Scientific Forecaster Discussion
Area forecast discussion
National Weather Service State College PA
917 PM EDT Wednesday Aug 27 2014
a cold front will clear the southern tier of the state overnight.
High pressure will arrive behind the front and bring dry weather
to the area through the end of the week. Above normal temperatures
and increasingly humid and unsettled conditions are forecast over
the Labor Day Holiday weekend and into the first week of
Near term /until 6 am Thursday morning/...
cap was fairly stubborn this evening...but isolated to scattered
coverage of showers and thunderstorms did evolve along and ahead
of the front over the southeast half of the commonwealth during
maximum heating. Zone of greatest instability extended from the
Laurel Highlands to the middle Susquehanna River valley where mesoscale
analysis depicted convective available potential energy locally exceeding 1200 j/kg. Several
storms garnered sufficient concern for spss and even a few for
warnings given their vertical development...but with little
ambient wind to work with and insufficient cold pool
generation...no severe reports have been fielded thus far.
For the overnight...isolated shower and thunderstorm activity
continues to weaken along and ahead of the slowly southeastward advancing
surface front...which extends at this hour from just southeast of kjst
northeastward to near kipt.
Drier air will continue to filter southeastward from the central mountains
south and east through the pre dawn hours. Skies have cleared
across the north...but a patch of cirrus extends from Southern
Lower Michigan through Northern Ohio which will filter across
central areas overnight. Isolated showers will end across the
south as the front clears my southern counties. Decoupling is
expected in most areas...leading to the usual River Valley fog
early Thursday morning. Mins should range from the refreshing
upper 40s north to the l60s in the southern tier.
Short term /6 am Thursday morning through 6 PM Thursday/...
cool Post-frontal northwest flow will make for a mostly sunny day over
most of the region. The only fly in the ointment might be the
approach of a lower cloud deck from the north/NE as a strong port maximum
drops S across New York state. Will keep probability of precipitation up near isolated numbers in
the NE...but not mention precipitation quite yet. A sprinkle is possible
in the NE though. Maxes will be about 8-10f below Wednesday/S
Long term /Thursday night through Wednesday/...
the medium range flow pattern will feature troughing in the west
and fairly high heights forecast to prevail over the east supported
by a subtropical ridge that should anchor over the southeast. This
ridge will allow high pressure to center over upstate New York at the
start of the period. This will slowly move off the New England
coast on Saturday. A long frontal boundary extending from an upper
level low centered over northern Canada...and to a negatively
tilting trough which should be moving into the Midwest. The
biggest moisture from the frontal boundary is prognosticated to stay
north of PA.
However...there should be enough moisture...with enough forcing
to warrant increasing probability/opportunity for rain Saturday
night into early Monday. Daytime convection will also be spurred
on by a warming trend with maximum temperatures 5-10f above normal over the
weekend and into the first week of sept. The best chance for
precipitation through this timeframe should be Sunday afternoon
into Sunday evening. There is some model variation so expect some
modifications as time progresses. A GFS and ec in the long range
are actually in fair agreement through the first half of next
week...including the substantial trough that should move through
Wednesday as more defined cold front should approaches the area.
Aviation /01z Thursday through Monday/...
cold front appears to be just through kbfd at 18z. One batch of
thunderstorms and rain over kagc is headed south of kjst. All but kbfd will
continue to have the possibility for thunderstorms and rain in the vcty...but have
only included vcsh/ts for now due to sparse coverage. This threat
should end around 23z-00z in ipt/unv but could linger until 03z in
the southern terminals. Wind shift to the northwest behind the front will
bring drier and cooler air. Normal valley fog is expected in the
northern valleys as the temperatures drop off well below the river water
temperatures. But there could be a little wind which could impede fog
formation. Will put MVFR fog in most tafs and IFR fog in bfd for a
few hours late tonight. The northwest winds pick up after sunrise but skies
and visible should be VFR. A low-end VFR cloud deck may drop down
from western New York state during the daylight hours on Thursday.
Fri-Sat...early morning fog restrictions possible...otherwise
Sun-Mon...mainly VFR. Scattered afternoon showers/tstms.