FOUS30 KWBC 010825
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
425 AM EDT Thu Oct 1 2026

Day 1
Valid 12Z Thu Oct 01 2026 - 12Z Fri Oct 02 2026

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE SOUTHERN PLAINS...

Latest trends in guidance signal a reputable chance for
significant rainfall over much of the more flash flood prone areas
of south-central Texas, including the I-35 corridor from Dallas-
Fort Wort to Austin-San Antonio with a secondary max situated
along the southern Rio Grande Village. Widespread 3+" rainfall
opportunities with a swath of 50-90% probabilities for the 3-inch
threshold. Rainfall potential over the Hill Country is the most
notable area for appreciable impacts as another period where 2-4",
locally higher totals are plausible leading to locally significant
flash flood prospects given the sensitivity of the area in general.
Hourly rates likely between 1-2"/hr with as high as 3-4"/hr for
intra- hour rate potential, a signature notorious for elevated
flash flood concerns within the Hill Country and the I-35 corridor.
Greater than 5" probs are very high over that area in Deep South
Texas with a large areal coverage of 60-90% situated just south of
San Antonio into the Rio Grande Village. The front will be slow to
progress through the state, so the convergence pattern along and
just ahead of the front will be long- lasting, creating an extended
period for potential training before the frontal passage occurs.
The Moderate Risk was maintained from South Texas to southeast Oklahoma.

Prolonged diffluent flow over the Plains into the Midwest sets the
stage for heavy rainfall over a broad area of uncharacteristically
high PW values thanks to an airmass coincident with the remnants
of Tropical Cyclone Polo. PW values between 2-2.25" over the
Midwest and Mid- Mississippi Valley will be upwards of 3-4 standard
deviations above normal, an anomaly that will likely flirt with
some of the daily and even monthly maxima for PWs over this general
area. A broad Slight Risk covers Texas to Wisconsin and northeast
Indiana for scattered to potentially widespread flash flooding. Models
are consistent in the heaviest precipitation footprint occurring
over the first half of the forecast period over Iowa into southern
Illinois as the remnant energy and anomalous moisture from Polo
will still be present with widespread thunderstorm activity likely
to occur over the course of Thursday morning before the front from
the northwest finally pushes through the region. This will end the
threat over Iowa/Wisconsin/northern Illinois, but not before
scattered flash flood concerns over the population centers based in
the area from eastern Iowa into adjacent Illinois. Widespread 1-3"
of additional rainfall is forecast for these areas. Priming today
will set the stage for more flash flood prospects the first part of
the D2 with the heaviest rainfall.

Campbell/Kleebauer
 

Day 2
Valid 12Z Fri Oct 02 2026 - 12Z Sat Oct 03 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
SOUTHERN/EAST-CENTRAL TEXAS...

The frontal boundary will be lingering in the region to provide
one last round of appreciable rainfall before conditions improve
moving into the weekend. An Additional 2-4" of rainfall possible from
Laredo to McAllen and areas just inland with a secondary max
possible over east-central Texas, mainly just east of the I-35 as
the front finally moves through on Friday morning. A Slight Risk
area cover much of South Texas, eastern portions of the Hill
Country and parts of eastern Texas.

Farther north and east, the cold front will continue to advance
southeast through the Ohio Valley, with some potential for heavy
rain along and ahead of the boundary. Supported by deep southerly
flow along the western extent of the subtropical ridge, guidance
continues to show a broadening pool of anomalous moisture spreading
from the Gulf Coast into this boundary. Mid- level energy embedded
within the flow may help produce areas of heavy rain, with some
guidance indicating heavy amounts along the Gulf Coast from
Mississippi to the Florida Panhandle this period. A broad Marginal
spans from Texas across the Gulf to western Florida and then
northeast to Ohio and Kentucky. These areas will likely see some
heavier rainfall rates >2"/hr considering the environment and
available instability in the area, however the FFG's are much
higher in these zones with the most notable areas of impact in the
more urbanized areas along the Gulf coast from Panama City over to Galveston.

Campbell/Kleebauer
 

Day 3
Valid 12Z Sat Oct 03 2026 - 12Z Sun Oct 04 2026

..THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM THE CENTRAL
GULF COAST NORTHWARD INTO THE TENNESSEE VALLEY...

During this period the upper level trough will continue to track
toward the east while slowly amplifying along the way to the
eastern U.S. Deep, anomalous moisture (2-2.5+ std dev above
normal) will be drawn along and ahead of a wavy front that is
forecast to extend southwestward from the southern Appalachians
back into the western Gulf early in the period. Mid- to-upper level
energy moving along the base of the broader scale trough will have
the potential to produce organized, highly- efficient storms,
resulting in areas of heavy amounts. Heavy rainfall is expected to
align along and ahead of the frontal boundary where the axis of
deepest moisture will be present. A Slight Risk for excessive
rainfall and potential flash flooding was maintained for much of
the central Gulf Coast and northward across Mississippi, northern
Alabama and northern Georgia.

Campbell/Pereira
 

Day 4 and Day 5
Valid 12Z Sun Oct 04 2026 - 12Z Tue Oct 06 2026

...THERE IS A SLIGHT RISK OVER PARTS OF THE CENTRAL GULF COAST...

For Day 4 (12Z Sun-12Z Mon) -- The one meaningful change compared
to yesterday's Day 5 ERO was to extend the Marginal all the way to
the Mid Atlantic and Southeast Coast. There is a handful of
guidance (including the 00Z ECMWF, EC ensemble mean, and EC-AIFS)
that are a bit more progressive with the southward extent of the
broad frontal zone, thus implying any outlook areas would be
shifted farther south toward the Gulf Coast. For now, have
maintained the Slight Risk across parts of the Central Gulf Coast,
though if the trends in the global guidance continue (amplifying
upper trough over the Great Lakes), later shifts may start peeling
away at the northern extent of the Slight (as well as Marginal)
with the faster surface cold frontal passage.

On Day 5, the only area of concern at this point is the Lower TX
Coast. This is where the surface front would more likely get hung
up, as both the 00Z ECMWF and GFS show stretched mid-level vort
lobes lingering across South TX. At this time, the guidance shows a
very compact area of heavier rain (higher deterministic and
probabilistic QPF) onshore from the Gulf, basically along the
Lower TX Coast and into eastern portions of the Rio Grande Valley.

Hurley
$$
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