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Area Forecast Discussion (AFD)

Issued by State College, PA (CTP)

FXUS61 KCTP 210307

Area Forecast Discussion
National Weather Service State College PA
1107 PM EDT Sat Jul 20 2019

Dangerously excessive heat and oppressive humidity will continue
through Sunday over parts of Central Pennsylvania. As the heat
wave starts to break down, there will be an increasing risk of
severe thunderstorms and flash flooding Sunday into Monday. 
Noticeably cooler and less humid air will finally provide 
relief from the sweltering heat by the middle of next week.


Oppressive heat and humidity continues late this evening with 
mid-upper 70s dewpoints over most of central PA. After only
isolated shra/tsra earlier this evening, more organized deep
convection has developed along the leading edge of 30 kt 850 mb
jet pushing into northwest PA. Strongest storm of the evening is
now moving through Clarion County. Further upstream a weakly
organized squall line extends from the northeast OH Lake Erie
shoreline to the southwest shore of Lake Ontario. Cold pools and
resulting convection will need to be monitored into the
overnight, despite overall weakening of convection over Lake
Erie as it moves into NY. Highest precip probs remain across 
the northern tier zones especially the northwest Alleghenies. 
SPC has maintained a MRGL risk SWO across much of the area 
through tonight.

Little relief from the heat/humidity tonight with lows 10 to 20
degrees above average in the 70-80 degree range. Record high- 
mins are likely to be set in some areas.


Dangerous heat continues across south-central PA on Sunday with
max HX values 100-110. Cloud cover from overnight t-storm 
complex may limit heating (similar to this morning) but temps 
should recover through the afternoon. 

Scattered thunderstorms are likely to develop Sunday afternoon
as sfc cold front advances southward into very moist and
unstable airmass across CPA. SPC D2 MRGL risk SWO covers most 
of the area (south of US-6). Deep layer shear is weak but steep
low level lapse rates and high CAPE should be enough to produce
marginally/isolated severe wind gusts in the strongest pulse or

We will be in the late innings of the heat wave by Sunday
evening as dewpoints drop below 70 across the northern tier.
Relief from the sweltering heat is expected to arrive through
early next week.


Our anomalous ridge and the accompanying heat wave will break
down rapidly early next week, to be replaced by an anomalous
trough and a much welcome break in the heat and humidity.

A cold front will drop into the region later Sunday and Monday.
With a deepening upper trough to the west, models slow the front
and bring a series of waves along it Monday and Monday night.
This will have the potential to bring widespread soaking rains
and possibly flooding to the region to start the new work week,
before we ultimately cool off and dry out for the Tuesday
through Friday timeframe.


VFR flying are expected over most of the region overnight. 
However, an isolated thunderstorm is possible through around 05Z
at KBFD and KJST.

A plume of higher moisture preceding an approaching cold front,
combined with orographic lift, could possibly result in a 
period of reduced cigs across the western mountains (KBFD/KJST) 
Sunday morning. Otherwise, widespread VFR conditions are 
expected to persist through Sunday. However, scattered 
thunderstorm impacts are possible Sunday PM over primarily 
central and southern Pa. 


Mon...Widespread showers and tsra impacts possible. 

Tue-Thu...No sig wx expected.


Excessive Heat Warning until 8 PM EDT Sunday for PAZ028-036-
Heat Advisory until 8 PM EDT Sunday for PAZ019-025>027-034-035-


NEAR TERM...DeVoir/Steinbugl
SHORT TERM...Steinbugl