611
FXUS61 KCTP 162025
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
425 PM EDT Wed Jul 16 2025

.SYNOPSIS...
* Elevated risk of excessive rainfall and flash flooding this
  afternoon and evening
* Scattered thunderstorms with locally heavy rain will remain in
  the forecast forecast on Thursday; trending drier on Friday
* Heat risk builds this afternoon and peaks on Thursday; modest
  cool down and less humid end the week

&&

.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
Issued flood watch for flash flooding in two parts for the
western and eastern portions of CPA until 10PM and midnight.
The latest MPD #708 from WPC highlights the current met watch
and emerging flash flood threat very well:

Summary...Scattered thunderstorms should increase in coverage
through the afternoon atop very sensitive local ground conditions
especially in Pennsylvania.  Flash flooding is likely - especially
later this afternoon and into the early evening.

Discussion...Recent radar/satellite imagery depicts a gradual
increase in convective coverage especially across
northern/northeastern Ohio into southwestern Pennsylvania.  The
cells in southwestern Pennsylvania are only loosely organized and
appear to be tied to 1) increased surface heating/destabilization,
2) ascent from a mid-level shortwave trough currently centered
over eastern OH, and 3) confluence on the northeastern extent of a
25kt 850mb jet along the Ohio River. The loose organization of the
cells has led to minimal convective training/repeating that has
largely held rain rates to less than 1 inch/hr in most areas
despite only modest (~15-20 kt) southwesterly steering flow aloft.
Flash flood potential is relatively isolated in the short term.

Concern exists that with progression through peak heating,
convective coverage will increase while spreading eastward across
the discussion area, leading to cell mergers, modest upscale
growth into clusters, and higher rain rates. Furthermore, the
higher rain rates are likely to materialize across very
sensitive locales especially across [central] Pennsylvania that
have experienced 2+ inches of rain in the past 48 hours. FFG
thresholds are relatively low - less than 1 inch/hr areawide and
near zero in a few spots. These factors suggest an eventual
increase in flash flood potential through the afternoon and
early evening hours (extending through 00Z/8p EDT). Scattered
instances of flash flooding are likely, and significant impacts
may occur where ground conditions are most sensitive.

Convection should gradually decrease in coverage and intensity
into late tonight. Expect another muggy summer night with lows
65-75F.

&&

.SHORT TERM /6 AM THURSDAY MORNING THROUGH FRIDAY NIGHT/...
*No change to the SPC severe t-storm outlook for Thursday with
 slightly higher potential for sporadic damaging wind gusts in
 the strongest storms

*Heat risk peaks Thursday afternoon across south central and
 southeastern PA with max heat index fcst to reach/exceed 100F
 in parts of the middle to lower Susquehanna Valley - a heat
 advisory may be needed in the next 1-2 forecast cycles

*Slightly cooler and less humid end to the week with dry wx for
 most of CPA

Previous Discussion Issued: 438 AM EDT Wed Jul 16 2025

On Thursday, model guidance is coming into focus that as a
northern stream short-wave (coming through MT this morning)
tracks eastward, a surface wave will develop and track north of
PA, from the Upper Great Lakes across upstate NY and into
northern New England. As this occurs, a surface cool front will
approach the Commonwealth from the NW and could impinge on the
region by late in the day or during the evening. Daytime heating
and some height falls aloft should lead to at least moderately
unstable conditions once again.

As opposed to today, the environmental flow looks stronger on
Thursday (mid-level winds of 30-40 kt) and there also appears to
be some drier air aloft to tap into. As a result, the threat of
severe weather (damaging winds/hail) looks a little better as
compared to today, with the flash flooding risk a bit reduced as
compared to today, given somewhat lower precipitable water
values with the aforementioned drier air aloft, and also faster
cell motions to potentially limit residence time of any heavy
downpours over a given location.

The other potentially high impact weather issue on Thursday is
the heat and humidity for PA`s southern valleys, where heat
indices could locally approach or exceed 100 degrees. However,
due to uncertainty with convective timing and coverage (which
could conceivably knock the heat down a bit in some areas),
we`ll take a wait and see attitude on any future Heat
Advisories.

On Friday, model guidance has generally trended faster with the
passage of the above mentioned cool front, with indications now
there that the front could be largely south of the Commonwealth
prior to peak heating Friday afternoon. Our southern tier
counties may still be close enough to the boundary for at least
isolated afternoon convection, however, confidence is increasing
that areas near and north of I-80 will see a rain-free day.

&&

.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
Still no real change to the large-scale pattern that has
persisted now for a couple of weeks, featuring an expansive
summertime upper ridge axis from the southwestern Atlantic
across most of the southern U.S., and a more progressive, zonal
northern stream belt of westerlies near the international border
with Canada.

As individual short-wave impulses within the northern stream
flow periodically track north of the Commonwealth, they`ll bring
just enough height falls to steer surface frontal complexes
across PA, with convective coverage maximized in the initial
warm advection pattern with these waves, and also just ahead of
approaching cool fronts, focused mainly during peak heating
(afternoon/early evening hours). If individual cool fronts can
push far enough south before stalling and/or washing out, we may
also squeeze out an occasional day with little to no rainfall.

At this early vantage point, it looks like the highest
probability for showers and thunderstorms is from late Saturday
through Sunday, with perhaps Monday as a mostly rain-free day.

Medium-range guidance is also suggesting that the upper ridge
may flex its muscle some by the middle of next week, perhaps
leading to building heat and humidity by then, after a
temporary break from such from late in the weekend into early
next week.

&&

.AVIATION /21Z WEDNESDAY THROUGH MONDAY/...
Late afternoon update.

Timing of the main band of showers and storms not bad, some
adjustments made this afternoon for isolated storms ahead of
the main activity.

Earlier discussion below

For the 18Z TAF package, went with VCSH all areas, as activity
has been forming on the radar screen the last few hours.

Expect more widespread activity later this afternoon, so used
a TEMPO group for thunder.

For the overnight period, went with lower conditions and
showers.

The main upper level wave moves east of the area Thursday
morning, so expect winds to shift more to the west and become
gusty. Still some chc of lower clouds and showers up to 18Z.
Thus used VCSH.

Much of the area could be mainly hot but rain free and VFR by
early afternoon on Thursday.

The cold front will be well behind anything on Thursday,
the front will be more of a feature later Thursday night.

Outlook...

Fri-Sat...Mainly dry.

Sun...Showers and storms likely.

Mon...Still a chc of a shower or storm.

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
Flood Watch until 10 PM EDT this evening for PAZ010>012-
017>019-024>027-033>036-045.
Flood Watch until midnight EDT tonight for PAZ028-041-042-046-
049>053-056>059-063>066.

&&

$$

SYNOPSIS...Steinbugl
NEAR TERM...Steinbugl
SHORT TERM...Jurewicz/Steinbugl
LONG TERM...Jurewicz/Steinbugl
AVIATION...Martin