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Area Forecast Discussion (AFD)

Issued by State College, PA (CTP)

FXUS61 KCTP 191151

Area Forecast Discussion
National Weather Service State College PA
751 AM EDT Mon Aug 19 2019

It will remain very warm and humid through early this week. 
A meandering trough of low pressure will keep the chance of 
mainly afternoon and evening showers and thunderstorms in the 
forecast. Cooler and much less humid air will arrive for 
Thursday through Saturday with dry conditions expected.


Significantly weakened MCS is falling apart across the Laurel
Highlands and Northwest mtns early this morning and should 
continue to dissipate during the mid-late morning hours from the
Central mtns to the Susq river Valley.

It will be another muggy start to the day and new workweek
with lows ranging from the mid 60s over the north to around 70F
SE. A light southerly breeze should preclude widespread fog, 
but still expect patchy fog where there was rain on Sunday, 
especially over the southeast half of the state, where the 
pressure gradient is weakest and surface dewpoints the highest
in the mid to upper 60s. 

Near zonal flow from PA through SE Canada will top a 1018 mb
bubble of high pressure Over Western PA or Eastern Ohio late
today and tonight.

Trimmed Pops down a bit for this afternoon and evening, since 
2-3 deg C of warm advection at the 700 mb level will be pushing 
east across the Commonwealth and capping off most deeper 
convection. Slightly lower dewpoints across the western half of
the CWA will also lead lower SB CAPE. Best chc for SHRA/TSRA
today will be along and to the east of the I-81 corridor, where
mid level temps will be the coolest and around 7-8C through 21z
Monday. This is confirmed by the areal coverage and timing of
convection via the latest SPC HREF.  

Mid and upper level debris clouds from the earlier MCS will cut
down on the the max temp in some areas today. Temps should be 
warmer than Sunday across the northern and western mtns, and 
similar over the Central and SE zones. Heat indices will be 
peaking near 100F across the Lower Susq Valley for a few hours 
this afternoon..


Approaching mid/upr level short wave trough and increasing south
to swrly LLVL flow along and to the south of a weak warm frontal
boundary will help ramp up convective parameters Tuesday 
afternoon, with scattered afternoon SHRA/TSRA expected in all 
parts of the state. 

Hi temps Tuesday will be 1-2 deg F lower than today's and range
from the Lower 80s across the NW Mtns and Laurel Highlands, 
while the Susq Valley and Southern Valleys of the state will see
max temps in the L90s. 

A slightly better probability for TSRA Wednesday afternoon and 
evening as a more vigorous upper shortwave and associated sfc 
CFROPA pushes Southeast through the CWA late Wednesday and Wed 


Upper low crossing eastern Canada will anchor a trough that
traverses the Great Lakes/Northeast US by the end of the period.
The sensible wx forecast is tied to the movement and eventual 
position of the leading cold front which is expected to cross 
the area on Thursday and stall out to the south of the Mason 
Dixon line. This scenario should eventually allow cooler and 
drier (less humid) air to spread into the region behind the 
front and bring a nice stretch of weather from late week through
the weekend. 

The cold front will be a focus for thunderstorms as it pushes 
southeast on Thursday. A severe storm risk upgrade is possible
across a portion of the area (most likely southeast PA). A 
trailing wave of low pressure riding along the stalled frontal 
boundary could bring another round of rain to the southern tier 
of central PA on Friday. This outcome is supported by the latest
operational ECMWF but considered a low probability outcome at 
this time given lack of support from other guidance. 

Still expect Thursday to be the transition day with frontal
passage fueling storms followed by push of cooler and drier 
air Thursday night. The FROPA will also spell some temporary 
relief from the recent hot and muggy conditions. High pressure 
and lower humidity should translate into pleasant and warm days
and comfortably cool nights with valley fog Fri-Sun.


Ceiling below alternate/near airfield mins at KIPT until 13Z. 
Otherwise, VFR expected to prevail through the afternoon. 
Convective corridor is focused over the eastern airfields and 
therefore only went with VCTS at KIPT, KMDT and KLNS. Clearing 
tonight should favor fog formation especially where it rains. 


Tue-Wed...Rounds of PM showers/thunderstorms. Late night and 
early morning fog/low clouds.

Thu...Trending VFR northwest; chance of t-storms southeast. 
FROPA Thursday night.

Fri...No Sig Wx.


Harrisburg tied the previous record high of 97 degrees 

Record highs for August 19:

Harrisburg 97 in 1966
Williamsport 94 in 1899
Altoona 91 in 1983
Bradford 86 in 1978
State College 96 in 1899




NEAR TERM...Lambert
SHORT TERM...Fitzgerald/La Corte/Ceru
LONG TERM...Steinbugl