Area Forecast Discussion
Issued by NWS State College, PA-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
FXUS61 KCTP 280907
Area Forecast Discussion
National Weather Service State College PA
507 AM EDT THU JUL 28 2016
The stalled surface front over the Mason Dixon line will move
northward today and tonight as a disturbance approaches from the
Ohio and mid Tennessee River Valleys. This will produce a soaking
rain over portions of central and south central PA tonight into
Friday morning. Behind this system system slightly cooler air
aloft moves over the region to usher in the weekend. But the
ridge may begin to build to our west again early next week.
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Moisture and clouds continue to slowly increase from the
southwest early this morning...as quasi stationary front near the
Mason Dixon line begins to lift northward in response to
approaching upstream troughing. Isolated showers are now lined up
along the MD/WV/PA border and extend into portions of the Laurel
Highlands and South Central Mountains...a sign of things to come
later today and tonight.
Deep layer moisture will continue to increase from south to north
today as southerly component to 5h flow increases. Impressive
moisture flux late this afternoon and evening will yield some
2.0"+ PW by this eve (00z Fri) and set the stage for some decent
rainfall over the southern third to half of central PA overnight
into Friday morning. Mins will generally range through the 60s
across northern and central sections...except for the southeast
which should bottom out around 70F.
.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/...
-- Changed Discussion --Impressive boundary layer convergence on the nose of a potent
40kt 850 mb jet will promote a well organized convective complex
that traverses the southern third to half of central PA...with
high confidence in a stripe of 1-2"+ rain totals by 15z Fri.
Latest guidance has shifted the ribbon of max qpf slightly
northward in proximity with the LLJ...and parts of the mid Susq
River Valley may get in on the soaking rainfall late tonight and
Friday morning. Areas well north of I80 may not see much...but
pops still increase to high chc/likely late tonight and Friday
with this wave. Flooding threat remains quite low, but WPC has
placed my far southern and southeastern counties in SLGT risk
(5-10%) of exceeding flash flood guidance. PHL and now LWX have
issued Flash Flood Watches just south and east of my area, and day
shift Thu may want to consider shifting north should latest
northward model trend continue.
For the remainder of Friday...expect only residual light scattered
showers over mainly the higher terrain of the west and north as
cooler air and slightly cyclonic flow come in the wake of the
With abundant cloud cover and showers on Friday...highs will be
cooler than recent days...and range from the upper 70s north to
the lower to middle 80s southeast. Again...the bulk of the rain
will come/wrap up by mid morning Friday...but far eastern sections
may linger into Friday afternoon.
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.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
In the medium to long-range period...conditions slowly revert to
near normal in temp and precip as several chunks of short wave
energy in the westerly flow aloft helps to carve out a mean 500 mb
trough axis over the Glakes and Ohio Valley region during the Thu-
The peak in unsettled weather (with perhaps some periods of down-
right rainy conditions) occurs Thursday night and Friday as a
well-defined wave of sfc-850 mb low pressure lifts ENE out of the
Ohio Valley and heads across the I-95 Megalopolis.
Followed a blend of EC/GEFS/superblend and NBM guidance for that
particular 24-36 hour period to arrive at likely pops for rain and
scattered TSRA. Some uncertainty in timing and areal coverage of
the convection led us to undercut the NBM by 10-20 percent for
now, recognizing issues with large scale model convective
parameterization schemes (and subsequent exaggeration of the areal
coverage and broader qpf amounts) means that we`ll likely see more
concentrated areas/bands of heavy convection, compared to the
model depicted, larger cold season stratiform look to the precip
Portions of Southern and Central PA...close to the track of the
1006-1008 mb sfc low will likely see some localized heavy 1-2
inch,12-24 hour rainfall amounts by Friday afternoon...with even
the potential for some pinpoint heavier amounts from embedded
TSRA, as a tongue of 2 inch pwat air lifts north and wraps
cyclonically into sern PA and the Lower Susq Valley.
For later Friday through the upcoming weekend, a large area of
high pressure (1020-1024 mb) near the border of southern Quebec
and Ontario will try to push drier air south into the Mid Atlantic
Another...apparently weaker wave of low pressure at the sfc and
aloft lifts NE out of the Ohio Valley over the weekend and brings
an enhanced chc for showers. Slight diffs in timing/location exist
between the EC/GEFS and NBM guidance. However...the target period
for the best chc of showers and isolated to sctd TSRA appears to
be late Sat into Sunday.
Afterward, heights begin to rise from the southwest, accompanied
by a ridge of surface high pressure building east into PA with
mainly dry conditions and a rebound in temps for early next week.
.AVIATION /09Z THURSDAY THROUGH MONDAY/...
06Z TAFS sent.
Some mid and high clds across the sw. Isolated showers along
the MD line.
Earlier discussion below.
VFR conditions across the region this evening. Expecting some
fog to develop overnight...affecting most airfields with MVFR
conditions. IFR conditions were introduced int KBFD TAF,
following the lead of what`s happened there for the last several
nights, with a low IFR stratus deck developing in the pre-dawn
Morning fog/haze will lift early Thursday. Showers and isolated
thunderstorms could move into the area from the southwest.
With POPs generally less than 50 percent, and scattered nature of
the rain, have left out of TAFs except for a VCSH in KJST for now.
More restrictions possible overnight Thursday into Friday with
the potential for rain and thunderstorms along with fog.
Conditions expected to improve Friday into the weekend.
FRI...Some restrictions in SHRA/TSRA and patchy fog...mainly
SAT-MON...Wide range of conditions expected with a chance
of showers and storms.