Area Forecast Discussion
Issued by NWS State College, PA

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FXUS61 KCTP 260608
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
208 AM EDT Fri May 26 2017

.SYNOPSIS...
An upper low directly overhead will slide quickly away today,
leaving northwest flow in it`s wake. Weak ridging will move in
but many chances for showers and a few thunderstorms are seen
through the holiday weekend. The fast flow aloft will keep it
unsettled. A cold front will pass through on Monday.

&&

.NEAR TERM /THROUGH TODAY/...
Upper low is over the eastern zones evidenced by the change in
storm motion which has occurred over the last few hours there.
Short wave dropping SE out of MI/OH will make some light rain in
the SW half of the area overnight. This area of showers will
likely begin to break up into more-cellular showers as the
daylight brings heating under the cyclonic low level flow.
Clouds around this morning call for mild temps and muggy air
in the morning, and a cooler than normal day on Friday. A
slightly confluent flow aloft should keep the showers from
growing too tall. Will keep POPs in the SCT range due to the
expected areal coverage at any time. But, a good forecast will
be that most places may get a little wet. The showers will be
moving along and, again, not tall. Thus, the chances for mod or
hvy rain and for thunder are very low. Maxes are a tough call
due to the clouds and possibility of showers knocking a few degs
off. If there can be more sunny breaks, it may rise above the
current guidance blend. Will stay close to but just a deg below
the locally-produced CTPblend of guidance.

&&

.SHORT TERM /TONIGHT THROUGH 6 PM SATURDAY/...
As the sun sets Friday, the showers should dissipate nicely
except perhaps in the NE cos. However, a ridge runner may drop
out of the upper Great Lakes into the state per the GFS. The NAM
has some convection just scooting to the south of the area, and
it is mainly on Saturday. This is also the rough idea of the 12Z
EC. This paints two opposing pictures of Saturday weather. Add
in the HiRes ARW and you get yet another. Too many differences
on timing and placement of possible convective complex(es) to
make a detailed forecast at this point. Will keep continuity
strong with chc POPs over the SW/SC cos and lesser numbers in
the N. Will peak the POPs during the daytime on Sat vs tonight.

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
A lower-amplitude but moderately strong westerly (zonal) mid
level flow will set up in the wake of the departing upper trough
with modest height rises/weak will ridging aloft into the
weekend. A warm front is progged to extend east from surface low
in the western Ohio Valley to the mid-Atlantic coast on
Saturday.

Central PA should reside on the north/east fringe of high
instability convective corridor/MCS type pattern expected to
evolve from the central and southern Plains to the southern mid-
Atlantic coast into Saturday night. The greatest risk for
scattered thunderstorms remains over the SW 1/3 of the CWA
which is consistent with previous fcsts. SPC has introduced a
MRGL risk into this area for D3. The remainder of the area
should see a mainly dry start to the holiday weekend but will
maintain slight chance POPs.

The large scale pattern will evolve into a broadly cyclonic
flow regime by Monday with upper trough parked over the Great
Lakes and southeast Canada into midweek. The aforementioned warm
front will lift north across the area on Sunday followed by a
series of weaker cold front associated with shortwave trough
rotating around parent upper low centered to the south of Hudson
Bay. Ensemble blend still supports max POPs on Sunday/Sunday
night into Monday with some additional shower opportunities into
midweek as series of shortwaves rotate around mean upper
trough. Temps should average near normal/seasonal climo to
close out the month of May.

&&

.AVIATION /06Z FRIDAY THROUGH TUESDAY/...
Relatively cool/moist westerly flow pattern behind low pressure
moving up the New England coast will spell MVFR/IFR conditions
for the western 1/2 of the airspace. MVFR to VFR conditions will
be common over the eastern 1/2 thanks to downslope flow east of
the Alleghenies. Lingering rain showers should focus around JST
early this morning with widely scattered coverage expected by
later today. Expect a gradual improving trend with most sites
VFR heading into tonight. Weak wave moving through the Ohio
Valley may bring showers into the western airspace by Saturday
morning. Confidence is low on the evolution of this system given
low predictability and large spread in the model guidance.

.OUTLOOK...

Sat...Chance of rain with sub-VFR possible.

Sun...Showers likely with sub-VFR especially Sunday night.

Mon-Tue...Scattered showers and a few Tstorms possible.

&&

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

&&

$$
SYNOPSIS...Dangelo/Gartner
NEAR TERM...Dangelo
SHORT TERM...Steinbugl
LONG TERM...RXR/Steinbugl
AVIATION...Steinbugl



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