Scientific Forecaster Discussion
Area forecast discussion
National Weather Service State College PA
227 am EDT Friday Jul 3 2015
shower and thunderstorm chances will be focused mainly to the
south of Pennsylvania through the end of the week...near a
nearly stationary frontal boundary. An upper level trough will
move across the area on Saturday accompanied by the greater risk
for more widespread showers for Independence day. A drier weather
pattern should briefly visit the region early next week before
unsettled conditions return by next Wednesday.
Near term /until 8 am this morning/...
1030 PM update...
everything is well on track. No adjustments needed.
730 PM update...
isolated rain showers in the southern mountains these are becoming less numerous by
the volume scan. Expect nothing to be left in an hour. Baroclinic
Leaf over eastern PA should slowly continue to move to the east.
Added some fog to the northern valleys under the mainly clear sky and
light wind. All is well. A relatively comfortable night is in
store for this time of year.
deep layer moisture gradient lies across the Mason Dixon line
early this afternoon...separating more soupy 1"+ precipitable water from sub
0.75" precipitable water across north central PA. Mean upper trough will lie across
the region this afternoon with weak shear axes tracking along and
south of the PA/Maryland border. One area of showers has moved east of
my southern tier by middle morning. With diurnal heating...expect
isolated to scattered convective development later on along and south of
this this same area.
With little to no boundary layer flow or surface moisture convergence...
isolated convective initiation should occur on higher terrain to the
south of my area this afternoon and meander east-northeast along the moisture
gradient... remaining mostly along and south of the Mason Dixon
line. Latest hrrr run continues to generate a cluster of showers which
would likely produce isolated thunder clipping the south central
mountains and lower susq River Valley this afternoon. Convection
dies down by 02z with fair conditions overnight and some late
night valley fog...especially south.
Mins tonight will be chilly in the north with readings in the
40s...and ranging from the 50s to the lower 60s across central
and southeast PA respectively.
Short term /8 am this morning through 6 PM Saturday/...
shortwave rounding base of upper trough over the Midwest will cause
stationary front to waggle northward during the day Friday as
as a weak area of low pressure ripples along it from the Ohio
Valley. Deep layer moisture increases south of the boundary
across the southern tier...increasing chance of showers there during
the afternoon. Isolated thunderstorms and rain possible across the Laurel Highlands and
south central mountains. North will still be largely protected
from convection thanks to much lower deep layer moisture and
Highs on Friday will range generally in the middle to upper 70s.
Long term /Saturday night through Thursday/...
despite minor timing differences among medium range models...the
overall pattern appears fairly certain. Mean upper level trough will
remain centered west of PA...resulting in regular opportunities
for rain. Ecens/gefs indicate the best chance for showers will
accompany passage of shortwaves Sat and Wednesday. Latest guidance
suggests scattered showers Sat will be light and concentrated very
early in the day...as deep moisture remains south of the border and
wave passes east of the state by midday. Current model runs are
showing a more organized band that will possibly move through the
state late afternoon into early evening. Have slightly increased
the chance of precipitation on Saturday. Diurnally- driven
convection sun- Tuesday...due to models depiction of a weak cut off
upper low over the central Appalachians. However...deep moisture
and opportunity for meaningful rainfall should hold off until
approach of cold front and positive precipitable water anomalies Wednesday.
Gefs/ecens output imply temperatures fairly close to average for early
July. Sat is likely to be a bit cool due to cloud cover/scattered showers
and lingering ll easterly flow. However...SW flow in advance of
an approaching cold front is likely to push temperatures a bit above
average by Tuesday/Wednesday of next week.
Aviation /06z Friday through Tuesday/...
local IFR/LIFR in fog will impact aoo and lns during the predawn
hours. Drier air pushing southward across the airspace may improve visible a
little sooner than forecast but will stick closer to July climatology for
onset of dissipation. Forecast fog at ipt/bfd with less confidence
although both sites had fog yesterday morning. Not expecting the
025 ceiling at unv to last so kept VFR..but cant rule out some
radiational fog here either toward daybreak. Same is true at MDT.
Followed persistence/last nights observation trends closely at
jst with little overall change in the local pattern. Once fog/haze
or shallow stratus lifts 12-14z...expect VFR to prevail into the
afternoon with scattered-broken ceilings developing around 050 from south to north.
Ohio Valley shortwave and surface low tracking eastward across the middle Atlantic will
bring rain showers and reduced flying conds to the entire
airspace tonight into Saturday.
Sat...MVFR in rain/shra.
Sun...becoming VFR. No sig weather.
Mon-Tue...VFR with low chance of showers/tstms.