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128
FXUS61 KCTP 240754
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
354 AM EDT Tue Sep 24 2024

.SYNOPSIS...
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An amplifying upper level trough and slow moving frontal
system will bring showery conditions to Central Pennsylvania
through at least Wednesday, along with a few rumbles of thunder.
As such, it will be cloudy and cool through midweek. The latter
part of the week looks milder with at least partial sunshine
expected into the weekend.
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&&

.NEAR TERM /UNTIL 10 AM THIS MORNING/...
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A moist llvl southeasterly flow will continue to sock in
widespread stratus and ridge-shrouding fog overnight through the
mid morning hours Tuesday across the bulk of the CWA east of
the Alleghenies. A Dense Fog Advisory continues for Schuylkill
Cty through 12Z Tues, focused on the I-81 corridor that runs
along the highest terrain of the county and experiences the
greatest, orthogonal upslope component to the wind in this
setup. Have trimmed back the mention of patchy fog only for
areas >= 1500 ft AGL as visibility restrictions will largely be
due to clouds and not so much for valley fog.

Scattered showers and areas of drizzle will continue through
mid morning, amounting to less than 0.10 of an inch as a deep
layer of mid level dry air spreads east over the aforementioned
moist low- level environment. Temps still on track to bottom out between
55 and 60F by daybreak.
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&&

.SHORT TERM /10 AM THIS MORNING THROUGH 6 PM WEDNESDAY/...
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Today and tonight night will feature several weakly coupled jet
segments lifting NE across the CWA, accompanied by an anomalous
southerly LLJ of around +2 sigma.

Good surge of moisture (PWAT of 1.4-1.7 inches) and forcing
comes across the CWA in the afternoon and evening. Some
instability will be present in the west, so mentioned isolated T
there. A MRGL risk of severe weather exists in extreme SW PA,
but only a general thunderstorm area for everywhere along and
west of US-15 in our forecast area. WPC has painted a MRGL risk
of excessive rainfall for portions of Somerset and Cambria up
through Warren County, though antecedent dry conditions should
limit the risk for flooding and rain will be mostly beneficial.

Highs today will remain several degrees below average thanks to
persistent cloud cover in southeast flow. Highs in the 60s (and
perhaps upper 50s in north central PA) will combine with gusty
southeast winds and occasional showers to make it a raw day.

Model guidance outlines another surface low-pressure system
tracking northeastward across the Great Lakes and into southern
Ontario on Wednesday, with slightly more moisture and lift
available as the warm front aligns itself north-to- south across
west-central PA. Given slightly better lift with this low-
pressure system overhead coupled with enhanced moisture, have
retained likely PoPs on Wednesday with highest chances during
the late morning to early afternoon hours. Heavy rainfall
threats look less robust compared to previous forecast cycles;
however, some instability will allow for thunderstorms across
the Laurels, brining some potential for locally heavy rainfall,
with maximum totals ~0.50" on Wed. Storm total rainfall (Tuesday
+ Wednesday) will generally remain below 1 inch, with 0.25" to
0.75" as the most likely range. This rainfall, spread out over
48+ hours, will be helpful for ongoing drought conditions across
southwest PA.
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&&

.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
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Lingering showers across mainly E PA will continue into
Thursday before a brief reprieve in rainfall Thursday evening
and into Friday morning. Rainfall chances begin to increase as
Friday morning progresses with the potential remnants of PTC9
approaching the area.

There is still some uncertainty in regards to how PTC9 will
impact central Pennsylvania, mainly dependent on interactions
with a trough stationed across the eastern Tennessee Valley. At
this time, deterministic and EFS model guidance shows modest
agreement in the bulk of rainfall keeping south/west of the
area while a rather narrow, neg tilt upper ridge holds strong
from the Great Lakes through the Upper Ohio River Valley and
Carolina Coast. Given the still existing uncertainty, did
not deviate much from continuity and NBM guidance once again
this model cycle.

If precipitation manages to make way into central Pennsylvania
in the Friday- Sunday timeframe, highest chances (25-35%) will
be across S/W PA along the Laurels with a SChc (15-25%) progged
west of the Susquehanna Valley. It looks like enough low-mid
level ridging will maintain a deep layer of dry air across the
NE 1/3 to 1/2 of PA to keep precip chcs minimal there through
the weekend.

Upper low and remnants of the tropical system will likely drift
east across the Commonwealth early next week with a fairly good
chc for showers.
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&&

.AVIATION /08Z TUESDAY THROUGH SATURDAY/...
For the late evening update and the 06Z TAF package, I added
a bit more detail.

Overall looking at low CIGS today into tonight, given a
southeast flow of cool, moist air. CIGS may be a bit higher
at MDT and LNS at times, but expect a lot of variation.

Any improvement with CIGS today, will be short lived, as
day light is shorter now, thus expect CIGS to come back down
toward sunset.

Visibilities not bad as of Midnight. The visibility may drop
some when showers become more widespread today, but dewpoints
not fcst to come up much, so time of day may offset the effects
rain become more widespread.

Outlook...

Wed...Low cigs/showers likely. Improving conditions possible
W Mtns Wed PM.

Thu...AM low cigs/showers likely.

Fri...No sig wx expected.

Sat...Chance of low cigs/rain Laurel Highlands.

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
Dense Fog Advisory until 8 AM EDT this morning for PAZ058.

&&

$$

SYNOPSIS...Lambert/Dangelo
NEAR TERM...Lambert/Banghoff
SHORT TERM...Lambert/Dangelo/Banghoff
LONG TERM...Lambert/NPB
AVIATION...Fitzgerald/Martin