Scientific Forecaster Discussion
Area forecast discussion
National Weather Service State College PA
428 PM EDT Wednesday Aug 27 2014
a cold front over northern Pennsylvania will clear the southern
tier of the state early tonight. High pressure will arrive behind
the front and bring dry weather to the area through the end of the
week. Above normal temperatures and increasingly humid and
unsettled conditions are forecast over the Labor Day Holiday
weekend and into the first week of September.
Near term /until 6 am Thursday morning/...
first few rain showers/thunderstorms and rain now showing up over kpit/kagc and over the
kccx site itself on top of Rattlesnake Ridge. Coverage is still
expected to be rather sparse but the backyard looks like it will
get wet soon. Hrrr and rap still place bigger concentration of
showers this evening where low level convergence is best - over the
Nero mtg and Poconos...and in The Laurels. However...the showers
in black show that the hot temperatures today are cooking up plenty of
instability. The convective available potential energy could be healthy enough to make some of the
storms tap into some of the 35-40kt winds aloft. Spic continues
to mention area in the day1 outlook. So...some marginal wind gusts
are still possible...but not widespread. The cold front lags
behind the current convection and will likely fire up more
isolated/scattered convection as it moves into the more-humid air over the
central and southeastern cos. Probability of precipitation in the chance/scattered category for any one
hour still seem like the best approach.
The front and drier air should arrive in the central cos around
sunset and move out of the County Warning Area headed south around midnight. Skies
should clear out nicely behind the front and temperatures could get into
the 40s in the nan mtg. Also...decoupling should occur in most
places. Thus...ye Olden River Valley fog is expected there. Mins
will probably stay in the l60s in the southern tier.
Short term /6 am Thursday morning through 6 PM Thursday/...
cool Post-frontal northwest flow will make for a mostly sunny day over
most of the region. The only fly in the ointment might be the
approach of a lower cloud deck from the north/NE as a strong port maximum
drops S across New York state. Will keep probability of precipitation up near isolated numbers in
the NE...but not mention precipitation quite yet. A sprinkle is possible
in the NE though. Maxes will be about 8-10f below Wednesday/S
Long term /Thursday night through Wednesday/...
The medium range flow pattern will feature troughing in the west
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. A long frontal boundary extending from an upper
level low centered over northern Canada...and to a negatively
tilting trough which should be moving into the Midwest. The
biggest moisture from the frontal boundary is prognosticated to stay
north of PA.
However...there should be enough moisture...with enough forcing
to warrant increasing probability/opportunity for rain Saturday
night into early Monday. Daytime convection will also be spurred
on by a warming trend with maximum temperatures 5-10f above normal over the
weekend and into the first week of sept. The best chance for
precipitation through this timeframe should be Sunday afternoon
into Sunday evening. There is some model variation so expect some
modifications as time progresses. A GFS and ec in the long range
are actually in fair agreement through the first half of next
week...including the substantial trough that should move through
Wednesday as more defined cold front should approaches the area.
Aviation /20z Wednesday through Monday/...
cold front appears to be just through kbfd at 18z. One batch of
thunderstorms and rain over kagc is headed south of kjst. All but kbfd will
continue to have the possibility for thunderstorms and rain in the vcty...but have
only included vcsh/ts for now due to sparse coverage. This threat
should end around 23z-00z in ipt/unv but could linger until 03z in
the southern terminals. Wind shift to the northwest behind the front will
bring drier and cooler air. Normal valley fog is expected in the
northern valleys as the temperatures drop off well below the river water
temperatures. But there could be a little wind which could impede fog
formation. Will put MVFR fog in most tafs and IFR fog in bfd for a
few hours late tonight. The northwest winds pick up after sunrise but skies
and visible should be VFR. A low-end VFR cloud deck may drop down
from western New York state during the daylight hours on Thursday.
Fri-Sat...early morning fog restrictions possible...otherwise
Sun-Mon...mainly VFR. Scattered afternoon showers/tstms.