FOUS30 KWBC 020101 CCA
QPFERD

Excessive Rainfall Discussion...CORRECTED
NWS Weather Prediction Center College Park MD
901 PM EDT Thu Oct 1 2026

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

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

001Z Update...
On-going heavy to excessive rainfall will continue into the
overnight hours along a plume of deep moisture extending from the
Gulf of America northward into portions of the Mississippi Valley.
Greatest rainfall rates are largely confined to southern and
central Texas as of early evening. Latest runs of the HRRR and the
WoFS keeps the focus for intense rainfall rates there into the
night where on-shore flow off the Gulf will enhance moisture flux
convergence. The line has been a bit more progressive than shown
by the guidance so the eastern boundary was expanded somewhat. The
threat of excessive rainfall extends northward from there into
portions of the Plains into the southern Great Lakes and far
western Ohio Valley. The moisture is not as deep nor is the
instability as strong as the area to the south...but the strength
of mid- level forcing (an upper circulation center over Kansas as
of 02/00Z upper air analysis and satellite imagery combined with a
baroclinic leaf signature aloft transiting the upper Plains
farther east) is enough to sustain sufficiently intense rainfall
rates for a long enough duration to result in excessive rainfall.

Bann


1930z Update: Just some minor updates to reflect latest
observational and high res model trends. Main change was to trim
the northwestern extent of the MDT risk across portions of
southeast OK and far northeast TX. Otherwise the event remains on
track with the 16z discussion from below still valid.

Chenard

..16z Update..

Texas: A slowly propagating line of thunderstorms across the Hill
Country and the I-35 corridor is bringing heavy rainfall and flash
flooding this morning. This line of storms is expected to continue
propagating eastward through the afternoon and support the
potential for a locally significant flash flood threat. Late
afternoon into the evening and overnight, there remains uncertainty
on the reformation of storms across the Hill Country and the I-35
corridor. A stalling front across the region, an increasing low
level jet of moisture transport through the overnight period, and
upper-level divergence from a right entrance jet streak in
association with an upper-level trough nearby will support a
favorable environment for very heavy rainfall if thunderstorms can
reignite over central Texas. If the line of storms this morning and
afternoon maintains organization and sweeps farther eastward
across Texas (via cold pools), the greatest instability and low
level moisture may push out of the Hill Country region and inhibit
a higher end flash flood event. If the line of storms weaken or
propagate eastward slower,instability and low level moisture will
not be as worked over and a greater threat of flash flooding may
exist over southern Texas into the Austin/San Antonio metro region
from thunderstorms that do reform. The higher confidence for areas
of 6+ inches of rain is across southern Texas near the Rio Grande
region where the greatest instability and low level moisture
exists. The ongoing line of storms is expected to stall over the
area this evening into the overnight in addition to developing
thunderstorm along and near the stationary front.

In terms of rainfall, model guidance is fairly wet with a
consistent signal among ensemble means of 3-6 inches from the
Austin/San Antonio metro area to South Texas with CAMS highlighting
the potential for local maxima greater than 10 inches in the
highest end QPF scenarios. Some of the higher end flash flooding
impacts is exemplified by 12z HREF probabilities of 40-60% of 24 hr
QPF exceeding 8 inches across this corridor. The flash flood
threat remains consistent with a Moderate Risk and the expectation
for numerous flash flooding. Life threatening and high end flash
flooding impacts are possible where the higher end rainfall totals
occur, particularly if it falls over an urban region where water
runoff is enhanced. There was not enough confidence in a High Risk
given high end flash flood impacts should stay isolated in nature,
and confidence in exact location of highest rainfall totals is
uncertain.

Florida: A Marginal Risk was issued along the east coast from
Miami to the Space Coast for this afternoon. Tropical moisture
streaming across Florida will bring locally heavy rainfall and
hourly rainfall rates that exceed an inch per hour, which will
bring an isolated flash flood risk to the urbanized I-95 corridor.

Wilder

...Previous Discussion...

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/CENTRAL TEXAS...

..20z Update..

