617
FXUS61 KCTP 171135
AFDCTP

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

.SYNOPSIS...
An area of low pressure centered near Charlotte, NC this
morning will drift slowly north into Virginia during the
middle of the week, before tracking east and off the coast
by Thursday. An upper level ridge over the Great Lakes is
likely to build into Pennsylvania by next weekend.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
A well-aligned ESE flow in the 925-850 mb layer has pushed the
leading, NW edge of a lower stratocu deck to around a KAOO to
KUNV and KSEG line as of 08Z, while variable amounts of mainly
high clouds were noted across the Laurel Highlands and Northern
Mtns of PA. Based on the 00Z HREF, there should be about another
30 NM of NW drift to these lower clouds before vertical mixing
entrains dry air from aloft and helps to erode the cloud deck
back toward the SE beginning about 14-15Z today.

A fair amount of mid and high clouds will blanket the region
for the midday and afternoon hours today, thanks to the deep,
serly flow on the Northeast side of the PTC-8 remnants. POPS
through the early afternoon hours today will be near zero in all
areas, though a few, non-measurable sprinkles are possible in
the south.

The persistent/deep SE to ESE flow will continue to transport
moisture off the Western Atlantic and

Some limited valley fog will be possible through 13Z today
in north central PA.

Temps to start the day will be about 5 deg warmer than yesterday
morning across the bulk of the CWA, whereas 24 hr temp change
in the northern tier is expected to be closer to 0.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH THURSDAY/...
Operational and EFS models runs continue to keep it drier than
earlier expectations for Tues night-Wed period as the weakening
sfc and upper low across North Carolina and VA drifts very
slowly NE and off the Delmarva coast by the end of this period.

Dry air holds tough in place in low and mid levels across much
of the Commonwealth. Drought begets drought. Per collaboration
with WFOs PHI and BGM, POPS were trimmed 10-15 percent across
Scent PA and portions of the Lower Susq region for Wed/Wed
evening.

The bulk of latest guidance continues to indicate that the
associated easterly low level jet and plume of Atlantic moisture
associated with 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 Today. Any rainfall that reaches Southern PA
Tuesday should be very light (0.10 of an inch or less).

Thickening cloud cover and an upsloping east-southeasterly
flow should hold temperatures down today across the Laurel
Highlands, where readings likely won`t climb get out of the
60s. Elsewhere, model RH profiles support filtered sunshine
through a veil of altocu and cirrus, with the brightest skies
near the NY border. Max temps across the remainder of the Susq
Valley, Central and Northern Mtns will be in the mid 70s to low
80s which is 5-10 deg F above normal for Mid September.

The best chance of showers or a few short periods of steadier
light rain across Central PA appears to come late tonight and
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 Monday 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 /12Z TUESDAY THROUGH SATURDAY/...
Restrictions based on low ceilings at all airfields outside of
BFD this morning are expected to continue through 16Z Tuesday
with moderate-to- high (60-70%) confidence. Low-level clouds
will have the potential to scatter out in this timeframe,
bouncing between IFR/MVFR thresholds with MVFR prevailing
throughout much of the 12-16Z timeframe. After 16Z, expect all
airfields to resolve towards VFR but cannot rule out a SCT deck
hovering near-MVFR conditions through 18Z(W)-20Z(E) with
slightly higher probabilities across the southern tier.

After 18Z, outside of the aforementioned scattered low-level
clouds, VFR conditions are expected with moderate-to- high
confidence (50-70%). Thickening clouds are expected to begin
pushing their way into the southern airfields around the 06Z
Wednesday timeframe with rainfall beginning to make way into the
southern airfields (JST/AOO/MDT/LNS) after 08Z. There is
slightly less confidence earlier in the rainfall period, so have
hedged with PROB30s and indicated -SHRA later in the TAF period
with MVFR conditions expected with lower ceilings. Outside out
southern PA, there will also be some potential for valley fog
formation at BFD/IPT with GLAMP guidance going fairly heavy on
lower ceilings. At this time, confidence remains too low (~30%)
with uncertainty on cloud cover so have kept lower (MVFR)
visibilities at both airfields with VCFG as increased cloud
cover could limit this potential.

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...Lambert/Dangelo
NEAR TERM...Lambert/Dangelo
SHORT TERM...Lambert/Dangelo
LONG TERM...Lambert/Dangelo/Bauco
AVIATION...NPB
CLIMATE...NPB