-- Discussion containing changed information from previous version are highlighted. --
905
FXUS61 KCTP 221830
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
230 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 /THROUGH TONIGHT/...
Shallow patchy river valley fog over the NC Mountains has
dissipated, so it`s back to rinse and repeat (very hot and
humid) to start the weekend as the early summer/mid June heat
wave tops out over the entire CWA. Record daily and even all-
time monthly high temperatures will be challenged this afternoon
with fcst maxT between 90-100F. Heat index values should reach
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.

In the midst of the heat and humidity, abundant CAPE will once
again help fuel t-storm development within weak sfc troughing.
SPC has shifted the MRGL risk SWO eastward to only include the
eastern third of the forecast area with scattered strong storms
capable of locally damaging wind gusts. Deep layer wind fields
remain weak, but should trend a bit stronger as mid level
heights slowly fall as the upper ridge begins to shift or
retrograde to the west/southwest.

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 /SUNDAY THROUGH MONDAY NIGHT/...
As we alluded to last night, it appears a more organized severe
threat is evolving to break the heat wave with SPC ratcheting
up the categorical svr tstm risk from level 1 to 2 out of 5
(MRGL to SLGT) for Sunday PM. A large scale upper trough will
move 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. There is a non-zero tornado threat, but higher probs are
located farther to the north in New England where better low
level shear/SRH combo overlap in closer proximity to sfc warm
front.

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 and could trigger
another round of scattered showers/t-storms. However, drier or
lower pwat air working into the area should result in a less
favorable setup for severe storms and the new D3 SPC outlook
call for general thunder. 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/...
-- Changed Discussion --
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.
-- End Changed Discussion --

&&

.AVIATION /18Z SATURDAY THROUGH THURSDAY/...
-- Changed Discussion --
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.
-- End Changed Discussion --

&&

.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:

6/226/23
State College 93 (1988)91 (1966)
Harrisburg 97 (1988)97 (1965)
Williamsport97 (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...Steinbugl
LONG TERM...NPB
AVIATION...Bauco/NPB
CLIMATE...Evans/Steinbugl/Colbert