Scientific Forecaster Discussion
Area forecast discussion
National Weather Service State College PA
719 am EDT Tuesday Sep 2 2014
a cold front over the Great Lakes will push southeast across PA
late today. High pressure will build along the East Coast late
this week...then another cold front will likely push south across
the region by Saturday.
Near term /until 6 PM this evening/...
radar loop at 09z showing a few -shra working through central PA ahead
of weak shortwave passing through the east Great Lakes. Waning lg scale
forcing should result in any remaining -shra falling apart around
sunrise. Subsidence in wake of this weak shortwave...as depicted
by darkening in WV imagery entering west PA...should result in a dry
morning across much of central PA. The day will start with low
clouds banked against the windward /west/ slopes of the
alleghenies...but diurnal heating/mixing within deepening blyr
should result in brightening skies across the West Mountains...while
mostly sunny skies prevail across the lower susq valley.
A potent-looking shortwave...over Iowa early this am...will push a
cold front through central PA late today and this evening. Storm Prediction Center
places much of central PA /with exception of lower susq valley/ in
a slight risk of severe weather with the primary threat being damaging
Cloud cover from upstream convection...along with am low
stratus...should act to limit destabilization today. Latest oper
and ens data produce only minimal convective available potential energy of below 1000 j/kg.
However...a belt of stronger westerly middle-level flow and deep layer
shear should help organize late day convection into line
segments/clusters that could support isolated damaging wind gusts.
Where skies remain mostly sunny into the afternoon...model 850temps support
highs in the u80s across the lower susq valley. Meanwhile...earlier
arrival of clouds/convection across the northwest mountains should limit temperatures
to the l/M 70s.
Short term /6 PM this evening through 6 PM Wednesday/...
evening convection should be most widespread across northern
PA...closest to track of middle level shortwave. Cold front and associated
shower threat will pass southeast of the region after 06z. Clearing
skies...a light wind and wet ground will likely lead to areas of
fog late tonight.
High pressure and associated drier air mass will be over the area
Wednesday...supplying mostly sunny and warm conds. Ens mean 800 mb temperatures near
15c should support maximum temperatures from the m70s northwest mountains to the m80s
in the susq valley.
Long term /Wednesday night through Monday/...
the high will move off the East Coast Thursday into Friday...allowing
more humid air to begin returning to the region. A surface low
slides from the northern plains across the Great Lakes and lifting
into S Canada on Friday...dragging a cold front along behind. As this
front approaches...an area of higher precipitable waters /1-2"/ surges into the
Ohio Valley...and then into PA Friday night into Sat. At same time a
broad upper trough sags southward. This will bring elevated
chances for showers/thunderstorms starting Friday night in the northwest and
spreading areawide on Sat. Ahead of cdfront...temperatures are likely to
peak Friday with mean 800 mb temperatures supporting widespread highs between
Behind the front...airmass change will usher in much cooler and
drier air for late weekend into early next week. Highs will fall
back about 10f...ranging from the upper 60s to middle 70s. As large
high pressure area tracks across New England...morning lows should
dip well into the 40s across the northern mountains...and in the lower
to middle 50s across the south.
Aviation /11z Tuesday through Saturday/...
expect most areas to be VFR by late morning.
Rather strong wind fields...so it will be breezy
Some risk of strong to severe thunderstorms this
afternoon and early evening...as the cold front
drops southeast. Limiting factor will be the amount of surface
Skies should clear out tonight. Some breeze expected
with lower dewpoints. Thus did not put fog in the
tafs at this point.
Mainly VFR conditions for Wednesday into Thursday...as high
Wed-Thu...patchy am fog...otherwise VFR.
Friday...mainly VFR. Chance of PM thunderstorms west.
Sat...VFR/MVFR with scattered showers/thunderstorms associated with cold frontal passage.