Scientific Forecaster Discussion
Area forecast discussion
National Weather Service State College PA
1039 am EDT Tuesday Sep 23 2014
high pressure will drift east across Pennsylvania this afternoon
then pass off the New England coast Wednesday. A low pressure
system will track up the middle Atlantic coast Wednesday and
Thursday...then out to sea by Friday. An anomalous upper ridge
will migrate eastward from the Great Lakes to Pennsylvania this
Near term /until 6 PM this evening/...
visible satellite imagery shows nearly cloud free skies over all of
Pennsylvania thanks to a sprawling 1030 mb surface high centered near
A splendid first...full day of fall for outdoor activities with
abundant sunshine and light wind. Gefs mean 925 temperatures between 12-14c
should translate to highs between 65-70f from northwest to southeast.
Short term /6 PM this evening through 6 PM Wednesday/...
tranquil conds expected tonight as surface high remains over the area.
Weakest gradient will be over the north mountains...where a calm wind and
clear skies should promote areas of late night valley fog. Further
south...a developing easterly breeze will limit the fog potential.
Also...warm air advection aloft ahead of upper low over the southeast Continental U.S. May spread
increasing cirrus into southern PA late tonight.
Although most of the region should dawn bright...expect increasing
cirrus to overspread central PA from the south on Wednesday...as
aforementioned upper low over the southeast Continental U.S. Drifts north. All
current model data keeps associated surface coastal low/plume of Atlantic
moisture just south of PA...so confidence is high that any rain
will hold off through the daylight hours. Temperatures Wednesday should be fairly
uniform around 70f due to the thickest clouds arriving over the
normally warmer southern counties.
Long term /Wednesday night through Monday/...
significant changes made to the Wednesday night/Thursday forecast...as all
medium range guidance now tracks coastal low across the Delaware-Maryland-Virginia.
This scenario will likely bring a period of rain to at least the
southeast counties on Thursday. Tight pressure gradient between high east of new
eng and surface low riding up the East Coast is resulting in anomalous
easterly winds/precipitable waters in the 00z gefs across southeast PA Wednesday night and
Thursday. Gefs and oper model quantitative precipitation forecast all support at least likely probability of precipitation
across the lower susq valley during this period and a chance of rain
as far west as the Allegheny plateau. Some ensemble and oper runs
indicate a substantial rainfall of over an inch is possible across
parts of southeast PA. Have increased min temperatures Wednesday night and lowered maximum
temperatures Wednesday significantly due to the expected cloud cover/rain.
General agreement among medium range guidance that coastal low will
exit the middle Atlantic coast Friday...bringing a return to fair
and mild weather. Anomalous upper level ridge over the Great Lakes is then
prognosticated to slide east into PA over the weekend...bringing the area
a period of fair and warm weather that should last into early next
week. Lg scale subsidence beneath this system should result in
mclear skies through the weekend as the 00z naefs cloud output
suggests. Gefs and European model (ecmwf) 925temps near 20c should support high
temperatures around 10f above normal...with afternoon readings between 75-80f over
much of the area.
Aviation /15z Tuesday through Saturday/...
VFR conditions for the next 24-46 hours...with just a few...to
several hour period of patchy 1/2sm...mainly valley fog between
A developing...deep and moderately strong easterly flow between high
pressure over the New England states...and upper level low
pressure system/surface trough over the southeast U.S. Will bring cloudy
skies and a chance for rain Wednesday night and Thursday...especially across the
eastern half of Penn. Widespread IFR to MVFR ceilings and visibilities in the
same category appear likely Wednesday night through Thursday.
Wednesday...patchy fog in the morning...otherwise VFR.
Wednesday night and Thursday...low ceilings and areas of -ra/dz likely.
Fri-Sat...patchy 1/2sm fog in the morning...otherwise VFR.
short term...Fitzgerald long