Severe Thunderstorm Warning 45, NWS State College, PA

Area Forecast Discussion
National Weather Service State College PA
255 PM EDT Sat Jun 22 2024

.SYNOPSIS...
*Ongoing heat wave peaks this weekend with some relief in sight
 for Monday
*Severe thunderstorm risk will ramp up over the weekend with
 scattered damaging winds most likely Sunday afternoon/evening
*A shorter duration summertime hot spell will precede a round of
 t-storms into the middle of the last week of June

&&

.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
Convective temps were realized early this afternoon off of the
higher terrain with isolated coverage of shra and a few rogue
storms, mainly along the Erie Lakeshore and over the Pocono
Plateau. Unlike previous days, today's lower DCAPEs are not
producing sufficient cold pools to initiate subsequent
convection along outflows, so most of what forms over western
and central PA rains out and decays, with the trend on regional
radar mosaic for dying cells at mid afternoon.

Looking at forecast soundings, a fair amount of CIN below 5k
feet may also be to blame for this, with cool pools being too
shallow to overcome this here in the mid afternoon hours, but
with additional surface heating by late afternoon, we could see
true surface based convection materialize that can last longer
and produce outflows strong enough to inititate secondary
convection. We shall see...it's very warm aloft and it'll be
hard to generate much more than heavy downpours from the cells
that do generate this afternoon into this evening.

Record daily and even all- time monthly high temperatures will
be challenged this afternoon with fcst maxT between 90-100F.
Heat index values reaching high- end advisory levels and push
warning criteria ~105F in portions of the mid and lower Susq
Valley. Major to locally extreme heat risk impacts are likely to
affect health systems, heat-sensitive industries, and some
infrastructure along with anyone without effective cooling
and/or adequate hydration. The early season heat persisting over
multiple days with light wind, limited cloud cover, and warm
overnight temperatures will exacerbate heat stress. If you have
plans to be outside, drink plenty of water even if you are not
thirsty and have options for getting relief (shade or AC) from
the heat. The lack of rain combined with the prolonged heat is
also contributing to rapid onset drought risk in some areas.

Isolated evening t-storms should dissipate by late tonight. Warm
and muggy overnight with low temps peaking in the upper 60s to
mid 70s or +15-20F above the historical average for mid June -
providing little to no relief from the daytime heat.

&&

.SHORT TERM /6 AM SUNDAY MORNING THROUGH MONDAY NIGHT/...
Looking ahead to Sunday, bulk shear increases and a front will
enter the picture to potentially focus stronger storms to break
the heat. SPC Slight risk still stands for Sunday. The breakdown
of the upper ridge continues on Sunday with upper trough base
moving from the Great Lakes into the Northeast accompanied by
stronger low/mid level flow overspreading a moderately unstable
environment. Trailing cold front and prefrontal boundary should
help to trigger scattered t-storms by the afternoon with
potential for organized cells/clusters to produce damaging
winds.

WPC has maintained a MRGL risk ERO for Sunday over the
Alleghenies given ribbon of higher pwats along the cold front,
but forward progression will be limiting factor concerning
flooding potential. Recent dryness has caused a large increase
in FFG over most of CPA with the lowest values in the northern
tier. The projected instability and available moisture should
support local 1-2 in/hr rates in stronger storms, but overall
flood risk is low. Storms should weaken moving to the southeast
later Sunday night.

The 500mb trough swings through on Monday while sfc dewpoints
fall into the 50s. There could be another round of scattered
showers/t-storms, but with drier boundary layer and and PW
air mass workin into the area, signs point to a General thunder
day for most. High pressure arrives by Monday night and will
provide a mainly clear and comfortable night with valley fog and
low temps dropping back closer to climo for this time of year
in the 55-65F range.

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...
A warming trend emerges on Tuesday as surface high pressure
builds across the Mid-Atlantic. Despite the warm-up into
Tuesday, MaxTs in the lower 90s across portions of the Lower
Susquehanna Valley will be the ceiling in this forecast cycle,
where 10-20% of ENS members outline temperatures exceeding 90F
during peak warming hours with less than 10% of GEFS members
outlining temperatures exceeding 90F.

Surging PWATs ahead of a sfc cold front begin to enter central
Pennsylvania late Tuesday evening into Wednesday morning, where
chances of precipitation return to the area. Deterministic model
guidance has notably shown less coverage in precipitation
Tuesday evening, and have limited PoPs towards the northern tier
where the best moisture and forcing will be available. PoPs
will begin to expand areawide through Wednesday, especially
during the afternoon/evening hours where the best daytime
heating will be available ahead of the cold front.

Mild conditions and drier air will return for Thursday in the
wake of the cold front and continue through Friday, with MaxTs
closer to seasonal averages for the end of June. Looking into
Saturday, considerable deterministic model spread begins to
bring uncertainty into the forecast with some potential for
diurnally driven showers/storms possible across the area.

&&

.AVIATION /19Z SATURDAY THROUGH THURSDAY/...
Scattered SHRA with some embedded TSRA have started to form
across central PA's airspace this afternoon. General thoughts
are that SHRA/TSRA will continue to form throughout the evening
hours before the loss of daytime heating allows for dissipation
in the 00Z-02Z Sunday timeframe. At this time, have kept the
majority of terminals at a period of VCSH due to pulsing nature
of SHRA this afternoon. Airfields across the Laurels (BFD/JST)
will have the best chance at escaping with SHRA/TSRA and have
outlined that in the 18Z TAF package.

