274
FXUS61 KCTP 201840
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
240 PM EDT Thu Aug 20 2026

.WHAT HAS CHANGED...
* Flood watch issued for most of central PA until 4/8PM
* Severe T-storm watch issued for a portion of the LSV until
  10PM
* Expanded fog coverage late tonight into early Friday morning

&&

.KEY MESSAGES...
1) Elevated flooding risk shifts from central into eastern PA
late this afternoon into the evening

2) A few strong to severe thunderstorms remain possible in far
southeast PA through early to mid evening

3) An unsettled weekend bookended by fair weather Friday and
early next week.

&&

.DISCUSSION...
KEY MESSAGE 1: Elevated flooding risk shifts from central into
eastern PA late this afternoon into the evening

The right entrance (upper jet) ascent pattern will remain
strong through the afternoon with a mature MCV moving eastward
from around KAOO as of 1730TUC. This feature will provide strong
dPVA to further enhance divergence/outflow aloft which should
invigoration additional convection as it tracks into the Lower
Susquehanna Valley later this afternoon.

Despite lack of lightning, rainfall has been efficient
particularly within the MCV comma head and banded rain features
extending to the northeast near the I-80 corridor. We`ve
expanded the flood watch issued earlier this morning eastward
through the mid and lower Susquehanna Valley where 3+ inch
rainfall totals are possible. Combination of the heavy rain,
complex terrain, and relatively saturated soil/low FFGs was also
a contributing factor in the watch issuance. The nature of the
flooding has been more inundation type vs. true flash flood with
some reports of ponding water/poor drainage flooding, flooded
basements, and a few road secondary closures.

Rain exits the eastern zones around 00Z with clouds gradually
clearing out later tonight. Widespread rainfall today followed
by gradually clearing conditions should allow for formation of
late night valley fog which may become locally dense with vis
1/2mi or less into early Friday morning.

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

KEY MESSAGE 2: A few strong to severe thunderstorms remain
possible in southeast PA through early to mid evening

Severe T-storm watch #604 issued for a portion of the Lower
Susquehanna Valley (LSV) until 10PM. The severe threat won`t
last that long, peaking in the next 1-3 hours and likely ending
by or shortly after 6PM.

Previous...
SPC highlighting the far southeast part of the lower
Susquehanna Valley for severe watch potential (80% probability)
via MCD#2052. MCV approaching that area should trigger
increasing t-storm development through 4-6PM, accompanied by the
risk of localized damaging wind gusts and perhaps a couple of
tornadoes.

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

KEY MESSAGE 3: An unsettled weekend bookended by fair weather
Friday and early next week

By Friday, the aforementioned front will drift south but remain
very close to the Mason-Dixon line. As such we can`t rule out a
spotty shower/t-storm in far southern PA Friday afternoon.
However, most locations will stay dry and Friday looks like a
fairly pleasant day with plenty of sunshine.

An upper trough carving out over the Great Lakes will bring
increasingly unsettled weather conditions over the weekend.
There is still considerable uncertainty with timing, intensity,
and coverage of storms, but it is not expected to be a washout
for anyone. This system will also deliver some relatively
cooler air both at the surface and aloft. This setup could prove
favorable for clusters of gusty t-storms with small hail both
Saturday and Sunday. A cold front will move across the region
Saturday and Sunday, helping focus severe weather potential. The
best chance for strong storms will be west of I-99 on Saturday
and then across eastern PA on Sunday.

In the wake of the cold front, the start of next week looks
quite nice. A decaying secondary cold front could bring some
light showers north of I-80 on Monday, but dry conditions
prevail otherwise. Mostly sunny skies, slightly below normal
temperatures, and lower humidity will provide some very pleasant
late August weather. Upper troughing will continue to support
near to below average temperatures and above average
precipitation into early September.

&&

.AVIATION /18Z THURSDAY THROUGH TUESDAY/...
A 100-125 NM wide area of steady moderate to heavy rain was
covering the Central and North-central Mtns, Middle Susq
Valley, and Laurel Highlands at 1815Z and will continue to move
steadily east at 35-40 mph.

Some breaks in the thick layered clouds across the far SE zones
From KTHV to KLNS will support vertical growth of the line of
low-topped TSRA heavy nearing the I-81 corridor just north of
KHGR.

Used a roughly 2 hour tempo group during the 19-21Z and 20-22Z
period respectively at KMDT and KLNS to cover some brief gusty
wind and lower CIGS/VSBYS associated with the TSRA. Elsewhere to
the North and West, steady moderate to heavy rain with IFR to
low end MVFR conditions will prevail through 20Z across the west
and about 22-23Z along and just SE of the Interstate 81
corridor.

For this evening, look for a brief, several hour period of
mainly VFR before the light wind and moist ground from today`s
rain lead to the formation of fairly widespread dense fog after
midnight through about 13Z Friday.

Conditions will become VFR in all areas by 14Z or shortly
thereafter, with SCT flat cu topped by thin cirrus. Winds will
be light and variable or light from the NW.


Outlook...

Fri...AM fog, otherwise trending VFR.

Sat-Sun...Scattered to numerous showers/t-storms likely. Breezy.

Mon...VFR returns for early next week.

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
Flood Watch until 8 PM EDT this evening for PAZ012-041-042-045-
046-049>053-057>059-065-066.
Flood Watch until 4 PM EDT this afternoon for PAZ017>019-
024>028-033>036-056-063-064.

&&

$$

WHAT HAS CHANGED...Steinbugl
KEY MESSAGES...Steinbugl
DISCUSSION...Steinbugl
AVIATION...Lambert/Bauco/Teare