548
FXUS61 KCTP 131058
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
658 AM EDT Sat Jul 13 2024

.SYNOPSIS...
*Another heat surge/significant heat wave Sunday-Wednesday with
 max heat index 100-110 over parts of south central PA
*While an isolated thundershower can`t be ruled out, most places
 stay dry this weekend. There is some potential for more
 organized/severe thunderstorms Monday through Wednesday
*Relief from the sweltering heat probable Thursday-Friday

&&

.NEAR TERM /THROUGH TONIGHT/...
Hires model consensus shows ongoing showers exiting the
southeast corner of the forecast area around 12Z, as the mid
level vort max and plume of highest pwats shift east. Any new
development should stay to the south/east of the CWA closer to
or along the I95 corridor.

Mainly clear skies and calm wind to the northwest of I-81 will
allow for valley fog formation through the predawn hours before
dissipating shortly after sunrise.

Rising heights, dry mid levels, and weak sfc high pressure
argue for dry weather over the vast majority of Central PA.
However, passage of a weak surface trough, strong diurnal
heating, and lack of a significant cap in model soundings opens
the possibility (10-20% chance) of an isolated thundershower
later this afternoon through the evening hours.

Model RH profiles support a mostly sunny start to the weekend
after any low clouds/fog mix out. Mixing down 850mb temps of
around 18C translates to expected highs in the mid 80s to around
90F or +5-10 degrees above mid July climo.

Mainly clear and muggy tonight with areas of fog and min temps
60-75F or +5-10 degrees above the historical average.

&&

.SHORT TERM /SUNDAY THROUGH TUESDAY NIGHT/...
Surface ridging and dry mid level air over Central PA should
result in rain-free weather for most of the area Sunday.
However, surging low level moisture ahead of a weak shortwave
combined with strong heating/instability to produce isolated to
widely scattered convection during the afternoon and evening
(15-25% chance).

850mb temps near 20C support highs in the upper 80s to mid 90s
Sunday. While mixing of drier air aloft may result in a slight
reduction in dewpoints during the afternoon, fcst max HX around
100F has prompted the issuance of a heat advisory for the Lower
Susquehanna Valley.

Heat pattern ramps up and peaks early next week as a large
Bermuda high pumps increasingly hot and very humid air into CPA.
850mb temps rising to around 22C supports highs peaking between
90-100F with max heat indices 100-110F. High confidence in
excessive heat risk lead to the issuance of a heat advisory for
the south central Alleghenies and middle Susquehanna Valley
Mon & Tue and xheat watch for the lower Susq where max heat
index could reach 105-110F.

The interaction of modest shortwave trough with very warm and
humid airmass should trigger PM t-storms on Monday. Shear will
likely be weak, mitigating the organized storm potential and
keeping the severe threat isolated/limited. Another round of
at least semi-organized/possible severe convection is possible
Tuesday PM ahead of cold front pressing southeast through the
Great Lakes toward Lake Erie.

&&

.LONG TERM /WEDNESDAY THROUGH FRIDAY/...
The latest GEFS and EPS both track a cold front into the region
Wed PM, likely accompanied by a round of showers/tsra, some of
which could be severe. Heat index values will likely push
100F or advy criteria over the Lower Susq Valley Wednesday
afternoon.

High pressure building in from the Grt Lks will likely bring a
return to fair and seasonable weather late next week (Thu-Fri),
with much lower humidity. However, there is some model spread
regarding how far south the dying cold front gets, so can`t
completely rule out convection lingering over the Southern tier
counties, especially on Thursday.

&&

.AVIATION /12Z SATURDAY THROUGH WEDNESDAY/...
Valley fog across northern Pennsylvania will dissipate quickly
this morning, while low clouds southeast of the Allegheny Front
will be a bit slower to dissipate.

Even the low clouds should gradually diminish through the
morning hours, leaving predominantly VFR conds across central
PA this afternoon. A stray shower or thunderstorm could pop up
this afternoon, but coverage will be sparse and most locations
should stay dry. Winds will be light today (generally 5 kts or
less).

Clear skies and light winds will allow patchy fog to develop
once again tonight.

Outlook...

Sun...AM fog quickly dissipating. A late-day SHRA/TSRA is
possible. Otherwise, predominantly VFR.

Mon-Wed...Scattered SHRA/TSRA possible areawide.

&&

.CLIMATE...
The duration of warm nights is noteworthy -- Harrisburg has not
dropped below 70 degrees since July 3rd. Here are the longest
stretches with temperatures at or above 70 on record at Harrisburg.

# OF DAYS   DATES      YEAR
17        7/19-8/04    2020
13        8/16-8/28    2021
13        7/13-7/25    2010
12        7/18-7/29    2022
12        7/17-7/28    1999
12        7/20-7/31    1940
11        8/04-8/14    1977
10        8/10-8/19    2016
10        7/14-7/23    2013
10        8/01-8/10    1968
10        7/21-7/30    1898
9         12 times, most recently 7/3-7/11/2020
8         7/04-7/12    2024
     .................................................

The minimum temp dipped to 68F yesterday morning (7/12) and
therefore ends the streak at 8 consecutive days. Tonight will
start another run of lows >=70F which should last until next
Thursday night (7/18 or morning of 7/19).

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
Heat Advisory from noon Monday to 8 PM EDT Tuesday for PAZ019-
025>028-034-035-045-046-049>053-058.
Heat Advisory from noon Sunday to noon EDT Monday for PAZ036-
056-057-059-063>066.
Excessive Heat Watch from Monday afternoon through Tuesday
evening for PAZ036-056-057-059-063>066.

&&

$$

SYNOPSIS...Steinbugl
NEAR TERM...Fitzgerald/Steinbugl
SHORT TERM...Fitzgerald/Steinbugl
LONG TERM...Fitzgerald
AVIATION...Evanego
CLIMATE...Steinbugl/Banghoff