Scientific Forecaster Discussion
Area forecast discussion
National Weather Service State College PA
634 PM 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 /through Wednesday/...
Sent an update to begin trimming back the watch as the line moves
into central PA.
Activity starting moving into central PA as one shortwave slides
from west PA with an area of showers/scattered thunderstorms...followed quickly by
second shortwave /over West Lake Erie/ that will help push an
approaching cold front through this evening. These shortwaves will
be accompanied by an increase in middle-level flow /winds 40-50 kts
at 500mb/ and deep layer shear which should continue to drive
convection through the afternoon and early evening hours. Though
middle-level lapse rates not overly impressive...Cape May approach
1000 j/kg as surface temperatures peaking a few degrees higher than
earlier anticipated with some extra sunshine this morning.
Activity will begin to slide into northwest mountains around 3 PM...and then
work across mainly northern half of County Warning Area as a strengthening line of
storms through the afternoon. More scattered activity should
develop on southern end of the line as it edges past the edge of
the cloud line into central PA. 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 wgusts.
Highs today likely about reached in the west where temperatures should
remain in the middle/upper 70s. Further east...we could add a few
more degrees onto current readings with temperatures peaking in the middle
to upper 80s.
Short term /Wednesday night/...
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 around 03z. Clearing
skies...a light wind and wet ground will likely lead to areas of fog
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 /Thursday through Tuesday/...
subtropical ridge centered over the Carolinas will be suppressed by
shortwave energy and moderate-intensity surface cyclone tracking northeastward
from the northern High Plains across western Ontario into northern Quebec Thursday through
Sat. Its trailing cold front remains the focus for precipitation heading into
the weekend with continued uncertainty in the southeastward frontal
progression. A slower trend may be emerging in the 12z GFS/gefs with
its frontal zone aligning closer with the European model (ecmwf)/Gem by 00z sun. Maximum
probability of precipitation shift from northwest to southeast over the County Warning Area from 00z Sat to 00z sun. Ahead
of cdfront...temperatures are likely to peak on Friday with mean 850 mb temperatures
+18-20c supporting widespread highs 85-90f.
The next question concerns how quickly the front clears southern PA on
Sunday with model data suggesting the upper level front hangs
back along the applchns/mid-Atlc Piedmont...as energy is sheared
northeastward through the northern New England and Canadian Maritimes and flow
aloft becomes oriented more westerly. Mean precipitable water fields show drier
air spreading into the region from the northwest behind the front as
high pressure becomes established in the northeast by early next
week. Therefore expect temperatures and probability of precipitation to trend lower during the
Aviation /00z Wednesday through Sunday/...
generally VFR conditions across central PA at 18z. But some
restrictions are in store for this afternoon and evening...especially
across the north and central mountains...as a shortwave with increasing
middle level flow triggers a line of showers/tstms. Most widespread
impacts will be across northern PA /generally north of I-80/ with
a more solid line of convection late this afternoon and early this
evening...though scattered thunderstorms also poss further south. The
strongest storms could produce damaging wind gusts and significant
reductions at airfields as they pass through.
Storms should clear the western half by 22-24z and the east by
01-03z. Then clearing skies...a light wind and wet ground will
likely lead to areas of fog late tonight.
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.
near term...Fitzgerald/la corte/rxr