Area Forecast Discussion
Issued by NWS State College, PA

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000
FXUS61 KCTP 131203
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
703 AM EST Wed Dec 13 2017

.SYNOPSIS...
A deep northwest flow of cold air will be over the region
through this afternoon, resulting in snow showers across the
Northwest Mountains and Laurel Highlands. A weak ridge of high
pressure will bring a lull in the winds and snowfall for several
hours this afternoon, followed by a fast-moving clipper system
tonight that will bring periods of light to moderate snow to
perhaps the entire region.

Several inches of additional snow can be expected by Thursday
morning across the Western Mountains, while a general 1 to 3
inches falls across the central Mountains, with slightly lesser
amounts throughout the Susquehanna Valley. Another ridge of high
pressure will slide across the region Thursday and Thursday
night with cold but mainly dry conditions. More snow showers
will occur Friday afternoon into Saturday morning.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
A gusty West-Northwest flow this morning will continue to push
several streamers of Lake Effect Snow showers well inland from
Lake Erie with an additional Coating to 2 inches expected across
the northern and western mtns of the state. mainly flurries
will occur to the SE of a KAOO to KUNV and KIPT line.

Winds will slacken steadily later this morning and this
afternoon as a weak ridge of high pressure slides quickly east
across the state, bringing some brief partial clearing (mainly
to the eastern half of the state) along with dry conditions.

High temps today will range from the Lower 20s across the
Northern and Western mtns, to the mid and upper 20s headed SE
across the central Mtns to the Lower Susquehanna Valley.

The passage of upper trough axis and pressure fall/rise couplet
early today will be accompanied by gusty winds and winds chills
in the single digits above and below zero.

Latest Bufkit soundings continue to support frequent gusts
between 30-35kts early this morning. Heavy winter coats, hats,
and good gloves/mittens will be in order for the morning commute
to work and school, especially at the bus stops this morning.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM THURSDAY/...
A fairly vigorous Alberta Clipper (994-996 MB) will race east
from the Ohio Valley and likely move cross the southern part of
the state tonight.

Large scale uvvel at the nose (thermally indirect, left exit
region) of a 115-120 kt upper jet and low to mid level warm
advection, will result in thickening clouds late today followed
quickly by a rather large shield of light (to briefly moderate)
snow near and to the north of its sfc warm front.

Best dynamics and low level orographic lift will favor up to 3-4
inches of snow across the Laurel Highlands with gradually
lesser amounts occurring to the north and east across the state.

A second/separate Winter Weather Advisory was recently issued
from the NW mtns to the Laurel Highlands for the 23Z Wed - 13Z
Thursday period and well Collaborated with surrounding WFOs.

As expected with a clipper, model omega/temp  time-sections
indicate fairly high snow/water ratios (perhaps around 20:1) with
max lift occurring within, or just below, the DGZ. These high
snow/water ratios could tip the scale for Advisories to be
expanded east across several Central PA counties encompassing
KAOO, and KUNV where a fluffy 3 or 4 inches may accumulate from
the latest model consensus and SREF mean of around 0.20-0.25
inches of LEQ.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
Highly sheared and rather shallow cold airmass with a gusty NW
wind of 20 to 25 mph will follow for Thursday with Partly to
mostly sunny skies SE of the Allegheny Plateau. Flurries with a
few isolated-sctd snow showers will occur from KJST to KFIG and
KBFD, with accums generally less than an inch.

Clearing and quite cold conditions for Thursday night under the
center of high pressure. Min temps will vary from the single
digits over the NW mtns, to the teens throughout the Susq Valley
and Southern Tier.

A weak, elongated vort lobe will push east through the region
late Friday/Friday night as low pressure moves across
southern/central Ontario, Canada. Expect to see isolated to
scattered snow showers across mainly the Northern and Western
mtns of the state, with generally light snow accums in the
typical Lake Effect/orographically enhanced locations.

High Pressure consolidates off the Mid Atlantic Coast for Sunday
with the large scale flow becoming southwesterly and milder air
(temps 8-10 F above normal) flooding the eastern half of the
Lower 48 States. Clouds will thicken up from the southwest late
Sunday through Monday with a likelihood of rain showers.

&&

.AVIATION /12Z WEDNESDAY THROUGH SUNDAY/...
* Cloud/Ceiling info will be missing at KBFD until new part can
  be installed *

A deep northwest flow of cold air will continue over the region
into this afternoon, resulting in IFR conditions (due to snow
showers) transitioning to MVFR over Northwest Mountains and
MVFR ceilings lifting to VFR by midday in the Laurel Highlands,
while the remainder of area will be generally VFR. WNW wind
will remain quite brisk into the mid afternoon, with sustained
speeds in the 15-20 mph range with gusts to 30-35 mph before
diminishing late in the day.

After a short lull, a fast-moving clipper system will impact
much of central PA this evening and overnight with periods of
light to moderate snow bringing reductions to IFR for areas
generally NW of I-81 beginning in the west between 22z-24z and
the east between 00z-03z. SE of I-81 generally MVFR conditions
are expected in lighter snow starting between 01z-04z. The snow
will taper off in the SE around 09z and will be winding down
elsewhere around 12z - though upslope snow showers and
reductions will persist in the NW Mtns and Laurel Highlands into
Thursday.

Outlook...

Thu-Fri...Sct snow showers NW/Laurels. Reductions western higher
terrain.

Sat...Sct snow showers NW with reductions poss. Mainly VFR
elsewhere.

Sun...Mainly VFR. Clouds will thicken up from the SW late with
a likelihood of rain showers Sun Night.


&&

.CTP WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 1 PM EST this afternoon for
PAZ005-010-017.
Winter Weather Advisory from 6 PM this evening to 8 AM EST
Thursday for PAZ004-005-010-017-024-033.
Lake Effect Snow Warning until 1 PM EST this afternoon for
PAZ004.

&&

$$
SYNOPSIS...Lambert
NEAR TERM...Lambert
SHORT TERM...Lambert
LONG TERM...Lambert
AVIATION...RXR



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