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942
FXUS61 KCTP 300825
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
425 AM EDT Thu May 30 2024

.SYNOPSIS...
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An upper level trough will swing over the region today, then
Canadian High Pressure will build southeast into Pennsylvania
Friday and Saturday. The high will pass off the East Coast by
late this weekend into early next week, then a cold front will
likely traverse the state next Thursday.
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&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Regional radar at 08Z shows the back edge of the rain exiting
the eastern edge of the forecast area associated with a potent
mid level shortwave lifting into Southern New England. A few
showers are also noted over the Laurel Highlands. However, a
drier northwest flow should cause any lingering showers in that
part of the state to depart by dawn.

Satellite imagery at 08Z shows extensive valley fog over
Northern PA, where skies have cleared. A decent pressure
gradient west of the low over Southern New England should keep
fog at bay over the eastern part of the forecast area this
morning, despite clearing skies and wet ground. However, current
dewpoint depressions indicate valley fog should become
widespread in the Ridge/Valley Region of Central PA by dawn.
Over the Laurel Highlands, a light upsloping northwest flow
should maintain low clouds and ridgetop fog through dawn.
Temperatures appear on track to bottom out from the low 40s
over the NW Mtns, to the low and mid 50s in the Lower Susq
Valley.

Any low clouds/fog should mix out to mainly sunny skies later
this morning, as a northwest flow advects drier air into the
area. Diurnal heating, combined with cool temps aloft and large
scale forcing ahead of an upstream trough, should support some
cumulus development and perhaps an isolated afternoon shower,
despite the arrival of drier air. The highest POPs of around
15 pct are painted across south-central PA where models
indicate slightly better low level moisture.

Mixing down 800mb temps of 1-2C supports max temps ranging from
the low 60s over the N Mtns, to the low 70s across the Lower
Susq Valley. Forecast soundings showing dry air above a weak
inversion supports undercutting NBM dewpoints this afternoon by
a few degrees.
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&&

.SHORT TERM /6 PM THIS EVENING THROUGH SATURDAY/...
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Nearly ideal conditions for radiational cooling are setting up
tonight across the western half of PA, as the upper trough lifts
out and Canadian High Pressure builds in, accompanied by clear
skies, dry air and a calm wind. Therefore, we have leaned
toward the cooler MAV temps tonight in place of NBM guidance,
with expected lows ranging from the mid 30s in the colder
valleys of the NW Mtns, where patchy frost is likely, to the
upper 40s over the Lower Susq Valley. A large water/air temp
difference of >25 degrees also favors patchy late night fog in
the deep river/stream valleys of the NW Mtns.

Large scale subsidence and low-pwat air points to abundant
sunshine Friday, as high pressure pushes into the state. Mixing
down 850mb temps of around 8C translates to highs from the upper
60s to mid 70s. Friday night should be another cool one, as the
surface high builds directly over PA, resulting in clear skies,
a calm wind and min temps below NBM guidance. The airmass in
general should be moderating, so expect readings not quite as
cool as tonight.

Upper level ridging is progged over PA by Saturday, as the
surface high slips off of the East Coast, resulting in a mostly
sunny and warmer start to the weekend. GEFS 2m temp anomalies
Sat afternoon are few degrees above climo, translating to highs
of 75-80 over most of Central PA.
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&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
Late evening update changes/deviations from National Blend are
rather small/minor. Main change was to lower PoPs 10-20pct on
Tuesday with chc range (30-50) as the top-end (west) and slight
chc in the east. It looks active after for the rest of the
week.

Prev...
Models diverge with the amplitude of a shortwave trough moving
through the region late Saturday night into Sunday. This feature
will bring the next chance of showers and thunderstorms to
central PA.

Longer range guidance shows multiple shortwaves moving through
the region into the middle of next week bringing renewed chances
for showers and storms, but confidence in the timing of these
features is low.

&&

.AVIATION /08Z THURSDAY THROUGH MONDAY/...
Looking at a wide range of conditions into mid morning.
Expect a mix of low clouds, mid clouds, and some fog early
on today. A bit of a breeze, dewpoints coming down this
morning, all should limit the potential for fog.

An upper level low will slowly pull away, bring an end to
the showers across the east early this morning.

Dewpoints this afternoon will be about as low as one gets
in late May, early June. Thus looking at mainly clear skies
later today, with very little potential for fog overnight
into Friday morning.

Outlook...

Fri-Sat...Mainly clear skies with VFR conditions.

Sun-Mon...Showers and thunderstorms possible.

&&

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

&&

$$

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