252
FOUS30 KWBC 051933
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
333 PM EDT Sun Oct 5 2025

Day 1
Valid 16Z Sun Oct 05 2025 - 12Z Mon Oct 06 2025

...THERE IS MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE CENTRAL PLAINS AND MIDWEST ALONG WITH THE CENTRAL GULF COAST
AND EASTERN FLORIDA...

...16Z Outlook Update...
The ongoing ERO is on track with only minimal changes needed to
current risk areas. Impressive QPF/totals are beginning to show on
high-res models along a focused axis from north-central KS into
west-central IA. However, dry antecedent conditions and lack of
urban flash flood potential/hydrophobic ground surfaces suggests
that any flash flood potential should remain isolated. Isolated 4-6
inch rainfall totals are possible especially along the KS/NE
border region and points between just north of Salina, KS to west
of Des Moines, IA.

Localized/marginal flash flood potential should exist for a
couple more hours near the Savannah, GA vicinity this morning,
although the temporal window for deep convection (and 2-3 inch/hr
rain rates) is relatively brief and should close early this
afternoon. Excessive runoff is possible, but coverage should
remain below 5% there.

Lastly, isolated flash flood potential exists from southeastern
Louisiana eastward across the north-central Gulf Coast today
through early evening. A weak low is drifting northward toward
southern Louisiana and loosely organized, banded convection should
develop toward the Marginal Risk area in an abundantly moist
environment (2+ inch PW values). Storms should be slow-moving
enough for local rain rates of 2 inches/hr to occur on an
isolated/sporadic basis. This scenario should result in at least
isolated instances of excessive runoff through the afternoon and
evening.

See the previous discussion below for more information.

Cook

...Previous Discussion...

...Central Plains/Midwest...

In the wake of an upper-level trough and surface low transiting
portions of the northern Plains, a cold front will be gradually
settling southeastward today and tonight across the central Plains
and Midwest. Showers and thunderstorms are expected to develop
along the front by this evening across areas of central and
northern KS up through southeast NE and through central IA. MLCAPE
values as high as 1000 to 1500 J/kg are forecast to pool along the
boundary along with a seasonably moist airmass characterized by PWs
of 1.25 to 1.5+ inches. Moisture transport along the front will be
aided by a southwest low-level jet of 30 to 40+ kts going through
00Z this evening which coupled with the instability should help
drive some heavier rainfall rates capable of reaching 1 to 1.5
inches/hour. Going through Sunday night, the convection is expected
to linger as at least modest right-entrance region upper jet
dynamics overhead continue to interact with the front. Some post-
frontal shower and thunderstorm activity is expected as a pool of
elevated instability and frontogenesis lingers over the region. A
consensus of the 00Z HREF guidance supports some spotty 2 to 3+
inch rainfall totals in a narrow axis along the front. Antecedent
conditions are quite dry, but with some localized cell-training
concerns and heavier rainfall totals, there may be some isolated
and mainly urbanized runoff concerns. A Marginal Risk of excessive
rainfall will be maintained across the region.

...Central Gulf Coast...

An elongated low to mid-level low center/trough over the northwest
Gulf of America is expected to focus a corridor of stronger
convergence and moisture transport across the central Gulf Coast
region, with potential for multiple bands of very heavy showers and
thunderstorms to evolve. The convection will be embedded within a
deep tropical environment characterized by PWs of 2 to 2.25
inches. This coupled with MLCAPE values of locally near 1500 J/kg
will help favor high rainfall rates that may easily reach 2 to 3
inches/hour with the stronger and more organized convective bands.
The 00Z HREF guidance generally supports the heaviest rainfall
totals remaining confined to the immediate Gulf Coast, however some
localized bands of convection that will be capable of cell-
training may be able to spread a bit farther inland including areas
of south-central to southeast LA through far southern MS and far
southern AL. Some urbanized Gulf Coast locations including New
Orleans and Mobile may be impacted going through Sunday night by
bands of heavy showers and thunderstorms. The latest REFS/RRFS
guidance is more aggressive with the rainfall potential, but a
HREF-led consensus of guidance would suggest some 2 to 4 inch
rainfall totals with spotty 5+ inch amounts not out of the question
where any cell-training occurs. The Marginal Risk area will be
maintained for the time being, with isolated areas of flash
flooding possible, and especially for the aforementioned urban
corridors. However, should the guidance trend any wetter, a Slight
Risk upgrade may be warranted for portions of the central Gulf
Coast.

