Severe Thunderstorm Warning 56, NWS State College, PA

Area Forecast Discussion
National Weather Service State College PA
730 AM EDT Fri May 16 2025

.SYNOPSIS...
* Periods of rain and thunderstorms through Saturday with some
  potential for localized damaging winds and flooding downpours
* Temperatures trend warmer Friday and Saturday with a notable
  uptick in humidity to end the week
* Breezy, cooler, and much drier (less humid) end to the weekend
  with rain-free conditions into early next week

&&

.NEAR TERM /THROUGH TONIGHT/...
Pockets of locally dense fog and low visibility could make driving
conditions hazardous through sunrise across the central and eastern
portion of the forecast area. Will be considering SPS/DFA based on
latest ASOS/RWIS visibility trends.

Overnight convection/MCS has been confined largely to the Lake Erie
vicinity. Although the intensity varies from model to model, the
latest hires guidance is in agreement with convection expanding to
the southeast across the Allegheny Front through 12Z/8AM and
eventually shifting eastward across central PA through midday.

We are monitoring storm clusters tracking southeast from near Erie,
PA. Brief gusty winds and small hail may be possible for the next
hour or so with this cell as it continues to move southeast toward
Warren County. Additional thunderstorms may develop later this
morning along/ahead of the MCS, but the overall environment should
remain unsupportive of an organized severe threat. Therefore, a
watch is not anticipated per recent SPC MCD #804.

A Flood watch remains in effect for Somerset and Bedford counties,
although confidence in heavy rain potential has been steadily
decreasing early this morning based on short term model and
radar trends.

In the wake of the AM convection, the afternoon t-storm setup looks
more nebulous given the absence of a strong forcing mechanism. There
will be plenty of instability available (MLCAPE 1000-2000 J/kg) with
cloud breaks yielding strong sfc heating within a very moist (mid-
summerlike) boundary layer comprised of Td in the 65-70F range over
south central PA. The lack of deep layer shear suggests the primary
threat this afternoon could be isolated downburst wind gusts/hail or
drenching downpours which could result in localized flooding --
particularly in areas that have been hit the hardest over the last
few days. Max temps will be +7-15 degrees above mid May climo with
highs in the 75-85F range.

While the D1 SLGT risk outlook area covering south central PA does
capture the best (albeit isolated) strong/severe storm potential
prior to 00Z/8PM, one has to think that it may be drawn with eye
toward downstream evolution of projected bowing segment tracking
eastward from the Ohio Valley late tonight into the predawn hours
Saturday (00-12Z Saturday window). This area appears to be on the
far northern periphery of whatever linear feature emerges based on
recent HRRR/RRFS model runs. Therefore, the precip fcst for tonight
is highly uncertain. Lows tonight in the 55-65F range will be very
mild at +15-20F above the historical average.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
A cold front will traverse the CWA by Saturday evening and likely be
accompanied by scattered showers and few t-storms. The best svr
potential will be ahead of the front over the eastern 1/4 of the
forecast area where the HREF shows best instability collocated with
more favorable 0-6km shear profiles. SPC expanded the SLGT risk
farther to the north with the initial D2 outlook, however there
remains some questions around the quality of the much weaker
buoyancy vs. Friday. The strong shear could offset that to some
extent, and cooling temps aloft could help in increasing the
potential for strong/damaging wind gusts.

A cooler, cyclonic/NW flow pattern persists for the remainder of the
weekend. Sunday looks rather breezy with frequent 25-35 mph wind
gusts. Max temps cool down by ~10 degrees across the board day over
day with fcst highs in the 60-75F range. There may even be some
lingering or diurnal showers Sunday PM especially in the northern
tier beneath the pocket of coldest temps aloft. NW breeze should
gradually weaken Sunday night with lows in the 45-55F range or
within a few degrees of climo.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
Dry conditions continue into the beginning of the long-term period
as an upper-level ridge supplies fair conditions through Tuesday
afternoon. Increasing moisture on Tuesday leads to a notable uptick
in cloud cover for the second half of the day for most, especially
across the Laurel Highlands as the next system pulls closer to the
region. Temperatures for Monday and Tuesday are expected to trend
slightly below seasonal averages, especially during the daytime
hours.

Model guidance promotes two different solutions for the area of low
pressure approaching central Pennsylvania in the late Tuesday/early
Wednesday timeframe. ECMWF/GDPS guidance tend to keep the
approaching area of low-pressure west of the area for quite longer
and does keep highest chances for precipitation until Wednesday
afternoon/evening. Recent GFS/UKMET guidance outline a solution
where the surface low-pressure dive further south and station over
MD by Wednesday morning, allowing for precipitation chances to
increase Tuesday night into Wednesday morning across the area. Given
some model differences, have stuck close to NBM guidance while also
trimming back timing on precipitation slightly due to some low-level
drier air in place. After precipitation onset, generally expect
showers to continue through the end of the long-term period given
favorable moisture and lift associated with the area of low-
pressure.

&&

.AVIATION /06Z FRIDAY THROUGH TUESDAY/...
Cluster of showers and thunderstorm will move east across the
airspace through the monring hours, primarily affecting the northern
airfields, IPT, UNV and BFD. PROB30 group for UNV and TEMPO for IPT
should handle this progressing line. The thunderstorms will likely be
weakening as they move in and encounter a more stable environment,
but we can't rule out a few strong wind gusts.

Conditions gradually improve during the late morning Friday behind
the line of storms, but additional thunderstorms will likely develop
Friday afternoon/evening.

Outlook...

Sat...Showers/storms especially in the afternoon. West winds
gusting 30-35 kts.

Sun...Some improvement, as a series of cold fronts move
southeast of the area.

Mon...Mainly dry with VFR conditions.

Tue...VFR with scattered showers across the west late.

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
A flood watch is in effect form late tonight through Friday morning
for Somerset and Bedford counties.

&&

SYNOPSIS...Steinbugl
NEAR TERM...Steinbugl
SHORT TERM...Steinbugl
LONG TERM...Beaty
AVIATION...Bauco/Gartner

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Preliminary Local Storm Report
National Weather Service State College PA
902 AM EDT Fri May 16 2025

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0825 AM     Flood            5 SSW Galeton           41.66N 77.66W
05/16/2025                   Potter             PA   Trained Spotter

            Reports of water over roadways near Galeton
            and Germania. Received 0.75 inches of
            rainfall in less than an hour.

&&

NPB

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