-- Discussion containing changed information from previous version are highlighted. --
520
FXUS61 KCTP 231128
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
728 AM EDT Sun Jun 23 2024

.SYNOPSIS...
A cold front over the Great Lakes will sweep eastward across
Central Pennsylvania this evening. A second cold front will push
across the region late Wednesday, then a building upper level
ridge is likely over the Mid Atlantic toward next weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
Model guidance tracks a relatively deep surface low north of PA
today, with the trailing cold front coming through the central
part of the state this evening. Falling heights, combined with
diurnal heating of a moist/unstable pre-frontal airmass
supports widespread, mainly discrete convection in the warm
sector across Central PA this afternoon. Convection-allowing
models indicate thunderstorms are likely to develop by around
midday over the NW Mtns, then spread eastward and become most
numerous by late afternoon. However, the presence of a lee
trough may support convection initiation over the Susq Valley as
early as noon. Strong large scale forcing ahead of the upper
trough, combined with +2-3SD pwats ahead of the cold front,
supports fairly high POPs areawide today in the 60-90pct range.

Deep layer shear in the 30-40kt range, combined with progged
CAPES in the 1000-1500 J/kg range, supports organized multicell
clusters, a few supercells and perhaps even an isolated tornado.
The best chance of a tornado appears focused over the N Mtns,
where model 850mb winds and 0-1km shear is strongest. The 00Z
HREF also projects STP values >1 across this area.

The early arrival of convection should result in an end to the
heat wave over the northwest half of the forecast area. However,
model 850mb temps near 20C still support one more day of max
temps between 90-95F across the southeast counties. A heat
advisory remains in effect today for the Susq Valley, where max
heat indices in the 95-100F range are expected.

High pwats and moderate instability will support locally heavy
downpours today. WPC has placed the N Mtns in a MRGL risk ERO,
where FFG values are relatively low from recent rain and where
the HREF indicates the potential for up to 2 inches in a few
isolated locations. However, the overall flood risk is low,
especially across the southern counties, where the ground is
quite dry.

Dwindling showers/tsra should work east across the area this
evening with the passing cold front, then much drier air is
slated to arrive overnight. Breaking clouds are expected
downwind of the mountains, but upsloping flow and low level
moisture trapped beneath a subsidence inversion is likely to
yield lingering stratocu across the Alleghenies.

&&

.SHORT TERM /MONDAY THROUGH MONDAY NIGHT/...
Low level instability associated with the passage of the upper
trough should result in a considerable amount of cu/stratocu
Monday over the N Mtns, where a stray shower is possible. A
tight pressure gradient and steep lower tropospheric lapse rates
should result in a very breezy Monday by late June standards.
Latest Bukfit soundings support afternoon wind gusts in the
25-30kt range over much of the region, which is significantly
higher than NBM guidance.

Fair and seasonable weather with diminishing winds are anticipated
Monday night, as high pressure builds into the state. Latest
NAMNest and SREF prob charts target the Alleghenies for late
night valley fog.

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...
Late evening update holds no changes from National Blend for the
Wed and beyond time frame.

Prev...
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 /12Z SUNDAY THROUGH THURSDAY/...
-- Changed Discussion --
Some patchy fog or low clouds will remain possible for the next
hour or two across the central part of the area before
dissipating. LLWS will also be possible across the northwest for
a few more hours before southwesterly surface winds begin to
increase.

The next batch of SHRA/TSRA will begin to form during the early
afternoon hours 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. 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. While the bulk of the thunderstorm
activity will be focused ahead of the cold front, a few HREF
members suggest the possibility of some showers or storms
developing during the late morning across the eastern part of
the area.

While ceilings will likely remain VFR across the east through
the entire TAF period, most guidance suggests that MVFR ceilings
will develop west of UNV as the storms move in. Brief periods of
IFR will be possible in any thunderstorms. The HREF suggests
around a 50% chance that these low ceilings stick around through
most of the night at BFD and JST as winds shift to the west
behind 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 on Sunday.

Daily record highs for Sunday June 23:

6/23
State College 91 (1966)
Harrisburg 97 (1965)
Williamsport94 (1923)
Altoona 90 (1994)
Bradford 86 (2013)

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

MDT:
* A record high temperature of 99 degrees was set at
  Harrisburg, PA on Saturday, Jun 22, breaking the old record of
  97 degrees set in 1988.

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.

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.

AOO:
* A record high temperature of 96 degrees was set on Saturday,
  Jun 22, breaking the old record of 91 degrees set in 1988.

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=1/
Harrisburg 10* (19-28th 1943) /current streak=6/
Williamsport 9 (18-26th 1923)   /current streak=6/
Altoona         8 (13-20th 1994)   /current streak=6/
Bradford        1 (23rd 2024)      /current streak=1/

*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 PAZ028-036-
049>053-056>059-063>066.

&&

$$

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