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268
FXUS61 KCTP 200930
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
530 AM EDT Fri Sep 20 2024

.SYNOPSIS...
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*Clear skies for much of today, but locally dense fog in the
 deeper valleys of Central and Northern PA through 9 am.

*Increasing chances for a few rounds of showers and maybe even a
 thunderstorm saturday afternoon or evening; Fall begins on
 Sunday

*Daytime temperatures peak +5-15 degrees above average into
 Saturday before trending seasonably cooler next week
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&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
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High pressure ridge extending from the St. Lawrence and
Champlain Valleys south into Central PA will bring abundant
sunshine today, light and variable wind and unseasonably warm
temperatures ranging from the upper 70s across the higher
terrain of the north and west, to the low and mid 80s throughout
the valleys of Central and Southern PA.

Air/water delta Ts; with air temps in the low to mid 50s across
northern PA and stream/reservoir temps in the upper 60s, will
yield locally dense fog through about 9 AM this morning.
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&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SATURDAY/...
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A developing but still relatively light southeast to southerly
breeze at the surface tonight and Saturday will bring and
increase in high based strato cu or more likely altocu early
Saturday as a weak warm front forms over/drifts into SW PA.

The approach of the left exit region of a relatively strong
upper level jet on Saturday will combine with moderately high
sfc dewpoints in the low to mid 60s (with corresponding PWAT of
around 1-1.25 inches) to spark an area of showers/scattered
embedded TSRA that could bring localized damaging straight-line
wind gusts and hail, mainly in the late afternoon/early evening
hours across much of Central PA and the Susq Valleys per
clustering/mean of high res models.

After a mainly clear and moderately cool night, the timing of
cloud cover in the morning hours Saturday will play a
significant role in the max temps and amount of CAPE to fuel the
convection in the afternoon and evening. Early cloud cover
(especially if the clouds move in right around sunrise after max
radiation cooling) will greatly flatten the temp curve and
subsequent intensity of convection that develops.

There is some uncertainty if the surface warm front and greater
instability pushes east of the Alleghenies, so the greatest
severe threat currently appears to be over the Laurel Highlands.

SPC has slightly expanded the MRGL Risk area for SVR TSRA to
cover nearly the Western half of PA (or about the western 1/3
of our CWA). This looks reasonable based on the timing of best
UVVEL/deep layer shear associated with the aforementioned upper
level jet and closer proximity to the SFC frontal boundaries.

Mean rainfall from the convection will likely be in the 1-3
tenths of an inch range with a few spots possibly receiving a
quick 0.5 inch of rain from a heavier TSRA.
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&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
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The global guidance indicates the shortwave and weak surface low
pass east of the region Sat night, then a cold air damming
scenario begins to develop between a stalled warm front along
the OH/PA border and high pressure over the Canadian Maritimes.
Forecast soundings indicate an upsloping southeast flow will
result in persistent stratus and perhaps a bit of drizzle over
the Central Mtns, with partly sunny skies possible over Eastern
PA. The cloud cover and flow off of the Atlantic should result
in markedly cooler afternoon temps Sunday than on Saturday, with
highs likely stuck in the 60s over the Central Mtns.

A trend toward cooler and cloudier weather appears likely into
the middle of next week associated with a cold air damming
scenario ahead of a slow moving warm front in the Ohio Valley
and high pressure over the Canadian Maritimes.

As for rainfall, a weak shortwave and associated plume of
enhanced pwats overrunning the warm front could produce
scattered showers Sunday night into early next week. Upsloping
flow could also yield patchy drizzle over the Central Mtns early
next week. The best chance for rainfall will come during the
middle of the week as an upstream trough approaches the region.
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&&

.AVIATION /09Z FRIDAY THROUGH TUESDAY/...
No major changes for the 06Z package. As noted last night,
less wind and less clouds overnight than last night, would
expect some fog and low clouds.

Earlier discussion below.

A few scattered high clouds are lingering across the airspace
this evening, but most sites will see mainly clear skies tonight
into tomorrow morning. Current model soundings suggest that fog
will form once again overnight across the northern half of
Central Pennsylvania, with BFD, IPT, and UNV being most likely
to see IFR or lower visibilities. The HREF and GLAMP suggest
that fog could be possible (~30% chance) at sites further to the
south as well, but confidence is low. The fog will dissipate by
14Z and give way to VFR conditions for Friday. Most of Friday
will feature calm winds and clear skies before clouds begin
building into Friday night ahead of a frontal system expected to
approach on Saturday.

Outlook...

Sat-Sun...Valley fog in the morning; scattered -SHRA/TSRA.

Mon-Wed...Scattered showers.

&&

.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/Steinbugl
NEAR TERM...Lambert/Fitzgerald
SHORT TERM...Lambert/Fitzgerald/Steinbugl
LONG TERM...Fitzgerald/Bauco
AVIATION...Martin/Bauco/Bowen
CLIMATE...Steinbugl/NPB