Scientific Forecaster Discussion
Area forecast discussion
National Weather Service State College PA
1116 am EDT Tuesday Sep 30 2014
a cold front will drop across the region this afternoon and
evening...bringing a chance of showers and thunderstorms.
Unsettled weather will move east of the region later
Wednesday...with dry weather expected through the end of the week.
A stronger cold front will push east into the commonwealth late
Friday night and Saturday.
Near term /until 6 PM this evening/...
fog and low clouds will continue to lift through middle day.
The cold front is moving into northwestern PA as of middle morning.
Steepening middle level lapse rates associated with the approaching
cold pool aloft suggest our main weather threat today will be
thunderstorms accompanied by hail. Convective available potential energy are expected to be rather
modest so the threat for severe hail should remain low...isolated
Boundary layer winds are weak...so the threat of strong wind gusts
will be minimal.
Short term /6 PM this evening through 6 PM Wednesday/...
4km Storm Prediction Center WRF indicates afternoon convection will linger well into
the evening hours over especially central and eastern sections.
After storms diminish early this evening...kept scattered showers
in these areas through late evening. Fog may once again become an
issue late tonight...especially over the east where surface ridge axis
builds and a weak inversion sets up in lights winds. Mins will
range through the 50s.
Slowly filling upper trough wobbles slowly eastward across the
commonwealth on Wednesday. It looks quite cloudy given fairly
steep lapse rates...but generally dry with only slight chance probability of precipitation
under the "cool" core aloft. An underwhelming upper low of 571 dm
tracks into southern New England by 00z Thursday...with rising heights
late in the day across western and central PA. Temperatures on Wednesday
however will be cooler than recent days...due to the cloud cover.
Expect highs to range from the upper 60s north to the lower 70s
Long term /Wednesday night through Monday/...
progressive upper low/compact trough axis over the northestern U.S. At the
start of the period is forecast to lift out by the end of the
week...as upper ridge rebuilds across the region into the early
part of the weekend. A second...much stronger and expansive upper
trough axis extending southward from an upper low anchored over northern
Ontario is forecast to sweep across the eastern U.S. Over the
Warmer weather makes a brief return Thursday...Friday and early Sat as
the upper ridge rebuilds....with maxes and mins at least several
degrees above climatology normals.
The arrival of the second trough will support a strong cold front
with deeper connections to the Gomex and the Atlantic
Ocean...thus potential for more widespread and heavier rainfall.
Passage of the front will also bring noticeably cooler temperatures to
the region for Sunday into Monday. A short wave within the then
expected cyclonic flow over the region will bring another frontal
system to the region with an increased chance of showers for the
end of the period.
Aviation /15z Tuesday through Saturday/...
IFR at southeastern terminals will continue to lift and improve through
Latest guidance suggest the showers currently entering northwestern PA
will be slow to advance east as the associated upper low slows. We
will be unstable which will lead to the development of another
area of scattered convection over the interior airspace/central
terminals in vicinity of jst/aoo/unv between 17-19z. Arrival of cooling aloft
associated with upper low favorably timed with daytime heating should
support isolated-scattered thunderstorm development...focusing along/ahead of surface
cold front. The cool temperatures aloft will favor hail as the primary
thunderstorm hazard. Expect conds to trend lower overnight as blyr cools
and showers linger into early Wednesday.
Outlook /Wednesday through Saturday/...
Wednesday...upper low will be slow to move northeastward therefore chance of showers
will continue on Wednesday. Some low ceilings possible as well.
Thursday...low ceilings likely early...and could persist through much of the
day or reform Thursday night due to high pressure wedge/maritime flow east of
Friday...showers and thunderstorms likely associated with well-defined
gusty cold frontal passage. Low level wind shear likely due to strong southerly winds ahead of the cold
Sat...am showers eastern areas. Breezy with improving conditions east of
the mountains due to westerly downslope. Isolated showers and local MVFR
possible over North/Western areas.
near term...devoir/la corte