Area Forecast Discussion
Issued by NWS State College, PA

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000
FXUS61 KCTP 182057
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
357 PM EST Sat Nov 18 2017

.SYNOPSIS...
Low pressure near Toledo, Ohio late this afternoon will move
northeast and intensify over the Lower Great Lakes tonight. A
strong cold front trailing south from this low will plow east
across the Commonwealth. Colder air with strong, gusty west to
northwest winds, and some lake effect snow will then affect the
area Sunday. Conditions will gradually improve into Monday.
High pressure will bring moderating temperatures and dry
conditions Tuesday through at least Friday.

&&

.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
A large swath of moderate to heavy rain (lifting gradually NE
across the NW mtns the Central Mtns and Lower Susq Valley) was
being generated by moderately strong south to swrly Isentropic
upglide within the 285-290K theta layer, at the nose of a 60 kt
850 mb swrly jet.

Sfc temps are struggling to reach 40F this afternoon throughout
the deepest central valleys of the CWA, while other locations
across the Wrn Mtns and Lower Susq will slowly creep through the
lower and mid 40s this evening, before peaking right ahead of
the approaching Cfront that`s progged to push across the Wrn
Mtns of PA around midnight, and 07-09Z Sunday across the Central
mtns and Susq Valley.

Expect a sharp drop in temps after the cfropa, and a quick
increase in wind as an area of 7-9 mb/3hr sfc pressure rises
moves NE from the Ohio River Valley to the Finger Lakes and
Pocono region of NEPA between 05Z-14Z Sunday.

The Wind Advisory previously in effect for the SW Mtns has been
expanded to cover the entire CWA late tonight through 17Z
Sunday. A Winter Weather Advisory for LES has also been issued
for Warren and McKean Counties in the NW snowbelt from 09Z-18Z
Sunday.

The layer below 850 mb stays quite stable across the central and
eastern 2/3rds of the CWA until just ahead of the Cold front
late tonight, when Lifted Indices AOA 850 mb dip to slightly
below zero, supporting a slight chance for a few TSRA.

An expanding region of elevated instability from Ecent Ohio
(that`s currently producing TSRA between I-70 and I-80), that
will move over about the SW half of PA late this afternoon/early
tonight. Included chc TSRA along with the predominant Periods
of light to moderate Rain.

Will continue to advertise a large area of 1-1.5 inch rainfall
amounts across the region of Central PA and northern PA from
along the 22/322 corridors and points north, where models show a
stripe of enhanced QPF from the steepest ascent of the moist
and increasing unstable air over the persistent/nearly
stationary llvl boundary.

The rain should become lighter and more intermittent across the
southern 1-2 layers of counties of PA for a while this evening
as the warm front lifts a bit more to the north.

&&

.SHORT TERM /6 AM SUNDAY MORNING THROUGH 6 PM SUNDAY/...
A very windy and cold day is on tap for Sunday with frequent
gusts of 40 to 50 mph during the mid to late morning hours as
the area of strong 3-6 hourly pressure rises moves NE across the
region.

SREF mean 850 mb temps of about -7C across the NW and -4 to -5C
across the SE support max temps in the l-m 30s INVOF KBFD and
KJST and mid to upper 40s INVOF KMDT and KLNS with upper 30s to
low 40s throughout the Central Mtn zones.

Scattered to numerous snow showers will bring a coating to 2
inches of wind whipped snow accum across the Laurels and
northcentral mtns, while the NW Snowbelt receives 3-5 inches of
LES. SE of the Allegheny Front, frequent flurries and a few
narrow, sinuous bands of snow showers/squalls could whiten the
ground quickly in some locations.

Some peeks of sunshine will mix in across the Lower Susq Valley
at times, with some brief, mixed rain/snow showers.

&&

.LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/...

The extended part of the forecast will see the season`s first
real lake effect snow event winding down early in the period,
followed by several days of cool but tranquil weather.

Model soundings show the inversion heights falling quickly
Sunday evening through Monday morning, which will begin the
process of shutting off the lake effect machine. Look for
accumulating snow to continue overnight over the normal snowbelt
areas of the NW and even down into the Laurels-with lesser
amounts. The snows will continue shrinking back closer to the
immediate vicinity of the lakes by Monday morning and by Monday
afternoon there should be little more than a few leftover
flurries as the high builds off to our south and we see the
thermal advection switch from cold to warm.

High pressure will keep conditions dry into Tuesday before a
weakening front sliding by to our north brings the small chance
of a snow shower to northern areas Tuesday night and Wednesday.

Another area of high pressure will build east and keep us mainly
dry at least through the end of the week, before a new frontal
system takes aim at the area.

&&

.AVIATION /21Z SATURDAY THROUGH THURSDAY/...
Poor flying conditions are expected to continue through at least
the first half of tonight across much of the region with
widespread MVFR and frequent dips into the IFR CIG/VSBY range as
a warm front lifts slowly NE across PA with shallow cool air
trapped in the deep valley of Central and Northern PA until the
passage of a strong cold front around 05-06Z across TAF sites
KJST and KBFD, then 07-09Z Sunday over the Central Valleys Susq
Region. Borderline LLWS will continue until the CFROPA as a
potent 50-60 kt southwesterly wind max tops the stable colder
airmass entrenched up through a few kft AGL.

Periods of rain will continue through the first half of tonight
across the west and into the early morning hours Sunday across
the East.

Southerly winds may become gusty late this evening over the
western and southern airspace, as strong winds aloft begin
mixing to ground level. Latest NAM/HRRR suggests gusts in the
25-30kt range are possible between 00Z-06Z Sunday. Some of the
ridge tops over the Laurel could see south to SSW wind gusts
topping 40KTS early tonight as the warm front lifts north of
that region and allows better vertical mixing of the higher
wind speed air from aloft.

Outlook...

Sun...Windy with frequent gusts 35-40kts from 270-300 degrees.
IFR snow showers NW trending MVFR central to VFR east.

Mon...AM shsn/reduced vsbys possible NW mountains.

Tue-Wed...No sig wx expected.

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
Wind Advisory from 4 AM to noon EST Sunday for PAZ006-012-018-
019-026>028-035>037-041-042-045-046-049>053-056>059-063>066.
Wind Advisory from 1 AM to noon EST Sunday for PAZ010-011-017.
Wind Advisory from 7 PM this evening to noon EST Sunday for
PAZ024-025-033-034.
Winter Weather Advisory from 4 AM Sunday to 1 PM EST Monday
for PAZ004-005.

&&

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


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