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FOUS30 KWBC 151559
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1159 AM EDT Tue Sep 15 2026

Day 1
Valid 16Z Tue Sep 15 2026 - 12Z Wed Sep 16 2026

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
NORTHEASTERN KANSAS INTO NORTHWEST MISSOURI...

...Central U.S...

16Z update... Signal remains strong for heavy rainfall to focus
near the juncture or Kansas, Nebraska and northwest Missouri. The
Moderate Risk was broadened slightly to reflect the current uptick
in amounts and coverage over the area. Otherwise the rest of the
region remains in good order with the Slight and Marginal Risk
areas.

Campbell

Current setup for Tuesday into early Wednesday morning continues to
look active with a prominent isentropic ascent pattern across
portions of the nations mid-section with the focus across the
Missouri River Valley between KS/MO and the southeastern corner of
NE. Cold front analyzed over NE will slide southeastward and fan
out as it migrates southward as it begins to feel the influence of
the ridge dominating the weather pattern over Mid-Mississippi
Valley and points south. Steady frontal progression will lead to
the front positioned over central KS and MO by the afternoon and
early evening hours with a sharp theta_E gradient pattern arising
just north of I-70. Aloft, a shortwave ejection out of the Central
to Southern High Plains will pivot northeast around the western
periphery of the broad upper ridge situated over the Southeast
leading to ample mid and upper level forcing to coincide with a
modestly unstable and moisture rich environment. PWAT anomalies
between +2 to +3 standard deviations are forecast across much of KS
into MO with values around 2" likely for areas along and south of
that established theta_E gradient. Mean flow aloft will run
relatively parallel to any front/boundary bisecting the area
leading to storm motions that will track generally west-southwest
to east-northeast after initiation. Best chance for convective
initiation will occur late-afternoon through the evening with the
evening and overnight time frame the most susceptible period for
heavy rain and flash flood concerns as LLJ influence allows for
fresh low-level moisture injection and a bit more low-level shear
to maintain mesocyclone maintenance.

Latest CAMs and associated HREF output at 00z this evening
indicated a wide swath of 2-3" areal average mean with the blended
mean guidance upwards of 3-5" over the area of northeastern KS
through much of northwestern MO. There's a growing consensus in the
heaviest rainfall occurring just north of Topeka to points
northeast, including areas like St. Joseph, Missouri, as well as
neighboring counties that have seen significant rainfall as
recently as this past morning causing localized flash flooding to
occur prior to the event. Areal FFG's for the 1 and 3-hr intervals
lean lower than normal with typical thresholds around 1 to 2
inches, respectively for the exceedance times referenced. HREF
probs for >1"/hr rates are running between 40-70% for several hrs
across the northeastern corner of KS into northwest MO which would
enhance the threat of FFG exceedance, matching the modest 3hr FFG
exceedance probabilities off the last succession of HREF runs. The
threat for heavy rain is also further south, closer to the expected
frontal positioning with areas along I-70, including the Kansas
City metro potentially seeing the heavy rain prospects that could
invoke flash flooding. The probabilities are more aligned for the
areas to the north, but there is a noted shift south from the
previous run of slightly better chances to the metro area, so want
to make reference given the setup is conducive for prolonged heavy
rain chances and some locally significant totals.

In coordination with the local WFO's in Topeka and Kansas City, a
Moderate Risk was added to the latest D1 update encompassing the
northeastern counties in Kansas, extending northeast into portions
of northwest Missouri. The MDT also clips the far southeast corner
of Nebraska along the Missouri River to reflect the higher
probabilities also situated in that area. A high-end SLGT is
forecast for the surrounding areas of northern MO and northeast KS,
down into the I-70 corridor in both states. This also encompasses
the entire Kansas City metro, reflecting the potential of heavy
rain and higher impacts extending further south. The SLGT extends
south through the High Plains along the cold front progression
occurring further west, especially southwest of I-35. SLGT extends
northeast into the Midwestern areas to account for heavy rainfall
chances occurring later this morning, and then another for the
following evening.

...Southwest...

16Z update... A westward nudge of the western boundary was made
across northwest Arizona and near the Utah and Nevada border for
some vulnerable areas to account for some of the convection that makes
its way further west per some of the guidance. The rest of the
region remains in good order with a broad Slight Risk covering the
more sensitive areas.

Campbell

The Southwest CONUS will remain active with a multitude of small
shortwave perturbations rounding the western periphery of the broad
ridge positioned over the Southern U.S, entering into the region
with PWAT anomalies firmly +2 or greater across eastern AZ into NM
and southern CO. Models continue to pinpoint areas of northern and
western NM as the beneficiaries of the setup with a secondary focal
point now encompassing the central and eastern sections of the
Mogollon Rim. Latest HREF mean QPF signals a solid 0.5-1" output
over the two main areas of concern with individual deterministic
outputs upwards of locally 2-3" in the hardest hit locations.
Neighborhood probabilities between 40-70% for >2" confirm the
individual ensemble members within the CAMs suite which would lead
to another scattered flash flood concern in-of the terrain
outlined. A broad SLGT remains positioned over the aforementioned
areas with an emphasis on eastern AZ and the western half of NM.

