Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
715 PM EDT Wed Sep 9 2026
Day 2
Valid 12Z Thu Sep 10 2026 - 12Z Fri Sep 11 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER THE UPPER OHIO
VALLEY INTO THE CENTRAL APPALACHIANS...

21Z Update..

A MRGL Risk area was introduced along the Gulf Coast in Louisiana
and Mississippi. A wave/surface trough feature in the northern Gulf
will promote southerly low-level flow onto the coast, bringing
along with it high PWAT values (>2.25"). This will support heavy
rainfall, with HREF/RRFS guidances suggesting medium-to-high
chances (~60-70%) of 1"/hr rain rates. Moisture moves eastward
through the coast, bringing heavy rain into AL, GA, and FL, but is
currently forecast to bring a shorter duration of heavy rainfall,
and as such, a MRGL was left out for now.

Elsewhere, nearly no change was made to the inherited SLGT risk
area in the Ohio Valley, other than a minimal westward nudge into
Ohio given a solid QPF EFI signature in the ECMWF. Minor
restructuring of the inherited MRGL Risk area in the Southwest was
also made to capture the latest run of global and early CAMs
guidance.

Blanco-Alcala

...Previous Discussion...

...Upper Ohio Valley into the Central Appalachians.. PW values 2+
standard deviations above the mean are forecast along the west-east
oriented frontal boundary sinking south through the Ohio Valley,
Central Appalachians and Mid-Atlantic region day 2. The previous
slight risk area was adjusted southward by approximately 80-100
miles to fit the latest model qpf consensus for potentially heavy
rains. H85 flow parallel to this front will support training
potential and also enhance uvvs in the upslope regions of the
Central Appalachians.

Marginal Risk areas.

...Southwest...
A marginal risk area was continued over portions of the Southwest
for potential for local heavy rains and isolated runoff issues in
the continued axis of above average PW values forecast across this
area. A marginal risk was also added for the Transverse Range of
Southern California where the RRFS was showing neighborhood
probabilities as high as 45%+ for 1"+ totals.

...Lower OH Valley, Mid to Lower MS Valley into the Southern
Plains...
A broad marginal risk area was maintained to the
southwest of the Upper OH Valley/Central Appalachians slight risk
area, extending into the Lower OH Valley, Mid to Lower MS Valley
and westward into the Southern Plains of OK and northwest TX.
Scattered convection likely along the surface frontal boundary
where PW values will remain high, 1.75-2.00"+, but with FFG values
high and confidence low with where convection may maximize, the
threat level was kept at marginal.

Oravec


Day 2 threat area: www.wpc.ncep.noaa.gov/qpf/98epoints.txt