Area Forecast Discussion
Issued by NWS State College, PA

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FXUS61 KCTP 200951

Area Forecast Discussion
National Weather Service State College PA
551 AM EDT Thu Jul 20 2017

Pennsylvania will be on the northern periphery of a subtropical
ridge passing across the southern states through the weekend.
A slow moving cold front will push through the area early next


09Z satellite loop showing fairly extensive valley fog across
central Pa, which should burn off by 13Z-14Z based on trends of
recent days and latest LAMP guidance. Main focus will then
shift toward a potential MCS tracking across the Grk Lks toward
northwest Pa. Latest convection-allowing model guidance,
including NCAR ensemble and SPC SSEO support likely POPs across
the northwest mountains during mid to late afternoon, with a
diminishing chance of showers/storms as convection progresses
southeast into the rest of central Pa this evening. Focus of the
strongest tstorms may be just north of Pa at nose of anomalous
low level jet. However, moderate CAPES and 0-6km shear of around
40kts are favorable for an organized severe weather threat
across the northwest half of the forecast area late today.

Other concern will be potentially dangerous heat indices across
the Lower Susq Valley, where combination of heat and humidity
should push heat indices to near 100F. Not sure we will achieve
the criteria of widespread 100F for 2+ hours, so have held off
on an advisory for now.


Both SPC SSEO and NCAR ensemble suggest a dwindling band of
convection will push southeast across the region overnight, as
best forcing ahead of shortwave shifts into New England and
trailing low level jet sags south across Pa.

Large scale subsidence and arrival of much lower PWATs progged
for Friday, resulting in a mostly sunny day for most if not all
of the forecast area. Have maintained just a slight chance of a
lingering shower across Somerset county, which will remain on
northern edge of ring of fire. GEFS mean 850 temps still around
17C-18C Friday, which should translate to max temps from the low
80s over the northern mountains, to the low 90s in the Susq


The Day 2 MRGL risk extends into west-central PA on the eastern
extent of upstream organized convective zone. Over the weekend,
pcpn pattern looks to reach a relative peak with max POPs based
on multi-model blend. Exact timing and location of pcpn will
depend on details not well resolved until the very short term
time frame. Therefore the later periods will keep a 40-60
percent POP given lack of confidence in highlighting any
specific areas/timeframe with concentrated pcpn potential.

Medium range models generally agree that a continued/gradual
weakening and east-southeast shift of the persistent central
U.S. upper ridge can be expected with time, as shortwave
troughing shifts slowly southeast out of the Canadian Prairie
across the northeast quarter of the country by early next week.
The associated cold front is progged by med range guidance to
push slowing southeast through the forecast area early next
week. Above average temperatures (+5-10 degree max T departures)
should trend toward mid to late July climo numbers by next


Another round of showers and thunderstorms moving through south
this evening. All convection is over for the evening and VFR is
currently dominating. with high minimum temperatures and high
dewpoints, another round of patchy fog/mist and low stratocu is
possible tonight into tomorrow. Best chances will be along the
south where it rained, especially MDT, IPT, AOO and JST.
 Expect any restrictions to improve between 12z to 14Z.
 Tomorrow will bring an increased chance showers and
thunderstorms through NW PA Thursday afternoon with better
chance tomorrow night in the central and southeastern areas


Thu...AM valley fog. Cig restrictions poss NW. TSRA PSBL NW Thu
aft, scattered TSRA central Mtns Thu eve.

Fri...AM valley fog/cig restrictions likely NW half. Isolated

Sat...AM valley fog poss. TSRA likely.

Sun...AM valley fog poss. TSRA likely north/scattered south.




NEAR TERM...Fitzgerald
SHORT TERM...Fitzgerald
LONG TERM...Fitzgerald/Steinbugl
AVIATION...Grumm/Ceru is the U.S. government's official web portal to all federal, state and local government web resources and services.