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493
FXUS61 KCTP 221536
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
1136 AM EDT Wed May 22 2024

.SYNOPSIS...
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*Summerlike warmth+humidity to fuel risk of severe t-storms this
 afternoon and evening; damaging winds and hail are the primary
 threats
*Showers & t-storms continue Thursday especially over south
 central PA; strong storm possible in the Lower Susq Valley
*Rain chances trend lower into Friday before increasing over
 Memorial Day weekend
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&&

.NEAR TERM /THROUGH TONIGHT/...
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Abundant sunshine this morning has helped temps rise into the
80s in most locations by midday. The biggest difference today
from yesterday is higher dewpoints. An increasing southwest
flow ahead of an upstream cold front has advected noticeably
more humid air into the area with dewpoints in the low to mid
60s. Today will be a classic summer-like day with max
temperatures in the 80-90F range or +10-15 degrees above late
May climo/approaching daily record highs in some locations (see
climate section).

Only subtle changes to the severe weather forecast this
afternoon. The SLGT risk area (level 2 out of 5) is still in
place for locations northwest of I-81. Current radar shows a
complex of storms in northeast Ohio that will continue to drift
into northwest PA over the next couple of hours. Behind that
batch of a showers, a mesoscale convective vortex could provide
focus for organization and enhanced rotation as it moves through
our northwest zones. The 2-4% tornado probability to the south
of Lake Erie effectively highlights where the "best" deep-
layer shear will exist.

Convection initiation is expected along the ridges of central PA
between 16 and 18Z with subsquent evolution into a relatively
messy storm mode. Multi-cell clusters are most likely but a few
discrete cells are possible. Storms will progress eastward
through the evening within a corridor of moderate instability
near a leading prefrontal trough. 0-6km shear decreases with
eastern extent across the CWA which remains somewhat of a
limiting factor concerning the overall severe potential.
However, mean MLCAPE in the 1000-1500 J/kg range along with
steep lapse rates will support isolated damaging wind and hail
threats. Limited wind shear should prevent a realization of
higher-end and/or sustained severe weather, but pulse storms
could produce isolated large hail and/or damaging winds. Fresh
green-up means tree canopies are healthy/strong and downed trees
will be possible even with sub-severe (<50kt) winds.

T-storm intensity and coverage should diminish into tonight as
the best forcing/height falls lift to the north and low level
stability increases with the loss of daytime heating. Will
maintain lower POPs into Thursday morning associated with the
arrival of a weakening cold front and a few rumbles of thunder
are possible as elevated convection persists. Patchy fog may
develop again toward daybreak in areas that receive rainfall,
particularly if cloud breaks help promote more efficient
radiational cooling. Lows in the 60s are rather mild for this
time of year or +15-20 degrees above the historical climate
average.
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&&

.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
More showers and t-storms are likely Thursday, primarily during
the afternoon, as the cold front stalls out near the Mason
Dixon Line and a shortwave rolls eastward from the Ohio Valley.
The focus for convection Thursday will be over the southern part
of the state. However, model RH profiles support a good deal of
high level cloudiness extending into Northern PA, which should
hold temps down. Expected high temps range from the mid 70s to
low 80s, but remain above climo for this time of year.

Rain chances trend lower from north to south into Friday as
upper level ridging builds over the area. Max POPs 30-40% are
over the southern tier of CPA near stalled/pivoting q-stnry
front and axis of highest pwats. The front lifts back to the
north as a warm front Friday night with showers likely by
Saturday morning over the western Alleghenies.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
A round of convection is forecast into Saturday afternoon.
Current model guidance supports a period of dry weather late
Saturday into Sunday associated with a weak surface high
building across the Lower Grt Lks into PA.

A deepening upstream trough will then likely result in a period
of wet weather Sunday night into Monday, as the associated
surface low tracks just west of PA. Medium range guidance
currently indicates the severe weather risk is low due to the
warm front hanging up west of the Appalachians. However,
ensemble plumes support a decent rainfall in the 0.5 to 0.75
inch range between Sunday night and Monday night. The deepening
upper level trough is progged to push into the region Tuesday,
marking a transition to cool weather with scattered, diurnally-
driven convection possible.

&&

.AVIATION /16Z WEDNESDAY THROUGH SUNDAY/...
Mainly clear skies will begin the day across central PA today.
Very little fog developed overnight, and temperatures are
beginning to heat up in the morning sunlight.

Height falls ahead of an approaching cold front bringing
convection to the region today with strong storms possible. The
best timing of showers and storms will be after 18Z today.
These showers could last through the late evening and into the
early morning hours on Thursday as the cold front finally passes
through and then stalls out south of PA. A few of these storms
could be locally severe with wind gusts being the main threat.

Conditions may dry out for Thursday afternoon, but the nearby
frontal system may keep some showers nearby into the holiday
weekend.

Outlook...

Thu...Chance of t-storms.

Fri-Mon...Mainly VFR, but chance of showers/AM patchy fog.

&&

.CLIMATE...
Daily record maximum temperatures for 5/22:

Harrisburg96/1941
Williamsport95/1941
Altoona88/2013
Bradford84/2013
State College89/1975

&&

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

&&

$$

SYNOPSIS...Steinbugl
NEAR TERM...Steinbugl/Banghoff
SHORT TERM...Fitzgerald/Steinbugl
LONG TERM...Fitzgerald
AVIATION...Bowen
CLIMATE...Steinbugl