Area Forecast Discussion
Issued by NWS State College, PA

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FXUS61 KCTP 270354
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
1154 PM EDT Fri May 26 2017

.SYNOPSIS...
An unsettled Memorial Day weekend in store...

A weak ridge will move across the region tonight ahead of a a
trough of low pressure expected to move through southern PA
Saturday. A cold front will approach the region Sunday, and pass
through Sunday night and early Monday.

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
Models indicate upper heights will continue to rise overnight as
a weak ridge moves through the region. The scattered sprinkles
of earlier have dissipated. GOES R fog product indicates skies
have scattered out or gone clear over much of the area along the
Mason-Dixon line to the Susq Valley with low clouds remaining
over much of the west and north.

A shower may return to the far SW before sunrise, but latest
guidance suggests that`s a low probability outcome.

Lows in the 50s will be near to a few deg above normal.

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH 6 PM SATURDAY/...
Approaching wave should give way to renewed light rain Sat
morning mainly across the southern part of the state. A dry Sat
aftn and early Sunday will give way to more rain Sunday
afternoon region wide. The other operational models are also
generating what looks to be an MCS upstream. The 06Z NAM has
some convection just scooting to the south of the area, and it
is mainly on Saturday. The EC is also placing a high QPF over
the upper OH valley and into the Mid-Atlantic on Sat morning.
There is a little better consensus on the timing and placement
of convection for the short term, so we will nudge the POPs up a
bit in the SW for the late tonight and Sat time frame.

&&

.LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/...
A shortwave ridge aloft over PA and departing 1016 mb area of sfc
high pressure over New England will highlight the start of the
extended period, providing dry weather and partly to mostly
cloudy skies for us under a light southeasterly llvl flow,
topped by increasing mid and high clouds late Sat night and
early Sunday.

After a mainly dry morning Sunday, a quick transition to
increasing deep layer moisture and higher PWAT air of 1-1.25
inches will occur Sunday afternoon through much of Sunday night.

A large-scale trough and increasing upper level divergence
(associated with a lead upper shortwave in the west/SW flow)
will lead to a fairly large area of moderately strong uvvel and
a widespread moderate rainfall along and ahead of a cold front.

GEFS Probs for GE 0.50 inch of rain/24 hours ranges from 50-80
percent across the wrn mtns of PA...to generally less than 50
percent across the eastern half of the state. This translates
into very high POPs for measurable rain (90 percent or more)
across the western half of the CWA, to between 70 and 90 percent
across the south-central mtns and Susq Valley.

12Z EC and 12z GEFS are in very good agreement on the
timing/location of the north/south sfc cold front during the
afternoon hours Monday across the eastern half of the state with
weak deep- layer ridging and drying for Monday afternoon and
night. Dry conditions expected Tuesday morning before
significant cooling aloft accompanies a pair of short waves late
Tuesday and later Wednesday.

POPs during this midweek period will be painted as chc -
translating to scattered showers with preference for the
majority of the QPF (albeit quite light at that)to be across the
typical west-nwrly flow upslope prone areas of the Laurel
highlands and NW mtns. The chance for any thunder will be very
minimal Tuesday through Thursday.

Generally dry NW flow occurs late in the week into next weekend as
a 1020 sfc high over the upper midwest Friday evening builds SE twd
the region. Pops Thur night through Fri night will be 30 percent or
less.

After our bout of coolish weather with temps several Deg F below
normal Sunday and Monday, GEFS mean temps rebound back to near or
slightly above normal (even under slightly cooling 850 mb temps)
for Tuesday through at least Thursday. ECENS mean temps are several
deg warmer than the GEFS and Nat`l Blend of Models temps. leaned
closer to the cooler solutions based on the few-svrl deg C of
cooling aloft with near to slightly below 850 mb temps.

&&

.AVIATION /04Z SATURDAY THROUGH WEDNESDAY/...
Pool of cold air aloft and associated low level instability is
resulting in persistent MVFR stratocu across the northwest
mountains late this evening. Bigger concern will come late
tonight, as skies clear and wind becomes calm, likely resulting
in areas of fog. Latest dewpoint depressions, as well as model
guidance, target BFD for the best chance of significant vis
reductions. However, can`t rule out some fog toward dawn at UNV
or IPT. Increasing mid level cloudiness should limit the fog
potential over the southern airfields. Probability of at least
tempo IFR visibility at BFD is about 70 pct late tonight.

Remnant meso/convectively enhanced wave tracking east across
the Ohio Valley should thicken clouds back up by Saturday
morning. As this feature moves through, expect a period of rain
to affect primarily central/southern Pa between 12Z-18Z,
probably not falling heavy enough to significantly reduce
visibilities. Latest SREF prob charts and model soundings
indicate MVFR cig reductions are likely at JST and possible,
but not likely, elsewhere.

.OUTLOOK...

Sun...AM fog possible. Evening showers/reduced cigs possible west.

Mon...AM showers/low cigs possible.

Tue...No sig wx expected.

Wed...Slight chance of showers/reduced cigs.

&&

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

&&

$$
SYNOPSIS...La Corte
NEAR TERM...La Corte
SHORT TERM...Dangelo/Gartner
LONG TERM...Lambert
AVIATION...Fitzgerald



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