806
FXUS61 KCTP 071023
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
623 AM EDT Fri Aug 7 2026

.WHAT HAS CHANGED...
* Mainly tranquil weather outside of fog this Friday morning.
* Updated Heat Key Message for heat index forecast for today,
  lower confidence in Heat Advisory at this time.

&&

.KEY MESSAGES...
1) Periods of showers/scattered thunderstorms through Saturday
will bring localized flash flooding risk across central
Pennsylvania. Strong-to-severe storms also possible this
afternoon/evening.

2) Very warm temperatures and humid conditions will lead to heat
index values approaching 100 degrees across portions of the
Lower Susquehanna Valley today.

&&

.DISCUSSION...
KEY MESSAGE 1: Periods of showers/scattered thunderstorms
through Saturday will bring localized flash flooding risk across
central Pennsylvania. Strong-to-severe storms also possible
this afternoon/evening.

Activity on Thursday was largely driven by the terrain in
combination with a very moist airmass. Overall a similar
situation today and Saturday. Location of the more active
weather on Saturday may be a bit further to the east and south.
That is still a ways out.

For the overnight hours into Friday morning, the main concern
aside from an isolated shower will be the potential for fog/low
stratus development with mainly clear skies and calm winds.

More information below.

This concern will be highest in areas that received heavy
rainfall across southern Pennsylvania on Thursday. Updated fog
forecast does outline this potential with valley fog expected
across the northern half of central Pennsylvania. Any fog
formation likely mixes out quickly after sunrise and is out by
9AM EDT.

First glance at the first couple of hours of 00Z 8/7 HREF
ensemble guidance outlines an uptick in shower activity across
northern Ohio overnight compared to previous runs. Thus, have
increased PoPs slightly earlier across NW PA closer to sunrise
compared to previous forecast. Increasing humidity throughout
the day with ample instability (~1000-2000 J/kg across N/W PA
and 2000+ J/kg across S/E PA) will likely allow for slightly
more widespread coverage with more height falls observed in
recent model guidance compared to this afternoon and evening.
In terms of a severe threat, expect scattered thunderstorms to
develop with potentially a slight uptick in coverage compared to
this afternoon. Isolated instances of strong-to-damaging winds
appear to be the main hazard with these, mainly in the form of
wet microbursts given the instability, moisture, and lift
(trough approaching the area) in play.

The overly moist air mass, with PWATs exceeding the 90th
percentile across all of central Pennsylvania, will brings
another round of flash flooding concerns on Friday and Saturday,
mainly during the afternoon/evening hours. This flooding threat
could be minimized by more progressive storm motions; however,
given the amount of moisture, any shower/storm will likely bring
efficient rainfall to the region and any location (especially
urban and poor drainage locations) that receive multiple rounds
of heavy rainfall could experience localized flash flooding.
Recent HREF PMMs does paint a corridor 2-3" rainfall amounts
along the Pennsylvania Turnpike Friday afternoon/evening, which
tracks with the ample moisture available. Do want to highlight
that while this signal exists, location of this corridor remains
the main point of uncertainty at this time so remain weather
aware and have multiple ways to receive warnings tomorrow
afternoon/evening. Heavy rain signal on Saturday is more muted;
however, if this heavier corridor of rain plays out as
predicted, some locations could need very little rainfall for
additional flooding concerns on Saturday.

   ------------------------------------------------------

KEY MESSAGE 2: Very warm temperatures and humid conditions will
lead to heat index values approaching 100 degrees across
portions of the Lower Susquehanna Valley today.

Current grids only show a few grid points getting close.
Also temperatures being push back down by showers and
storms, temperatures may not stay up in that range for
very long anyway.

More information below.

Increasing heat and humidity throughout the afternoon hours
ahead of the aforementioned showers/storms will lead to another
hot day across portions of the Lower Susquehanna Valley and
surrounding locations. Recent model guidance does indicate a
slight decrease in temperatures tomorrow with increasing cloud
cover during the late morning/early afternoon hours across the
region which could limit peak heating slightly. That being said,
moisture will be plentiful with dew points expected to reach
into the mid-70s during the afternoon hours ahead of forecast
precipitation. Recent HREF guidance of heat index values
exceeding 100F appear to be more confined to the south and east
of Lancaster County. Highest probabilities max out around
~30-40% for far southern Lancaster County. For reference,
similar guidance was highlight probabilities closer to ~60-70%
for similar locations this afternoon/evening. Given the
uncertainty, have decided to let the upcoming midnight shift
handle heat headlines for Friday to get another run of HREF/NBM
model guidance to assist in this decision. Whether or not a heat
headline gets posted, hot and humid conditions are expected for
the Lower Susquehanna Valley tomorrow before a slight decrease
in heat/humidity for the upcoming weekend.

&&

.AVIATION /10Z FRIDAY THROUGH TUESDAY/...
For the 12Z TAF package, main changes were to adjust to the
current fog situation and add more detail to the period after
06Z.

Mot of the activity so far on the radar has lifted NE.

More information below.

Convection has cleared out of PA, leaving in its wake low level
moisture for overnight/early morning restrictions. Despite
forecaster confidence restrictions in some capacity will impact
the main TAF sites tonight, high res guidance has pushed back
some of the timing.

As of 06Z, BFD and AOO have the greatest confidence in
prevailing IFR restrictions tonight. Whereas guidance still
indicates some will build in at UNV and IPT in the
late night/early morning, but confidence is lower it will be as
widespread at those terminals. Lingering cloud cover should
prevent too much radiational cooling at MDT and LNS, but
abundant low level moisture from daytime rain may still be
enough for some visibility drops into the MVFR category.

Some guidance has an early round of TSRA moving through NW PA in
the late morning/early afternoon, but confidence in its
maintenance isn`t high enough to warrant an FM group, so kept
it as PROB30 at BFD. Included PROB30s with TSRA with visibility
restrictions for scattered afternoon thunderstorms at the TAF
sites. Like earlier today, storms will be hit or miss, but high
PWATs and heavy downpours mean storms may be capable of brief
IFR visibility restrictions should they cross paths with a
terminal.


Outlook...

Sat...Pockets of fog in the morning. Scattered showers/isolated
t-storms with heavy downpours and localized restrictions.

Sun...Mostly dry, some potential for isolated showers across far
W PA. Restrictions possible.

Mon-Tue...Scattered showers/storms. Restrictions possible.

&&

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

&&

$$

WHAT HAS CHANGED...Martin/Beaty
KEY MESSAGES...Martin/Beaty
DISCUSSION...Martin/Beaty
AVIATION...Martin/Lambrech