502
FXUS61 KCTP 171453
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
1053 AM EDT Mon Jun 17 2024

.SYNOPSIS...
*Long duration and potentially dangerous heat wave this week
*High temperatures 90+ degrees into next weekend

&&

.NEAR TERM /THROUGH TONIGHT/...
1015AM/1415UTC: Latest MRMS radar mosaic shows a couple of
showers dissipating over Warren County this morning. This
activity appears to be tied to SBCAPE axis extending northward
from WV and weak/diffuse warm frontal zone analyzed near the
PA/OH border. Minor adjustments were made to POPs based on radar
trends and hourly temps which were running a few degrees warmer
that previous fcst.

The other callout for today (this afternoon) is the addition of
a marginal risk SWO (level 1 out of 5) that covers the northern
tier. This is in response to convective cluster/MCV moving
eastward across southern Ontario/northern Lake Erie which should
influence (increase coverage) diurnal pulse t-storm development
over the NW Alleghenies. Despite weak 0-6km shear generally less
than 25kt, can`t rule out a locally strong wind gust given steep
low level lapse rates indicative of very moist/unstable airmass.

Previous Discussion Issued: 547 AM EDT Mon Jun 17 2024

A long duration heat wave will begin later today, as an
anomalous 500mb subtropical ridge builds over the region. Warm
mid level temps should largely suppress convection, but can`t
rule out (10-20% chance) an isolated shower or t-storm this
afternoon along the spine of the Alleghenies, where the elevated
heat source could aid in breaking the cap. Slightly higher POPs
near 30% have been placed along the NY border late today. This
is associated with an approaching MCV over SE Michigan.
The latest HRRR indicates convection will wane later this
morning as it tracks along the north shore of Lk Erie. However,
regeneration is possible this afternoon, as the mid level vort
max tracks across upstate NY.

Any convection should fade with loss of heating after sunset.
Mostly clear skies, light wind and surging low level moisture
appears likely to result in patchy late night valley fog across
the Central Mtns based on latest NAMNest and SREF prob
charts. See no reason to deviate from NBM min temps, which range
from 65-70F.

&&

.SHORT TERM /TUESDAY THROUGH THURSDAY/...
The heat and humidity are progged to ratchet up slightly Tuesday
and Wednesday, as the center of the subtropical high lifts north
over PA. Current guidance suggests heat indices will reach
95-100F in valley locations across Central PA Tuesday afternoon.
Upon coordination with neighboring offices, have issued a Heat
Advisory Tuesday afternoon.

Scattered, pulse-type convection remains possible under the
heat dome Tuesday afternoon, primarily along the spine of the
Alleghenies. The threat for PM convection looks even more
limited on Wednesday as temps continue to warm aloft. The heat
wave rolls on through midweek with highs 90-95 forecast with max
HX approaching 100F. Additional heat headlines may be needed.

&&

.LONG TERM /THURSDAY NIGHT THROUGH SUNDAY/...
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 /15Z MONDAY THROUGH FRIDAY/...
Main change for the 12Z TAF package is to add a tempo group
for a very brief period of fog for around 12Z Tuesday. As
the airmass becomes a bit more humid, very light wind fields
could result in some fog.

Otherwise looking at VFR conditions today into this evening, as
high pressure remains over the area.

Winds were gusty at times since Sunday afternoon, but will
weaken a bit more here this morning, as radar VAD winds have
been on the decrease since Midnight.

The strong June sun and mixing may kick winds up at times later
this afternoon.

Highest chance of any showers or storms today will likely be
near the lower Great Lakes.

Not much change to conditions the next several days. If the
dewpoints come up later in the week, then there could be
some patchy fog.

Outlook...

Tue-Fri...Predominantly VFR, with building heat. 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)

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
Heat Advisory from noon to 8 PM EDT Tuesday 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...Fitzgerald/Steinbugl
SHORT TERM...Fitzgerald/Steinbugl
LONG TERM...Guseman/Bauco
AVIATION...Martin
CLIMATE...Steinbugl/NPB