811
FXUS61 KCTP 150720
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
320 AM EDT Tue Jul 15 2025

.SYNOPSIS...
* Other than widely scattered afternoon and evening showers and
  thunderstorms over southern portions of the Commonwealth,
  we`ll enjoy a relative break from rainfall today
* Summertime humidity builds again Wednesday and Thursday, along
  with a return to more widespread, afternoon and evening
  focused showers and thunderstorms, containing localized
  downpours

&&

.NEAR TERM /THROUGH TONIGHT/...
Early this morning, a fairly solid lower stratus deck covers
much of central and eastern PA, with areas of river valley fog
back into the northwestern counties of the state. We don`t see a
great deal of change in this pattern through 8-9 am, with any
areas of fog locally dense. For much of the region covered by
lower stratus clouds, thicker fog should primarily be
concentrated over the higher terrain.

By mid to late morning, lower clouds and fog should burn off,
allowing for a partly-mostly sunny and seasonably warm day.
Afternoon highs will largely range in the 80s, although a few of
our typically warmer valleys could top out near 90 degrees.

As for the humidity, we`re expecting a bit of a moisture
gradient across the Commonwealth this afternoon, with very muggy
conditions still present over the Cumberland and Lower
Susquehanna Valleys (surface dew points in the lower 70s), near
a stalled low-level boundary close to the Mason Dixon line. In
the meantime, for portions of northern PA, somewhat drier air
will attempt to filter in, perhaps allowing dew point values to
locally drop into the upper 50s.

With much of the Commonwealth behind the above mentioned frontal
boundary during peak heating this afternoon, we think the
coverage of showers and thunderstorms will be far less than
yesterday, with hit and miss showers and storms relegated mostly
to areas near and south of US-22/I-78.

Overnight, any isolated evening convection over southern PA
should dissipate rather quickly. Areas of stratus clouds/higher
elevation fog (most widespread over eastern and south-central
PA), along with patchy river valley fog, are likely to form once
again.

&&

.SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/...
On Wednesday, we should see a more sultry air mass (surface dew
points in the 70s) return to much of the Commonwealth, along
with more widespread and afternoon/evening focused showers and
thunderstorms. Synoptic forcing mechanisms consist of a surface
warm front returning northward across the state, the gradual
approach of height falls aloft/short-wave energy from the west,
and the development of a 25-35 southwesterly kt low-level jet
in the OH Valley, placing parts of the Commonwealth in a region
of low-level speed convergence on its leading edge. Given
increasing precipitable water values returning to near 2",
embedded torrential downpours seem likely, and HREF/NBM
probability matched mean values of 1.5-3" (representing
potential point maxima of rainfall) look reasonable. Given
hydrologic sensitivity from recent excessive rainfall for
portions of the state, this is something we`ll continue to
monitor closely. At this juncture, a mention of locally heavy
rainfall will continue in our Hazardous Weather Outlook.

Wednesday night looks warm and sticky, with a gradual reduction
in convective coverage, owing to a loss of heating/instability.

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
On the large-scale pattern, no big changes are foreseen. An
expansive summertime upper ridge axis will continue to extend
from the southwestern Atlantic through most of the southern
CONUS, while a more progressive zonal flow pattern in the
upper-levels exists to the north over southern Canada and the
northern tier states of the CONUS.

The above synoptic-scale pattern will place PA near the far
southern edge of the westerlies, but also on the northern
periphery of the upper ridge`s sphere of influence. Generally
speaking, this will mean frequent bouts of afternoon/evening
focused showers and thunderstorms, whenever any wave packets
aloft traverse the southern end of the westerlies and attempt to
push surface cool fronts to the south and east. However, much
like we`ve seen recently, any real change in air mass (cooler
and drier) seems unlikely, or at least quite short-lived, as
surface boundaries are not able to push very far southward.

From this early vantage point, although predictability horizons
tend to be narrow trying to pinpoint summertime convection,
perhaps Saturday and Monday we could see less rainfall, with
more widespread, afternoon/evening favored showers and
thunderstorms on Thursday, Friday, and Sunday.

&&

.AVIATION /07Z TUESDAY THROUGH SATURDAY/...
A mix of VFR, MVFR and IFR conditions late tonight under
clearing skies should steadily go downhill through MVFR and
likely settle into the IFR/LIFR range for several hours leading
up to sunrise Tuesday with fairly widespread fog forming
- aided by light wind, relatively high dewpoints in the 60s to
low 70s and moist ground from the recent rain.

Conditions will gradually improve back to widespread VFR by 16Z
Tuesday and the chance for a few afternoon showers or a
thunderstorm (with brief MVFR conditions) will be confined to
the southern third of the airspace, in close proximity to a
stalled out frontal boundary (that will be pushing south across
the state tonight).

Outlook...

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

Thurs-Sat...Sct/Nmrs SHRA/TSRA.

&&

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

&&

$$

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