449
FXUS61 KCTP 131901
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
301 PM EDT Sun Sep 13 2026

.WHAT HAS CHANGED...
*Day 1 Severe Weather Outlook has been upgraded from MRGL to
 SLGT north and west of a line from Johnstown to Williamsport.

&&

.KEY MESSAGES...
1) A broken line of strong to severe thunderstorms
is likely to develop across northwestern Pennsylvania later
this afternoon, posing a threat of locally damaging wind gusts
before weakening as it moves southeastward late this evening.

2) A taste of fall to start the workweek will be followed by
increasing humidity and chances for rain for the second half of
the week.

&&

.DISCUSSION...
KEY MESSAGE 1: A broken line of strong to severe thunderstorms
is likely to develop across northwestern Pennsylvania later this
afternoon, posing a threat of locally damaging wind gusts
before weakening as it moves southeastward late this evening.

The Erie lake breeze will work in tandem with an approaching
cold front to provide sfc convergence to initiate convection
during the mid to late afternoon hours. A jet max at the base of
an approaching upper trough will result in 40-45 kts of 0-6 km
shear by this evening. A few discrete supercells can not be
ruled out, but the predominant storm mode should be linear due
to the large scale forcing of the cold front. MLCAPE will be as
high as 1500 J/kg before decreasing after sunset. Given the
straight hodographs present ahead of the cold front, the tornado
threat appears to be low. The vertical profile is also not
particularly moist above the boundary layer, so updrafts will
content with dry air entrainment as they become established.
Nonetheless with strong winds at the mid and upper levels
pushing storms along at 35 kts, it wouldn`t take much storm
scale dynamics to push sfc gusts into the 45-50 kts range,
especially north/west of Clearfield and prior to sunset, when
the boundary layer is still unstable.

Storms will be on a weakening trend as they move southeastward
into State College and Altoona late this evening. Much of the
guidance has the storms falling apart before reaching the Lower
Susq Valley (maybe a 10 pct chance of holding together).

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

KEY MESSAGE 2: A taste of fall to start the workweek will be
followed by increasing humidity and chances for rain for the
second half of the week.

Dewpoints will fall rapidly behind the cold front, from near 70
this afternoon to the 40s and 50s by early Monday. The northern
tier will see some low stratus downwind of the Great Lakes on
Monday in NW flow. Otherwise, expect clear skies and a pleasant
September afternoon across much of central PA on Monday. With
high pressure building overhead, radiational cooling will be
effective Monday night bringing temperatures down into the 40s
for much of central PA with patchy river valley fog possible.
Valley fog will be possible again Tuesday night.

Return flow on the back side of the high pressure system moving
offshore will bring increasing humidity for the middle and
latter part of the week. A slight chance for precip returns to
the forecast by mid week, with increasing chances for rain
by early in the following week as the upper level pattern
becomes more amplified.

&&

.AVIATION /18Z SUNDAY THROUGH FRIDAY/...
Improvements to flight conditions continue this afternoon with
all TAF sites VFR at 18Z. An approaching cold front in NW PA
will likely trigger a line of late-afternoon showers and storms.
In terms of TAF sites, the highest chance of TSRA will be at
BFD (60 pct) particularly 2100-2400 UTC. JST sees the next
highest chance (50 pct), followed by AOO and UNV seeing chances
closer to 25 pct. Thunderstorms will continue to weaken as they
move southeast, with only spotty light showers expected as the
front passes over KMDT/KLNS overnight. Flow will shift from
westerly to northwesterly behind the front, with post- frontal
winds of around 5-10 kts helping to mitigate fog development,
though stratocumulus may bring intermittent MVFR to perhaps IFR
ceilings (primarily for upslope terminals, KBFD/KJST).

Outlook...
Mon...Primarily VFR conditions, except for some cig restrictions
in northern tier stratocu

Tue-Wed...AM fog possible, otherwise mainly VFR.

Thu-Fri...Increasing SHRA/TSRA chances, mainly NW.

&&

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

&&

$$

WHAT HAS CHANGED...Colbert
KEY MESSAGES...Colbert
DISCUSSION...Colbert
AVIATION...Colbert/Teare