521
FXUS61 KCTP 120916
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
516 AM EDT Sat Jul 12 2025

.SYNOPSIS...
* Continued seasonably warm and humid through much of the coming
  week
* Although at least hit and miss, afternoon and evening focused
  showers and thunderstorms are expected through Monday, the
  most widespread activity, featuring locally heavy downpours,
  will be Sunday afternoon and evening
* Tuesday looks primarily rain free

&&

.NEAR TERM /THROUGH TONIGHT/...
Clear-partly cloudy skies covered much of the Commonwealth early
this morning, with patchy areas of lower clouds and river valley
fog across central and northern portions of the state. Also,
some maritime origin lower clouds have slowly been backing into
the far eastern counties as we approach sunrise. A small
convective cluster, owing to low-level warm advection and some
short-wave support, was crossing eastern Lake Erie into western
NY, but expectations are that this area of showers and storms
will both weaken and stay north of the Commonwealth this
morning.

By mid-late morning, patches of lower clouds and valley fog are
expected to burn off, yielding hazy sunshine, very warm and
sticky conditions for much of the daylight hours Saturday.
Afternoon highs should range from the mid 80s over the higher
terrain, to the lower 90s in the typically warmer valleys of
south-central PA. Apparent temperatures could reach the mid-
upper 90s in some of these same valley locales.

Although PA will generally be in a synoptic environment
characterized by height rises aloft and a lack of focusing low-
level boundaries today, enough instability should bubble up for
widely scattered and terrain favored convection to form by
later this afternoon and early evening. We think that most of
the focus will be from about the Middle Susquehanna Valley up
into the Endless Mountains region. Although coverage should be
relatively isolated in the grand scheme, a seasonally sultry air
mass, weak shear, and slow/erratic cell motions could lead to
locally heavy rainfall, with point amounts of 2-3" suggested by
model probability matched mean values.

Later tonight, convective coverage should wane with diurnal
stabilization, although some of our high-resolution models are
suggesting that isolated activity could continue well into the
overnight. For now, we have fairly low probabilities (around
20%) for late night showers and storms.

It will be another sticky night, with lows ranging from the mid
60s over the higher terrain, to the lower 70s in the Cumberland
and Susquehanna Valleys.

&&

.SHORT TERM /SUNDAY THROUGH MONDAY/...
Model guidance remains consistent in depicting widespread
coverage of showers and thunderstorms for central PA Sunday
afternoon and evening, as a surface cool front approaches from
the west, along with some height falls aloft. Since the main
synoptic-scale westerlies are expected to remain well north of
the state on Sunday, creating a weak shear environment, any
severe concerns from localized damaging winds seem to take a
back seat to heavy rainfall considerations. Pooling of late day
and evening surface dew points (up to the mid 70s) from the
Susquehanna Valley up into the Endless Mountains region should
lead to columnar precipitable water values near 2". This,
combined with the potential for slower cell motions and training
from the aforementioned weak shear pattern, along with
sensitive antecedent soil conditions from recent rainfall,
raises concern for localized excessive rainfall. Model
probability matched means suggest point amounts of 2-3" and
given the above described pattern, up to 4" on a very localized
basis is not out of the realm of possibilities. We`ll continue
to highlight heavy convective rain potential in our Hazardous
Weather Outlook and briefing packages.

The above referenced cool front will continue its slow push to
the south and east on Monday. As such, it should shift the main
focus for diurnally favored showers and thunderstorms in those
same directions. As a result, we`ve gone with numerous afternoon
and early evening showers and thunderstorms in the Lower
Susquehanna Valley and the western edge of the Pocono plateau,
but notably lower rainfall probabilities elsewhere across
central PA.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
With the large-scale pattern, not a great deal of change is
anticipated during the middle and latter portions of next week.
An expansive summertime upper ridge should stay situated from
the southwestern Atlantic across the southern tier of states,
while a progressive zonal flow regime resides over southern
Canada and the northern tier of the CONUS.

It appears PA will remain situated near the southern edge of the
westerlies, generally close enough to it for at least isolated-
scattered afternoon and evening focused thunderstorms, while
also enough under the influence of the southern CONUS ridge to
keep summertime warmth and humidity at play. Generally speaking,
Tuesday looks to be the "driest" day (least convective
coverage), while Friday could see the most widespread showers
and storms, with another surface cool front potentially on
approach by then.

&&

.AVIATION /09Z SATURDAY THROUGH WEDNESDAY/...
Isold showers have developed early this morning vicinity BFD
and in the eastern parts of the airspace. Areas of fog have
formed as well and will continue past sunrise. A marine layer
and associated low clouds were also observed drifting westward
towards southeastern PA, and will have to monitor this trend as
this could impact the Lower Susq Valley (MDT/LNS) into the
morning.

Fog/low clouds should dissipate Saturday morning, generally post
sunrise, giving way to at least partial sunshine. Scattered
showers/storms will once again develop in the warm, muggy
airmass on Saturday afternoon. This has not been noted in the
TAFs yet, so mentioning the possibility here in the AFD.

Outlook...

Sun...Numerous SHRA/TSRA developing ahead of a CFRONT.

Sun night-Mon...CFROPA; Widespread SHRA/TSRA, mainly southeast.

Tue-Wed...Mainly VFR. Isold PM TSRA poss, mainly south.

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

SYNOPSIS...Jurewicz
NEAR TERM...Jurewicz
SHORT TERM...Jurewicz
LONG TERM...Jurewicz
AVIATION...Gartner/Evanego