Preview of NWS' New Version of Forecast
This preview is not operational and should not be used for support decisions.

Area Forecast Discussion (AFD)

Issued by State College, PA (CTP)

FXUS61 KCTP 180946

Area Forecast Discussion
National Weather Service State College PA
546 AM 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 for the next 4 days. Cooler and 
much less humid air will arrive for Thursday through Saturday 
with dry conditions expected.


The main concern early today is associated with areas of dense
fog that formed in areas where skies were partly cloudy
overnight and the wind essentially calm.

Areas most likely to see fog will be northern Pa and areas east
of the Susq River, where the ground is wet from rain earlier 

A wavy and slow-moving warm front extending from Eastern Lake
Erie to SW PA and NRN VA, back up through the Lower Susq Valley
will drift slowly to the north today and be the focus for
scattered showers and TSRA this afternoon and evening. Mid and
Upper Level winds are somewhat weaker and more Swrly than
Saturday, so the threat for SVR seems to be a bit less without
significant large scale lift and RIJ into individual storm
cells/multi-cell clusters.

Still, the presence of the aforementioned llvl front and the 
very warm and juicy airmass will help to focus and enhance 
convection across the northern third of the state this 
afternoon/early evening (with more isolated convection expected 
across the southern tier) where SPC has a day 1 MRGL Risk for 

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. 

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.


Fog/visibility restrictions early this morning will give way to
VFR by mid morning. While largely a persistence forecast, 
confidence is a bit lower given area of high clouds across a 
good portion of the airspace. More isolated thunderstorms 
through the afternoon into the evening. Sparse coverage and lack
of model signal results in low confidence in t-storm impacts.  


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 




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