Kleebauer
 

Day 2
Valid 12Z Wed Sep 16 2026 - 12Z Thu Sep 17 2026

...THERE ARE SLIGHT RISKS FOR EXCESSIVE RAINFALL OVER PORTIONS OF
THE CENTRAL PLAINS, MISSOURI AND OHIO VALLEYS, AND THE SOUTHWEST
U.S...

...Central Plains to Ohio Valley...

The upper ridge centered over the Southeastern U.S. will begin to
shift more to the west and center over the Lower Mississippi Valley
by mid-week while also strengthening with global deterministic
forecasting 500mb heights encroaching on 600dm for the center of
the ridge. This will allow for increasing heights to the north as
the ridge flexes and provides a greater influence in the
latitudinal positioning of our frontal boundary situated over the
Central U.S. extending into the Ohio Valley. Wednesday morning will
see continued heavy rain over northern MO as the previous period's
activity lingers and migrates eastward before dissipating with the
loss of the LLJ influence as we move forward in the period. By the
late-afternoon and evening hours, expectation is for front to stall
and eventually lift north slowly as move into the evening hours.
Scattered convection will occur over the Ohio Valley during the
peak of diurnal heating with an increase in coverage anticipated
until the evening hours. A relatively buoyant environment and
elevated PWATs situated over the area will allow for some isolated
to perhaps widely scattered flash flood prospects across IL/IN/OH
with the current forecast depicting localized areas of 1-3" where
impacted by convection. Most notable areas will be along the
positioning the front due to a greater propensity for cells to
anchor and sit over the region, or train with the mean flow
aligning a bit more parallel to the front leading to the threat.
The greatest concerns are being referenced from central IL into IN
where CAMs are more aggressive with the signal given better
instability fields and PWATs overhead providing a more suitable
environment for higher rates for flash flooding potential.

By the evening, another shortwave from the Central Plains will
rotate around the northern periphery of the ridge and help initiate
a nocturnal round of convection in-of IA into northern IL leading
to another scattered flash flood concern around the vicinity of the
I-80 corridor. Models have backed on a more prolific opportunity
compared to the past few nights leading into the forecast, but the
threat is still worthy of a SLGT risk when you add the antecedent
moist soils that will be focused across the intended area of impact
for Wednesday evening into early Thursday morning. Some of the
guidance is still relatively aggressive in local 2-3" totals along
the area extending from Des Moines to just west of the Chicago
metro, including those suburbs in the Chicago metro. NBM probs for
>2" remain between 20-40% over the region of interest, a noteworthy
signal for at least a localized threat of flash flood concerns,
especially within those more urbanized settings referenced. A broad
SLGT risk extends from the Missouri River between southeast NE,
northeast KS to points east covering much of IA, northern MO,
through the northern-third of IL. The SLGT extends east into the
central portions of IN to account for the previously referenced
convective threat downstream of the nocturnal setup.

...Southwest...

Another period of scattered to widespread convective activity is
forecast for much of the Southwestern U.S. with a broad axis of
heavy rainfall prospects likely to occur over the eastern two-
thirds of AZ into almost all of NM and southern CO on Wednesday.
Guidance continues to reference a more robust shortwave ejection
out of Mexico providing further mid and upper level ascent that
can exacerbate an already formidable environment in place. The
latest model 500mb vorticity forecasts are noting a potential MCV,
or organized vorticity field lifting north out of the southern
Baja over the next 48 hrs that will likely materialize from an area
of convection that spurred up this evening. PWAT anomalies are
forecast to reach firmly into the +2 to +3 standard deviation
range, perhaps even flirting with upwards of +4 standard deviations
as the latest ECENS output reflects areas of NM approaching
monthly max PWATs when assessing the climatological percentiles.
Ensemble means remain very aggressive for Wednesday afternoon into
early Thursday morning with some models printing out 2-3", locally
higher, in spots across central and southeastern AZ into western
and northern NM, areas where flash flood concerns will be elevated
from the repeated nature of this pattern, as well as the location
of the more sensitive burn scar locales within each state. Latest
HREF probs for >2" between the 12-00z time frame Wed/Thu are
upwards of 70-90% for portions of southeastern and south-central AZ
centered over the Mogollon Rim, as well as over the Sacramento and
Sandias Mountains in NM, a testament to a growing threat for more
widespread flash flood concerns when you consider the environment
advecting into the region. This threat maintains a higher end SLGT
risk forecast with a chance for even an upgrade further over
portions of AZ and NM with the primary area of interest within the
Mogollon Rim down into the mountains of southeastern AZ, and
perhaps into the Sacramento Mountains to account for the still
sensitive burn scars in place near Ruidoso.

Kleebauer
 

Day 3
Valid 12Z Thu Sep 17 2026 - 12Z Fri Sep 18 2026

...THERE ARE SLIGHT RISKS OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE NORTH-CENTRAL PLAINS, UPPER MIDWEST, & SOUTHWESTERN U.S...

