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Area Forecast Discussion (AFD)

Issued by State College, PA (CTP)

FXUS61 KCTP 190255

Area Forecast Discussion
National Weather Service State College PA
955 PM EST Mon Feb 18 2019

A large area of high pressure will become centered over the 
state Tuesday. A new storm system will move into the region
Wednesday with high pressure building back in for Thursday and


The back edge of the strato-cu and flurries is moving east
through western PA, and will bring about continued slow but
steady improvement overnight.

Northwest winds will continue to gust 15-25 mph before slowly
diminishing later in the evening and overnight. 

Overnight lows will drop into the very chilly single digits over
the far north, and range to around 20 over the lower Susq


Much of the area will be clear by Tuesday morning, though RAP
soundings indicate that some patchy thin and low stratocu are
possible across the Northern Mtns of PA. 

The Center of a sprawling area of high pressure covering the 
NErn half of the CONUS will be centered over New York and PA.
However, low pressure will gather over the lower MS Valley Late
Tuesday and Tuesday night with a strong southerly flow of WAA
and Gulf Moisture out ahead of it, leading to a rapidly
blossoming area of Precip across Tennessee and Lower/Mid Ohio
River Valleys. 

The leading edge of this precipitation shield (in the form of
snow) will move quickly up the OH River Valley and should start
in the Laurels up to a few hours before sunrise Wednesday, and 
spread north and east to the Central Mtns and Susq Valley 
between 11-14Z.


Looking at Wednesday into Thursday there is a little more certainty 
in the timing of the event. The system should initially start as snow
but transition to FZRA/sleet in the afternoon. All models are 
trending colder with GEFS having less probability of rain. Given
the increase in confidence a watch was issued with the heaviest
amounts of snow through the far southwest. Iced accumulation 
should be an issue in the afternoon from from the warm air aloft
and cold sfc temps. 

For most of the period from Thursday into at least early Saturday,
not a lot going on. I did cut back on POPS and weather where I 
could. Temperatures borderline, so used a mix of rain and snow.

Main question is if a deep low will form and lift across the lower 
Great Lakes on Sunday. Latest EC and GFS are trending towards 
each other though EC is trending further north.


Late evening satellite loop shows stratocu breaking up across
central Pa, with MVFR cigs still noted over the higher terrain 
of the Appalachians at 0230Z and VFR conditions further east. 
High pressure will build into the region tonight, causing winds 
to diminish and remaining stratocu to break up. Linear extrapolation
of upstream clearing in satellite imagery suggests lingering mvfr
cigs over the central mountains will break up between 04Z-06Z.

The arrival of high pressure will bring a near certainty of VFR
conditions and light winds over the entire region Tuesday. 


Wed...Snow to a wintry mix. 

Thu...AM light freezing rain/low cigs possible.

Fri...AM low cigs possible W Mtns.

Sat...PM rain/low cigs possible. 


Winter Storm Watch from Wednesday morning through Thursday 
morning for PAZ058.
Winter Storm Watch from late Tuesday night through late 
Wednesday night for PAZ024>026-033>036.
Winter Storm Watch from Wednesday morning through Thursday 
morning for PAZ027-028-056-057-059-063>066.


SYNOPSIS...La Corte/Lambert
NEAR TERM...La Corte/Lambert
SHORT TERM...Lambert
LONG TERM...Dangelo/Ceru