Area Forecast Discussion
Issued by NWS State College, PA

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FXUS61 KCTP 231813
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
213 PM EDT Wed Aug 23 2017

.SYNOPSIS...
A large are of high pressure will build southeast across the
region and bring mainly dry and cool weather with comfortably
low humidity during the day. A weak upper level disturbance and
pool of cold air aloft could spark some scattered showers or
sprinkles across the central and northwest mountains Thursday
afternoon.

&&

.NEAR TERM /THROUGH TONIGHT/...
Southern edge of much cooler mid level temps will slide across
northern PA this afternoon bringing vertically enhanced cu and
possibly a few sprinkles. Elsewhere across central and southern
PA, much flatter fair weather cu will be generally in the
scattered sky cover category.

Temps will be pretty close to normal in the SE half of the fcst
area, but about 3 to 5F below normal in the NW half, especially
on the hill tops.

Cold air in the form of 8H temps as low as +6C (1-2sigma below
normal) will slide across the Great Lakes and settle in for
quite a few days. Boundary layer decoupling will lead to calm
air tonight which will help to maximize radiational cooling and
help fog to form in the valleys, but some cloud cover over the
west may keep the fog in check. Mins will be 45-60F across the
area.

&&

.SHORT TERM /THURSDAY/...
A potent short wave trough will push across the Great Lakes
late Thursday or Thursday night. The NAM is quickest with this
feature, but most other models delay the window of best forcing
until Thurs night. This feature is strong enough that - even
without anything more than meager lake moisture - it could
generate an organized area of showers. Due to the timing
uncertainty and lack of deep moisture, POPs were capped at 50
percent across the northwest mountains, and generally slight
chance across the central ridge and valley region of the state.

High temps Thursday will be about 5-6F lower than this
afternoon`s (Wed) values, or in the m60s NW-m70s SE PA.

&&

.LONG TERM /THURSDAY NIGHT THROUGH WEDNESDAY/...
An extended period of refreshingly cool, pleasant and dry
weather will continue through the upcoming weekend as high
pressure remains in control of the weather pattern over the
northeast quarter of the CONUS. It will feel more like early
fall than late summer. A few spots in north-central PA could
see morning lows dip into the upper 30s over the weekend.

Global models suggest isolated, terrain-induced convection may
be possible within return flow along the spine of the central
Appalachians later in the period. However, ensemble means favor
a continuation of the mainly dry and seasonable pattern through
the end of August, as upper level ridging building into the
Western U.S. supports troughing downstream over the central and
eastern states.

Interesting to note that the both the 12Z GFS/00Z ECMWF bring
the remnants of Harvey toward the area by early September.
After what appears to be a mainly dry end to the month of
August in central PA, this could be something to monitor down
the road.

&&

.AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
Widespread VFR conditions will prevail for the next several
days and more as a large area of high pressure builds in from
southern Canada and the Upper Midwest.

Some bkn cu with bases of 3.5-4.5 kft will occur (mainly) across
the northern and western mtns this afternoon and again Thursday
afternoon as a few mid level thermal troughs slide SE over that
area.

The northwest wind will average 8-12 kts this afternoon with
gusts into the upper teens to low 20KT range through 00Z as
vertical mixing tops out around 5-6 kft agl.

Some patchy dense valley fog is likely late tonight and early
Thursday morning - especially across northern PA where air/water
temp differences will reach 20-25 deg F.

A pool of cold air aloft will drift SE across central and nrn
PA airfield Thursday afternoon and evening with brief MVFR
conditions possible in scattered showers.

.OUTLOOK...

Friday-Sunday...Other than a few hrs of low cigs and vsbys in
patchy dense valley fog between 09-12Z Friday, Sat and Sunday
mornings, No sig wx is expected.

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$
SYNOPSIS...Lambert
NEAR TERM...Lambert
SHORT TERM...Lambert
LONG TERM...Steinbugl
AVIATION...Lambert


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