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Area Forecast Discussion (AFD)

Issued by State College, PA (CTP)

FXUS61 KCTP 220107

Area Forecast Discussion
National Weather Service State College PA
907 PM EDT Sun Jul 21 2019

The dangerous heat wave will last one more day today before
cooler and less humid air spells relief from the sweltering
conditions this week. As the heat wave breaks down,
thunderstorms with a wind damage and significant flash flood
threat are possible on Monday across the southern tier of 
central PA. An extended period of dry weather is forecast 
Tuesday through the remainder of the upcoming week.


Pretty active late afternoon and evening of convection with some
very tall storms and verified both severe hail and measured
severe wind gusts over the Lower Susq River Valley. Anomalously
high PWATs 1.5-2.0 inches and 2000-3000 J/kg of ML CAPE
supported the storms, which are weakening overall as daytime
heating fades. However still seeing heavy rain over my southern
tier late this evening and will watch closely for training
and/or repeat trips over areas which saw earlier heavy rainfall.
After midnight, intensity of storms and overall coverage should

Low temps will be in the low 60s tonight to the north of the 
quasi stationary boundary draped near the I-80 corridor. Another
warm night across south central PA with lows in the 70-75 range.
Showers may ramp up late tonight into Monday morning across the
western part of the area as forcing/lift begin to trend to the
upside ahead of shortwave crossing the Great Lakes.


*Thunderstorms with a wind damage and significant flash flood
 threat are possible across the southern tier of central PA

Synoptic forcing associated with an approaching upper level 
trough and attendant surface cold front combined with anomalous
moisture and narrow ribbon of instability and favorable shear 
will support multi hazard risk of flash flooding and severe 
t-storms Monday afternoon and evening. We are not surprised to
see the heat wave broken with the potential for very active

WPC ERO was upgraded to MDT risk overnight and the latest SWO
has increased categorical risk from MRGL to SLGT across the far
southeast zones. Will issue Flash Flood Watch in collaboration 
with PHI and LWX where there is a multi-model signal for heavy
to excessive rainfall. Multiple round of showers/tstorms are
possible across the southeast as the front slowly shifts to the
east and exits the CWA Tuesday morning. 

Max temps will be much cooler tomorrow across most of CPA as
early clouds and showers hold readings in the upper 60s to mid
70s. Only the far southeast should reach into the 80s with max
HX values in the mid-upper 90s possible over the extreme
southeast part of the CWA (far southeast York & Lancaster Cos).
Lows drop back into the 50s in the north and lower to mid 60s
across south central PA.


Lingering showers and maybe a tstm early on Tue over the SE as 
front and deep moisture finally exit the area.

By the end of Tuesday we will see markedly less humid air 
moving into the forecast area. This will be the beginning of a 
period of pleasant mid-summer days with daytime temperatures 
near normal and overnight lows running several degrees cooler 
than normal, plus with lower dewpoints and humidity. 

Models agree with keeping the anomalous eastern upper trough the
dominant feature through the end of the week when some
indications of rising heights and gradually rising
temps/dewpoints begin over the Ohio Valley and western PA.


Scattered showers and thunderstorms will diminish in coverage
after sunset. However, a slight chance of a thunderstorm will
persist overnight, as the region remains in the vicinity of a
stalled frontal boundary. 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 Monday afternoon through late Monday 
night for PAZ035-036-056>059-063>066.


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