Scientific Forecaster Discussion
Area forecast discussion
National Weather Service State College PA
1112 am EDT Tuesday Sep 1 2015
hot and humid weather will continue the recent Summer encore in
central Pennsylvania...as the calender flips to September 2015.
The precipitation pattern should be a mainly dry one with very
isolated showers and thunderstorms possible through the end of
Near term /until 9 PM this evening/...
fog/stratus almost gone except for the patch over Tioga Colorado. This
too shall pass. The cumulus have already popped up in The Laurels and
middle susq/Poconos. However...the deep mixing to happen this afternoon
may wipe some of those away despite the currently high surface
dewpoints. Dewpoints may drop back into the l60s and perhaps u50s
in the highest elevs this afternoon. Chance for precipitation is still mighty low
given dry atmosphere and weak subsidence. Only The Laurels or northestern
mountains may have a shot at a sprinkle.
Short term /9 PM this evening through Thursday night/...
south of the lower lakes...a slow moving closed low/upper level
wave currently in vicinity of Illinois/in will push slowly eastward on day 1 along or
just north of the Ohio River...reaching WV by 12z Wednesday. The models
including the hrrr seem to like the idea of developing very isolated
to widely scattered convection ahead of this feature from the Ohio Valley to
The Spine of the Appalachians along instability axis. Therefore
cut back on extent of schc probability of precipitation over scentral areas and confined
mention to the southern/southwestern laurels as per a consensus of the hi res
data and global guidance. Despite the calendar saying its sept
1st...the main sensible weather story will be the continued middle
Summer-like heat/humidity with daytime highs pushing 90f in the
middle-lower susq valley. Patchy radiational fog is also likely to form
again later tonight into Wednesday morning.
The highest areal average probability of precipitation /40-50 percent/ over the next 72 hours were
painted in for day 2/Wednesday across the south central mountains...as the
aforementioned upper level wave weakens and slides east-southeastward across
the central Appalachians. Expect another very warm and humid day
with afternoon highs similar to today. Kept schc probability of precipitation in for day 3/Thursday
although confidence is low given increasing model spread and weak/subtle
shortwave energy upstream. The 00z GFS is clearly more aggressive
in generating convection along a backdoor front slipping southward from
New York state later Thursday into Friday. Overall the short term period
should end up being mainly dry and relatively hot for this time of
Long term /Friday through Monday/...
an anomalous upper level ridge is forecast to dominate the large
scale pattern over the northeastern Continental U.S. Into early next
week...with high pressure taking control at the surface. This pattern
should support above-normal temperatures and very limited to
no rainfall across central PA through the Labor Day weekend.
The GFS remains more bullish vs. The European model (ecmwf) with convection on
Friday. High pressure initially centered over Quebec will drop southward
over the weekend and bring slightly cooler and drier/less humid air
into the region. No risk of rain again until probably next
Tuesday as a cold front approaches from the Great Lakes/Ohio Valley.
Aviation /15z Tuesday through Saturday/...
clearing skies have allowed for the regions where winds have
calmed to go MVFR to IFR. Bfd and ipt will continue to have LIFR
and lower conditions through the first half of the morning. The
patchy to dense valley fog will slowly dissipate by 15z once the
west to northwest winds mix down to the surface.. otherwise...high
pressure off the East Coast will ensure widespread VFR conds and
light winds on Tuesday. Another round of valley fog is possible
Wed-Sat...patchy am fog poss...mainly kipt/kbfd. Isolated PM thunderstorms and rain
impacts possible...mainly west.
preliminary data indicates Harrisburg and Williamsport recorded
near-normal temperatures and precipitation for the month of
August. More details can be found in the monthly climate
summaries which will be issued later this morning.