Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
400 PM EDT Wed Sep 9 2026
Day 1
Valid 01Z Wed Sep 09 2026 - 12Z Thu Sep 10 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM SOUTHEAST
KANSAS INTO SOUTH CENTRAL MISSOURI, OVER SOUTHEAST COLORADO, SOUTHEAST
ARIZONA AND FAR SOUTHWEST NEW MEXICO...
16Z Update..
Minimal changes were made in this update, other than minor
adjustments to the inherited MRGL risk areas in the Southwest and
an expansion of the MRGL in the Mid-West. Latest CAMs guidance
depict a progressive line of thunderstorms forming along a cold
front, which per the latest HREF/RRFS guidance will support 1"/hr
rainfall rates in the newly expanded MRGL Risk area over the Mid-
West. Given the consistency over the expected progression, the risk
level was kept as a MRGL. In the Southwest, a removal of the MRGL
over the Sonora Desert in Arizona and California was needed given
updated QPF guidance suggesting reduced precip chances, and a lack
of a solid QPF signal among the majority of guidance. Otherwise,
the previous outlook and discussion remain in good shape.
Blanco-Alcala
...Previous Discussion...
An axis of above average PW values, 2+ standard deviations above
the mean, expected along the surface cold front pressing generally
southeastward day 1 through the Great Lakes into the Northeast and
southward through the Mid Mississippi Valley and into the Central
Plains. The northeastern portion of the front moving across the
Great Lakes into the Upper Ohio Valley and Northeast will be very
progressive, limiting any widespread runoff issues. Widespread
moderate to locally heavy rains possible along and ahead of this
potion of the front, with the risk level kept at marginal given the
expected progression.
..Central Plains into the Lower Missouri Valley...
Slower movement of the frontal boundary expected from the Central
Plains into the Lower Missouri Valley/Mid Mississippi Valley where
it will become more aligned to the westerly mid to upper level
flow. Simulated radars from the CAMS show general agreement with
the potential for training of cells in a west to east direction in
the 0000- 1200 UTC Thursday time period. HREF and RRFS
neighborhood probabilities for 1, 2 and 3"+ totals remain high in
the slight risk area from southeast Kansas into south-central
Missouri. A small slight risk area was introduced over southeast
Colorado where there is consensus for potentially heavy rains where
low level easterly to southeasterly flow is expected to strengthen
in the early hours of Thursday. HREF and RRFS probabilities of 3
hourly precip exceeding FFG values are in a similar area over
southeast Colorado early Thursday, with probabilities as high as 30
to 40%+ in the 0600-1200 UTC Thursday period.
...Southwest...
No changes made to the coordinated slight risk area across
southeast Arizona into far southwest New Mexico. Additional
scattered convection likely in the above average PW axis. The
slight risk area continues to coincide well with where the RRFS
and HREF show max probabilities of 3 hourly precip exceeding FFG
values. The RRFS is more emphatic than the HREF with these
probabilities, with values as high as 45-60%, compared to the HREF
range of 15-30%. No changes made to remainder of the broad
marginal risk from the Sierra, southward into Southeast CA and
eastward across portions of AZ and NM.
...Southwest Florida...
A weak mid level wave pushing west across South Florida will help
enhance uvvs in the tropical airmass, PW values 2.00-2.25"+. A
marginal risk area was added for Southwest Florida where HREF and
RRFS neighborhood probabilities are high for 1, 2 and 3"+ amounts.
The HREF is more emphatic about heavy rains, showing probabilities
of 3 hour precip exceeding FFG values as high as 40-60% late
Wednesday afternoon. This heavy rain potential may lead to
localized runoff issues, especially in more urbanized areas.
Oravec
Day 1 threat area:
www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
400 PM EDT Wed Sep 9 2026
Day 2
Valid 12Z Thu Sep 10 2026 - 12Z Fri Sep 11 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER THE UPPER OHIO
VALLEY INTO THE CENTRAL APPALACHIANS...
20Z Update..
A MRGL Risk area was introduced along the Gulf Coast in Louisiana
and Mississippi. A wave/surface trough feature in the northern Gulf
will promote southerly low-level flow onto the coast, bringing
along with it high PWAT values (>2.25"). This will support heavy
rainfall, with HREF/RRFS guidances suggesting medium-to-high
chances (~60-70%) of 1"/hr rain rates. Moisture moves eastward
through the coast, bringing heavy rain into AL, GA, and FL, but is
currently forecast to bring a shorter duration of heavy rainfall,
and as such, a MRGL was left out for now.
