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Area Forecast Discussion (AFD)

Issued by State College, PA (CTP)

FXUS61 KCTP 251821

Area Forecast Discussion
National Weather Service State College PA
221 PM EDT Sat May 25 2019

Warm temperatures and high humidity will last into Sunday.
Showers and thunderstorms will also be around, mainly during 
the afternoon and evening hours each day. Memorial Day will 
feature near normal temperatures and comfortably lower humidity.
A few more rounds of showers and scattered thunderstorms with 
gusty wind and locally heavy rain appear likely for both Tuesday
and Wednesday afternoons and evenings.


Cluster of storms over nrn WV is just crossing the PA border.
These storms have prompted a couple of SVRs already, and they
are headed for the Laurels/SWrn CWA. The upper ridge axis is
currently right over that area, so if it does not move too
quickly to the east, these storms may diminish as they get
there. Warm and much more moist air is flowing in from the
south, now and is destabilizing most of the CWA. As this feature
rolls across the CWA, the forcing does eventually outrun the
best instability. But, as far as the central mtns, there will
still be some showers/isold storms from this first volley.

The main threat area for late this aftn and mainly this evening
is over the nrn counties as the lake breeze boundary is 
expected to flare up and upper flow brings those storms down 
into better heat and higher humidity/CAPE. A strong short wave
trough pushes across OH this aftn and through PA by 06Z. The 
mode of convection could be discrete supercells, but they could
be organized into a line or two. 40-50KTs of deep-layer shear
are significant. The LCLs are fairly high for tornadoes, but 
one cannot be ruled out, esp in the vicinity of any subtle 
boundaries running around from this first batch of showers. 
PWATs are high, but not excessive. That main threat for 
excessive rainfall is more where multiple cells cross a point. 

The timing of the storms has been tweaked slightly to reflect a
quiet post-midnight time-frame. The storms should be gone from
BFD by 01Z, IPT/UNV by 03Z and the srn cities by 05Z or 06Z at 
the latest. The wind does not die off completely, but fog could 
form in the wake of the storms where the sky initially clears 
out. Much drier air will dip into nrn PA overnight. Mins will be
still be in the 60s, though, and it will stay muggy for the srn
half or more of the CWA. 


Muggy air will hang around the srn half of the state on Sunday.
Additional showers and storms will fire up - with the SWrn part
of the CWA still in a MRGL to SLGT risk for excessive rainfall.
Will nudge the PoPs a little higher for the SW, and downward a
notch for the nrn tier. Max temps will be a little cooler than
Sat in the N and W, but warmer by a deg or two in the SE thanks
to the downslope flow. MRGL-SLGT risk for severe still exists in
roughly the same area as the ERO, but a little farther to the
south where the best instability will be. 


110 pm update... On the large-scale, a western CONUS
upper trough/eastern CONUS upper ridge pattern still looks to 
prevail for most of next week, before the ridge flattens a bit 
towards next weekend, as an eastern Canadian trough perhaps 
builds southward. In general, this means continued warm
temperatures through at least mid-week, perhaps cooling towards
the end of the period. 

As for the daily sensible weather, as a cold front settles south
of the Commonwealth and high pressure noses down from Canada, we
should dry out Sunday night, with a nice Memorial Day likely on
tap. On Tuesday, a warm front should approach from the south and
west, with this boundary probably stalling out somewhere near or
over the Commonwealth Wednesday-Thursday. This means that 
unsettled weather comes back into the forecast, with daily 
chances for showers and thunderstorms. A cold front may sweep 
much of the moisture south and east of the region for the end 
of the week, with cooler and drier weather possible at that time

Daily highs will mostly range from the mid 70s-mid 80s through
at least Thursday, with some cooling anticipated thereafter.


Storms already nearing JST and showers near BFD around 18Z. The
storms across SWrn PA will likely continue into our southern
half but die off as they move deeper into PA. Not likely that
any of these will get into MDT/LNS before sunset. A lake breeze
and strong short wave trough aloft will team up to fire up
widespread thunderstorms across nrn PA (VCTY BFD) late this
aftn, and all this will drop S/SE through the evening. The
storms will get to UNV/IPT btwn 01-03Z, and slide to the south 
of MDT/LNS before 06Z. The storms will contain some hail, but 
high wind gusts are the main threat today. Generally S/SW sfc 
flow will turn to the W as the main line/bunch of storms moves 
past. Expect some fog to begin to form where the sky clears out
initially after the storms pass this evening/early tonight.
However, the wind stays up more than 6-7KTs all night in most
places. So, mixing may keep fog from getting dense. Low CIGs
poss at BFD tonight, but most other places should not dip back 
to IFR.

Drier air over the northern half of the airspace Sunday will
keep showers and storms pretty much at bay for BFD and IPT.
Still a small chc for a shower at UNV/MDT/LNS. Best (worst) chc
for storms will be at JST and AOO during the aftn and early
evening. Dry air then pushes across the entire area for Sunday
night and all of Monday.


Sun...Restrictions possible near scattered thunderstorms.

Mon-Tues AM...VFR.

Tues PM-Thurs...Mainly VFR, although spotty showers/storms are
expected each aftn/evening.




NEAR TERM...Dangelo
SHORT TERM...Dangelo
LONG TERM...Jurewicz