Scientific Forecaster Discussion
Area forecast discussion
National Weather Service State College PA
648 am EDT Wednesday Aug 24 2016
a seasonably warm and humid late-Summer weather pattern will
continue across central Pennsylvania through the weekend. The
most likely periods for thunderstorms are Thursday and early next
Near term /through tonight/...
minor update to hourly temperatures. Valley fog will dissipate by
8-9am. High pressure retreating off the northeast coast will
ensure another dry day with southerly return flow bringing warmer
temperatures and a gradual uptick in dewpoints/humidity levels.
Forecast maximum temperatures this afternoon are running about 5
degrees above normal for late August.
Multi-model/high resolution ensemble blend still highlights northwest PA
to the west of US-219 with Max pops /20-40 percent/ in the 00-12z
Thursday period. The risk for showers is coincident with surge of
Theta-E/warm advection and moisture flux on nose of 20-30kt west-southwest
low level jet. Milder overnight readings in the low-mid 60s.
Short term /Thursday through Friday night/...
a closed 594dm upper high initially centered over the deep south
will slowly migrate northeastward into the southern mid Atlantic
by the end of the period. A de-amplifying shortwave trough moving
through Ontario/Quebec will send a cold front through the lower
lakes on Thursday. The front is forecast to weaken as it continues
to push southeast encountering the building ridge aloft. A moist
and unstable airmass will reside in advance of the weakening cold
front which should prove favorable for the development of isolated
to scattered convection from the Ohio Valley into western PA during
the afternoon/evening hours. Storm Prediction Center d2 marginal remains focused from the
Ohio Valley into far western PA where the strongest mean wind fields
are projected. The front/sfc trough becomes very diffuse on
Friday as it slips south toward the Mason Dixon line. Weak
instability and rich boundary layer moisture in advance of the
weak front/sfc trough supports maintaining very low tstm probs
/20 pct or less/ primarily across the southern 1/2 to 1/3 of the
County Warning Area. However, this may be overdone given increasing large scale
subsidence and falling pwats. Temperatures and humidity will be on
the rise with 90f heat likely returning to the lower Susquehanna
valley by Friday.
Long term /Saturday through Tuesday/...
the deep-layer ridge will gradually slide off the mid Atlantic
coast this period, which allows another frontal boundary to sink
southward from the lower lakes and become quasi-stationary over
PA early next week. This will favor unsettled conditions Mon-Tue
with pops trending upward following a mainly dry weekend. Temps
will remain above normal by late August standards.
Aviation /12z Wednesday through Sunday/...
expect VFR conditions early this morning to give way to some
areas of MVFR and local IFR conditions in fog.
Morning fog will give way to another VFR day on Wednesday.
Approaching front with increased moisture could bring a chance of
thunderstorms and rain on Thursday, mainly in the west.
Wed...patchy am fog possible, otherwise VFR.
Thu...generally VFR, but with isold PM tsra impacts possible,
mainly W mtns.
Fri...morning low cigs possible across the western mountains,
Sat-sun...no sig wx expected.