226
FXUS61 KCTP 141641
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
1241 PM EDT Sun Jul 14 2024

.SYNOPSIS...
Another prolonged and significant heat wave is expected today
through Wednesday with max heat index values reaching between
100 and 110 degrees F over parts of south-central PA and the
Susquehanna Valley.

Isolated late afternoon or early evening thunderstorms are
expected to develop from the heat and humidity, however,
most places are expected to stay dry through tonight.

More organized, and potentially strong to severe thunderstorms
are expected each afternoon and evening, Monday through
Wednesday.

&&

.NEAR TERM /UNTIL 11 PM THIS EVENING/...
Storms over the Schuylkill moving east, but additional
showers/storms are starting to pop, as anticipated, over the
rest of the SE, esp Leb/Lanc Cos. The good news there is that
the rain may help cool it off a few degs, even where it does
not rain thanks to outflow or just plain extra shade from the
cloud cover. Expect the storms to get a bit stronger than
earlier storms with ML CAPE into the 1500+ range and expected to
peak in the mid-2000s. Very warm air will keep large hail
threat low, but D-CAPE of 1200+ could allow for some stronger
gusts, and perhaps a severe gust or two. Taller cu over the
Laurels/S-cent mtns may produce isold SHRA/TSRA, too. But, air
is getting drier there thanks to a little subsidence. These
would slide east into the lower Susq, too. So, have put PoPs
higher there than elsewhere.

The storms should die down as we lose daylight or even before.
However, a few will drift in from the NW as those in the SE
wane. Heat Advy and watches will remain in place for the time
being, but we do anticipate upgrading some of the area to
excessive heat warning later today.

&&

.SHORT TERM /11 PM THIS EVENING THROUGH MONDAY NIGHT/...
Cloud cover across N/W PA from weakening convection will
provide fairly uniform MinTs tonight into Monday morning,
ranging from the mid- to- upper 60s to the lower 70s across the
LSQ.

Confidence in excessive heat risk is higher on Monday, and has
lead to the issuance of a Heat Advisory (see NPWCTP) for the
south-central Alleghenies and Middle Susquehanna Valley on
Monday. The interaction of a modest shortwave trough, coupled
with a very warm and humid airmass is currently expected to
trigger thunderstorms Monday afternoon into the evening hours
with a slightly higher severe threat than over the weekend with
shear being be the biggest limiting factor.

Collaborated with LWX to maintain the Excessive Heat Watch
(through a few more model cycles) for Monday afternoon into
Tuesday for the lower Susq given some model uncertainty in SFC
dewpoints and precip amounts/impacts from afternoon convection.

SPC has placed all of the CWA within a MRGL risk of Severe TSRA
Monday as stronger mid and upper diffluence and the approach/presence
of a better defined left exit region of the jet will lead to
enhanced larger scale lift to help break any weak cap. The Susq
Valley and points east, along with sou swrn zones may see the
best chance of SHRA/TSRA though on Monday.

Precipitation becomes more limited to NW PA overnight Monday
and into Tuesday morning. The more important sensible weather
overnight into Tuesday will be the lack of reprieve from warm
temperatures with MinTs ranging in the upper 60s (N PA) to the
mid-to-lower 70s (LSQ) with muggy conditions.

&&

.LONG TERM /TUESDAY THROUGH SUNDAY/...
Heat pattern ramps up and peaks Tuesday afternoon 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 aforementioned cold front, expected to push through
Wednesday night, will provide some relief from the heat as well
as the best chance for widespread showers and Thunderstorms on
Wednesday afternoon. Thursday should see a return to seasonable
temperatures with scattered convection possible as the front
stalls out. Friday will have fair weather return to the
commonwealth with high pressure building and humidity expected
to be lower for the end of the week.

&&

.AVIATION /16Z SUNDAY THROUGH THURSDAY/...
A few pop-up SHRA/TSRA are starting over the Sern counties, with
LNS and MDT most probable to have TS/gusty/variable wind due to
the staorms. We may add VCTS to MDT and LNS as the trends in
convection unfold. High heat and humidity will make for
slightly longer than normal landings/takeoffs. The convection in
the SE should diminish in the evening hours with storms drifting
east and also calming down as we lose heating. A stray
shower/storm or two will pop up elsewhere across the airspace,
but not enough confidence in coverage or probability to add
anything of a mention of TS to any of the other terminal
forecasts at this point. Fog may again form overnight in the
valleys as the humidity remains. But, we`re not expecting IFR at
any terminal at this point.

Outlook...

Mon-Tue...Scattered, mainly aftn, SHRA/TSRA possible.

Wed...More widespread SHRA/TSRA, with brief restrictions likely.

Thu...Lingering -SHRA diminishing.

&&

.CLIMATE...

The duration of warm nights is noteworthy. Here are the longest
stretches with temperatures at or above 70F 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
     .................................................

&&

.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 until 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/Dangelo/NPB
NEAR TERM...Dangelo
SHORT TERM...Lambert/NPB
LONG TERM...Bowen
AVIATION...Lambert/Dangelo/Evanego
CLIMATE...Evans