-- Discussion containing changed information from previous version are highlighted. --
162
FXUS61 KCTP 180948
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
548 AM EDT Tue Jun 18 2024

.SYNOPSIS...
*Long duration and potentially dangerous heat wave this week
*Near-record high temperatures 90+ degrees into the weekend

&&

.NEAR TERM /THROUGH TONIGHT/...
Just a few sprinkles left in Sullivan Co. Dry elsewhere. Fog has
started to form (generally in the valleys) where it rained in
the past 8 hrs, mainly in the N-Central mtns and Blair/Hunt Cos.
The air is light/variable, so there won`t be a hurry to clear it
out in the AM. But, sunrise comes so early, now, with only a
couple of days left until Solstice. Therefore, we`ll mention fog
thru 13Z.

Upper high pressure (325dam at 7H) will reside directly overhead
for today. That should help to keep a lid on things trying to
grow very tall. But, we had similar heights yesterday, and quite
a few storms got going over the nrn tier and wrn mtns. So, we
expect similar developments this aftn. The RAP (03Z run) erases
the llvl CINH by Noon-1 PM at BFD and JST (per model
soundings), but upper levels still very warm. Little shear means
they could just rain themselves out as they move little from
their intiation spots. 1.6" PWAT is nothing to sneeze at, but
the cells shouldn`t last all that long to make for a flooding
risk today. SPC has put the Allegheny Plateau into a MRGL risk
for SVR. The hot air means there is no svr hail risk, and
it makes for a cap to overcome. Without wind/shear, organization
will be poor. CAPEs get to 1500 from the RAP and GFS, and 3000
from the NAM - but only with a boost from the elevations and
interacting outflow boundaries. Seeing what happened Mon
aftn/eve, it`s probably going to be another very limited threat
for svr storms again today.

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
The heat and humidity are progged to build through midweek, as
the center of the subtropical high lifts north over PA. Current
guidance indicates heat indices will reach 95 to around 100F
especially in the valley locations during the afternoons Tue-
Thu. We extended the heat advisory through 8pm Thursday which
aligns well with neighboring WFOs to the west, north, and east.

Model guidance continues to favor isolated to scattered diurnal
t-storm risk Tue-Thu downwind of Lake Erie and over the higher
terrain along the spine of the Alleghenies. Thursday looks like
the hottest day of the period with maxT 90-95F or +10-20F above
climo.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
Heat looks like it will continue into the weekend. Trying to
make decision on if and for how long to extend the heat advy.
Friday looks like the hottest day, and some spots could get near
105 HI on Friday in the SE. But, very few spots. At this point,
we`ll just add another day onto the area-wide heat advy, and run
it thru Friday evening. Could easily see us continuing to push
the advy out thru the weekend, but the NW half of the CWA may
not come close to criteria Sat and Sun.

Prev...
Late evening update brings about little changes outside of
potentially some lower MaxTs (still well above climo for mid-
to-late June) with slightly higher dewpoints keeping heat index
values high into the weekend. Diurnally driven afternoon showers
and thunderstorms remain plausible across the northern tier,
with some uptick towards Chc PoPs across the Endless Mountains.

Prev...

Medium range guidance continues to show that a prolonged heat
wave will continue throughout at least early this weekend.

A 595-600 dm 500 mb ridge looks to begin breaking down by late
week, but temperatures will still easily reach the 90s across
most of the region each day with heat indices in the upper 90s
and low 100s.

Northern PA will stand the best chance of any afternoon/evening
showers/thunderstorms through the period closer to an
approaching upper trough and farther away from the core of the
upper ridge. Better rain chances and possibly a reprieve in the
heat could materialize by late weekend or early next week
depending on the evolution of the aforementioned trough to our
north/northwest.

&&

.AVIATION /10Z TUESDAY THROUGH SATURDAY/...
-- Changed Discussion --
Looking at a few more hours of patchy fog at sites like BFD, IPT
and AOO. The fog should burn off by mid morning.

Winds will remain rather light into Wed morning.

There is a slight chc of a gusty shower or storm later this
afternoon or this evening, but overall most of the day will
be dry.

Less chance of fog Wednesday, unless widespread convection
gets going later today.

Outlook...

Wed-Sat...Predominantly VFR, with building heat and iso TSRA.
Density altitude concerns possible.
-- End Changed Discussion --

&&

.CLIMATE...
A period of much warmer than average temperatures is expected
across much of central Pennsylvania next week, with record high
temperatures being challenged. The record high temperatures for
some sites across central PA are outlined below:

 Jun 18 Jun 19 Jun 20 Jun 21

Harrisburg      97/1957     98/1994     98/1931     98/1923
Williamsport    97/2018     96/1929     101/1923    97/1933
State College   94/1923     94/1931     94/1953     94/1988

Highest Max Temperature for June:

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)
Harrisburg 10* (19-28th 1943)
Williamsport 9 (18-26th 1923)
Altoona 8 (13-20th 1994)
Bradford 0 (has not occurred in POR since 1957)

*Harrisburg had a run of 11 days that started on 26th and ended
 on July 6th in 1901

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --
Heat Advisory from noon today to 8 PM EDT Friday for
PAZ004>006-010>012-017>019-024>028-033>037-041-042-045-046-
049>053-056>059-063>066.
-- End Changed Discussion --

&&

$$

SYNOPSIS...Steinbugl
NEAR TERM...Dangelo
SHORT TERM...Dangelo
LONG TERM...Guseman/NPB
AVIATION...Martin
CLIMATE...Steinbugl/NPB