Area Forecast Discussion
Issued by NWS State College, PA

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FXUS61 KCTP 110703
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
203 AM EST Sun Dec 11 2016

.SYNOPSIS...
High pressure will build south of the region overnight. Meanwhile
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 /UNTIL 6 AM THIS MORNING/...
Some minor adjustments to the grids as of mid evening.

Clear across most of the area, but some high clouds just to the
west as of mid evening.

Snow is still well to the west. Did adjust wording some on the
statement, as any snow will be very light Sunday morning.

Most of the lake effect now north of our area. Abnormally warm
water of the Great Lakes is keeping activity going, as winds shift
more to the west and southwest.

Earlier discussion below.

Lows will drop back into the mid teens to lower 20s overnight.

Latest timing shows warm advection snows beginning over my western
zones before dawn on Sunday.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM MONDAY/...
A Winter Weather Advisory has been issued.

Snow will overspread most of the region tomorrow morning. Precip
type Sunday will favor snow as the temps aloft will stay cold
enough during the day. Enough warm air may sneak into SWRN zones
to bring a wintry mix by late in the day, but the best chance of a
mix looks to hold off until Sunday night over SRN zones. The
biggest question for southern PA tomorrow will be if they get
dry-slotted after the initial shot of warm advection scoots
through. This complicated the advisory decision a bit with the
main reasoning for headlines over southern areas being the
expected ice, which should hold off until late day or overnight.
But the quick burst of snow during the day will likely start
things off with deteriorating travel conditions so we decided to
keep the headlines simple.

&&

.LONG TERM /MONDAY NIGHT 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 /06Z SUNDAY THROUGH THURSDAY/...
VFR conditions under thickening mid-high clouds will trend lower
this morning with MVFR/IFR conditions developing in -SN across the
western 3/4 of the airspace. Area of snow should lift north and
focus across the northern 1/2 of the airspace this afternoon
through the evening. Meanwhile, the southern airspace should see a
lull in pcpn ~11/20z-12/03z before the main burst of pcpn arrives
late tonight. Warm air surging in aloft via strong swly 40-50kt
LLJ (LLWS possible west) will result in mixed wintry pcpn with
fzra/ip south and snow/sleet north from ~12/03-12/12z. Pcpn tapers
off Monday morning as light rain in most areas with slowly
improving conditions into Monday afternoon.

Outlook...

Tue-Wed...MVFR/IFR snow showers NW. VFR elsewhere.

Thu...MVFR/IFR snow showers NW. Windy. SNSQs psbl with arctic
fropa.

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 1 PM EST Monday for PAZ004>006-
010>012-017>019-024>028-033>037-041-042-045-046-049>053-
056>059-063.

&&

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


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