...Northern Plains & Midwest...

Our broad upper ridge will continue to flex over a large portion of
the CONUS as we head into Thursday with the northern fringes of
the height field extending into the Upper Midwest and expanding as
far west as the Central High Plains. As we move through Thursday, a
robust shortwave ejecting out of the Southwestern U.S. will pivot
up through the Central Rockies, rounding the northwestern flank of
the ridge and entering into the Northern Plains as we head into
Thursday evening. This shortwave will also provide a significant
PWAT increase as noted via both the the ensemble anomaly plots and
IVT climatological percentiles approaching the 95-99th percentile
up across South Dakota into southern portions of MN. Given the
strength of the forecast shortwave ejection, regional forcing will
increase significantly as the disturbance approaches leading to
more organized convective clusters to materialize by Thursday
afternoon and evening, lingering through the overnight hours to
Friday morning. Model outputs have become increasingly bullish for
a swath of 2-4", locally higher occurring within the confines of
the shortwave impulse as the environmental conditioning and ascent
pattern remain favorable within proximity to the disturbance. This
setup is becoming more favorable for at least scattered flash flood
prospects over the Northern Plains into the Upper Midwest with the
primary threat likely occurring over those urbanized areas in the
zones referenced. Considering the source region of this moisture
advection pattern, we will be monitoring the necessity for a higher
risk potential over the area of SD into MN for the activity
occurring Thursday night into early Friday morning. For now, a
broad SLGT risk remains forecast for the region with a MRGL
surrounding.

...Southwest U.S...

Prevailing southerly flow will maintain a steady plume of elevated
moisture across the Southwestern CONUS, but the shortwave
disturbance associated with the proliferation of the previous
period's convection will vacate to the northeast allowing for a
gradual de-escalation of the convective magnitude over the region
in time for Thursday. That said, lingering PWAT anomalies ranging
from the 90-99th percentile of climo will allow for another busy
afternoon of widespread convective potential over much of NM and
eastern AZ leading to an elevated flash flood concern, once again.
Precip totals between 1-3" are forecast for the Sangre de Cristos
down through much of the terrain focused in the interior areas of
NM. This allowed for a high-end SLGT forecast to remain across
these aforementioned areas of NM into southern CO. Pending the
impacts from the prior period, a higher risk is also non-zero and
could be added in future forecasts as sensitive grounds could
enhance the threat for flash flooding further within the region.

Kleebauer
 

Day 4 and Day 5

Valid 12Z Fri Sep 18 2026 - 12Z Sun Sep 20 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE UPPER MIDWEST & GREAT LAKES...

The Days 4-5 period (Fri Sep. 18 - Sat Sep. 19) is highlighted by
an expansive and highly anomalous upper-level ridge of high
pressure taking hold over much of the Southern U.S., while an
upper-level trough in the Northern Rockies on Friday makes its way
east over the Upper Midwest by Saturday. There is also a deep
upper-trough tracking through eastern Canada, which in contrast
with the upper-ridge to the south will create tight thermal and
moisture gradient from the Great Lakes to the Northeast. The 850mb
ridge will remain positioned over the Mid-South and is ideally
located to produce an extended fetch of southerly flow over the
Southern Plains.

This results in unusually strong IVTs over the Great Plains and
Midwest on Day 4. The Midwest becomes the focus for flash flood
potential as a pair of jet streaks; one over the Great Lakes and
another emerging from the Rockies, place their divergent jet streak
quadrants overhead. Combined with PWs >1.75", which is above the
99th climatological percentile for mid-September, this serves as
an ideal setup for additional rounds of excessive rainfall. The
Midwest will have also dealt with heavy rainfall the first half of
the week, making overly saturated soils a key player in potential
flash flooding late week. A Slight Risk remains in place over parts
of the Upper Midwest with 1-3" of rainfall possible. By Day 5, the
anomalous IVT mentioned for Day for moves into the Great Lakes and
Northeast. ECMWF SATs show >90th climatological percentile IVTs
aimed at these regions. When combined with increasing instability
and a nearby frontal boundary present, the expectation is for
numerous showers and thunderstorms capable of producing localized
flash flooding to occur. WPC QPF highlights Michigan's Lower
Peninsula and as far west as eastern WI as being the wettest, so a
Slight Risk was issued there for Day 5.

Lastly, the Southwest remains mired in a steadfast monsoonal flow
regime that is pumping copious amounts of moisture into the region.
Day after day, scattered thunderstorms will produce locally
excessive rainfall rates in excess of 1"/hr, keeping the threat for
flash flooding in place into the start of the upcoming weekend.
The ridge in the Southeast will begin to weaken late week, and thus
the axis of heavy rainfall is likely to shift farther east into
eastern NM and western TX and the TX Panhandle. A large Marginal
Risk encompasses these sections of the Southwest and western TX
through Day 5.

Mullinax
 

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



$$