Scientific Forecaster Discussion
Area forecast discussion
National Weather Service State College PA
722 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 thunderstorms with torrential rainfall have dropped an
estimated 3+ inches of rain in Elk County just west of Ridgway
this evening. Upper level forcing remains nearly stationary and
while diurnal maximum in activity has been reached...we'll still
be watching locally heavy rainfall over portions of the northwest
mountains through middle evening.
Stabilization will end activity in most areas by 900 PM.
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 /23z Thursday through Tuesday/...
Isolated showers and thunderstorms will continue to diminish with
loss of heating.
Generally VFR conds and light winds are expected except at
terminals where a stray storm could bring a brief period of IFR.
The threat of this will be minimal by midnight.
Patchy fog will once again become the main concern tonight...with
IFR conditions most likely at Bradford...but restrictions down to
2-4 miles common elsewhere for a few hours around sunrise.
Friday...patchy am fog possible. Scattered PM thunderstorms and rain impacts possible.
Sat - Tuesday...patchy am fog possible...mainly kbfd/kipt.