Area Forecast Discussion
Issued by NWS State College, PA

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000
FXUS61 KCTP 130456
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
1156 PM EST Tue Dec 12 2017

.SYNOPSIS...
A deep northwest flow of cold air will be over the region
through Wednesday afternoon. This will result in snow showers
across the mountains tonight and early Wed.

Low pressure will track across southwestern Pennsylvania
Wednesday night. This low will bring a period of light snow to
the area Wednesday night.

A complex weather pattern will be across the region this
weekend, and early next week. This will result in some snow
showers from time to time, but a moderating trend into next
week.

&&

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
Skies have cleared across a large portion of central Pa this
evening, as low PWAT arctic air overspreads the region on
northwest flow. Although the dry air will hinder lake effect
snow overall, long fetch Lake Huron band is progged by models to
slip southward across northern Pa late tonight. Have timed
highest POPs to correlate with arrival of this band based on
latest NAM/Canadian 925mb the fields.

Based on model blended qpf and an expectation of snow/water
ratios near 20/1 (max omega occurring within DGZ), believe
additional snowfall between 03Z-12Z will range from up to 6
inches over the snowbelt of northwest Warren County, to a fresh
coating across the northeast quadrant of the forecast area.
Despite favorable upslope flow, believe overnight accums across
the Laurel Highlands will be only an inch or less due to the
aforementioned dry air.

For most of the forecast area, the cold air and low wind chills
will be the main story overnight. Temperatures falling into the
teens, combined with gusty winds, will result in wind chills
in the lower single digits late tonight across the southeast
counties and the lower single digits below zero across the
Allegheny Plateau. Passage of upper trough axis and pressure
fall/rise couplet late tonight will likely be accompanied by an
increase in wind gusts during the early morning hours. Latest
Bufkit soundings support frequent gusts between 25-35kts early
Wed morning. Heavy winter coats, hats, and good gloves/mittens
will be in order if going out tonight, especially at the bus
stops Wednesday AM.

&&

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/...
Key point is it will be a very cold day with lots of wind.
Windchill values will be below 0F in the northwest and range the
single digits above zero over the southeast. Bundle the kids up
for school.

A very cold December kind of day. Snow guns should be blazing at
ski resorts.

The snow should continue though at lesser rates in the northwest
and in the higher terrain of the southwest mountains.

Clouds will increase during the day as a fairly vigorous Alberta
Clipper zips on towards us. As the rule of clippers go this one
should pass just to our south, the old school sweet spot.

Most of the larger scale models imply 0.1 to 0.3 inches of QPF
Wed night, with the greatest amounts over the Laurel
Highlands/Central Mtns. Not a lot of spread with regards to
model timing of this fast-moving feature, so expect snow to
overspread the forecast area between 22Z-02Z and end before
dawn Thursday.

As expected with a clipper, model omega/temp timesections
indicate fairly high snow/water ratios with max lift occurring
within, or just below, the DGZ. Will wait for arrival of HREFV2
to make decisions on headlines, but current indications are for
several inches across the Allegheny Plateau, with an inch or
two across the Susq Valley.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
Complex pattern for late in the week into next week.

I did lower temperatures and dewpoints for the first part of the
weekend, as the northern system looks stronger now, may result
in cold air building southward into the area.

Also cut winds and gusts down, as I have done the last few days,
given the trend away from a deep low on Sunday.

Models show southern branch of the westerlies trying to come
into play on the large scale next week, but for now did not go
real high with POPS.

&&

.AVIATION /06Z WEDNESDAY THROUGH SUNDAY/...
IFR conds in snow showers and and blowing snow will affect
mainly the northwest mountains for the next 12 to 24 hours. MVFR
and a few snow showers will affect the central mtns with VFR
elsewhere.

A short wave could bring light snow into western areas Wednesday
afternoon into Thursday. This could lower CIG/VIS in many
western areas from KJST-KAOO-KUNV but this is beyond our current
forecast period.

Outlook...

Wed...Snow showers with IFR NW Mtns. Sct snow showers with MVFR
NW half. Otherwise VFR.

Wed night...Alberta Clipper could bring light snow and more
widespread reductions.

Thu-Fri...Sct snow showers NW. Reductions west and southwest mts.

Sat...Mainly VFR. Perhaps a snow shower north and east early.

Sun...Mainly VFR. Perhaps a few showers late.

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 1 PM EST Wednesday for PAZ005-
010-017.
Lake Effect Snow Warning until 1 PM EST Wednesday for PAZ004.

&&

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



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