-- Discussion containing changed information from previous version are highlighted. --
175
FXUS61 KCTP 211752
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
152 PM EDT Tue May 21 2024

.SYNOPSIS...
*Surge of summerlike warmth and humidity through midweek
*Strong to severe t-storms possible Wednesday afternoon
*Seasonably warm & unsettled Thursday through Memorial Day

&&

.NEAR TERM /THROUGH TONIGHT/...
Mostly sunny skies are firmly in place today as temperatures
have surged into the upper 70s and low 80s at noon. A scattered
deck of fair weather cumulus will develop at higher elevations
across the Laurel Highlands and northwest mountains this
afternoon as temperatures rise into the mid 80s, which is
~10-15F above late May climo. Can`t rule out a stray shower or
thunderstorm across the west where a narrow plume of ~500 J/kg
MLCAPE will develop this afternoon. Have added mention of
isolated showers/storms to the forecast, but expect most
locations to stay dry. Dewpoint temperatures will stay in the
mid to upper 50s, which will help keep the humidity at a
manageable level today.

Fair weather cumulus will collapse tonight with the loss of
daytime heating and a few high clouds may still drift overhead.
The gradual advection of higher dewpoints through daybreak
Wednesday along with clear skies will likely result in patchy
fog again tonight. Highest fog potential based on SREF and HREF
probabilities will be the central ridge and valley region where
deeper valleys can effectively decouple. A comfortable night is
in store as temperatures bottom out in the upper 50s to low
60s.

&&

.SHORT TERM /WEDNESDAY THROUGH FRIDAY/...
Wednesday will be the warmest day of the week with summerlike to
near record max temps forecast in the mid to upper 80s. See
the climate section of the AFD to find out which sites have the
best shot at tying or setting a new daily record high for 5/22.
In addition to anomalous heat, dewpoint temperatures will rise
into the low 60s making for a noticeable uptick in humidity
compared to today. The newly-released NWS HeatRisk product
(available at www.weather.gov/ctp/heat) indicates the potential
for heat-related impacts to those especially sensitive to heat,
especially those without effective cooling and/or adequate
hydration.

The combination of summerlike warmth and dewpoints in the
low/mid 60s will support moderate destablization Wednesday
afternoon with MLCAPE values progged in the 1000-1500 J/kg
range. While 0-6km shear values are fcst to remain <30kts over
most of CPA, the instability/steep lapse rates may be sufficient
to support isolated strong to locally damaging wind gusts with
t-storms into the early evening. SPC has upgraded the northwest
1/2 of the CWA to a Slight risk or severe t-storm risk level 2
out of 5. If the Slight risk remains in place for the Day 1
forecast tomorrow, it will be the first Day 1 SLGT in our area
since April 17th! Latest hi- res models show t-storm clusters
developing ahead of an eastward advancing cold front/near a
leading pre frontal trough and moving west to east across the
area from around midday through the late evening. This
convection could be enhanced by remnant MCVs associated with Day
1/Tue convection as they propagate into the Lower Great Lakes
within southwesterly flow aloft.

The morphology of storms into Wednesday night and Thursday
morning remains a bit fuzzy at this time. A break in the
shower/storm activity is probable Wednesday evening with
subsequent activity ranging from stratiform rain showers to a
continued severe threat through midnight. Much will depend on
the evolution of storms in the Plains today and their
progression eastward over the next 24 to 36 hours. By daybreak
Thursday, some patchy fog is once again possible, especially if
any breaks in the clouds help promote more efficient radiational
cooling overnight.

More showers and t-storms are likely on Thursday as the primary
cold front slowly moves through the area and settles near the
MD line Thursday night. The focus for stronger storms shifts
into far southeastern PA on Thursday afternoon with the D3 MRGL
SWO just clipping Lancaster County. High temps will cool off a
bit over most of CPA on Thursday into the mid 70s to lower 80s,
but remain above climo for this time of year. Low temps Thursday
night/AM Friday in the 55-65F range will not be as warm/humid
as Wednesday night.

&&

.LONG TERM /FRIDAY NIGHT THROUGH MONDAY/...
-- Changed Discussion --
Looking at above normal temperatures into the holiday weekend.

The proximity of a frontal boundary to the south and west of
PA into at least early next week, will keep some chance of a
shower and perhaps a storm across the region from time to time
through Monday. Highest chance will be across the far south and
far west.
-- End Changed Discussion --

&&

.AVIATION /18Z TUESDAY THROUGH SUNDAY/...
-- Changed Discussion --
A few CU forming as of 1 PM across the ridge tops. While
dewpoints not real high and the airmass aloft rather warm,
intense afternoon heating could form a shower or storm across
the higher terrain in spots like BFD and perhaps JST.

Otherwise just looking at mainly a few clouds into late morning
on Wednesday. Have a TEMPO for fog in at MDT and LNS, but less
chance than during the past few mornings. Main thing going for
a bit of fog in the far southeast will be rather light wind
fields.

Timing of showers and storms with the cold front late Wednesday
into early Thursday will be after 18Z. Did have a VCSH in at
BFD after 17Z.

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

Outlook...

Thu...Chance of t-storms.

Fri-Sun...Mainly VFR, but chance of showers.
-- 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...Martin
AVIATION...Martin
CLIMATE...Steinbugl