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Area Forecast Discussion (AFD)

Issued by State College, PA (CTP)

FXUS61 KCTP 220837

Area Forecast Discussion
National Weather Service State College PA
437 AM EDT Mon Jul 22 2019


A wavy front will settle slowly south of the region, finally
delivering some cooler and drier air for Tuesday through the end
of the week. High pressure will move offshore, bringing warmer 
conditions for next weekend.



Meso-anal shows a weak boundary extending from a 1011 mb low
near Columbus OH east to near PIT to UNV then snaking down to 
near PHL. Deep tropical air is pooling all along the boundary 
with PWATs 1.80" or higher from Long Island to Ohio.

Radar is showing blossoming convection over SWRN PA and ERN OH
ahead of a deepening mid level shortwave. RAP meso-anal shows
this area to under a broad upper jet entrance region and
strengthening divergence. 

Guidance agrees in taking the surface low through CTRL PA during
the day today, dragging a cold front into the region this 
afternoon. The heavy rain signal is far from focused. The CAMs 
as well as the GFS and NAM and ECMWF all have a stripe of 1" or 
greater rains over much of Central and Northern PA, while the 
GEFS focuses its stripe of heaviest rain over my SERN zones 
where we have a FF Watch. The HREF shows a more general 1" or 
more rain with just spotty amounts of more than 1.5" over my 
SERN zones this evening through Tuesday morning. The bottom line
is I have little confidence justifying any adjustment to the 
current Watch configuration.

SPC has highlighted the SE with a Slight Risk for severe storms
today. SREF/GEFS both generate moderate instability with CAPEs
in excess of 1200J. The RAP shows surface based CAPE in the
2000-3000J range while the GFS and NAM have values of 3500J or 
greater. As the surface low moves through central PA, expect
storms to intensify under the increasing low level convergence
and eroding stability. Deep layer shear is only expected to be
on the order of 25-35kt in the warm air, but there is a not
insignificant amount of helicity cranked out by the RAP
associated with the low center. While SPC says the greatest
threat for severe will be from strong straight line winds, I
won't be surprised to see some rotating cells develop.

The front is made to move slowly through the SE zones this 
evening and overnight, maintaining a good chance of lingering 
showers into at least early Tuesday. Drier air working into the 
region behind the front should bring much lower dewpoint air to 
most of the CWA by this time tomorrow.



Tuesday will be cooler and drier with high temps several deg
below normal for a change. With the upper trough yet to move
through, a stray shower cannot be ruled out. But most of the 
area will remain dry. 

Highs in the 70s should feel quite nice as a change from the
recent blast furnace we experienced for several days.

Yesterday's high of 97 capped 6 straight days above 90 in
Harrisburg. The 95 reading in Williamsport was the 4th straight
day above 90. 



Several days of refreshing cooler than normal readings are in 
store before moderating temps start to creep back in for Friday 
into the weekend.

With few exceptions, the upcoming week will be dry before
increasing humidity brings the chance of some diurnal convection
for the end of the weekend.


Strange evening outside, storms moving back to the north. 
Only about 2 storms left now.

Line of showers and storms across the Ohio Valley to work
eastward later.

Expect system to keep moving, so by late afternoon, the amt  
of activity should slowly taper off.

CIGS could lower behind the system, not all that normal for 
mid July.

Adjusted the fcst some for these things, 06Z TAFS sent.

Earlier discussion below.

Scattered showers and thunderstorms could produce a brief vis
reduction in spots late this evening. An area of low pressure 
lifting into the region will spread widespread showers and 
lowering cigs into the northwest part of the state late tonight.
Latest model soundings and SREF probability charts support low 
mvfr cigs across the Allegheny Plateau by around or shortly 
after dawn. 

The low pressure system will track across southern Pa Monday,
bringing rain and reduced cigs across the mountains of 
central/northern Pa. An examination model soundings suggests IFR
cigs are possible over the higher terrain from KBFD south 
through KJST. Across the southeast part of the state, there is a
good chance of an afternoon thunderstorm, followed by lingering
showers and mvfr cig reductions late in the day. 


Tue...Early AM low cigs possible Laurel Highlands. 

Wed-Fri...No sig wx expected.


Flash Flood Watch from 2 PM EDT this afternoon through late 
tonight for PAZ035-036-056>059-063>066.


NEAR TERM...La Corte
LONG TERM...La Corte