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Area Forecast Discussion (AFD)

Issued by State College, PA (CTP)

FXUS61 KCTP 201900

Area Forecast Discussion
National Weather Service State College PA
300 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.


Clouds faded through midday giving way to a mostly sunny sky
over CPA. Hourly temps had been lagging over the northwest but 
are recovering nicely through the 80s. Max heat index values
ranged from 95 to 105 at 18Z from the south central Alleghenies
into the mid-lower Susquehanna Valley. Max HX values may come up
a little short of the century mark over the higher terrain but
not enough to cancel advisory. Only changes to existing heat
headlines involved timing as we felt it made sense to simplify
and run straight through tonight. 

Low confidence with regards to convective activity through
tonight. Blend of CAMs seems to suggest another t-storm complex
may drop southeast across Lake Erie later tonight into early 
Sunday morning. Continued to lean toward the HREF mean which 
places highest precip probs across the northern tier zones
especially the northwest Alleghenies. SPC has maintained a MRGL
risk SWO across much of the area through tonight.

Near-record high temperatures are forecast today in the upper
80s to upper 90s along with dangerous heat index values 100-115.
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 expected through most of the period. Low confidence
for thunderstorms with the highest probs over the northwest
airspace tonight into early Sunday. 


Sun...AM low cigs possible W Mtns. Scattered PM tsra impacts

Mon...Widespread showers and tsra impacts possible. 

Tue-Thu...No sig wx expected.


Heat Advisory until 8 PM EDT this evening for PAZ004>006-
Excessive Heat Warning until 8 PM EDT Sunday for PAZ028-036-
Excessive Heat Warning until 8 PM EDT this evening for PAZ019-
Heat Advisory from 8 PM this evening to 8 PM EDT Sunday for 


NEAR TERM...Steinbugl
SHORT TERM...Steinbugl
LONG TERM...La Corte