Elsewhere, nearly no change was made to the inherited SLGT risk
area in the Ohio Valley, other than a minimal westward nudge into
Ohio given a solid QPF EFI signature in the ECMWF. Minor
restructuring of the inherited MRGL Risk area in the Southwest was
also made to capture the latest run of global and early CAMs
guidance.
Blanco-Alcala
...Previous Discussion...
...Upper Ohio Valley into the Central Appalachians.. PW values 2+
standard deviations above the mean are forecast along the west-east
oriented frontal boundary sinking south through the Ohio Valley,
Central Appalachians and Mid-Atlantic region day 2. The previous
slight risk area was adjusted southward by approximately 80-100
miles to fit the latest model qpf consensus for potentially heavy
rains. H85 flow parallel to this front will support training
potential and also enhance uvvs in the upslope regions of the
Central Appalachians.
Marginal Risk areas.
...Southwest...
A marginal risk area was continued over portions of the Southwest
for potential for local heavy rains and isolated runoff issues in
the continued axis of above average PW values forecast across this
area. A marginal risk was also added for the Transverse Range of
Southern California where the RRFS was showing neighborhood
probabilities as high as 45%+ for 1"+ totals.
...Lower OH Valley, Mid to Lower MS Valley into the Southern
Plains...
A broad marginal risk area was maintained to the
southwest of the Upper OH Valley/Central Appalachians slight risk
area, extending into the Lower OH Valley, Mid to Lower MS Valley
and westward into the Southern Plains of OK and northwest TX.
Scattered convection likely along the surface frontal boundary
where PW values will remain high, 1.75-2.00"+, but with FFG values
high and confidence low with where convection may maximize, the
threat level was kept at marginal.
Oravec
Day 2 threat area:
www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
400 PM EDT Wed Sep 9 2026
Day 3
Valid 12Z Fri Sep 11 2026 - 12Z Sat Sep 12 2026
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FROM THE LOWER
MISSISSIPPI VALLEY INTO THE TENNESSEE VALLEY AND SOUTHERN
APPALACHIANS, OVER THE UPPER MISSISSIPPI VALLEY INTO THE CENTRAL
PLAINS AND OVER PORTIONS OF THE SOUTHWEST AND SOUTHERN GREAT
BASIN...
20Z Update..
Only cosmetic adjustments and changes to match with the latest run
of global and ensemble guidance were made. High QPF was noted in
central to northeast Minnesota, with a cold front expected to bring
short-lived, fast-moving, and efficient rainfall. However, there
is a lack of consensus between global model guidance as to the
location of the heaviest rainfall, with solutions ranging between
central and northeast Minnesota. Given the uncertainty, and
moderate-to-severe drought conditions, no upgrade was introduced
with this update.
Blanco-Alcala
...Previous Discussion...
...Lower MS Valley, TN Valley into the Southern Appalachians...
Above average PW expected across much of the southeast quarter of
the nation from the Lower MS Valley, eastward across the TN Valley
and into the Southern Appalachians during day 3. Models are
showing some trof amplification across this area, with broad upper
difluence in this above average PW axis supporting widespread
scattered convection. With low confidence in qpf details and high
FFG values across these areas, the threat level is kept at
marginal.
...Upper MS Valley into portions of the Central Plains...
A surface front expected to push east southeastward across the
Northern-Central Plains into the Upper MS Valley day 3. Model
consensus is for potential of locally heavy rains along and ahead
of this front. The previous broad marginal risk was narrowed to fit
the latest qpf axis consensus.
...Southwest into the southern Great Basin...
Increasing westerly mid level flow on the south side of the
amplifying closed low over the Pac NW day 3 will help push the
primary anomalous PW axis over the Southwest eastward from the day
2 position, becoming oriented from Southeast CA, into Arizona and
northward into the Great Basin. While there are the typical amount
of model qpf spread in this type of flow regime at day 3, there is
general consensus for scattered convection in this anomalous PW
axis, 1 to 2+ standard deviations above the mean. Locally heavy
rains and isolated runoff issues possible, with low confidence in
any qpf details.
