FXUS61 KCTP 210645

Area Forecast Discussion
National Weather Service State College PA
245 AM EDT Fri Jul 21 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


Satellite loop at 06Z showing fairly widespread low clouds and
fog have formed where rain fell last evening over northern
Pa. Based on 06Z dewpoint depressions, expect valley fog to
become more extensive toward dawn. However, little if any fog is
anticipated across the Lower Susq Valley, where no rain fell
yesterday and 06Z dewpoint depressions remain fairly high.

It will be another very warm and muggy night with min temps
from the mid 60s over the northern mountains, to the mid 70s
across the Lower Susq Valley.


Model soundings and LAMP guidance indicate early low clouds/fog
should mix out by around 14Z, then large scale subsidence and
arrival of much lower PWATs should result in a mostly sunny
Friday for most if not all of the forecast area. Have maintained
just a slight chance of an afternoon thunderstorm near the Mason
Dixon Line, which will remain on northern edge of ring of fire.
GEFS mean 850 temps still around 18C today, which should
translate to max temps from the mid 80s over the northern
mountains, to the low 90s in the Susq Valley. The southeast
counties fell just short of heat advisory criteria yesterday and
expect a similar scenario today with heat indices over that part
of the state peaking in the upper 90s.


Upstream developments Friday night and Saturday will largely
determine convective impacts across western and central PA on
Saturday as large MCS may propagate 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.


A weakening line of what is now mainly showers is moving
southeastward across Central Pennsylvania at 00z this evening.
The only cluster of activity that will affect central
Pennsylvania airfields is in the southwest. This will bring some
rain and maybe a rumble of thunder in the next hour or so to
KJST, and a possibility of -SHRA to KAOO. A single isolated
shower in northwest Lycoming County may sneak into KIPT as well,
but this is showing signs of weakening, so have not included in
the TAF at this point.

Models continue to insist that visibility restrictions will
occur overnight at all airfields, with an accompanying low
stratus deck across the west and north by morning. Have
maintained this thinking in the TAFs for now, but with most of
the airfields avoiding precipitation this afternoon, am a bit
skeptical on just how much low level moisture will be around
overnight to bring in the stratus. Visibility restrictions in
BR/HZ are likely though.

Mainly VFR Friday, but isolated to scattered SHRA/TSRA still
possible, mainly south.


Fri...AM BR/HZ with CIG restrictions possible North and West.
Isolated TSRA in the afternoon, mainly south.

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

Mon...AM valley fog possible. Scattered TSRA.





NEAR TERM...Fitzgerald
SHORT TERM...Fitzgerald/Gartner
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