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Area Forecast Discussion (AFD)

Issued by State College, PA (CTP)

FXUS61 KCTP 181602

Area Forecast Discussion
National Weather Service State College PA
1202 PM EDT Sun Aug 18 2019


Heat and humidity will increase further into early this coming
week and a meandering trough of low pressure will keep the 
mention of mainly afternoon and evening showers and 
thunderstorms in the forecast through mid week. Cooler and much
less humid air will arrive for Thursday through Saturday with 
dry conditions expected.



Early morning fog and low clouds have burned off with most of 
the region now bright and sunny. An earlier line of storms moved
through my NRN Mountains and diminished, and a new line of 
storms has formed in the axis of highest CAPE from NW McKean 
down through ERN Warren and Forest Counties. This is associated
with an instability line that can be seen on the satellite and
should be the instigator for additional showers/storms as we
continue to heat up the atmosphere. 

The HRRR has not been much help in this environment over the 
last few days, and today keeps most of the area rain free 
through at least mid afternoon. With the CAPEs expected to
exceed 2000J over the western slice of the region, and also over
the SERN zones where dewpoints are in the low to mid 70s, it
would seem logical that these two areas will be the most likely
to light up as we get deeper into the day. Warmer mid level
temps over the SE will likely act to hinder developments
relative to the western areas where mid levels are cooler and
winds aloft are stronger.

SPC has outlooked the northern third of the state with a
Marginal Risk for severe with isolated strong wind gusts will 
be the main threat. With a very humid airmass in place, HPC has 
highlighted most of the region with a Marginal Risk for 
excessive rain as well.

High temps this afternoon will vary from the L-M 80s across the
Northern and Western Mtns to the L90s in the Susq Valley and 
adjacent Scent Valleys. Heat indices will top out near 100 for a
couple of hours during max heating.

It will remain muggy tonight with lows ranging from the low 60s
over the north to around 70F SE.


Scattered, diurnally-driven convection is expected again on

A hot and humid Monday is on tap with heat indices near 100 for
much central PA in the valleys. Scattered afternoon and evening
showers and thunderstorms may knock some temps down but it will
feel muggy. Moderate capes in the 1000-2000 j/kg range could 
support a few strong storms, but fairly weak 0-6km shear 
suggests little risk of organized severe weather. 

Model soundings indicate max temps will be about 1-3F warmer 
than Saturday, with highs ranging from the low 80s along the NY
border to the lower 90s in the valleys of southern Pa. The 
combination of heat and humidity will likely drive heat indices 
into the upper 90s over the Lower Susq Valley for a few hours 
again Monday afternoon.


Guidance continues to show a fairly vigorous upper trough 
crossing the northeast quadrant of the lower 48 this period. 
Within the upper trough, there are still smaller scale detail 
differences that will affect progression/speed of the leading 
surface cold front and will take more time to be resolved. The 
cold front will be a focus for convection as it pushes southeast
Wed-Thu. While predictability is too low and limited at this 
range, severe storm risk upgrades are possible into the short 

Late-summer heat episode continues into midweek with max temperature 
anomalies +5-10F above normal on Wednesday. At this time, expect 
Thursday to be the transition day with a relative cooling trend and 
push of drier air throttling temps back to near/slightly below avg. 
Friday into the weekend. Lower humidity will spell pleasant days and 
comfortably cool nights.



All terminals have seen the early fog and stratus burn off and
are VFR as of late morning. This will continue with brief
restrictions developing at terminals affected by the afternoon
and evening scattered showers and thunderstorms. Confidence in
coverage and timing is too low at this point to include in the 

Abundant low level moisture, light winds and at least partial 
clearing should favor fog formation again late tonight into 
early Monday morning. 


Mon-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.


Record max temperatures for August 19:

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




SYNOPSIS...La Corte/Lambert
NEAR TERM...Fitzgerald/La Corte/Lambert
SHORT TERM...Fitzgerald/La Corte/Lambert
LONG TERM...Steinbugl
AVIATION...La Corte/Steinbugl