499
FXUS61 KCTP 170919
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
519 AM EDT Thu Sep 17 2026

.WHAT HAS CHANGED...
* Level 1 excessive rain risk expanded to all of CPA for today
* Cooler temperature moderation next week

&&

.KEY MESSAGES...
1) Very humid with locally heavy rainfall possible this
afternoon

&&

.DISCUSSION...
KEY MESSAGE 1: Very humid with locally heavy rainfall possible
this afternoon

Highly anomalous moisture for this time of year (NAEFS mean
pwat values near climatological maximum percentiles) pooling
around the periphery of subtropical high over the southern
Plains and lower MS Valley will interact with a surface cold
front moving slowly south/southeastward from the lower Great
Lakes to produce periods of showers and a few locally heavy
thunderstorms across Pennsylvania later today. 17/00Z HREF
indicates the potential for spot rain amounts of 2-3 inches.
It`s very likely that most of central PA picks up some rainfall
by tonight. However, we do not anticipate an all-day rain/washout.
Cloud trends remain a tough call with early morning convection
over north central PA, but fcst instability this afternoon across
south central PA will be more than supportive for thunderstorm
development. SPC continues to maintain a general (non-severe)
convective outlook for today which is likely due to the lack of
deep layer shear (displaced farther to the north) and poor mid
level lapse rates (very moist, tall/skinny soundings with warm
cloud depths greater than 10kft).

Another taste of Fall is on the way for the end of the week
with noticeably cooler and much drier/less humid air poised to
return behind the front (Td crashing into the 40s/50s). Expect a
crisp and cool overnight Friday into Saturday morning with some
upper 30s possible across the northern tier. Dry/fair wx
conditions are forecast to start the weekend and last through
the day on Saturday followed by periods of potentially heavy
rainfall Saturday night through early next week. Both NAEFS and
ECMWF SATs show at least 90th percentile PWs returning the the
region which is supportive for at least a marginal excessive
rain signal. NBM temps have also cooled/moderated quite a bit
Mon-Wed with most locations struggling to exceed 70F for
daytime highs.

&&

.AVIATION /08Z THURSDAY THROUGH MONDAY/...
Highly variable conditions ranging from MVFR to brief periods of
LIFR/VLIFR across Central and Western PA airfields, while mainly
VFR dominates conditions across the Susquehanna Valley terminals
early this morning.

During the late morning hours, conditions at most terminals
should improve to higher end MVFR or VFR as temps warm,
improving vsbys and raising ceiling heights.

For this afternoon, the very slow moving cold frontal boundary,
draped along the Interstate 90 corridor in Northwestern PA and
Northern Ohio this early this morning, will drift southeast
bringing a trend toward a few brief periods of MVFR cigs and
vsbys as a result of widely scattered showers and a few
thunderstorms.

As the front pushes through the NW Mtns (this afternoon) and
Central and Southern PA (tonight), sfc winds will shift to the
northwest and precipitation will end.

Lowering cigs and vsbys (into mainly the MVFR range) will occur
in the wake of the front tonight/early Friday associated with a
layer of stratocu clouds.

Outlook...

Fri-Sat...Valley fog and the likelihood of a MVFR stratocu cloud
layer in the morning (mainly across the Central and NW Mtns);
otherwise VFR.

Sat night-Monday...Periods of rain and sub-VFR likely.

&&

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

&&

$$

WHAT HAS CHANGED...Steinbugl
KEY MESSAGES...Steinbugl
DISCUSSION...Steinbugl
AVIATION...Lambert/Tyburski