Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
340 PM EDT Wed Sep 30 2026
Day 1
Valid 16Z Wed Sep 30 2026 - 12Z Thu Oct 01 2026
...THERE ARE MODERATE RISKS OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE CENTRAL AND SOUTHERN PLAINS, AS WELL AS THE CORN BELT...
...Front Range to Southern Plains...
16Z Update: Only minor adjustments were made to the previous
forecast MDT risk areas across the Front Range and the Southern
Plains, respectively. The general pattern remains in tact with our
broad ULL currently moving slowly between the AZ/NM border with the
remnant energy of Polo ejecting into the Central Plains according
to the latest WV satellite and radar trends. Latest 500mb
mesoanalysis indicates the mid-level vorticity from Polo is
migrating north-northeast out of the TX Panhandle, accompanied by a
more robust multi-cell cluster and locally heavy rainfall expanding
through the OK Panhandle into southern KS. The threat for
significant rainfall remains in tact across portions of the Front
Range with a textbook upslope pattern within the Sangre de
Cristos, along with a developing axis of deformation on the
northwest flank of the surface low positioned off the lee of the
Rockies. Expectation of the core of the heaviest rain to occur
within that area of upslope flow with convective potential highest
across the southeast corner of CO, northeastern corner of NM, and
the far western OK Panhandle. ULL progression into NM will
eventually pivot more to the northeast leading to enhanced upper
ascent underneath and just to the north of the general ULL center,
coincident with where the heaviest rainfall will occur. General
1-3", locally higher is forecast in this zone which when combined
with the primed soils from the past rainfall would present an
opportunity for flash flooding, especially in the terrain and
overlapping any areas that took appreciable rainfall the past 48
hrs.
Further south into the Southern Plains of TX/OK, the overall setup
remains conducive for heavy rain materializing along and ahead of
an expected cold front migrating through west TX during the
afternoon and evening hours. High EAS probs (50-90%) for >1" on
the latest 12z HREF exist from the eastern fringe of the Big Bend
area of TX to the north-northeast with the highest probs centered
over the Concho Valley, North TX, and just west of the DFW
metroplex. HREF blended mean QPF was quite robust within these
zones with a general 2-4" with the local maxima over 5". This
signal is more than sufficient for a maintenance of the previous
MDT risk with only some minor adjustments made to match the latest
prob fields from the 12z CAMs suite.
..Previous Discussion..
There will be a continued heavy rain threat across the Sangre de
Cristos into the San Juan Range as the flow shifts out of the
northeast along the northwest periphery of the surface low,
creating an upslope flow regime to perpetuate the rainfall over
the terrain of southern Colorado into northern New Mexico. The
prospects of flash flooding will be enhanced due to the antecedent
moist soils brought about by prior periods of rainfall, some of
which will likely cause flash flooding in their own right, leading
to a heightened probability for flooding given the overlapping
nature of heavy precip. Accumulations of 2-4" with locally higher,
of additional precip within the mountains of the Southern Rockies
into the Front Range as the combination of upslope flow and
enhanced axis of deformation will lead to two primary periods of
heavy precipitation; once in the morning and then once again in
the evening as the surface low intensify and strong mid- level
vorticity advection pivots around the ULL center.
Across the Southern Plains from Oklahoma down through Texas, the
setup is more classic with regards to increasing low-level
convergence along a propagating cold front that will materialize
from the surface cyclogenesis over the High Plains. The flow will
be fairly meridional ahead of the slow-moving mean trough/ULL
moving through the Southwest U.S. creating a broad area of
relatively backed flow across portions of west Texas into the Red
River Valley down through the Central Rio Grande Valley and
Edwards Plateau by evening and into early Thursday morning. Heavy
convection expected along the front as it migrates out of the High
Plains of Texas with the western periphery of precip likely
developing from the western Rolling Plains down into the Lower
Trans Pecos and adjacent Concho Valley by late Wednesday afternoon.
This will set the stage for a broadening convective footprint over
the Southern Plains as the warm sector environment with deep
tropical moisture presence will interact with the frontal
progression as it slowly moves eastward through the area Wednesday
night. Models indicate a formidable 35-45kt LLJ structure situated
from the RGV up into the Central Plains as the warm sector
maturation will be well-defined with continued moisture advection
poleward until the front passes over any given area. MLCAPE between
1500-2500 J/kg bisecting the eastern two-thirds of the region will
offer plenty of instability to couple with 30-40kt Effective Bulk
Shear, creating an environment conducive for stronger mesocyclone
cores and merging multi-cell clusters that will provide heavy rain
for a large area come Wednesday evening.
