Scientific Forecaster Discussion
Area forecast discussion
National Weather Service State College PA
910 PM EDT Friday Aug 29 2014
high pressure over the central Great Lakes will build southeast
and bring fair...dry weather with comfortable humidity through
early Saturday. Temperatures and humidity will gradually increase
over the upcoming Labor Day weekend...triggering isolated to
scattered...mainly afternoon showers and thunderstorms.
Near term /until 6 am Saturday morning/...
scattered cirrus tracking from the northwest mountains into the
north central and central mountains at this hour...as the 500 mb
ridge axis crosses central PA. Deeper layer moisture will
gradually increase overnight and into the pre dawn hours
Saturday...while boundary layer convergence increases over the
western third of PA as well. This will bring a gradual increase in
cloudiness overnight to the western half of the
commonwealth...particularly in the pre dawn hours. As previously
mentioned...local upslope and stratus are possible over the south
central mountains as well.
The light southeast wind - especially on the hills - will keep
temperatures very close to normal tonight. Mins will range through the
Short term /6 am Saturday morning through 6 PM Saturday/...
surface high will be well off shore on Sat and the Gulf opens up.
Enough moisture will start to build up in the western half of the
state and temperatures may get hot enough to grow some tall cumulus or even
make a sprinkle or two off the higher elevations. Probability of precipitation almost not
Worth the 15 or 20 that have been painted in there. But enough of
the models generate a pixel or two of convective precipitation and sref
probability of precipitation pretty high to just ignore. 800 mb temperatures try to rise close to 20c
near pbz and are well into the middle and upper teens across all of
the state. The temperatures will likely be kept under full potential with
some lower clouds possible in the morning in the S/east and high/middle
clouds thickening up all over the area. Maxes in the m70s in the
eastern mts and up to the lower 80s elsewhere. But it will be more
muggy and probably a little hazy. Summer finally shows up at the
end of the party.
Long term /Saturday night through Friday/...
throughout the middle to long term range a series of large upper
level lows should be moving through and at times...centered
over northeast Canada...will be driving the weather pattern.
Saturday evening the upper level ridge will be shifting off into
the Pacific as the flow flattens and the upper level low continues
to rotate. This low should shift southwesterly flow to the region
and should bring ample moisture to the region Saturday
evening and overnight through Sunday. A middle to upper level short
wave propagating underneath the predominant low should be the
catalyst that when coupled with daytime heating on Sunday...should
be enough forcing for showers and thunderstorms Sunday into Sunday
evening. Depending on the timing of the wave and the strength of
the shear to maintain any convection...storms could continue well
into the evening hours.
By early Monday...the short wave should have lifted to the east
and a negatively tilted ridge should bring divergent flow along
with drier and weaker flow to the region. This reprieve will be
short lived as another trough...stemming from another low...moves
through the Canadian provinces. That trough and corresponding
front should move through the region Tuesday into Wednesday.
The timing between the ensembles is fairly close up to that
point...especially since the operational ec and GFS are fairly
close in position and strength. After Tuesday night the models
begin to diverge in their solutions...though both have a weak
zonal flow over PA. The ec tends towards a ridge...and the GFS
tends towards keeping a low over Canada and PA being on the
outskirts. However...in either solution the weak westerly flow
should persist. The question is if there is strong enough daytime
convection with enough moisture present to allow for convection.
Have generally left out any mention of probability of precipitation after midweek...though
the best chance in the long term current should be Friday
afternoon. Temperatures should trend above normal through the
period...with warm days and warmer nights.
Aviation /01z Saturday through Wednesday/...
high pressure and associated dry air mass along the East Coast will
provide the area with mclear skies and light winds through late this
evening. As the high pushes off the coast early Sat morning...a
developing southerly flow will draw increasing moisture into the
region...possibly in the form of broken stratus towards dawn. Can/T
completely rule out a period of MVFR ceilings during late am over the
central mountains from kjst north through kaoo and kunv. However...southerly
flow and model soundings suggest ceilings will be between 3-5kft. Other
area of concern will be klns...where a nearly calm wind and mclear
skies may result in some fog between 09z-12z.
High based stratocu may linger across eastern PA into Sat afternoon.
Further west...arrival of warm front will bring the chance of a few
late day thunderstorms and rain across the West Mountains VFR conds and light wind should
predominate across the entire area during the PM hours.
sun-Tue...scattered PM thunderstorms and rain impacts poss each day...mainly VFR.
Wednesday...ts/shra poss am...clearing poss PM.