As mentioned above, SHRA/TSRA is expected to dissipate after
sunset and VFR conditions are expected overnight with moderate
to high (50-70%) confidence. There remains some persistence in
LLWS potential at BFD in the 10-14Z Sunday timeframe low-level
winds increase ahead of an approaching frontal boundary. Despite
the persistence in some model guidance, lower confidence
coupled with the marginal nature of LLWS parameters limits
mention in the TAF for this cycle.

The next batch of SHRA/TSRA will begin to form during the early
afternoon hours on Sunday ahead of a cold frontal passage.
Guidance (GLAMP/HREF/RAP) have shown some potential for SHRA in
the 15-17Z Sunday timeframe at BFD/AOO/UNV, outlined in this TAF
package. Later in the afternoon (mainly after 18Z), there is
higher confidence in SHRA/TSRA impacts at airfields across
central PA with continued daytime heating ahead of the front.

Outlook...

Mon...Predominantly VFR, with brief restrictions possible in
scattered SHRA/TSRA as a cold front crosses the area.

Tue...VFR, no sig wx expected.

Wed...Restrictions possible in TSRA.

Thu...AM SHRA/TSRA with restrictions possible, drying out late.

&&

.CLIMATE...
A heat wave will continue through the weekend with near-record
temperatures forecast in some locations Saturday and Sunday.

Daily record highs for Saturday June 22 and Sunday June 23:

					6/22			6/23
State College 		93 (1988)		91 (1966)
Harrisburg 			97 (1988)		97 (1965)
Williamsport		97 (1988)		94 (1923)
Altoona 			91 (2022)		90 (1994)
Bradford 			93 (2022)		86 (2013)

The following records have been set during this stretch of heat:

BFD:
* A record high temperature of 89 degrees was tied at Bradford
  on Friday June 21st, tying the record set in 2022.
* A record high temperature of 90 degrees was set at Bradford on
  Thursday June 20th breaking the old record of 88 degrees set
  in 2012.
* A record high temperature of 88 degrees was set at Bradford on
  Wednesday June 19, breaking the old record of 87 degrees set
  in 1987.

IPT:
* A record high temperature of 98 degrees was set at
  Williamsport on Friday June 21st, breaking the old record of
  97 degrees set in 1923 and tied in 1933.

Highest Max Temperatures for Central Pennsylvania Observing
sites for June (date of occurrence is in parentheses:

State College 	96 in 1952 (26th) and 1933 (29th)
Harrisburg 		100 in 1966 (27th), 1952 (26th), and 1934 (29th)
Williamsport 	104 in 1925 (5th)
Altoona 		97 in 1971 (28th) and 1953 (21st)
Bradford 		93 in 2022 (22nd)

Longest run of consecutive days with max temp >=90 in June:

State College 	6 (24-29th 1966)   /current streak=0/
Harrisburg 		10* (19-28th 1943) /current streak=5/
Williamsport 	9 (18-26th 1923)   /current streak=5/
Altoona 		8 (13-20th 1994)   /current streak=5/
Bradford        1 (20th 2024)      /current streak=0/

*Harrisburg had a run of 11 days with temperatures greater than
 90 degrees that started on 26th and ended on July 6th in 1901.

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
Heat Advisory until 8 PM EDT this evening for PAZ004>006-
010>012-017>019-024>027-033>035-037-041-042-045-046.
Heat Advisory until 8 PM EDT Sunday for PAZ028-036-049>053-
056>059-063>066.

&&

SYNOPSIS...DeVoir/Steinbugl
NEAR TERM...DeVoir/Steinbugl
SHORT TERM...DeVoir/Steinbugl
LONG TERM...NPB
AVIATION...Bauco/NPB
CLIMATE...Evans/Steinbugl/Colbert

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Special Weather Statement
National Weather Service State College PA
440 PM EDT Sat Jun 22 2024

PAZ018-019-222130-
Northern Centre PA-Southern Centre PA-
440 PM EDT Sat Jun 22 2024

...A STRONG THUNDERSTORM WILL IMPACT CENTRAL CENTRE COUNTY THROUGH
530 PM EDT...

At 439 PM EDT, Doppler radar was tracking a strong thunderstorm near
Bellefonte, moving east at 25 mph.

HAZARD...Wind gusts of 50 to 55 mph.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects.

Locations impacted include...
Bellefonte, Zion, Milesburg, Blanchard, Julian, Bald Eagle State
Park, Howard, and Unionville.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

If on or near Bald Eagle Lake, get out of the water and move indoors
or inside a vehicle. Remember, lightning can strike out to 10 miles
from the parent thunderstorm. If you can hear thunder, you are close
enough to be struck by lightning. Move to safe shelter now! Do not
be caught on the water in a thunderstorm.

&&

LAT...LON 4106 7756 4105 7758 4102 7756 4095 7755
      4085 7800 4097 7804 4111 7772
TIME...MOT...LOC 2039Z 248DEG 21KT 4096 7789

MAX HAIL SIZE...0.00 IN
MAX WIND GUST...55 MPH

Colbert

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