...Eastern FL...

Moist and locally convergent low-level easterly Atlantic flow will
continue along the FL East Coast today. There are some locally
heavier rainfall signals showing up along the Space and Treasure
Coasts and stretching inland somewhat as the potential once again
for some broken bands of locally heavy showers and thunderstorms
sets up. Where any cell-training occurs within these bands, some
spotty rainfall totals of 2 to 4+ inches will be possible. This
may result in there being a highly localized concern for some
runoff problems. A Marginal Risk of excessive rainfall will be
maintained at this time.

Orrison


Day 2
Valid 12Z Mon Oct 06 2025 - 12Z Tue Oct 07 2025

...THERE IS SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE MID-SOUTH AND WESTERN OHIO VALLEY...

...TN and OH Valley...

...1900 UTC Update...

Based on the latest (12Z) CAM guidance, including the full HREF
probabilistic suite, per collaboration with the WFOs have hoisted a
Slight Risk area across far northeast AR, southeast MO, western
TN-KY, southern IL, and southwest IN (essentially the confluence
of the OH and MS River basins). As noted from the previous
discussion (below), warm-rain processes will be fairly optimal
given the abundant low-mid layer moisture associated with the
subtropical shortwave (TPWs approaching 2.00", or 2 standard
deviations above the norm, along with WBZ levels aoa 13.5kft).
Therefore despite not much deep-layer instability (MUCAPEs 500-1000
J/Kg), rainfall rates will nevertheless be highly efficient. HREF
neighborhood probabilities of 24hr rainfall amounts exceeding 3 and
5 inches are highest within this Slight Risk area (60-70% and
40-50% respectively).

Hurley

...Previous Discussion...

850mb vorticity fields indicate the tropical disturbance in the
Gulf is likely to lift northward on Monday brining increased PWs
and the potential for areas of slow moving convection. Scattered
convection is expected during the day, although the better focus
for high rainfall amounts should come Monday night as the
approaching cold front from the west helps increase convergence.
The environment appears to favor efficient warm rain
processes...with the presence of the low level vorticity from the
Gulf and PWs around or above 2" (over the climatological 90th
percentile). Only weak instability is forecast, which could end up
being a limiting factor for flash flooding. However, given the
expected efficient warm rain, there should still be enough
instability to get hourly rainfall rates into the 1-2" range in
spots. The latest WPC deterministic QPF is 1-2" across the area,
although several models indicate locally higher amounts. Given the
environment in place amounts locally getting into the 2-4" range
seems reasonable within the Marginal risk area.

Expect at least localized instances of flash flooding to be
possible, especially by Monday night. There is a bit of uncertainty
regarding the exact rainfall axis, with the new 00z ECMWF shifting
farther east into more of TN and KY. The eastern extent of the
Marginal risk was extended in this direction to account for this
potential...although the broader model consensus still favors a
slightly farther west axis, in line with the WPC QPF.

...Eastern FL...

Easterly low level flow will continue to support scattered
convection over eastern FL Monday into Monday night. Model guidance
continues to depict a modest uptick in rainfall coverage and
magnitudes on Monday compared to Sunday. Localized urban flash flood
impacts will remain possible.

...Central Plains...