HREF neighborhood probs for >3" are upwards of 50-80% over the
area from the Lower Trans Pecos to the central Red River Valley
between TX/OK with an average of 40-60% over the entire stretch
from Del Rio, Texas to just across the Red River into OK. This is
a substantial area of heightened probs for 3" with modest probs
(25-40%) for >5" locally with the best signal over the Lower Trans
Pecos and northern Hill Country between San Angelo and Fort Worth.
...Central Plains into the Corn Belt...
16Z Update: The current forecast remains sufficient for a continued
MDT risk across areas of the Central Plains into the Corn Belt for
the D1 period with the heaviest rainfall occurring over the course
of the late-afternoon hours today, carrying through the overnight
period as the evolution extends heavy rainfall to the northeast
into the Midwest. Current satellite and radar analysis depicts some
of the mid-level remnants of Polo migrating out of the TX Panhandle
with sights on KS as we move into the afternoon hours. This will be
a major player in term so where the heaviest rains will occur,
coupled with the alignment and position of a warm front lifting
north into the vicinity of northern KS and southeastern NE. Mean
flow will align parallel to the front with the remnant energy of
Polo lifting north-northeast and eventually northeast as it reaches
the latitude of I-70. The overlap of the front and general
instability max bisecting areas along and south of the front will
aid in maintaining a well-defined warm sector environment allowing
convection to be common occurrence for several hours before a cold
front finally sweeps everything southeast by early tomorrow
morning.
Current probabilities for >3" are gaudy, to say the least, with
neighborhood probs between 70-90+% located from north-central KS up
through much of southeast NE into western IA, bisecting both the
Omaha and Des Moines areas in the spatial representation. The >5"
probabilities are also very noteworthy with a solid 40-70%
neighborhood area along the Missouri River Valley with the focal
point centered over Omaha and areas just south. This signal has
been prevalent across much of the CAMs suite this morning, and has
merit within the ensemble probs from every the global ENS outputs
the past 24 hrs. This sets the stage for an appreciable flash flood
scenario for the aforementioned region. Rainfall totals between
2-4", local to 6" will be common within an axis extending from 50
miles east of Goodland, KS to about 50 miles northwest of Des
Moines with the max likely over southern and southeastern NE. The
MDT risk was maintained with now a high-end SLGT forecast for the
area comprised of north-central to northeastern fringes of KS up
through southeast NE, including the Omaha area, and western IA.
..Previous Discussion..
A mature cyclone will be moving through the central U.S. with a
progressive warm front extending from the central low pressure
across the Plains. Rainfall from isentropic ascent will already be
occurring on the northern periphery of the low, but limited
instability will maintain more "subdued" rates that are coincident
with more appreciable flash flood prospects. PW anomalies of +2 to
+3 deviations will have advected into the region creating a
formidable deep layer moisture profile to couple with the tall,
skinny CAPE signatures expected over the Central Plains into
northern Missouri and southern to central Iowa.
Heavy rainfall will likely align along a SW-NE axis from northern
Kansas to eastern Iowa as a strong shortwave ejects out across the
Plains coinciding with an increasing low level jet ahead of the
approaching trough over the Rockies. Convection is expected to
develop during the afternoon hours while spreading northeast into
the Missouri River Valley and neighboring Corn Belt by
evening/overnight. Training of cells near the warm front is
anticipated and move northeast, in tandem which will eventually
feed into the likely convective cluster migrating along the front
from north- central Kansas into southern Nebraska, eventually
making headway into western and central Iowa after nightfall. Hourly
rainfall rates are depicted to reach between 1-2"/hr in the
strongest cell cores with some repeating action along the warm
front. Robust signals in the deterministic CAMs and associated
HREF blended mean QPF output which shows a general 2-4", locally as
high as 6" over the course of Wednesday afternoon into early
Thursday morning.
The most notable area was that corridor from the Kansas/Nebraska
border up through Omaha over into Des Moines with a higher QPF
footprint situated along and south of I-80. There will likely be a
sharp cutoff in the greatest threat for flash flooding as north of
the warm front will allow for a more stable environment and less of
the threat of the higher rates coincident with flash flooding.
Kleebauer
Day 1 threat area:
www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
340 PM EDT Wed Sep 30 2026
Day 2
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...
