Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
855 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
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