304
FXUS61 KCTP 171837
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
237 PM 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/...
14z Update....
Low clouds cover more than 3/4 of central PA as of mid morning,
with variable high clouds across the far north and NW
Mountains. Deep ESE flow will maintain the deck across the south
and east while entrainment from the NW should help erode some of
the lower cigs back toward the southeast during the late morning
and afternoon hours. Still, it will remain mostly cloudy
throughout given variable mid and high clouds above it all.

Previous Discussion...
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 FRIDAY/...
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 /FRIDAY NIGHT THROUGH TUESDAY/...
Higher confidence in dry wx/no rainfall particularly early in
the period (through the upcoming weekend) thanks to deep layer
ridge pattern at the sfc and aloft. While model variability
remains elevated into next week, the ensemble means generally
favor weak upper troughing centered around the Great Lakes which
will support a marginal increase in rainfall/shower potential
along/ahead of an approaching front by next Monday or Tuesday.
Forecast max temps 75-80F peak +5-10F above mid/late September
climo to start the weekend and trend modestly cooler to 65-75F
(near the historical average) into early next week.

&&

.AVIATION /18Z TUESDAY THROUGH SUNDAY/...
MVFR to low VFR ceilings will hold steady into this evening and
trend lower tonight across the southern portion of the airspace.
We have above average confidence >70% in MVFR to IFR conditions
developing late tonight into Wednesday morning over this area.

Mainly clear skies in the far northern tier may allow for fog
formation overnight with reduced confidence <=50% in local
visibility restrictions.

The highest probability of rain will be over the southern
terminals on Wednesday and have mentioned VCSH with this TAF
cycle at KJST/KAOO/KMDT/KLNS.

Outlook...

Thu...MVFR cigs possible in the southern and eastern portions of
the airspace.

Fri-Sun...Valley fog in the morning; otherwise VFR/no sig wx.

&&

.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/DeVoir/Dangelo
NEAR TERM...Lambert/DeVoir/Dangelo
SHORT TERM...Lambert/Dangelo
LONG TERM...Steinbugl
AVIATION...Steinbugl
CLIMATE...NPB