239
FXUS61 KCTP 161647
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
1247 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, with a reduction in
  rainfall anticipated on Friday
* Heat risk builds this afternoon and likely peaks on Thursday,
  with potential for heat indices to exceed 100 degrees for
  portions of southern PA

&&

.NEAR TERM /THROUGH TONIGHT/...
Early this morning, clear-partly cloudy skies covered much of
the Commonwealth, with areas of river valley fog continuing to
develop, owing to light winds and wet soil conditions.
Interestingly, maritime type stratus clouds are notably absent
compared to the last couple of mornings, and given that sunrise
is fast approaching, their development seems increasingly
unlikely.

Areas of locally dense river valley fog are expected to burn
off before 9 am in most locales. This should lead into a period
of hazy sunshine for the late morning and early afternoon hours,
which should allow the atmosphere to heat up and destabilize.

By this afternoon, we still expect a mid-level short-wave trough
to be on approach from the OH Valley, along with perhaps the
remnants of a MCV, seen this morning on satellite imagery over
central KY. Forced lift from these features, along with a
remnant low-level warm front lifting back northeast across PA,
should lead to increasing coverage of showers and thunderstorms
by mid to late afternoon, lasting well into the evening hours.

Given steadily increasing precipitable water values, generally
ranging from 1.7 to 2.2" by early evening, a water loaded
vertical column (lack of any real dry layers), and relatively
light wind flow through a deep layer (progged winds of 20 kt or
less all the way up through about 400 mb), the environment
would seem to favor torrential downpours and isolated flash
flooding as the main concern of the day, with isolated damaging
wind gusts via wet microbursts a distant second. Although, as
just mentioned, the concern for isolated flash flooding is
there, lack of confidence in which areas will see the most
persistent thunderstorms and repeat rounds makes placement of
any Flood Watches difficult at this time. Thus, the preferred
strategy would be to wait until later today when radar trends
and near- term, high resolution model output can be evaluated,
to see if the need exists for any smaller, targeted Flood Watch
areas.

Overnight, although convective coverage should decrease late
behind the above mentioned short-wave, a juicy air mass and only
gradually reducing instability may keep at least isolated showers
and thunderstorms at play.

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
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 TUESDAY/...
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 /18Z WEDNESDAY THROUGH MONDAY/...
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 from 5 PM this afternoon to midnight EDT tonight
for PAZ028-041-042-046-049>053-056>059-063>066.

&&

$$

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