-- Discussion containing changed information from previous version are highlighted. --
558
FXUS61 KCTP 221720
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
120 PM EDT Wed May 22 2024

.SYNOPSIS...
*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

&&

.NEAR TERM /THROUGH TONIGHT/...
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 subsequent 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.

&&

.SHORT TERM /THURSDAY THROUGH SATURDAY/...
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 25-35% are
over the southern tier of central PA near a stalled/pivoting
quasistationary front and axis of highest PWATs. Friday looks
like a pleasant day across most of the region with temperatures
in the upper 70s to mid 80s and a good amount of sunshine.

The front lifts back to the north as a warm front Friday night
with showers likely by Saturday morning over the western
Alleghenies. More widespread showers and storms will develop
Saturday afternoon with daytime heating and some enhancement
with a prefrontal trough. Saturday will not be a washout by any
means, but those with outdoor plans should monitor the weather
and head inside if you hear thunder.

&&

.LONG TERM /SATURDAY NIGHT THROUGH TUESDAY/...
Compared to Saturday, the chance for showers and thunderstorms
on Sunday will be lower, owing to a weak surface high building
across the Lower Grt Lks into PA. However, with a warm front
approaching, we do carry slight chance to chance PoPs Sun
afternoon, with PoPs increasing to likely Sunday night as the
warm front crosses through the region.

A deepening upper trough will then likely result in a period of
unsettled weather continuing into Memorial Day and the first
half of the upcoming week with mainly scattered, diurnally-
driven convection expected.

&&

.AVIATION /17Z WEDNESDAY THROUGH SUNDAY/...
-- Changed Discussion --
Put timing into the 18Z TAF package for the main area of storms
to the west. Added some TEMPO groups for isolated showers and
storms near sites like AOO and UNV. The isolated activity
formed, given the intense heating across the higher terrain.

Further southeast the activity will get going more toward late
afternoon into this evening. The cold front is still well to the
west, over the central Great Lakes.

Lower clouds and showers will work into the area later tonight
into Thursday morning, as front stalls as it heads into far
southeast PA.

Still expect conditions to improve later Thursday.

Outlook...

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

&&

.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...Steinbugl/Banghoff
LONG TERM...Fitzgerald/Colbert
AVIATION...Martin
CLIMATE...Steinbugl