FOUS30 KWBC 050819
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
419 AM EDT Sun Oct 5 2025

Day 1  Valid 12Z 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...

...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 MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF 
EASTERN ARKANSAS INTO THE OHIO VALLEY AND OVER EASTERN FLORIDA...

...TN and OH Valley...

A Marginal risk was maintained from portions of eastern AR 
northeastward into southern IN. 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 MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF 
THE TENNESSEE AND OHIO VALLEY, OVER SOUTHEAST FLORIDA, AND PORTIONS 
OF NEW MEXICO...

...TN and OH Valley...

A Marginal risk was maintained from TN northward into portions of OH 
and southwest PA. 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
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