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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KCTP 201936
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
336 PM 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 8 PM THIS EVENING/...
Shortwave energy/weak defined cold front moving across the
eastern Great lakes is helping to force strong to severe
convection east of Lake Ontario. Broken line of weaker
showers/storms is trying to develop over northwest PA. Both
areas are moving E/SE and will have potential impact on parts
of central PA later this afternoon and evening. Severe
Thunderstorm Watch #424 included Tioga and Sullivan counties
until 8PM. Elsewhere, isolated showers/storms remain possible
into this evening, but most places will be rain free today.

Hot and very humid weather will continue across the CWA at
least today and tomorrow. Across the Lower Susq Valley,
combination of heat and humidity will likely push heat indices
above 100F for at least a couple of hours later this afternoon.
Thus have issued a Heat Advisory til 8PM for of the lower susq
counties and as far west as Fulton County.

&&

.SHORT TERM /8 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 THURSDAY/...
-- Changed Discussion --
Upstream developments Friday night and Saturday will largely
determine convective impacts across western and central PA on
Saturday as large MCS may propogate ESE towards the Ern GLAKS
Sat morning. It is possible that this feature continues ESE as a
derecho into southwest PA and the panhandles of MD/WV. Latest
SPC outlook covers southwest 2/3 of PA in SLGT RISK on Saturday
and this appears well placed, but exact location of pcpn will
depend on details not well resolved until the very short term
time frame. Will keep high chc to likely POPs going for this
timeframe given higher than usual confidence in widespread
convection to affect the region.

Beyond Saturday, today`s medium range models generally agree
that 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...as WNW upper flow and persistent
southeast Canadian and ern GLAKS upper troffing become
prevalent by the middle of next week.
-- End Changed Discussion --

&&

.AVIATION /20Z THURSDAY THROUGH TUESDAY/...
A weak cold front moving across the eastern Great lakes is
helping to force strong to severe convection/thunderstorms
east of Lake Ontario. Broken line of weaker showers/storms is
trying to develop over northwest PA. Both areas are moving E/SE
and will have potential impact on parts of the airspace, mainly
northern TAF sites, this afternoon and evening. Severe
Thunderstorm Watch #424, including Tioga and Sullivan counties,
is in effect until 8PM. Elsewhere, isolated showers/storms
remain possible into this evening, but confidence remains too
low to include at other TAF sites with most air fields will be
rain free today.

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 and Tue...AM valley fog poss. Scattered TSRA.

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
Heat Advisory until 8 PM EDT this evening for PAZ035-036-056-
057-059-063>066.

&&

$$
SYNOPSIS...Fitzgerald/Gartner
NEAR TERM...Fitzgerald/Gartner
SHORT TERM...Fitzgerald/Gartner
LONG TERM...DeVoir
AVIATION...DeVoir/Gartner