20Z Update: Continuation of the flash flood threat across the
Midwest to Southern Plains is still forecast with a broad MDT risk
centered over much of Texas into southeastern Oklahoma. Latest
trends in guidance signal a reputable chance for significant
rainfall over much of the more flash flood prone areas of south-
central TX, including the I-35 corridor from DFW to Austin-San
Antonio with a secondary max situated along the southern RGV. 12z
HREF neighborhood probabilities are quite bullish for widespread
3+" rainfall opportunities with a swath of 50-90% probabilities for
the 3-inch threshold. The most notable areas within the higher
probs are located in a north-south alignment from Broken Bow, OK
down into Zapata County in Deep South Texas, encompassing areas in-
between, including within that I-35 corridor from Dallas to San
Antonio proper. >5" probs are very high over that area in Deep
South TX with a large areal coverage of 60-90% situated just south
of San Antonio into the RGV, a formidable coverage of such
pronounced probabilities for totals that would undoubtedly cause at
least scattered flash flood prospects, even in areas that are not
as prone to flooding. Instability fields are robust within much of
the area impacted in TX, especially the zone south of I-10 where an
areal average MUCAPE will be on the order of 1500-2500 J/kg
through much of the D2 period. 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.
Current forecast is for the front to finally push beyond the
longitude of I-35 by the end of the D2 period (Friday AM), so
there's a growing concern where heavy rainfall will impact areas
for most of Thursday and Thursday evening with a slow-decay in the
threat as you move westward thanks to the frontal passage.
Expectation is for widespread flash flooding with the threat for
locally considerable flash flood impacts to occur in areas
scattered across TX into southeast OK. The MDT risk was maintained,
but shifted slightly eastward to account for the trends in guidance
that push the front a bit further east at the end of D1 into the
D2 period, thus ending the concern for areas west of 100W.
For the Midwest and Mid-Mississippi Valley, continued threat of
heavy rainfall as the last bit of sheared vorticity stemming from
the remnants of Polo will eject to the northeast and become diffuse
by Thursday afternoon leading to a more textbook frontal
convergence regime to couple with the advancing upper trough over
the Central Plains. Models are consistent in the heaviest precip
footprint occurring over the first half of the forecast period over
IA into southern WI and IL 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 IA/WI/northern IL, but
not before scattered flash flood concerns over the population
centers based in the area from eastern IA into adjacent WI/IL.
Widespread 1-3" of additional rainfall is forecast for these areas
which will fall on top of any rainfall that came the prior D1 time
frame. Priming today will set the stage for more flash flood
prospects the first part of the D2 with the heaviest rainfall,
leading to a maintenance of the SLGT risk forecast for this
particular area.
Further south into KS and MO, heavy rains will linger longer into
the second half of the period, most notably into KS as the upper
level trough progression will move into the vicinity and provide
ample ascent to produce one last round of heavy thunderstorms
before the front finally drives past the area by Thursday evening.
Additional totals of 1-3", locally as high as 4" are expected in
both the KS and MO areas with the latter area more notably
impacting the northern half of the state as the cold front
approaches and provides significant low-level forcing/convergence.
Probabilities for >2" are quite elevated with modest probs for >3"
located in the area near Wichita to just south of Kansas City. This
has been a favorable trend the past 24 hrs. with consistency among
the CAMs for this prolonged heavy rain threat back into the Central
Plains. A broad SLGT risk remains in effect for these areas with a
high-end SLGT now forecast for that area of south-central KS into
much of Missouri.
..Previous Discussion..
Considerable rainfall to continue across south-central Texas into
Eastern Oklahoma as the cold front slowly advances through the
Southern Plains. The primary instability axis is positioned right
across the Southern Plains into the the southern area of the
Midwest within a broad warm sector that will have developed over
the course of the prior 24 hours. 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. The Moderate Risk area was maintained from
South Texas to southeast Oklahoma.
Prolonged diffluent flow over the Plains into the Midwest 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.
Kleebauer
Day 2 threat area:
www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
340 PM EDT Wed Sep 30 2026
Day 3
Valid 12Z Fri Oct 02 2026 - 12Z Sat Oct 03 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
SOUTHERN TEXAS...
20Z Update: The previous forecast remains on track with another
round of heavy rainfall forecast across the southern half of TX, as
well as the beginning of a very wet period on tap for the Central
Gulf Coast. Latest ensemble mean QPF and subsequent probabilities
for at least 2" of rainfall signal the greatest chances to occur
over the southern RGV with the front lingering in the region to
provide one last round of appreciable rainfall before conditions
improve moving into the weekend. Additional 2-4" of rainfall are
plausible in the area from Laredo to McAllen and areas just inland
with a secondary max possible over east-central TX, mainly just
east of the I-35 as the front finally moves through on Friday
morning. A SLGT risk remains in effect for these areas due to the
continued prospect of convective impacts.