We opted to remove the Marginal risk that stretched from northeast
KS into southern IA with this update. A localized flash flood risk
still exists on day 1, but by Monday the areas hit hardest on day 1
will be well north of the surface front. Thus most of the
instability will be gone, and rainfall rates should be much lower.
Thus the additional rainfall is not expected to be enough to result
in flash flooding. A bit more instability may reside over MO, but
this is south of the forecast rainfall axis on Sunday, and thus the
rainfall Monday is not expected to be enough to overcome the drier
antecedent conditions here.

Chenard


Day 3
Valid 12Z Tue Oct 07 2025 - 12Z Wed Oct 08 2025

...THERE IS SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS NORTHERN
TENNESSEE AND MUCH OF KENTUCKY INTO WESTERN PORTIONS OF WEST
VIRGINIA...

...TN and OH Valley...

...1900 UTC Update...

Only minor tweaks were made to the Marginal Risk area, however as
with the Day 2 ERO, we`ve added a low-end Slight Risk area on Day 3
from portions of northern TN and much of KY east-northeast into
western WV. This again follows along with the subtropical wave and
TPW plume that will be absorbed by the longwave (synoptic scale)
trough and associated surface front. Just as with Day 2, the deep-
layer instability isn`t overly robust (MUCAPEs 500-1000 J/Kg tops),
while at the same time the flattening mid-upper trough across the
area (increasing deep-layer westerly flow) should allow for more a
faster W to E progression of the shortwave and surface front later
in the period (late Tue-Tue night). Still, anomalous deep-layer
moisture (warm rain processes as WBZ levels remain over 12KFT) will
allow for rather efficient short-term rainfall rates.

Hurley

...Previous Discussion...

Increasing moisture ahead of an approaching cold front
will likely lead to greater convective coverage and areas of heavy
rainfall. The forcing and moisture will be enhanced by the same
low level vorticity feature that was upstream on Monday and over
the Gulf on Sunday. With PWs forecast over the climatological 90th
percentile do expect some warm rain processes, which should help
overcome marginal instability and help produce heavy rainfall
rates. Also note a well defined upper divergence signature centered
over this region within the right entrance region of an upper jet.
Thus the ingredients are there for widespread rainfall and at
least some pockets of heavy rates.

The main question for flash flood potential will be the duration of
these higher rates. Overall the front looks pretty progressive,
which should limit this duration. However, guidance does indicate
that some training could occur for a period Tuesday before the front
clears through, with the favored axis somewhere in the vicinity of
central to eastern KY. While differing on location, most 00z
deterministic models indicates a swath of 2-3" of rainfall, which
seems reasonable given the environment in place. In fact would not
be surprised if totals locally exceed 3". Overall this seems like a
solid Marginal risk with localized areas of flash flooding probable.
Can not rule out an embedded Slight risk upgrade on future updates
pending model trends.

The northern extent of the Marginal risk was cut out of the
Northeast with this update. Instability really drops off with
northern extent which will impact rainfall rate potential. These
lower rates combined with the drought conditions suggest flash
flooding is unlikely. We would probably need higher rates to overcome
the dry soil conditions, and this seems unlikely given the currently
forecast instability. So it is looking more like a beneficial
rainfall, with most areas around 0.75" but locally as high as 1.25"
or so.

...Southeast FL...

Expecting another day of scattered convection within the easterly low
level flow Tuesday. Compared to previous days the threat should
mostly be focused over southeast FL by this time, and a localized
urban flash flood risk is possible.

...NM...

A Marginal risk was maintained for portions of central and eastern
NM on Tuesday. Easterly low level post frontal flow will help
locally enhance convergence and upslope and scattered convection is
likely to develop. With PWs around 1" and CAPE only forecast between
500-1000 j/kg this is likely a lower end threat. Nonetheless,
locally heavier convection with high rates could result in isolated
flash flooding, particularly over any more sensitive burn scars or
basins.

Chenard


Day 1 threat area: https://www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Day 2 threat area: https://www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Day 3 threat area: https://www.wpc.ncep.noaa.gov/qpf/99epoints.txt