Severe Thunderstorm Warning 137, NWS State College, PA

Area Forecast Discussion
National Weather Service State College PA
1226 PM EDT Sat Aug 3 2024

.SYNOPSIS...
* Another round of thunderstorms capable of drenching downpours
  and strong gusty winds this afternoon into the evening
* Rain-free in most areas Sunday into Monday with surge of late
  summer heat and humidity
* Increased storminess likely on Tuesday followed by seasonably
  cooler and potentially unsettled/wet conditions to the north
  of TD Four through the middle to later part of next week

&&

.NEAR TERM /THROUGH TONIGHT/...
...1615Z Update...
After consultation with neighboring offices, decided upon a
Flash Flood Watch for most of our CWA through early this
evening. Slow moving training cells already producing 1-2" per
hour stripes across western/central/south central parts of my
CWA. Highest threat for excessive rainfall will be over SC to SE
parts of central PA including the Ridge and Valley region, where
more robust deep layer moisture, training cells and tall skinny
CAPEs give greater rainfall rates. Will run the Flash Flood
Watch through 02z. Southeast areas may see a damaging wind
threat for a few hours this afternoon as CAMs suggest the
potential for a bowing line segment in response to model
increase in bulk shear and mid level drying evident in lower PWs
nosing into the Laurel Highlands. Beneficial rainfall will be
received by many, but some will see too much in too short a
period of time.

...Previous Discussion...
Slow moving 5H trough tracking across
central PA today with humid conditions prevailing. We're
tracking slow moving downpours across parts of central and north
central PA this morning, and expecting at least a marginal
severe weather threat across southern and southeastern sections
where some speed shear may support bowing segments. Training
will be a sighnificant concern with this pattern, both in the
pivot area over north central PA and across SC and SE portions
of central PA before any line segments become progressive/bow.
Key messages again center around 1) potential for locally heavy
to excessive rainfall/flooding risk and 2) scattered strong to
severe storm clusters capable of producing damaging wind gusts.
Both threats are maximized in southeast PA.

Slow moving upper trough will shift east from the lower Great
Lakes/Ohio Valley toward the northern Appalachians and Mid
Atlantic vicinity through tonight. A prolonged period of
favorable moisture transport/flux of rich pwats 1.5-2" along
and ahead quasi stationary/slow moving sfc front suggests
potential for high rain rates particularly within a corridor
near/east of the I81. Recent rainfall has made a dent in
reducing FFG in some parts of the Lower Susquehanna Valley (LSV)
and the hires model signal is bullish for spot amounts over 2-3
inches based on 03/00Z HREF PMM/LPMM. Depending on how model
guidance and radar trends evolve through the late morning, the
dayshift may consider a short-fused FF watch for portions of the
LSV. WPC has upgraded this area to a slight risk ERO or level 2
risk (out of 4).

Secondary concern today is severe t-storm threat which is also
focused over the far southeast part of the CWA. To the east of
the aforementioned slow moving boundary, a very moist and
unstable airmass will reside with Td in the low 70s. Effective
shear magnitudes trend higher vs. yesterday and peak around
30kts over the far southeast zones offering a greater risk of
severe storms; SPC has upgraded to a slight risk corridor
(level 2 of 5) with accompanying 15-29% damaging wind probs
which includes the eastern portions of York and Lancaster
County.

Convection should weaken/decrease in coverage by late evening
with max POPs for lingering showers overnight in the eastern
portion of the CWA.

Fcst high temps in the upper 70s to upper 80s are near to a few
degrees above early August climo, with the largest departures
from the historical average (+5F) over the mid and LSV. Another
humid/muggy night ahead with patchy dense fog into early Sunday
morning.

&&

.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
The northwest half of CPA should enjoy a rain-free end to the
first weekend of August. Latest guidance suggests a slightly
drier (lower pwat) westerly flow behind the exiting trough will
provide fair weather Sunday across this part of the forecast
area along with lower humidity. Meanwhile, showers and non-
severe t-storms/downpours will be possible particularly over
the extreme eastern/southeastern portion of the CWA Sunday
afternoon/evening.

Sfc ridge briefly building into CPA in the wake of departing
upper trough/sfc front brings dry wx along with areas of fog
again for Sunday night into early Monday morning with lows
60-70F.

While Monday PM looks to be mainly dry on balance particularly
for the southern half to 2/3 of the area, a sfc frontal zone
sinking southward from the St. Lawrence Valley impinging on a
very warm/hot/humid airmass could trigger a couple of tstm
clusters capable of producing strong/dmg winds over the northern
tier of CPA. SPC has introduced a marginal risk SWO for day 3
(level 1 of 5) that includes the north central PA counties to
the north of I80. There is increasing variability within the
model output regarding convective activity along/ahead of the
southward advancing boundary and potential upstream MCS diving
southeast from the Great Lakes Monday night.