The Gulf coast will be the next area of interest with a prominent
return flow regime off the Gulf leading to elevated moisture
advection and enhanced frictional convergence regime developing
between the Central TX coast over into the FL Panhandle. 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. A broad MRGL risk will
encompass these areas for the D3.
Further north, the main change from the previous forecast issuance
was to expand the MRGL risk to include more of the eastern Ohio
Valley into WV where models are trending towards more convective
potential into the terrain that remains more on the sensitive side
thanks to quite a wet month of September. MRGL expands through all
of the Tennessee Valley into parts of the Southeast, mainly west of
I-65.
Kleebauer
..Previous Discussion..
Gulf moisture will continue to drawn into a lingering low level
boundary to continue to produce heavy rainfall, impacting some
areas that are likely to be left vulnerable to excessive runoff by
the previous day(s) heavy rains. Guidance continues to depict a
signal for additional heavy accumulations centered across parts of
South to South-Cental Texas. Therefore, a Slight Risk for
excessive rainfall was maintained for this period.
Farther north and east, a cold front will continue to settle
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.
Campbell
Day 3 threat area:
www.wpc.ncep.noaa.gov/qpf/99epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
340 PM EDT Wed Sep 30 2026
Day 4 and Day 5
Valid 12Z Sat Oct 03 2026 - 12Z Mon Oct 05 2026
...THERE ARE SLIGHT RISKS OF EXCESSIVE RAINFALL FROM THE CENTRAL
GULF COAST NORTHWARD INTO THE TN VALLEY DAY 4 AND ALONG THE CENTRAL
GULF COAST DAY 5...
2030Z Update...
Previous outlook in pretty good shape. More questions revolve
around placement of the heaviest rainfall in the Tennessee Valley
and Southeast given the placement of the upper ridge and a signal
in the 12Z runs to back off the highest-end of QPF. Opted to make
no significant changes on the Day 4 and only minor nudges to the
periphery of the Slight risk on Day 5. The overall forecast
reasoning remain fundamentally unchanged.
Bann
Previous Excessive Rainfall Discussion...
A broad upper trough will continue to shift east from the Plains
and Mississippi Valley, gradually amplifying as it moves into the
eastern U.S. over the weekend. 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. Following
the axis of deepest moisture and the anticipated position of the
front, a Slight Risk extending from the central Gulf Coast
northeastward into southern portions of the Tennessee Valley was
maintained on Day 4. With the front continuing to push southeast,
the focus for heavy rainfall is likely to become confined more
along the Gulf Coast, where a Slight Risk was focused on Day 5.
Forecast confidence was limited by model spread with regards to
the timing the upper trough and the embedded shortwave elements.
While the outlook areas were drawn according to where the ensemble
guidance currently showed the greater threats for heavy amounts,
significant adjustments may be required in future updates.
Pereira
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
340 PM EDT Wed Sep 30 2026
Day 4 and Day 5
Valid 12Z Sat Oct 03 2026 - 12Z Mon Oct 05 2026
...THERE ARE SLIGHT RISKS OF EXCESSIVE RAINFALL FROM THE CENTRAL
GULF COAST NORTHWARD INTO THE TN VALLEY DAY 4 AND ALONG THE CENTRAL
GULF COAST DAY 5...
2030Z Update...
Previous outlook in pretty good shape. More questions revolve
around placement of the heaviest rainfall in the Tennessee Valley
and Southeast given the placement of the upper ridge and a signal
in the 12Z runs to back off the highest-end of QPF. Opted to make
no significant changes on the Day 4 and only minor nudges to the
periphery of the Slight risk on Day 5. The overall forecast
reasoning remain fundamentally unchanged.
Bann
Previous Excessive Rainfall Discussion...
A broad upper trough will continue to shift east from the Plains
and Mississippi Valley, gradually amplifying as it moves into the
eastern U.S. over the weekend. 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. Following
the axis of deepest moisture and the anticipated position of the
front, a Slight Risk extending from the central Gulf Coast
northeastward into southern portions of the Tennessee Valley was
maintained on Day 4. With the front continuing to push southeast,
the focus for heavy rainfall is likely to become confined more
along the Gulf Coast, where a Slight Risk was focused on Day 5.
Forecast confidence was limited by model spread with regards to
the timing the upper trough and the embedded shortwave elements.
While the outlook areas were drawn according to where the ensemble
guidance currently showed the greater threats for heavy amounts,
significant adjustments may be required in future updates.
Pereira
