Area Forecast Discussion
Issued by NWS State College, PA

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FXUS61 KCTP 201510
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
1110 AM EDT Thu Jul 20 2017

.SYNOPSIS...
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
week.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
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 Grt 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.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/...
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
Valley.

&&

.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
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
Tue-Wed.

&&

.AVIATION /15Z THURSDAY THROUGH MONDAY/...
Morning fog and low clouds have burned off and visible imagery
shows cumulus building over the higher terrain of the Laurels
and South Central Mountains. Focus is upstream on weakening
MCS tracking across the Great Lakes toward NW PA this afternoon.

TSRA probs become likely over the west by mid to late
afternoon, likely organizing along lake breeze and pushing
eastward with 850 mb 20kt jet. A lesser chance of showers/
storms for points eastward as activity 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.

In addition, isolated convection may develop over the Lower Susq
around peak heating, but confidence too low to include at TAF
sites there.

Tonight, scattered convection over central mtns will be
diminishing. Areas of valley fog will again become likely, with
CIG restrictions poss over the NW.

Isolated TSRA poss on Fri, with VFR otherwise. TSRA become
likely again for Sat and Sun as humid airmass remains in place.


.OUTLOOK...

Fri...AM valley fog. Cig restrictions likely NW half.
Isolated TSRA.

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

Mon...AM valley fog poss. Scattered TSRA.

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$
SYNOPSIS...Fitzgerald
NEAR TERM...Fitzgerald
SHORT TERM...Fitzgerald
LONG TERM...Fitzgerald/Steinbugl
AVIATION...DeVoir/RXR



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