587
FXUS61 KCTP 241027
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
627 AM EDT Fri May 24 2024

.SYNOPSIS...
Upper level ridging will build into Pennsylvania through early
Saturday. A shortwave passing north of the region will push a
weak cold front through the state late Saturday. Low pressure
will then track west of Pennsylvania Sunday night into Memorial
Day, with the trailing cold front coming through Monday evening.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
45-50F dewpoints are already over NWrn PA, and the upper level
ridge moving in from the west should help direct even more dry
air into the CWA. The slow-moving frontal boundary remains close
to JST-MDT line seen in the dewpoints still near/above 60F there
and south and slight srly component to the wind over the
Laurels. The convergence there should help with continuance of
isold/sct SHRA in the Laurels and S-Cent mtns this morning. As
the ridge build in, the frontal boundary should finally slip S
of the border later this AM/early aftn.

Early morning valley fog across the north and patchy fog
elsewhere will burn away, leaving just high clouds N of rte 30,
and the cu across the S near the front should go away with the
front. The sunshine and deep mixing should dip dewpoints into
the m40s N of I-80, and 50-55 down to the Turnpike. Maxes will
be very similar to Thurs, perhaps just 1F lower.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH SUNDAY/...
Surface ridging over the state should ensure fair weather
tonight and the first half of Saturday. Mins tonight should be
in the 50s (coolest N) except perhaps the Lower Susq where
they`ll be right around 60F.

Later Saturday, a shortwave knocks the minor ridge aloft down to
a more-zonal flow. Expect a brief lowering of the stability for
the late aftn into early Sat night mainly NW of AOO-UNV-IPT.
Thus, the SHRA/TSRA should break up as they try to drop SE thru
the area. Unimpressive PWAT and the progressive nature of this
feature indicate rainfall amounts will be generally light. QPF
may reach 05-1.00" across the far NW where storms are most
likely. Mins will be 55-65F (NW-SE) and some fog is expected in
the NW where it may clear out overnight.

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, mainly across
the higher terrain of 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.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
All medium range guidance tracks a surface low west of PA
through the Grt Lks Sunday night into Monday, with the trailing
cold front likely coming through Monday night. Falling heights
and surging pwats along the attendant low level jet should
result in numerous showers/tsra beginning Sunday night and
lasting into Memorial Day. Ensemble median rainfall during this
time period is 0.75-1.00 inch for much of the area. Current
guidance indicates the best chance of severe weather will be
west of the Appalachians Mon PM, with less cape east and an
east-southeast flow to the east of the mountains.

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.
Expect a downward turn in temperatures with 850 mb temps in the
single digits only supporting highs in the 60s to low 70s by
Wed-Thu. 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. However, a trend
toward drier/warmer conditions looks likely.

&&

.AVIATION /12Z FRIDAY THROUGH TUESDAY/...
Widespread VFR conds outside of JST/LNS where some lower vsbys
have been observed this morning. Isolated SHRA across western PA
will continue to track towards JST/AOO; however, given
relatively dry air aloft expect SHRA to come down as they
approach the terminals. All airfields across central PA are
expected to prevail VFR in the 12Z-14Z Friday timeframe with
widespread VFR conds expected to continue through 06Z Saturday
with high (> 80%) confidence with SKC and light winds for a
majority of the period.

After 06Z Saturday, models begin to outline some deterioration
at IPT/LNS with lowered vsbys. Clear skies will promote some fog
formation with model soundings outlining low-level moisture
across the area. A light breeze keeps fog concerns less at IPT
while calm winds at LNS brings about higher probs of IFR and
below cigs at LNS. Given uncertainty on how quickly calm winds
resolve, have trended LNS`s vsbys down in the 12Z TAF package
but have not pushed them down to IFR thresholds at this time.

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 possible.

&&

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

&&

$$

SYNOPSIS...Dangelo
NEAR TERM...Dangelo
SHORT TERM...Fitzgerald/Dangelo
LONG TERM...Fitzgerald
AVIATION...NPB