in time for the next system to approach for
Sunday. Lows will drop back into the mid teens to lower 20s.

&&

.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
Increasing warm advection
ahead of mid level wave moving into the Great Lakes should spread
light snow into western areas by early Sunday. The main surge of
WAA moisture arrives Sunday night into early Monday morning in
association with strong 50kt SSW 850mb LLJ. The models show the
warm moist air overrunning the cold airmass currently in place
which likely results in a ptype transition /snow to sleet-freezing
rain/ from south to north. This changeover is most likely to
happen in the 00-12z Monday period and impact the Monday morning
commute. Confidence in forecast snow and ice amounts is below
average given complex nature of wintry mix event and uncertainty
in the 850mb 0C line. That being said, a winter weather advisory
may be needed and will allow the dayshift to make a final
assessment. Steady to slowly rising (non-diurnal) temps early
Monday morning should continue to warm through Monday afternoon
with any lingering pcpn falling mainly in the form of rain/dz.

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...
Scattered snow showers Monday night across the Western Mtns of PA
will diminish as a weak ridge of high pressure at the sfc slides
east from the Ohio Valley. Tuesday will begin a cool down in temps
over a several day period as progressively cold chunks of arctic
air move southeast ahead of the main, sub-500 dam Polar Vortex
that will be moving to near James Bay Canada by late Wednesday
night.

The coldest airmass of this young winter will spread into the region
for Thursday and Friday. Temps Thursday could conceivably struggle
to get above 10F for highs across the NW mtns. The GEFS shows a
small area of -2 to -3 sigma temps at 850 mb with values around -18
F.

West-Northwest wind gusting between 25 and 30 mph both Wednesday and
Thursday will create wind chills of 5-10 below zero during the
morning hours Thursday (mainly across the NW mtns), and only in the
single digits during the daylight hours. Skies will become mainly
clear with the wind dying off Thursday night as a 1025 mb sfc high
build east from the nation`s heartland. This will set the stage
for frigid temperatures - but several degrees above record lows.

Min temps early Friday  could dip to zero to 5 below across the
fresh snow covered ground of the Laurel Highlands and NW mtns, and
will be in the single digits to teens.

Fair and dry (but very cold) weather is expected to persist Friday
night. However...a moisture-laden storm will likely impact a large
chunk of the region (beginning Friday) with snow changing to mixed
precip of from the SW.

Saturday and Sunday, clouds will thicken up quickly and
precipitation will begin shortly afterward Saturday morning. It`s
too early to give specifics on that storm w/resp that storm. 10/00Z
EC and GEFS do infer a widespread wintry (snow) precip
event...likely changing to some light sleet or fzra as the thicker
seeder/feeder cloud shield slides off to the east.

&&

.AVIATION /17Z SATURDAY THROUGH WEDNESDAY/...
Cold WNW flow pattern will continue the snow showers and MVFR/IFR
conditions over the western 1/3 of the airspace. Low VFR to MVFR
cigs will prevail at the central terminals with brief MVFR vis
possible. VFR over the southeast.

Outlook...

Sun-Mon...Widespread MVFR/IFR in wintry mix changing to mainly
rain by Monday afternoon.

Tue...MVFR ceilings and light snow showers possible western 1/3.
VFR central/east.

Wed...Restrictions possible with next wintry system.

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$
SYNOPSIS...La Corte/Steinbugl
NEAR TERM...La Corte/Steinbugl
SHORT TERM...Steinbugl
LONG TERM...Lambert
AVIATION...La Corte/Steinbugl



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