949
FXUS61 KCTP 220121
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
921 PM EDT Mon Sep 21 2026

.WHAT HAS CHANGED...
* QPF slightly lower for the Laurels, risk of flooding just to
  the drier side of borderline.

&&

.KEY MESSAGES...
1) Periods of light to moderate rain tonight through Wednesday.
Greatest areal coverage tonight and Tuesday morning. Widespread
flooding unlikely, isolated minor flooding possible.

2) Trending drier later in the week as a coastal storm develops
offshore.

&&

.DISCUSSION...
KEY MESSAGE 1: Periods of light to moderate rain tonight
through Wednesday. Greatest areal coverage tonight and Tuesday
morning. Widespread flooding unlikely, isolated minor flooding
possible.

A quasi-stnry area of mid-level frontogenesis beneath the right
entrance region of upper jet max will strengthen into the
middle of the overnight hours over the I-80 corridor in West-
Central PA (Near KFIG to KUNV) before moving gradually south and
weakening on Tuesday as the best lift associated with the
aforementioned jet quadrant shifts to a location SE of Cape Cod
while a second jetlet focused some meso-B UVVEL across the
Laurel Highlands and points south.

Rainfall rates thus far per MRMS have maxed out between 0.10 and
0.25 of an inch per hour, but part of these higher rates area
likely the result of bright-banding around the 9 kft AGL (from
each RDA site such as KCLE, KPIT, KCCX and KBUF).

These rainfall rates (at least for the time being) are well
below the amounts needed to pose a flooding threat.

Locations that will see between 0.50 and 1.00 inch overnight
will be near or just SW of the current main area of the rain.

The Laurel Highlands, mainly our SW 4 counties, have the lowest
FFG/FFHs. But, much of the statistical guidance keeps rain
intensities (QPF/1,3&6hr time frames) above those thresholds for
flooding to occur. There is still a ~20% chc for rainfall
intensities to exceed FFG tonight/Tues AM in the SW, but we`d
need to get some instability and deep convection to tap all the
1.5" PWAT overhead. We`re going to continue to hold off on any
flood watches.

Expect some minor (ponding of water on roads/ditches, and small
creeks/streams) flooding due to the extended duration of the
light to moderate rainfall. Dry air continues to be shoved into
the area from the N through the next 48 hours. A tight gradient
of precip may occur along or just north of I-80 this evening as
a slight enhancement to the rain is expected while a short wave
trough/MCV moves overhead W to E along I-80. There could be a
ltg strike/thunder rumble here or there, but it will be sparse.

We`ll continue to evaluate the near term guidance for hints of
heavier than currently-expected precip.

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

KEY MESSAGE 2: Trending drier later in the week as a coastal
storm develops offshore.

Northeast flow Wednesday into Thursday between 1038 mb high in
Quebec and a developing coastal low will advect in dewpoints in
the 40s and perhaps even the 30s at the sfc Wed-Thu, with even
drier air in the 500-850 mb layer. This should bring an end to
the rainfall for at least a couple of days. The next feature to
monitor will be the coastal storm, which may meander off the New
England and Mid Atlantic coast into the early part of next week
with this blocking high to its north. Such blocky patterns
are notoriously difficult to predict with respect to sfc
features and precip potential/placement/timing. Depending on the
size of the coastal storm and how much it retrogrades, rain will
be possible in at least east central PA between Fri and early
next week, but confidence is low. Higher confidence in wind
gusts of 15-25 mph and below normal temps through the end of the
week.

&&

.AVIATION /00Z TUESDAY THROUGH SATURDAY/...
A nearly stationary area of steady light to moderate rain
stretched from near KFKL to KDUJ, KUNV and KSEG at 01Z will
will sag slowly to the south and southwest overnight.

The bulk of the rainfall through 05Z will be focused in a rather
narrow, east/west band, near and just to the south of the I-80
corridor. The southern edge of this rain area will be just to
the NE of a KIDI to KAOO line before drifting slowly south
later tonight.

ill be just to the north of a KIDI to KUNV for the
next several hours before waning in coverage and intensity late
tonight.

MVFR cigs will begin to overspread the region and once more,
MVFR and IFR will become prevailing at most sites by 06Z except
for MDT and LNS where the rain brushed by just to the north - so
far.

Any notable improvement looks unlikely on Tuesday with
continued rain chances and thick layered clouds sticking around
for most of the day.

Outlook...

Tue-Thu...Restrictions possible from -SHRA/BR and low ceilings,
mainly S.

Fri...VFR favored as a developing coastal low looks to bring subsidence
overhead, though -RA and lower cloud ceilings associated with this
system may reach our eastern terminals.

&&

.CLIMATE...
As of 5 PM, 1.05 inches of rain fell at AOO (Altoona) PA today.
This broke the old record of 0.73 inches set in 1957.

&&

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

&&

$$

WHAT HAS CHANGED...Lambert/Dangelo
KEY MESSAGES...Lambert/Dangelo
DISCUSSION...Lambert/Dangelo/Colbert
AVIATION...Lambert/Bowen
CLIMATE...Martin