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746
FXUS61 KCTP 232334
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
734 PM EDT Thu May 23 2024

.SYNOPSIS...
A front will remain just south of the Commonwealth tonight and
Friday, while a ridge of high pressure slides east across the
state bringing a couple of nice days with dry conditions and
comfortably low humidity. More clouds and an uptick in humidity
will arrive for Saturday and persist through Memorial day with
a period or two of showers and possible thunderstorms, mainly on
Saturday and again Sunday night into Monday.

&&

.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
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The 23Z surface analysis places a stalled frontal boundary from
Southern Somerset County northeast into the Lehigh Valley. A
mix of cumulus and cirrus is noted in the satellite imagery
south of the front, while the arrival of much drier air has resulted
in mostly clear skies north of the front.

The main focus for tonight will be on a potent-looking shortwave
over KY, which is progged to track eastward across VA late
tonight. Latest model guidance keeps the bulk of the convection
associated with this feature south of PA. However, increasing
large scale forcing, combined with modest instability south of
the stalled front, could support a few showers/tsra across the
southern tier of PA later tonight.

Low level moisture pooling in the vicinity of the front may
result in patchy late night valley fog across Southern PA.
Across the NW Mtns, clear skies, a calm wind and dry air should
result in efficient radiational cooling, so have shaved a couple
of degrees off of NBM guidance and added patchy fog toward dawn
in the deep river/stream valleys of the NW Mtns. Min temps
should range from the upper 40s over the NW Mtns, to the low 60s
over the Lower Susq Valley.
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&&

.SHORT TERM /6 AM FRIDAY MORNING THROUGH SUNDAY/...
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Any showers over the southern tier should end by mid morning
Friday, as the associated shortwave passes off of the Mid
Atlantic coast. Large scale subsidence behind this feature
should ensure fair weather for the rest of the day. Surface high
pressure nosing southeast from the Grt Lks should push the
stalled front south of PA by afternoon, with mainly sunny skies
even in the south by that time. Model soundings mix to 800mb,
where temps around 10C support highs ranging from the upper 70s
over the Alleghenies, to perhaps the mid 80s over parts of the
Susq Valley.

Surface ridging over the state should ensure fair weather Friday
night into early Saturday. By late Saturday the focus will shift
to a shortwave lifting across the Eastern Grt Lks. Diurnal
heating, combined with surging moisture ahead of a trailing
cold/occluded front, will likely result in a round of
showers/tsra in many locations late Saturday afternoon or
evening. Unimpressive pwats and the progressive nature of this
feature indicate rainfall amounts will be fairly insignificant
(<0.25 inches).

Model guidance supports fair and warm weather Sunday, as upper
level ridging builds over PA ahead of an upstream trough and a
weak surface high builds in from the Grt Lks. However, a
diurnally-driven late day shower/tsra is possible across
Southern PA, where modest capes are noted in the model guidance.
GEFS 2m temp anomalies are close to 10 degrees above normal
Sunday afternoon, translating to highs ranging from the upper
70s in the Endless Mountains to the mid 80s through the
Susquehanna Valley.
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&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
The chance for rain will increase into Sunday night as a warm
front crosses through the region. According to the latest NBM
guidance, the wettest period looks to be from Sun night
through the first half of Mon night. Ensemble median rainfall
during this time period is 0.75-1.25 inches for much of the
area. The rain will likely come in batches, with the first batch
Sunday night, potentially a lull early Monday, and then heavy
showers and thunderstorms Monday afternoon, putting outdoor
Memorial Day activities at risk.

A longwave trough will then set up over the eastern US and
persist through much of the upcoming week, with several
shortwave troughs rotating through the base of the trough. With
850 mb temps only in the single digits, our highs on Tue-Thu
will be noticeably cooler, topping out in the 60s to low 70s.
Given the low level instability beneath the cold pool aloft, we
have moderate confidence in scattered diurnal showers and
isolated thundershowers Tue-Wed, with the highest PoPs in NW
zones (closer to the upper low). Models diverge in timing the
departure of the trough late in the week. PoPs are lower on Thu
as some ensemble members have high pressure building in.

&&

.AVIATION /00Z FRIDAY THROUGH TUESDAY/...
Dry air at midlevels has translated to a dry afternoon across
central PA airspace. Expect VFR conds into the evening and
overnight. A few isolated showers may pop up across the southern
airspace, near the MD border during the evening hours, where a
cold front slows its southward advance and taps into some deeper
moisture.

Guidance continues to show the chance of low vsbys and cigs
late tonight into Friday morning, with recent GLAMP guidance
and RAP guidance suggesting JST may experience an extended
period of IFR/LIFR conditions. Given some uncertainty with
regards to extent, have kept IFR restrictions limited to JST
from 10z-14z, with MVFR conds at AOO and UNV.

Generally VFR conds will prevail on Friday.

Outlook...

Sat-Sun...Mainly VFR, but chance of showers (mainly Sat)

Sun PM - Mon PM...Restrictions possible with periods of
SHRA/TSRA

Tue...Scattered SHRA poss

&&

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

&&

$$

SYNOPSIS...Lambert/DeVoir
NEAR TERM...Fitzgerald
SHORT TERM...DeVoir/Fitzgerald
LONG TERM...Lambert/Colbert
AVIATION...Gartner/Colbert