The main change in the ERO forecast across Texas was to expand the
Slight Risk northward to encompass the Dallas-Fort Worth metro
region. Convection is likely to be ongoing in the morning hours
across the I-35 corridor from central Texas, including parts of the
Hill Country, to southern Texas and the Rio Grande as storms
reform overnight into the early morning along and ahead of a
quasi- stationary frontal boundary. Afternoon guidance shows an
additional 1-3 inches of rainfall from thunderstorms that form over
central and southern Texas with instability on the order of
500-2000 J/Kg, PWATS over 2 inches, and a stalled front nearby
serving as a source of lift. This rain will fall over areas that
will have received several inches of rain today and have lowered
flash flood guidance exceedance values. This will increase the
likelihood of observing impacts from excessive rainfall.

Across the Southeast,the Marginal Risk was trimmed out of much of
interior Louisiana, Mississippi, and Alabama. The edit was made in
response to lowering QPF amounts in model guidance. The Marginal
Risk ERO along the immediate Gulf Coast from Louisiana to the
Florida Panhandle remains on track as tropical moisture lifts
northward into the region and supports 1-2 inch hourly rainfall
rates with an isolated flash flood risk.

Wilder

...Previous Discussion...

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 ALONG THE CENTRAL
GULF COAST...

..20Z Update..

Similar to the day 2 forecast, the Slight Risk was trimmed out of
the interior Southeast across Mississippi, Alabama, and Georgia in
areas where ensemble QPF was generally less than an inch. This also
aligns with the greatest moisture and instability remaining closer
to the Gulf Coast. The Slight Risk remains intact across the
Central Gulf Coast as a mid-level disturbance approaches the region
and brings a tropical moisture plume across the region with PWATS
over 2 inches possible. This disturbance will support locally heavy
rainfall capable of bringing scattered instances of flash flooding
and ponding to urbanized and low lying regions.

The Marginal Risk was also expanded eastward across the Carolinas
where a mid-level wave and surface frontal boundary may bring
increased precipitation on the order of 1-2 inches with the
potential for locally higher amounts possible. The signal for
higher QPF has increased in time across the region, but lower
instability forecast in the region and relatively high flash flood
guidance precludes a Slight Risk introduction at this time.

Wilder

...Previous Discussion...

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
INTO PARTS OF THE SOUTHEAST US...

2030Z Update...
There were few changes needed in the Day 4 period given good run
to run continuity between the 01/00Z and 01/12Z suite of numerical
guidance and their respective ensembles. Introduced a Marginal
Risk area across parts of the Southeast US on Day 5 in proximity to
a quasi- stationary front draped across the region. With the
boundary separating deep moisture over the Gulf from a cooler and
much drier airmass to the north being fed in by high pressure over
the eastern US...there could still be convection capable of
producing heavy rainfall from coastal Louisiana eastward across
northern Florida and adjacent areas of Alabama and Georgia. The
Marginal risk area largely encompasses an area where both the
01/00Z EC Ens and the 01/12Z GEFS had members showing 3 inch per 24
hour QPF contours. There were not many members but enough to
support a Marginal Risk area.

Bann

Previous Discussion...

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


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/qpf/94epoints.txt__;!!DZ3fjg!_0xQGwZrIfHgZiXE0dk0FBCcVEuSgCJVQkKBRWmj-622mbc3DaIHx91IlNNKgAoOA_gHekNvXPUdh-Hn9lc3NyrJl8s$
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/qpf/98epoints.txt__;!!DZ3fjg!_0xQGwZrIfHgZiXE0dk0FBCcVEuSgCJVQkKBRWmj-622mbc3DaIHx91IlNNKgAoOA_gHekNvXPUdh-Hn9lc3pUi0Oj0$
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/qpf/99epoints.txt__;!!DZ3fjg!_0xQGwZrIfHgZiXE0dk0FBCcVEuSgCJVQkKBRWmj-622mbc3DaIHx91IlNNKgAoOA_gHekNvXPUdh-Hn9lc38JqeGyo$



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