307
FXUS61 KCTP 231856
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
256 PM 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/...
Increasing bulk shear and SRH is evident in radar signatures the
last 45 minutes with cells gaining the propensity to rotate, and
mature cells able to bow out over northern Tioga County and
produce (warned) thunderstorm wind damage.The aforementioned
parameters only increase through late afternoon as LCLs from
roughly the I-80 corridor northward range from 550m to 900m.
SPC evaluating for potential Watch, but we`re waiting to see
where storms will be most likely to more consistently organize,
so perhaps it`ll be beyond 19/20z but it`s even possible that
severe threat remains isolated enough to preclude Watch
issuance.

Elsewhere, broken mid clouds have limited sfc heating, but still
plenty of warmth and humidity farther south and east as a slow
moving front sags into the region late this afternoon and
evening. As we mentioned earlier, we`ve been focused on shear
parameters as they increase through late afternoon, with latest
HRRR runs indicating favorable 0-3km SRH exceeding 300m2s-2 in
pockets, and low LCLs supporting warm RFDs and the potential for
an isolated tornado or 2 over mainly north central PA.

Trailing cold front crosses northwest PA this afternoon and
reaches the central mountains this evening. Wide range of
solutions from the CAMs, but NAM3km is handling things
reasonably well and continues to indicate increasing coverage
and intensity across western and central areas by late
afternoon. Lee trough may finally support convection initiation
shortly over the Susq Valley. Strong large scale forcing ahead
of the upper trough, combined with +2-3SD pwats ahead of the
cold front, supports fairly high POPs into the evening in the
60-90pct range. The increasing 0-6km bulk 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 HREF also projects STP values >1
across this area. Locally heavy downpours will also occur, but
progressive storm motions should preclude significant flooding
concerns in most areas.

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 WEDNESDAY/...
Relief from the heat comes Monday behind the upper trough with
sfc dewpoints dropping into the 50s.  A tight pressure gradient
and steep lower tropospheric lapse rates should result in a
very breezy Monday by late June standards. 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.

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.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
Showers and storms will gradually exit to the the southeast on
Wednesday night as high pressure builds in. The midweek cold
front will reset the cycle similar to what today`s cold front
will do and usher in a similar stretch as Monday & Tuesday. Thursday
and Friday will consist of about 48 hours of lower dewpoints,
temperatures closer to average for this time of year, and plenty
of sunshine. Afternoon highs in the 70s and 80s, overnight lows
in the 50s and 60s (perhaps even upper 40s in the northern
mountains Friday morning), and dewpoints below 60F will feel
especially good with the persistent stretch of heat.

As high pressure shifts to the east on Friday, southerly flow
will support increasing temperatures and moisture into the
weekend. The chance for showers and storms will also ramp up
Saturday and Sunday as a warm front lifts across the region.

&&

.AVIATION /19Z SUNDAY THROUGH FRIDAY/...
Multiple rounds/lines of storms are expected today across the
region. The first round of showers is across northwest PA at
11AM and has struggled to produce lightnign at this point. That
line of showers will begin to intensify during the early
afternoon hours ahead of a cold frontal passage. There is higher
confidence in SHRA/TSRA impacts at airfields across central PA
after 18Z with continued daytime heating ahead of the front.
While the bulk of the thunderstorm activity will be focused
along the cold front this afteroon, a few storms may develop in
the Lower Susquehanna Valley ahead of the main line and bring
restrictions to MDT/LNS between 18 and 20Z.

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.

&&

.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...DeVoir/Fitzgerald
NEAR TERM...DeVoir/Fitzgerald
SHORT TERM...DeVoir/Fitzgerald
LONG TERM...Dangelo/Banghoff
AVIATION...Banghoff/Bauco
CLIMATE...Evans/Steinbugl/Colbert