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Area Forecast Discussion (AFD)

Issued by State College, PA (CTP)

FXUS61 KCTP 210959

Area Forecast Discussion
National Weather Service State College PA
559 AM EDT Wed Aug 21 2019

It will remain very warm and humid today with scattered showers
and isolated thunderstorms over the northwestern half of the 
state this morning. A pair of cold fronts will push southeast 
through the state, the first arriving late today and tonight, 
and the second Thursday afternoon and evening. Cooler and much 
less humid air will move in for Friday and will last through 
much of the upcoming weekend.


Plume of high PWAT air (1.5-2.0 inches) over the Central
Appalachians will provide the fuel for numerous showers across
the NW half of the CWA through much of this morning, followed by
showers and scattered strong to svr tsra this afternoon as a
compact upper trough (moving east from Lake Michigan attm) and 
nose of a 60KT, 300 mb jet to its south adds moderately strong
MESO-B lift across the state this afternoon and evening. 

Fairly linear vertical shear favors Multi-cell TSRA clusters
(with some mini bows echoes) that will form in one or two waves
across the Central Mtns this afternoon, and push gradually east
during the afternoon and early evening hours.

Localized very heavy rain of over one inch in just a 30 minute 
period will occur where several showers and thunderstorms train
over the same locations, mainly SE of a KAOO to KUNV and KELM 

Forecast high temps (ranging from the low 80s in the north to
L90s in the Middle and Lower Susq Valley) may need to be trimmed
by 1-2 deg F in many some locations based of the rather
extensive showers and mid clouds across the Northwest half of
the state this morning. 

After the most potent TSRA gradually diminishes and moves SE of
the region this evening, the CWA will be sandwiched between a
pair of Cold fronts with the potential for some clearing and 
and formation of valley fog (mainly in the deeper, northern PA 
valleys containing the larger streams, creeks and rivers).


A secondary SFC cfront and CFA dropping SE from the Glakes 
Thursday should trigger a few afternoon showers/TSRA across 
the region. er range mainly the SE half of PA. 700 mb temps 
will likely cool off by at least 2-3C during the day Thursday.

Trailing upper trough, the mdtly strong UVVEL within the
thermally direct RE region of an upper level jet max will be  
riding over the secondary frontal boundary that will slow down
or stall out temporarily somewhere across central or Southern PA
as the flow aloft backs Thursday into Friday. 

Depending on the exact location of the Quasi-stnry front and
area of enhanced lift beneath the RE region of the upper jetlet,
there could even be a few periods of steady light, to briefly
moderate rain across Central or Northern PA and some elevated 
TSRA cores. Rainfall amounts later Thursday afternoon into
Friday should total a few to several tenths of an inch. 

Conditions should improve from West to East late Friday, and  
into the upcoming weekend.


An extensive area of high pressure will bring fair and dry 
weather to central PA this weekend. Heading into next week, the
question will be how quickly can return flow moisture make it
back into the area? GFS is rather bullish early next week in
contrast to the ECMWF which favors continuation of dry wx. These
models seem to agree that developing southeast low level flow 
may advect clouds into the area which could result in lower
highs Mon-Tue. Given the uncertainty, the day 4-8 NDFD forecast
closely follows the National Blend of Models (NBM) which shows 
a gradual increase in low chance POPs Mon-Tue. 

Temperatures over the weekend will be near to slightly below 
average with pleasant and warm afternoons and comfortably cool 
nights. Another brief hint of autumnlike air with September
right around the corner. As mentioned above, could see temps
trend a bit lower early next week before moderating through


Coverage of showers across the western airspace should trend 
lower as they drift eastward through the morning before ramping
back up again this afternoon/evening. Cloud cover should limit 
fog formation this morning but some lower ceilings are possible
especially across the western airfields. A cold front will push
slowly northwest to southeast across the airspace late tonight
through Thursday with high pressure building in by Friday. 


Thu...PM thunderstorms southern 1/2.

Fri...Chance of showers southern 1/4. 

Sat-Sun...AM fog possible.




NEAR TERM...Lambert
SHORT TERM...Lambert
LONG TERM...Steinbugl