Oravec
Day 3 threat area:
www.wpc.ncep.noaa.gov/qpf/99epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
400 PM EDT Wed Sep 9 2026
Day 4 and Day 5
Valid 12Z Sat Sep 12 2026 - 12Z Mon Sep 14 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PARTS OF THE
LOWER MISSOURI VALLEY AND UPPER MISSISSIPPI VALLEY THIS WEEKEND...
2000 UTC Update -- Mainly minor adjustments were made to the Day 4
ERO (12Z Sat-12Z Sun), based on the latest deterministic guidance
and trends, along with the latest ECMWF/GEFS/CMC probabilistic
suite. The Slight Risk became slightly more confined to (mainly)
eastern KS and western MO.
On Day 5 (12Z Sun-12Z Mon), with the upper height rises and as
stationary boundary lifts north as a warm front, the guidance
appears to be converging on a wetter scenario farther north of the
Day 4 Slight Risk area, i.e. eastern NE/SD into southern MN, much
of IA, and western WI. This would be the path of where the next
MCS activity ("ridge crawlers") would take according to the growing
guidance consensus. The latest global QPF exceedance probabilities
are highest within the new Day 5 Slight Risk area, which is
essentially what we used to delineate the Slight vs. surrounding
Marginal Risk area.
We also added a Marginal Risk on Day 5 across parts of the
Southwest and Four Corners region. The monsoonal characteristics
remain in play Sunday, albeit perhaps more confined and shifted
farther west from Saturday. Some of the guidance, especially the
GFS and AIGFS, are actually more bullish with the QPF in that area
on Sunday vs. Saturday.
Hurley
Previous discussion below...
...Central Plains and Missouri Valley...
Multiple rounds of storms are possible across the Central Plains
and Missouri Valley on Saturday. A well-established low-level jet
will be in place across the area as a progressive cold front sweeps
across the upper Great Lakes Friday night. The front will stall out
over this region due in part to the countering southerly flow of
the LLJ. Meanwhile, in the upper levels, disturbances will move
northeast with the flow, in part spurred on by those thunderstorms.
At the surface, a leeside low over the TX/OK Panhandles into Kansas
will keep the southerly LLJ going right into the stalling front.
The result will be likely training storms over some part of the
area, with the guidance showing their usual spread as to exactly
where that happens. For the second consecutive day, the guidance
has been largely targeting eastern Kansas as the centroid of the
action. Given the relative consistency from 24 hours ago, increased
forecasted rainfall, and a favorable pattern for slow-moving and
training storms, confidence increased to issue a Slight Risk for
the area on Saturday. All of this not to mention that there will
likely be storms into eastern Kansas on Friday night that will
likely prime the soils in advance of the storms Saturday and
Saturday night.
Elsewhere, large Marginals remain in place from tech central Gulf
Coast into the Mid-Atlantic. The I-95 corridor from DC to NYC was
added to the Marginal with this update. Plentiful tropical moisture
will surge northward in the wake of a warm front that made for a
nice Labor Day Weekend in the Mid-Atlantic when as a back-door cold
front the moisture was shoved out of the Mid-Atlantic and into the
Southeast. Late in the day Saturday, a strong cold front moving
through will allow that moisture to fuel numerous thunderstorms.
Those storms will have the potential for training ahead of the
front in the unidirectional southwesterly flow. Given the urban
sensitivities, that allowed the Marginal to be expanded.
On Sunday, a developing Plains leeside low, fueled by a strong
upper level bowling ball low, will track northeastward across the
northern Plains. The aforementioned LLJ over KS/MO on Saturday will
continue northward into the upper Midwest due to that low driving
it and all its associated moisture northward with it. Since the low
itself will be tracking roughly parallel to the flow with the upper
level low also moving northeast, a prolonged period of
unidirectional southwesterly flow will allow for training and
backbuilding storms, that while moving, will impact many of the
same areas repeatedly Sunday into Sunday night. The area of
greatest concern is from far northeastern Nebraska northeast across
much of Iowa, southern Minnesota, and into western Wisconsin. PWATs
of 2-2.25 inches will allow the storms to be very capable of heavy
rainfall. Both surface and upper level lows will be on the
stronger side compared to climatology, so forcing will also not be
a problem. Additional upgrades are likely in the coming days should
this pattern persist in the guidance. For now it remains a Marginal
until consistency on where the strongest storms will occur is
better ironed out.
