Area Forecast Discussion
Issued by NWS State College, PA

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FXUS61 KCTP 172124
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
424 PM EST Fri Nov 17 2017

.SYNOPSIS...
High pressure will build across the state today. A potent
weather system will impact the region Saturday into Monday
morning. A cold front will push through Saturday night. Gusty
winds and some lake effect snow will then last through Sunday
night. High pressure will then improve the weather for the first
half of next week.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Mostly sunny conds will continue remainder of the day with high
clouds on the doorstep for later this evening. Low clouds have
finally dissipated across the nw. Max temps will only be u30s
to near 50F thanks to the ridge axis staying to the west until
late in the day.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SATURDAY/...
High clouds will already be thickening up as the storm off to
our west musters. The high pressure continues steadily off to
the east and contributes southerly/moist flow into the system,
allowing for deepening. The low which is barely noticeable in
the sfc pressure over the high plains will deepen to about 994mb
as it cross the MS river. Warm air never really has a chance to
make a difference for our temps, and just slides overhead. Rain
showers will begin around sunrise in the NW and spread quickly
across most of the region on Saturday. The heaviest rainfall
will be over the northern counties, where many places could get
between 1 and 1.5 inches. The far SE is progged to get the
least rain, but there could be some instability which could
enhance the showers. SPC general thunder area covers most of the
CWA on Day2. The air gets cold enough quick enough that there
could be some light snow at the tail end of the rain Saturday
night in the western/northern mtns, but not much more than a
dusting.

&&

.LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/...
One-two punch of gusty West to Northwest wind, then a quick
transition to the first significant bout of Lake Effect Snow
this season across the NW mtns of PA in the wake of a strong
cold frontal passage Saturday night.

The synoptic set-up of a deepening low moving down the St
Lawrence River valley and a potent short wave trough aloft
swinging around the base of the longer trough is quite favorable
for strong winds.

The center of an area of very sharp pressure rises (10 mb/3
hours) moves ENE right over the region during the mid to late
morning hours Sunday. We could easily see Wind Advisory Criteria
with this type of fall/rise couplet passing directly overhead,
and possibly even a High Wind Watch/Warning scenario with west
to northwest gusts in the 50-60 mph range. It`s still far
enough out to look for consistency in this feature and decide
whether to go the High Wind Watch route at ~4th period.

The second punch is the deep/strong cold air advection with -10C
air at 850 mb crossing Lake Erie Water temps in the mid-upper
40s, which results in an extreme Lake-850 mb Delta T of 18C
Sunday afternoon and evening across the perennial snowbelt of NW
PA.

Winter Weather Advisory criteria will likely be reached from
this upcoming bout of LES, considering anticipated 4-8 inch
forecast snow amounts over an extended 24-36 hour period.
Elsewhere, much lighter snow amounts of a coating to 2 inches
will occur from sinuous bands of snow showers and briefly heavy
squalls that should make it well into the Central Ridge and
Valley Region and portions of the Susq Valley based on fairly
strong 35 to 45 kt nw winds in the deep and cold boundary
layer.

High pressure sliding by to our south will influence the
weather to start Thanksgiving week, bringing a couple of cool-
dry days. Temperatures will begin to moderate Tuesday with a
gusty SW flow expected to develop as potent sub-1000 mb low
pressure passes by across southern Ontario and Quebec. Tuesday
will be the lone day in the Mon-Fri period when 850 mb temps
will poke a few to several deg C above zero.

Though the jet stream will remain north of the region, a quick
moving trough will brush the region on Wed followed by a weak
shortwave Wed night, which will bring chance for periods of snow
showers (with light accums of a coating to 2 inches) back into
the NW zones, along with a return of slightly cooler air.
Flurries or brief snow showers will occur just SE of the
Allegheny Front.

12Z GFS and EC have trended into better agreement on a deepening
upper low across southeastern Canada or the NE U.S. over the
Thanksgiving weekend. Surface and 850 mb temps could be a few
deg colder than our upcoming cold outbreak later this weekend.
&&

.AVIATION /21Z FRIDAY THROUGH WEDNESDAY/...
As high pressure builds across the region, expect VFR conds
through at least the late eve hours and overnight at most
airfields. Stratocu cigs have finally lifted at KBFD

Complex frontal system will affect the region through the
weekend with rain spreading west to east starting late tonight.

Outlook...

Sat...Rain with low cigs possible, mainly KBFD. LLWS possible.

Sun...Windy with gusts 30-40kts. MVFR in snow showers NW.

Mon...MVFR cigs/sct -shsn psbl early NW 1/4.

Tue...No sig wx expected.

Wed...Cold fropa. Shra/shsn psbl, mainly northwest.

&&

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

&&

$$
SYNOPSIS...Dangelo/Gartner
NEAR TERM...Gartner
SHORT TERM...Dangelo/Gartner
LONG TERM...Lambert
AVIATION...Fitzgerald/Gartner


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