Monday will be very warm to hot with max temps +5-10F above
climo in the 85-95F range. Heat index values may approach the
century mark in the LSV. Monday looks like the hottest day next
week.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
Most medium range guidance develops an upstream wave on the
stalled front, tracking it across Central PA Tues PM into Wed.
This scenario supports a decent chance of showers/tsra in the
late Tuesday to Wednesday timeframe.

Odds appear to favor fair weather with near to slightly below
normal temperatures during the second half of next week
associated with high pressure building across the Grt Lks.
However, there remains some uncertainty with regard to how far
south Wednesday's cold front gets before stalling out.

&&

.AVIATION /18Z SATURDAY THROUGH THURSDAY/...
Showers with an embedded -TSRA will continue south of a KJST-
KAOO-KMDT line to begin the forecast period.

Most high res guidance suggesting there will be fog potential
for all sites from UNV north. This is already occurring at KBFD
and KIPT. There is lower confidence in fog development across
the southern half of the area, but there is around a 20-30%
chance of MVFR visibilities impacting MDT and LNS.

Fog conditions will gradually improve after sunrise but this
will be just in time for the return of -SHRA and -TSRA/VCTS from
south to north. Tried to time the transition to precipitation
using high res short term models. Feel confident (>70%) in this
scenario as they have initialized well with respect to the
current conditions.

Another round of thunderstorms is expected this afternoon, with
storms initially developing across the west during the late
morning/early afternoon, then moving and developing eastward.
These storms will reach eastern sites by ~20Z. This timing may
need to be refined with later TAF issuances as the development
takes place. Gusty winds and brief restrictions will be possible
with any of the storms.

Outlook...

Sun...Periods of showers and storms expected over the weekend.

Mon...Lingering scattered TSRA/SHRA with a stationary front to
the north.

Tue...Scattered SHRA/TSRA mainly NW PA, restrictions possible.

Wed...Restrictions possible in SHRA/TSRA.

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
Flood Watch until 10 PM EDT this evening for PAZ006-010>012-
017>019-024>028-035>037-041-042-045-046-049>053-056>059-
063>066.

&&

SYNOPSIS...DeVoir/Steinbugl
NEAR TERM...DeVoir/Steinbugl
SHORT TERM...DeVoir/Steinbugl
LONG TERM...Bauco/Bowen
AVIATION...Bauco/Tyburski

Hazardous Weather Outlook
National Weather Service State College PA
121 PM EDT Sat Aug 3 2024

PAZ012-017>019-024>028-035-041-042-045-046-049-050-041730-
Northern Clinton-Clearfield-Northern Centre-Southern Centre-Cambria-
Blair-Huntingdon-Mifflin-Juniata-Fulton-Northern Lycoming-Sullivan-
Southern Clinton-Southern Lycoming-Union-Snyder-
121 PM EDT Sat Aug 3 2024

...FLOOD WATCH IN EFFECT UNTIL 10 PM EDT THIS EVENING...

This Hazardous Weather Outlook is for central Pennsylvania.

.DAY ONE...This afternoon and tonight.

Please listen to NOAA Weather Radio or go to
weather.gov/StateCollege on the internet for more
information about the following hazards.

   Flood Watch.

.DAYS TWO THROUGH SEVEN...Sunday through Friday.

The probability for widespread hazardous weather is low.

.SPOTTER INFORMATION STATEMENT...

Spotters are encouraged to report significant hazardous weather.

PAZ033-034-041730-
Somerset-Bedford-
121 PM EDT Sat Aug 3 2024

This Hazardous Weather Outlook is for central Pennsylvania.

.DAY ONE...This afternoon and tonight.

There is an elevated risk of excessive rainfall this afternoon that
could result in isolated flooding particularly in urban areas.

.DAYS TWO THROUGH SEVEN...Sunday through Friday.

The probability for widespread hazardous weather is low.

.SPOTTER INFORMATION STATEMENT...

Spotters are encouraged to report significant hazardous weather.

PAZ057>059-064-041730-
Dauphin-Schuylkill-Lebanon-Adams-
121 PM EDT Sat Aug 3 2024

...FLOOD WATCH IN EFFECT UNTIL 10 PM EDT THIS EVENING...
...SEVERE THUNDERSTORM WATCH 591 IN EFFECT UNTIL 9 PM EDT THIS
EVENING...

This Hazardous Weather Outlook is for central Pennsylvania.

