Scientific Forecaster Discussion
Area forecast discussion
National Weather Service State College PA
259 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/...
isolated showers and thunderstorms are developing over parts of
the central PA mountains threat of localized heavy rain from slow
moving storms will persist until shortly after sunset. Most
locations however...will not see any precipitation.
The deep- layer flow will be rather weak under broad upper
ridging which should limit potential for organized severe storms.
However sub-severe water- loading-related wind gusts under 50kt will
be possible and may produce localized/minor damage. Nocturnal blyr
stabilization should reduce convective coverage/intensity
considerably this evening with any lingering storms likely
dissipating into tonight. Persistence and time of year make a
strong case for overnight fog/reduced visibility into Friday
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 Wednesday/...
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...but
a consensus solution holds back higher probability of precipitation until Wednesday-Thursday in
association with a stronger shortwave/surface cold front. So timing
diffs will need to be resolved.
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 /19z Thursday through Tuesday/...
cumulus field expanding this afternoon as expected ahead of weak surface
boundary moving south toward PA. Isolated showers and thunderstorms
are the result in the warm and humid airmass over PA.
Generally VFR conds and light winds are expected for the rest of
today. Isolated to scattered PM thunderstorms and rain across the area will result in brief
visible reductions. The hiest chance for thunderstorms and rain is over the western
half of the state through 01z.
Patchy fog will once again become the main concern tonight...with
IFR conds likely at kbfd and possible at kipt.
Friday...patchy am fog possible. Scattered PM thunderstorms and rain impacts possible.
Sat-Tue...patchy am fog possible...mainly kbfd/kipt.