Area Forecast Discussion
Issued by NWS State College, PA

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FXUS61 KCTP 220735

Area Forecast Discussion
National Weather Service State College PA
335 AM EDT Sat Jun 22 2024

*Ongoing significant 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


Expect areas of fog to expand across the northern tier into the
mid Susq Valley early this morning as high clouds peel off to
the east. Locations that received rainfall yesterday will be
especially prone to fog and reduced visibility. Fog will
dissipate by 13Z.

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.


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

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.


No substantial changes will be forthcoming with the late evening
update. Frontal passage mid-week should knock back the return of
the heat.


Behind the cold front, we expect still warm but much less humid
conditions to arrive by Monday and last into Tuesday, as
dewpoints drop into the 50s. This temporary relief from the heat
will give way to another surge of heat and humidity for late
Tuesday through Wednesday before a more refreshing air mass
arrives for Thursday and Friday of next week.


Patchy fog has developed across the northern half of the area
and MVFR visibilities are being reported at BFD as of 05Z. The
fog will likely make it to IPT in the next few hours and could
potentially push as far south as UNV. Most guidance suggests
that visibilities at sites that see fog will remain at 3 miles
or above, but there could be brief periods of IFR.

VFR conditions will prevail once the fog dissipates with only
very brief restrictions possible from an isolated shower or
thunderstorm in the afternoon. While any rain that develops will
likely be accompanied by thunder, have held off on including
thunder in any TAFs until timing of the storms becomes more
clear. Today will be the warmest day of this stretch for most
locations and pilots can expect high density altitude


Sun...Restrictions will be possible with thunderstorms in the
afternoon. Continued heat will present density altitude

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

Tues...VFR, no sig wx expected.

Wed...Restrictions possible in thunderstorms.


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:

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:

* 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.

* 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.


Heat Advisory until 8 PM EDT this evening for PAZ004>006-
Heat Advisory until 8 PM EDT Sunday for PAZ028-036-049>053-



NEAR TERM...Steinbugl
SHORT TERM...Steinbugl
LONG TERM...DeVoir/Dangelo