.DAY ONE...This afternoon and tonight.

Please listen to NOAA Weather Radio or go to
weather.gov/StateCollege on the internet for more
information about the following hazards.

   Flood Watch.
   Severe Thunderstorm Watch.

.DAYS TWO THROUGH SEVEN...Sunday through Friday.

The probability for widespread hazardous weather is low.

.SPOTTER INFORMATION STATEMENT...

Spotters are encouraged to report significant hazardous weather.

PAZ036-051>053-056-063-041730-
Franklin-Montour-Northumberland-Columbia-Perry-Cumberland-
121 PM EDT Sat Aug 3 2024

...FLOOD WATCH IN EFFECT UNTIL 10 PM EDT THIS EVENING...

This Hazardous Weather Outlook is for central Pennsylvania.

.DAY ONE...This afternoon and tonight.

Please listen to NOAA Weather Radio or go to
weather.gov/StateCollege on the internet for more
information about the following hazards.

   Flood Watch.

.DAYS TWO THROUGH SEVEN...Sunday through Friday.

The probability for widespread hazardous weather is low.

.SPOTTER INFORMATION STATEMENT...

Spotters are encouraged to report significant hazardous weather.

PAZ065-066-041730-
York-Lancaster-
121 PM EDT Sat Aug 3 2024

...FLOOD WATCH IN EFFECT UNTIL 10 PM EDT THIS EVENING...
...SEVERE THUNDERSTORM WATCH 591 IN EFFECT UNTIL 9 PM EDT THIS
EVENING...

This Hazardous Weather Outlook is for central Pennsylvania.

.DAY ONE...This afternoon and tonight.

Please listen to NOAA Weather Radio or go to
weather.gov/StateCollege on the internet for more
information about the following hazards.

   Flood Watch.
   Severe Thunderstorm Watch.

.DAYS TWO THROUGH SEVEN...Sunday through Friday.

The probability for widespread hazardous weather is low.

.SPOTTER INFORMATION STATEMENT...

Spotters are encouraged to report significant hazardous weather.

PAZ004-005-041730-
Warren-McKean-
121 PM EDT Sat Aug 3 2024

This Hazardous Weather Outlook is for central Pennsylvania.

.DAY ONE...This afternoon and tonight.

The probability for widespread hazardous weather is low.

.DAYS TWO THROUGH SEVEN...Sunday through Friday.

The probability for widespread hazardous weather is low.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not expected at this time.

PAZ006-010-011-037-041730-
Potter-Elk-Cameron-Tioga-
121 PM EDT Sat Aug 3 2024

...FLOOD WATCH IN EFFECT UNTIL 10 PM EDT THIS EVENING...

This Hazardous Weather Outlook is for central Pennsylvania.

.DAY ONE...This afternoon and tonight.

Please listen to NOAA Weather Radio or go to
weather.gov/StateCollege on the internet for more
information about the following hazards.

   Flood Watch.

.DAYS TWO THROUGH SEVEN...Sunday through Friday.

The probability for widespread hazardous weather is low.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not expected at this time.

Special Weather Statement
National Weather Service State College PA
1224 PM EDT Sat Aug 3 2024

PAZ063-065-031700-
York PA-Cumberland PA-
1224 PM EDT Sat Aug 3 2024

...A STRONG THUNDERSTORM WILL IMPACT NORTHWESTERN YORK AND CENTRAL
CUMBERLAND COUNTIES THROUGH 100 PM EDT...

At 1223 PM EDT, Doppler radar was tracking a strong thunderstorm over
Carlisle, moving northeast at 20 mph.

HAZARD...Wind gusts up to 40 mph and pea size hail.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects. Minor hail damage to vegetation is
         possible.

Locations impacted include...
Carlisle, Mechanicsburg, Plainfield, Schlusser, Boiling Springs,
Dillsburg, Mount Holly Springs, Shiremanstown, New Kingstown,
Wertzville, Siddonsburg, Hogestown, Carlisle Springs, Messiah
College, and Penn State Dickinson School Of Law.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

Very heavy rainfall is also occurring with this storm and may lead to
localized flooding. Do not drive your vehicle through flooded
roadways.

This storm may intensify, so be certain to monitor local radio
stations and available television stations for additional information
and possible warnings from the National Weather Service.

&&

LAT...LON 4015 7736 4030 7712 4031 7705 4031 7703
      4017 7690 4006 7712 4007 7714 4003 7719
      4002 7722 4002 7723
TIME...MOT...LOC 1623Z 233DEG 16KT 4013 7722

MAX HAIL SIZE...0.25 IN
MAX WIND GUST...40 MPH

Martin

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