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Area Forecast Discussion (AFD)

Issued by State College, PA (CTP)

FXUS61 KCTP 210818

Area Forecast Discussion
National Weather Service State College PA
418 AM EDT Tue May 21 2019


A ridge of high pressure will build east across the Commonwealth 
today and slide off the Mid Atlantic Coast Wednesday evening. 

Much higher humidity will surge into the state from the Ohio 
Valley Wednesday night and Thursday, bringing an increasing 
chance for showers and Thunderstorms. 

Pennsylvania will be on the northern periphery of a building 
subtropical ridge late this week and over the upcoming weekend.
This will mean occasional bouts of mainly afternoon and evening 
showers and thunderstorms. 

Moderately strong cold advection in the 925-850 mb layer was
leading to a rather extensive area of stratocu clouds across
most of the state, except for the NW corner and SE counties
where skies were mainly clear early this Tuesday morning.

21/06Z RAP guidance shows the clouds persisting for a few hours
after sunrise, then gradually breaking up into a sct-bkn flat cu
field as gustiness in the NW wind rebounds into the teens and
low 20 mph range and the boundary layer deepens to 3-5 kft AGL,
helping to mix in plenty of dry air from above and beneath the 
cloud layer.

Temps will start out on the chilly side early this morning,
with mins ranging from near 40F across the NW mtns, to the upper 
40s to lower 50s respectively across the Central Mtns and Susq 

High temps this afternoon will be in the lower 60s across the
north and 65 to 70 in most locations south of I-80 with the
exception of the Laurel Highlands where upper 50s to lower 60s 
will be common during the mid to late afternoon hours given 925
mb temps peaking near 13C. 


North/South sfc ridge of high pressure extending over Central PA
and the Susq Valley tonight will be accompanied by clear to ptly
cloudy skies and light wind. Given the still dry air over much
of the CWA (PWATs of 15mm or less across the NE half of the 
state), expect similar, if not cooler min temps early Wednesday

Min temps at sunrise Wed will vary from the upper 30s in the
perennial cold spots of the north, to around 50F in the larger
metro areas of the southeast. 

Southeasterly llvl flow will increase during the day Wednesday
as the high pressure ridge drifts off the NJ Coast. Several
layers of clouds will also form/advect east into region as the
nose of much higher PWAT air (30-35mm or +2-3 sigma) spreads 
into Western PA late in the day. A small chc for showers exists
across the northern tier and Alleghenies of west-central PA 
later in the afternoon and evening Wednesday,


00Z NAEFS indicates Pennsylvania will be on the northern 
periphery of a building subtropical ridge late this week into 
next weekend. 

A much higher chc for SHRA/TSRA will develop late Wed night and
early Thursday, associated with an area of +2-3 sigma 850 mb 
moisture flux (as depicted by the latest - 00Z GEFS) that will 
spread east across the CWA accompanied by elevated instability 
and 850 mb LIs dipping t between -2 and -4C.

Pops were nudged up into the high chc to low likely range
Wednesday night/early Thursday. 

Shortwaves riding over the top of the aforementioned ridge will
bring back the daily chance of convection. However, bulk of med
range guidance supports a brief period of fair weather Friday, 
as drier air builds in behind a Thursday PM cold front.


The cold front continues to exit the region leaving only a few
forecast questions over the period. The first will be the
continuation of MVFR cigs over the NW MTNS. Due to the gusty
upslope flow these cigs should continue overnight before the
drying NW air filters down tomorrow morning between 11Z to 14Z. 
 The next issue is the timing of the gusty winds to end. Expect
a few hours after sunset, between 00Z to 02Z the cooling SFC
temperatures will allow for the inversion to form which will cut
off the stronger upper level winds. However, the persistent
northwesterly flow will continue overnight with around 10 to
15kt winds at all TAF sites. VFR conditions will dominate the
weather pattern tomorrow. 


Tue-Wed...Mainly VFR.

Thu-Fri...Isolated to scattered restrictions possible from 
potential showers and thunderstorms.




NEAR TERM...Lambert
SHORT TERM...Lambert
LONG TERM...Lambert/Gartner