Scientific Forecaster Discussion
Area forecast discussion
National Weather Service State College PA
1124 PM EDT Thursday Sep 3 2015
above normal temperatures will continue into next week with
gradually decreasing humidity levels. Isolated showers and
thunderstorms are possible today and again Friday afternoon. High
pressure will ensure fair and dry weather for Labor Day weekend.
Near term /until 6 am Friday morning/...
still watching the slow dissipation of diurnally fueled convection
over the northwest mountains...which are being maintained along
the eastern periphery of nearly stationary 500 mb shear axis over
eastern Ohio. Earlier locally heavy rainfall has decreased...but
western portions of Warren County are still seeing heavy late
evening downpours as cells slowly weaken and drift west-northwest.
Extended probability of precipitation beyond 03z across the northwest mountains and Laurel
Highlands...where isolated showers are still propagating. Much
weaker forcing continues to maintain isolated showers over
Lancaster County and the Piedmont region of southeast PA.
Continued stabilization should end activity in most areas by
midnight. Persistence and time of year make a strong case for
overnight fog/reduced visibility into Friday morning.
Short term /6 am Friday morning through Saturday night/...
upper level ridging will remain a dominant feature into the
weekend. Short term model guidance still shows a low to medium
chance for isolated/scattered thunderstorms Friday afternoon as weaker shortwave
impulses drift southeastward within shear/instability/mstr axis from the
Great Lakes across the north-central Appalachians. A backdoor cold
front should align itself near this axis and provide enough low
level convergence to spark some convection over central and
especially southern PA per multi model consensus. Diurnal cooling
should allow any storms to dissipate through Friday evening. The boundary
should pivot to a north-northwest/south-southeast orientation on Saturday while being
shunted southwestward...as a large dome of surface high pressure moves from eastern
Quebec into New England. Risk area for storms on day 3 should be
positioned to the west of the local County Warning Area. Temperatures should cool
off a bit with noticeably less humid air arriving by Saturday
Long term /Sunday through Thursday/...
not much to change in a slowly evolving extended forecast. High
pressure should maintain dry weather Sunday-Monday. Lead cold
front advancing eastward from the Great Lakes/Midwest and potential
onshore flow moisture may impact the forecast by Tuesday with scattered thunderstorms
poss...but a consensus solution holds back higher probability of precipitation until Wednesday
or maybe even Thursday in association with a stronger shortwave/surface
cold front. So timing diffs will need to be resolved as the ridge
slowly breaks down.
The global numerical models/ensembles are coming into better
agreement on a pattern change during the second half of next week
with a shuffling of the longwave flow allowing eastward progression of
the western trough into the central states and recent ridge over
the eastern United States off the coast into the western Atlantic. This
should eventually bring an end to the recent hot/dry spell. A
return to seasonal temperatures and more active precipitation pattern
seems probable by next weekend in the new flow regime.
Aviation /04z Friday through Tuesday/...
Isolated showers and thunderstorms linger over warrencounty...but
the rest of the area is rain free.
Sites are still VFR...but viz is starting to creep down. Patchy
fog will once again become the main concern...with IFR conditions
most likely at Bradford...but restrictions down to 2-4 miles
possible elsewhere for a few hours around sunrise.
Friday...VFR after early fog. Scattered PM thunderstorms and rain impacts possible.
Sat - Tuesday...patchy am fog possible...mainly kbfd/kipt.