903
FXUS61 KCTP 010538
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
138 AM EDT Wed Jul 1 2026

.WHAT HAS CHANGED...
* Confidence in a prolonged heat spell has increased, and heat
  products have been issued into Saturday for affected areas.
* Bumped PoPs up for isold-sct SHRA/TSRA this PM and Wed PM

&&

.KEY MESSAGES...
1) Significant, long duration, and dangerous heat wave expected
from the last day of June into Independence Day/4th of July
holiday weekend

2) Isolated to scattered showers and thunderstorms possible
again Wednesday afternoon/evening

&&

.DISCUSSION...
KEY MESSAGE 1: Significant, long duration, and dangerous heat
wave expected from the last day of June into Independence
Day/4th of July holiday weekend

The main issue and over-arching message is the excessive heat
throughout the remainder of the week and even into the 4th.
The big upper ridge over the OH/TN Valleys will shift east and
a little north through the next several days. Abundant sunshine
and high moisture will make being outside feel incredibly
uncomfortable. As we have been messaging for many days, we
expect a spell of 5 days of heat indices over 100 for at least
part of the CWA. The peak of the heat and humidity will be
Wednesday and Thursday with nearly identical head index values
both afternoons. Much of the area will have heat indices between
100 and 110 those two days. Due to the high confidence in that
part of the forecast, we have issued appropriate excessive heat
warnings and heat advisories for the next few days. The humidity
creeps into Warren Co today, while the dewpoints stay in the
60s in the SE. The heat expands on Wed with temperatures nearing
100 in the urban areas of east. We`ve made very minor tweaks to
the temps and dewpoints each day in collaboration with the
neighbors. The heat will start to abate Fri and a little more
Sat. Not much, but likely enough to start tapering off the
advys/warnings.

As we have been encouraged to do, we chose to use the low end
of the scale to base the WWAs. So, while on the forecast map,
>=50% of Cambria Co does not get to 100HI any day, we felt it
was wise to include them in the advy due to Johnstown`s few
pixels that do reach 100. Many of the people most vulnerable to
heat stress/illnesses live in the urban area of the Conemaugh
Valley. Also, we considered leaving McKean and Potter Counties
out of the heat advys, but decided to include them as there were
a few pixels of 100HI there, and keeping in mind that NY
state`s threshold for advy is only 95 (PA is 100). Now, Somerset
Co is the odd man out for this go `round. We`ve left them out
of the advys because their heat index numbers just weren`t
close enough to make a strong case for inclusion based on
forecaster judgment/nudgers. This matches with LWX leaving
their highest- elevation Cos out of the products - for now.

Height falls hail the approach of a minor cold front which
should arrive on Friday or Saturday. Natural fireworks for the
4th. The increased cloud cover and some rain should help knock
down the temps, and knock out most worries for heat products.
Temps in the SE half of the CWA will come down 3-5F for Sat
(from the 100s of Friday). So, it won`t be a big change, but
probably enough to drop the advys for the NW and downshift the
warning to an advy for the SE half. Sunday should be "cold"
enough to be done with heat products. It will likely not be until
Monday or Tuesday of next week when we see highs return to the
mid to upper 80s across central PA.


   -------------------------------------------------------

KEY MESSAGE 2: 2) Isolated to scattered showers and
thunderstorms possible again Wednesday afternoon/evening

Showers and storms have been to our northeast so far today.
With the setting of the sun, and a decent cap noted on 00Z
Wednesday observed soundings, expect any activity to be
limited overnight, and mainly late if anything holds together
from upstate NY and southern Ontario.

Synoptic pattern for Wednesday similar to the setup we had
today.

More information below.

Changes have been very minor with the main change nudging PoPs
up this aftn/evening and Wed aftn/evening with two shortwave
troughs rolling over the strong upper ridge and nipping the N
and E with some forcing. This forcing, combined with the
help/lift of the Central PA ridges, should be enough to trigger
a couple of SHRA/TSRA. SPC general thunder supports this idea,
but most should be N & E of the CWA. A wild card will be the SE
third of the area on Wed, where CAPEs get super high and the
possible dip in upper level temps may allow isold/sct storms to
pop up there. In collab with PHI and LWX, we added 20-30 PoPs
there for Wed PM.

&&

.AVIATION /06Z WEDNESDAY THROUGH SUNDAY/...
A large scale upper level ridge will continue to build
northeast across central PA Wednesday into Thursday. The warm
air aloft will serve as a cap, keeping the chance of showers and
storms on the low side. With that said, a PROB30 for 6SM -SHRA
was added to KBFD, where weak shortwaves on the periphery of the
ridge are bringing showers and a few thunderstorms. This
activity will trend northeastward & taper off as ridging
continues to build in. While the airmass is quite humid, the
chance of fog is on the low side tonight.

Intermittent MVFR ceilings are possible early today as diurnal
mixing rejuvenates the daytime cumulus deck within this
hot/humid air mass, primarily outside of the Lower Susquehanna
Valley (KMDT/KLNS) where low-level moisture is less favorable
(RHs around 60-80%). Otherwise, westerly winds of 5-10 kts with
a few gusts to 15 kts are expected during the day, with VFR
cumulus deck in the afternoon trending towards mainly clear
skies during the evening as ridging builds in. Thunderstorm
chances remain low despite the heat & humidity due to mid- level
subsidence and dry air aloft (mean 700-300 mb RH around 20%),
with convective activity continuing to favor Upstate NY and New
England.

For Wednesday night, winds will trend light and variable with
mainly clear skies. Patchy overnight fog may once again develop
given the humidity, though rain-free conditions and plentiful
sunshine during the daytime will continue to mitigate the
overnight fog potential.

Outlook...

Tue-Sat...AM fog; otherwise VFR. Hot & humid with isold PM
t-storms psbl. High density altitude concerns possible.

Sun...Restrictions possible in afternoon t-storms

&&

.CLIMATE...
Triple digit max temps are forecast in the Lower Susq Valley
(LSV) on Thursday and Friday bookended by upper 90s Wednesday
and Saturday.

The last time Harrisburg observed consecutive days with maxT
greater than or equal to 100F was back in 2011 on July 21-22.

The record number of consecutive days with maxT >= 100F is 3
and has occurred 5 times: (all in the month of July)

1999-07-16 to 1999-07-18
1999-07-04 to 1999-07-06
1991-07-19 to 1991-07-21
1966-07-02 to 1966-07-04
1936-07-09 to 1936-07-11

The last time Harrisburg hit the century mark was July 16th in
2024. Prior to that, it was July 19th in 2020.

Harrisburg averages 1 day annually with a maxT >100F. The most
number of days observed in a year is 6 in 1999.

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
Heat Advisory until 8 PM EDT Friday for PAZ004.
Heat Advisory from noon today to 8 PM EDT Friday for PAZ005-
006-010>012-017-018-024-025-034-035-037-041-042.
Extreme Heat Warning from noon today to 8 PM EDT Friday for
PAZ019-026>028-036-045-046-049>053-056>059-063>066.
Heat Advisory from 8 PM Friday to 8 PM EDT Saturday for PAZ019-
026>028-036-045-046-049>053-056>059-063>066.

&&

$$

WHAT HAS CHANGED...Dangelo/Martin/Bowen
KEY MESSAGES...Dangelo/Martin/Bowen
DISCUSSION...Dangelo/Martin/Bowen
AVIATION...Martin/Teare
CLIMATE...Steinbugl