955
FXUS61 KCTP 132139
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
539 PM EDT Sat Jul 13 2024

.SYNOPSIS...
*Another heat surge/significant heat wave is headed our way for Sunday-
 Wednesday with max heat index 100-110 over parts of south
 central PA and the Susquehanna Valley
*While an isolated late afternoon or early evening thunderstorm
 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 /UNTIL 6 AM SUNDAY MORNING/...
21Z Update: Small tweaks to the near-term where some scattered
showers have formed across east-central PA. At this time,
generally pulsing up towards producing a strike or two of
lightning before falling apart. This trend is expected to
continue. The complex west of the area has been trending
downwards, but could see some precipitation into portions of
Clearfield County. Fog formation across N/SE PA is possible,
especially in areas where showers manage to form throughout the
rest of the evening.

Previous Discussion Issued at 1:58 PM EDT:

Rising heights, dry mid levels, and weak sfc high pressure
extending from the Lower Great Lakes into PA will bring a nice,
warm early Summer day with abundant sunshine and dry weather
over the vast majority of Central PA.

However, passage of a weak surface trough, combined with strong
diurnal heating, and lack of a significant cap in model
soundings opens the possibility (10-20% chance) of an isolated
thunderstorm later this afternoon through the evening hours.

Additionally, subtle llvl convergence zones (across the
Northern Tier counties and Laurel Highlands) leading to some
building cu this afternoon, especially across the southeast-
facing slopes of the Laurel Highlands where the better late
morning/early afternoon heating occurred. Will linger SCHC POPS
for several of our Scent/SW counties into the evening hours and
diminish them elsewhere where terrain and any outflow boundary
effects to enhance additional convection will be minimal.

Early afternoon temps are right on track to reach highs ranging
from the mid 80s acrs the Northern and Western Mtns to the Low
90s in many of the Southern Valleys and Susq region...or +5-10
degrees above mid July climo.

Tonight will be mainly clear and muggy with areas of fog and
min temps 60-75F or +5-10 degrees above the historical average.

&&

.SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/...
Another rather nice (but very warm to hot), rain-free summer
day is on tap for most of the area Sunday, thanks to surface
ridging and dry mid level air over Central PA. GEFS shows a
channel of near normal (approx 1 to 1.2 inch PWAT air extending
from the NCent Mtns to the Laurel Highlands on Sunday with
values around 1.5 inches across the far West and SE parts of
the state.

Still, these PWAT values ahead of a weak shortwave combined
with strong heating/instability should be able to produce
isolated to widely scattered convection from the mid afternoon
into the 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.

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...
No significant changes from the previous guidance runs.
Confidence is increasing for the likelihood of thunderstorms
crossing the state on Wednesday as the cold front pushes
through. Mainly fair weather is currently expected for the
beginning of the weekend.

Prev...
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.


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 /22Z SATURDAY THROUGH THURSDAY/...
Predominantly VFR conds will be found across central PA through
the rest of this afternoon/evening.

Highly isolated showers or thunderstorms will pop through 00Z
Sunday, but coverage will be sparse and practically all
locations should stay dry. Winds will be light and variable in
direction today (generally 5 kts or less).

After any convective wanes this evening, 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 Monday and
Tuesday with the best chance coming Wednesday afternoon/evening
with the passage of a cold front.

&&

.CLIMATE...

RECORD TEMPERATURE - A record high temperature of 86 degrees
was set today at Bradford, PA. This ties the old record which
was set back in 1979.

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...Lambert
NEAR TERM...Lambert/NPB
SHORT TERM...Lambert/Steinbugl
LONG TERM...Fitzgerald/Bowen
AVIATION...Lambert/Evanego
CLIMATE...Evans