Scientific Forecaster Discussion
Area forecast discussion
National Weather Service State College PA
1100 am 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 /through tonight/...
1030 am update...
some u30s-mins this morning. High clouds spilling over northern PA but
more sunshine/thinner clouds on their way east from western PA. Temperatures
struggling a bit right now...but deeper mixing this afternoon should
allow temperatures to still get to curr forecast maxes. Fair skies and light
southeast wind should last into the evening. High pressure slides to the
east and off shore tonight. Clouds will thicken up aloft overnight
and the light southeast wind - especially on the hills - will keep temperatures up near
normal tonight. The deeper valleys will still get closer to 50f.
Short term /Saturday/...
surface high 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 will be 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.
Long term /Saturday night through Thursday/...
the medium range flow pattern will feature troughing in the Midwest
and fairly high heights forecast to prevail over the east supported by
a subtropical ridge that should anchor over the southeast. This
ridge will allow high pressure to center over upstate New York at the
start of the period. This will slowly move off the New England
coast on Saturday. The big forecast question is the timing of a
shortwave that should be moving through the Great Lakes region and
into the northeast late Saturday into Sunday. The models vary on
timing and amplitude of this wave. The GFS/NAM propagates it
faster...where the ec slows the timing down...and has a more zonal
flow Sunday into Monday. Even given the inconsistencies...there
should be enough moisture...and daytime heating should be spurred
on by a warming trend with maximum temperatures 5-10f above normal this
weekend and into early next week...showers and thunderstorms
should spark along a long frontal boundary that should extend in
between the systems. As such have increased the chance for
precipitation Sunday into Monday morning. The greatest moisture
flux should be along and ahead of the frontal boundary but is
prognosticated to stay north of PA.
The long range pattern will be dominated by a large upper level
low centered over the Hudson Bay. This rotating low will allow
for mainly zonal flow through the region through middle week. The GFS
and ec in the long range are actually in fair agreement through
the first half of next week...though the GFS has far more
amplitude in the waves...with deeper troughs propagating through
periodically...where the ec keeps a more zonal pattern. As such
have left chance probability of precipitation daily through Tuesday.
Aviation /15z Friday through Tuesday/...
expect VFR conditions into tonight with high pressure sliding off
shore. Strong warm advection starts tonight. This may trigger a
few showers and thunderstorms Sunday into Tuesday...but any convection
on Sat afternoon would be so sparse that it deserves no mention in the
tafs. Winds become southeast on Saturday. Dewpoints and humidity levels
will really come up on Sunday...higher than hat we have seen so
sun-Tue...scattered PM thunderstorms and rain impacts poss each day.