Area Forecast Discussion
Issued by NWS State College, PA

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FXUS61 KCTP 271941
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
341 PM EDT Thu Jul 27 2017

.SYNOPSIS...
A cold front over the lower Great Lakes early this afternoon
will drift southeast and cross the state tonight and Friday
morning. The front will stall along the Maryland border for
Friday and an unusually strong wave of low pressure for mid
summer will form and move east along this boundary, pulling
abundant moisture up and over the front from the south. Heavy
rain is expected later Friday into Saturday, especially across
the southern tier of PA. A much cooler airmass will overspread
the commonwealth over the weekend. Temperatures this weekend
will be more like mid fall than mid summer.Dry and warmer
conditions will return to the area early next week.

&&

.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
SPC cut back on the outlook for this aft. Updated HWO.

Some heating in the local area and points west, but stronger
wind fields to the northeast.

Thus cut back more on POPS through tonight.

Minor adjustments to temperatures etc.

&&

.SHORT TERM /6 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/...
Did cut back POPS some early Friday.

Models still show several sfc lows and QPF max with each.

Behind this, a digging upper level low to follow and result
in deepening.

Not clear how all this will phase and how much rain will
fall. For now went with a flash flood watch southern PA
starting at 18Z. Some plumes very wet. Key will be how
convection over the plains this afternoon comes into play.

Models been showing several sfc lows and the upper lvl low
digging for several days now, thus after touching base,
went with a flash flood watch. Watch extends out to 18Z
Saturday, later shift can push it further out in time and
space. Did not go as far north as Lycoming County, very
wet there, but QPF is fcst to be lower. Still have to watch
how the moisture is advected up the mid Susquehanna Valley,
the mountain range to the south of IPT often has a large
influence on things.

Only adjusted max temperature a little on Friday. Later starting
time of the heavy rain may allow high temperatures to be not
that cold. Main concern would be on Saturday. More info. below.

Max temps Friday and Saturday will almost certainly be several
Deg or more lower than most MOS guidance given the widespread
light to moderate rain and a trajectory of the anomalously
strong llvl wind from the New England Coast in contrast to the
Mid Atl Coast.

&&

.LONG TERM /SATURDAY THROUGH THURSDAY/...
Weather highlights are front-end loaded this period with rare
(unusually strong for late July) rainstorm continuing to impact
southern portions of the area on Saturday. Model and ensemble
guidance shows an anomalously strong minus 3.5-4.0 sigma below
normal closed 500mb low over the southern Mid Atlantic by the
weekend. Organized heavy rainfall is expected along and north of
its associated surface wave which is projected to consolidate
and gradually amplify as it tracks east- northeast along frontal
zone from the OH Valley across northern VA/D.C. into the
Delmarva Friday night-Saturday morning before shearing and
weakening off the coast Saturday-Sunday. A secondary low is fcst
to develop and lift north off the Mid Atlantic coast Mon- Tue
but at this time does not look to impact the wx here in central
PA.

Steadier rains early Saturday across the southern tier counties
should generally taper off from northwest to southeast later
Saturday into Saturday night. High pressure and accompanying
push of abnormally dry/below normal PW air will work into the
area by Sunday with dry and pleasant wx continuing early next
week. A stray shower to T`storm is possible Tue-Wed as warmer
temperatures and higher dewpoints return to the area. NAEFS and
ECENS favor a continuation of the western ridge/eastern trough
pattern which should allow for one or more weakening cold front
to push southeast from the Great Lakes later next week.
Temperatures will start off well below average on Saturday with
fcst departures on the order of -10 to -15 degrees. Following
the unseasonably cool start, a gradual warming trend is expected
with max/min temperatures returning to seasonal normals heading
into August.

&&

.AVIATION /19Z THURSDAY THROUGH TUESDAY/...
Still some lower CIGS across the east.

Clearing across the west, with VFR conditions.

Not much on the way of showers on the radar. Perhaps
a shower in a few spots into early this evening.

Expect some fog and haze later tonight again.

Widespread showers and storms with heavy rain expected
later Friday into Sat.

.OUTLOOK...

Friday night-Sat...Scattered SHRA north with more numerous and
heavier SHRA/TSRA across the south.

Sun...More shower activity possible.

Mon-Tue...No sig wx.

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
Flash Flood Watch from Friday afternoon through Saturday
afternoon for PAZ024>028-033>036-056-057-059-063>066.

&&

$$
SYNOPSIS...Lambert/Martin
NEAR TERM...Martin
SHORT TERM...Lambert/Martin
LONG TERM...Steinbugl
AVIATION...Ross/Martin


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