Wegman
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
400 PM EDT Wed Sep 9 2026
Day 4 and Day 5
Valid 12Z Sat Sep 12 2026 - 12Z Mon Sep 14 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PARTS OF THE
LOWER MISSOURI VALLEY AND UPPER MISSISSIPPI VALLEY THIS WEEKEND...
2000 UTC Update -- Mainly minor adjustments were made to the Day 4
ERO (12Z Sat-12Z Sun), based on the latest deterministic guidance
and trends, along with the latest ECMWF/GEFS/CMC probabilistic
suite. The Slight Risk became slightly more confined to (mainly)
eastern KS and western MO.
On Day 5 (12Z Sun-12Z Mon), with the upper height rises and as
stationary boundary lifts north as a warm front, the guidance
appears to be converging on a wetter scenario farther north of the
Day 4 Slight Risk area, i.e. eastern NE/SD into southern MN, much
of IA, and western WI. This would be the path of where the next
MCS activity ("ridge crawlers") would take according to the growing
guidance consensus. The latest global QPF exceedance probabilities
are highest within the new Day 5 Slight Risk area, which is
essentially what we used to delineate the Slight vs. surrounding
Marginal Risk area.
We also added a Marginal Risk on Day 5 across parts of the
Southwest and Four Corners region. The monsoonal characteristics
remain in play Sunday, albeit perhaps more confined and shifted
farther west from Saturday. Some of the guidance, especially the
GFS and AIGFS, are actually more bullish with the QPF in that area
on Sunday vs. Saturday.
Hurley
Previous discussion below...
...Central Plains and Missouri Valley...
Multiple rounds of storms are possible across the Central Plains
and Missouri Valley on Saturday. A well-established low-level jet
will be in place across the area as a progressive cold front sweeps
across the upper Great Lakes Friday night. The front will stall out
over this region due in part to the countering southerly flow of
the LLJ. Meanwhile, in the upper levels, disturbances will move
northeast with the flow, in part spurred on by those thunderstorms.
At the surface, a leeside low over the TX/OK Panhandles into Kansas
will keep the southerly LLJ going right into the stalling front.
The result will be likely training storms over some part of the
area, with the guidance showing their usual spread as to exactly
where that happens. For the second consecutive day, the guidance
has been largely targeting eastern Kansas as the centroid of the
action. Given the relative consistency from 24 hours ago, increased
forecasted rainfall, and a favorable pattern for slow-moving and
training storms, confidence increased to issue a Slight Risk for
the area on Saturday. All of this not to mention that there will
likely be storms into eastern Kansas on Friday night that will
likely prime the soils in advance of the storms Saturday and
Saturday night.
Elsewhere, large Marginals remain in place from tech central Gulf
Coast into the Mid-Atlantic. The I-95 corridor from DC to NYC was
added to the Marginal with this update. Plentiful tropical moisture
will surge northward in the wake of a warm front that made for a
nice Labor Day Weekend in the Mid-Atlantic when as a back-door cold
front the moisture was shoved out of the Mid-Atlantic and into the
Southeast. Late in the day Saturday, a strong cold front moving
through will allow that moisture to fuel numerous thunderstorms.
Those storms will have the potential for training ahead of the
front in the unidirectional southwesterly flow. Given the urban
sensitivities, that allowed the Marginal to be expanded.
On Sunday, a developing Plains leeside low, fueled by a strong
upper level bowling ball low, will track northeastward across the
northern Plains. The aforementioned LLJ over KS/MO on Saturday will
continue northward into the upper Midwest due to that low driving
it and all its associated moisture northward with it. Since the low
itself will be tracking roughly parallel to the flow with the upper
level low also moving northeast, a prolonged period of
unidirectional southwesterly flow will allow for training and
backbuilding storms, that while moving, will impact many of the
same areas repeatedly Sunday into Sunday night. The area of
greatest concern is from far northeastern Nebraska northeast across
much of Iowa, southern Minnesota, and into western Wisconsin. PWATs
of 2-2.25 inches will allow the storms to be very capable of heavy
rainfall. Both surface and upper level lows will be on the
stronger side compared to climatology, so forcing will also not be
a problem. Additional upgrades are likely in the coming days should
this pattern persist in the guidance. For now it remains a Marginal
until consistency on where the strongest storms will occur is
better ironed out.
Wegman
