221
FXUS61 KCTP 170613
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
213 AM EDT Tue Sep 17 2024

.SYNOPSIS...
An area of low pressure off of the South Carolina coast will
lift north into Virginia by the middle of the week, before
tracking east and off the coast by late week. An upper level
ridge over the Great Lakes is likely to build into Pennsylvania
by next weekend.

&&

.NEAR TERM /UNTIL 8 AM THIS MORNING/...
Added just a mention of a sprinkle or two over the Laurels later
tonight/Wed AM as weak lift is progged as moisture increases.
There are a few radar returns in ern WV, central VA at 02Z. But,
the closest observation with precip is KLYH in srn VA.
Otherwise, the current forecast is good with just some minor
tweaks to T/Td.

Prev...
High clouds moving overhead are more opaque than transparent.
Sky cover grids have been tweaked to increase them a bit more.
Otherwise, SEG is diving to the botoom of the temp list without
any wind. However, Td is still in the 50s and not expected to
decrease much or at all overnight, so min temps look OK at this
point.

Valley fog will be possible again tonight in north central PA.
Farther south, increased moisture and thicker cirrus aloft will
inhibit radiative cooling enough to make fog less likely. For
much of the Lower Susq valley, temps tonight are progged to be
about 5 deg warmer than last, whereas 24 hr temp change in the
northern tier is expected to be closer to 0.

&&

.SHORT TERM /8 AM THIS MORNING THROUGH THURSDAY/...
Latest runs of many models continue to keep it drier than
earlier expectations for Tues-Wed. Dry air in place in low and
mid levels. Drought begets drought. Have bumped PoPs down
during the short term period using NBM (which also has the
falling PoPs) as a basis. WPC MRGL EROs are now kept to our S,
which seems very likely.

Prev...
Whether or not Potential Tropical Cyclone Eight organizes into
a named system, the disturbance will track northwest to near
Charlotte NC by late Tuesday. The bulk of latest guidance
indicates the associated easterly low level jet and plume of
Atlantic moisture linked to this system will weaken quickly as
the disturbance moves north. However, it will come close enough
to support a slight chance of showers over the southern tier
counties late Tuesday. Any rainfall that reaches Southern PA
Tuesday should be very light.

Thickening cloud cover and an upsloping easterly flow should
hold temperatures down Tuesday across the Laurel Highlands,
where readings will likely not get out of the 60s. Elsewhere,
model RH profiles support filtered sunshine through a veil of
cirrus, with the brightest skies near the NY border.

The best chance of showers across Central PA appears to come
Wednesday, as the remnant low makes its closest pass to PA
before shifting off of the East Coast late in the week. The
bulk of recent guidance keeps the easterly low level jet and
associated highest pwats just south of the Mason Dixon Line.

The combination of increased moisture and large scale forcing
ahead of the upper low currently targets areas just south of PA
for locally heavy rain. Most likely rainfall by late Wed based
on ensemble output ranges from <0.1 inch over Northern PA to
around 0.5 inches over the southern tier. Recent dryness
suggests the threat of flooding is low, even if a northward
shift in the models brings the heavier rain into Southern PA.

A 20-30 pct chance for rain continues into Thu, as various small
low pressure centers attempt to take shape off the Mid Atl
coast.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
1030 PM Update holds minor changes for the late week and
weekend. Only small/20 PoPs for the most part, and mainly for
the SE.

Prev...
An upper level low over the region will keep clouds and showers
around through most of the extended period. The best timing for
showers remains unclear as this will be dependent upon the
timing of multiple surface lows that will track near Central PA.
Uncertainty begins to increase towards the weekend as there is
quite a bit of spread in the guidance with respect to a building
ridge to our west and how quick it pushes eastward. Ensembles
suggest that the upper low will be slower to be replaced by
ridging than had been shown over the past few days which will
keep the chance for a few showers around through the weekend.
Temperatures will generally be on a slight downward trend
through the period with highs in the upper 60s and low 70s by
Sunday and Monday.

&&

.AVIATION /06Z TUESDAY THROUGH SATURDAY/...
Lower ceilings across southern PA are being observed with
MDT/LNS already down towards high-end MVFR restrictions as of
06Z Tuesday. Expect restrictions to continue at MDT/LNS through
~14Z with high (70-80%) confidence before lower-level clouds
begin mixing out. Model guidance shows modest agreement with
regards to lower clouds making their way into AOO/JST near 08Z
with lower-level clouds continuing to bring MVFR restrictions
through 18Z Tuesday. GLAMP guidance has been persistent with
regards to IFR thresholds being met at JST, and given higher
probabilities of IFR conditions in the 10-12Z timeframe have
continued to outline these conditions with moderate (~60%)
confidence in this timeframe. Uncertainty remains with
northward progression of the lower-level cloud deck brining MVFR
conditions to UNV/IPT so have outlined SCT lower-level clouds
with a brief period of MVFR conditions at UNV near sunrise.

In the 18Z Tuesday timeframe through the end of the TAF period,
VFR conditions are expected with moderate-to-high confidence
(50-70%). Some lower-level clouds could begin pushing their way
into the southern airfields (JST/AOO/MDT/LNS); however, the best
chances for restrictions come after 06Z Wednesday so have opted
to keep mentions of scattered low-level clouds at this time.

Outlook...

Wed...SHRA w/ Isolated PM TSRA, highest chances across SE PA.

Thu-Fri...Lingering showers possible, mainly across the east
and south.

Sat...Mainly dry conditions.

&&

.CLIMATE...
The first day of Autumn 2024 (Fall Equinox) begins at 8:44 am
EDT on September 22nd.

&&

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

&&

$$

SYNOPSIS...Fitzgerald/Dangelo
NEAR TERM...Dangelo
SHORT TERM...Fitzgerald/Dangelo/Colbert
LONG TERM...Dangelo/Bauco
AVIATION...NPB
CLIMATE...NPB