-- Discussion containing changed information from previous version are highlighted. --
291
FXUS61 KCTP 172152
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
552 PM EDT Mon Jun 17 2024

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

&&

.NEAR TERM /THROUGH TUESDAY/...
-- Changed Discussion --
6 pm update... A broken band of showers and thunderstorms, tied
to an upper-level disturbance over Lake Ontario, extends from
western and central NY, through western and north-central PA,
then back into OH at 6 pm. An isolated strong or perhaps
marginally severe storm could still impact areas north of I-80
and about as far east as the I-99 corridor through 8 pm or so.
Thereafter, waning instability and the development of weak
subsidence behind the aforementioned disturbance should cause
any residual storms to weaken and dissipate.

We still anticipate some patchy fog later tonight, owing to
increasing surface dew points, locally wet ground conditions,
and light surface flow.

Lows by daybreak should generally range from 65 to 70.

Previous discussion... Still anticipate a gradual uptick in
[isolated] convection over the NW Alleghenies this afternoon on
the southern periphery of remnant MCV moving eastward across
southern Ontario. SPC has maintained the MRGL risk SWO and
recently sent MCD #1302 which included a portion of Warren
County. The limited vertical shear generally <20kt and weak
forcing for ascent suggest storm organization will remain
limited and therefore a WW is not expected (20% probability).
Recent radar loop showed a couple of t-storms developing near
KBFD which is reporting a dewpoint of 70F. One of those storms
briefly pulsed up over northern Elk County with a 50dBZ core
reaching the -20C level, prompting a short duration SPS.

Isolated to scattered convection mainly over northwest PA
should fade with loss of heating after sunset. Mostly clear
skies, light wind and surging low level moisture will likely
result in patchy valley fog late tonight. A muggy night with low
temps in the 65-70F range or +10-15F above climo in most spots.
-- End Changed Discussion --

&&

.SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/...
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 /THURSDAY NIGHT THROUGH MONDAY/...
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 /22Z MONDAY THROUGH SATURDAY/...
TSRA/CB occurring across the Alleghenies, including BFD as a
hot/humid airmass builds in. Have included VCTS through 20Z, but
may amend with a TEMPO if additional upstream development
continues. Could see some brief IFR/MVFR visibilities from
these, but not expecting this to persist.

Elsewhere, VFR conditions are largely expected to prevail
underneath south/southwest winds of up to 10 knots or so. Winds
will diminish this evening with patchy fog possible,
particularly in areas that get rain this afternoon. Have
maintained MVFR reductions at BFD later tonight/early Tuesday
morning.

Could see additional isolated to scattered storms early Tuesday
afternoon over similar areas, but not expecting enough coverage
at this time to warrant mention.

Outlook...

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

&&

.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...
Heat Advisory from noon Tuesday to 8 PM EDT Thursday for
PAZ004>006-010>012-017>019-024>028-033>037-041-042-045-046-
049>053-056>059-063>066.

&&

$$

SYNOPSIS...Steinbugl
NEAR TERM...Jurewicz/Fitzgerald/Steinbugl
SHORT TERM...Fitzgerald/Steinbugl
LONG TERM...Guseman/Bauco
AVIATION...Guseman/Martin
CLIMATE...Steinbugl/NPB