Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
850 PM EDT Sun Sep 13 2026
Day 1
Valid 01Z Mon Sep 14 2026 - 12Z Mon Sep 14 2026
...THERE ARE MARGINAL RISK AREAS FOR EXCESSIVE RAINFALL OVER
PORTIONS OF THE SOUTHWEST, PLAINS AND MID-ATLANTIC...
...Plains and MS Valley...
An uptick in moisture transport will result in increased
convective coverage later tonight over northeast KS, eastern NE,
northwest MO, western IA and southeast SD. While some brief
training is a possibility, activity should generally push off to
the northeast at a decent clip. Given this storm propagation and
only modest forecast instability, currently not anticipating an
organized flash flood risk to evolve. Recent HRRR runs and the
AIFS point towards the NE/IA/MO border area as seeing the greatest
convective coverage by later tonight, but generally only expecting
1-2" amounts. A few locally higher totals could result in an
isolated flash flood potential, but a Marginal risk should suffice
to cover this threat.
...Southwest...
Isolated convection will continue across the Southwest this
evening. While we should see the typical nocturnal decrease in
convective coverage and intensity, a bit more persistence than
normal is expected given some larger scale forcing in place to go
along with low level moisture transport and lingering instability.
Thus a localized flash flood risk could continue through much of
the night in spots.
...Mid-Atlantic...
Convection along a cold front may locally exceed the lowered FFG
across portions of WV and far southwest PA this evening. Quick
cell motions should limit overall rainfall magnitudes, and would
thus only expect to see very localized totals approaching or
marginally exceeding FFG.
Chenard
Day 1 threat area:
www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
340 AM EDT Mon Sep 14 2026
Day 1
Valid 12Z Mon Sep 14 2026 - 12Z Tue Sep 15 2026
...THERE IS A MODERATE RISK FOR EXCESSIVE RAINFALL OVER PORTIONS OF
CENTRAL AND SOUTHWESTERN IOWA...
...Midwest...
The beginning of the week will feature a significant shift in the
upper pattern across the northern tier of the CONUS with a strong
mid-level trough ejecting out of the Northern Rockies into the
Northern Plains on Monday and beyond leading to a pronounced area
of diffluent flow centered over the Northern High Plains to Midwest
corridor. Further south, a strong upper level ridge continues to be
a factor in the overall longwave pattern across the CONUS leading
to a true stalemate in the progression southward of any cold air
advection regime and associated frontal boundary. Expectation has
been for a cold front to sweep southeast into the region of the
I-80 corridor, perhaps a bit further south, but truly slow in its
progression as the front encounters prevailing southerlies in place
over the Mississippi Valley back into the High Plains thanks to
the strong ridge centered over the Southeastern U.S. The progged
synoptic progression, along with the mid and upper level evolution
will aid in the initiation of a prolonged heavy rain threat with a
bimodal distribution of convective impacts with the time frames of
interest occurring in the morning and evening of D1, and eventually
in the days following.
A deep, moist environment centered over the nations mid-section
will provide the necessary element for deeper, stronger convective
cores capable of producing heavy rainfall prospects whenever
convection can materialize. According to the latest ECENS and NAEFS
anomaly fields, PWATs will be on the order of +2 to +4 standard
deviations leading to true values of 1.7-2.1" with a sharp gradient
on the northern edge of a quasi-stationary front that will bisect
the region by later this evening. Multiple mid-level shortwave
disturbances will motion out of the Central High Plains, the first
of which occurring in the morning hours today, along with an
approaching warm front, will lead to an initial wave of convection
migrating southwest to northeast, but remaining relatively
progressive in its progression. Heavier rainfall will occur in the
afternoon time frame further northeast into the Upper Midwest with
this particular disturbance, but the forward propagation speed will
likely deter a more appreciable rainfall footprint leading to
perhaps some isolated flash flood concerns in mainly urbanized
zones centered from the Missouri River Valley up through the
southern-third of MN.
By the evening hours, a shortwave will enter the region from the
southwest with the primary shortwave trough migrating through the
Dakotas leading to increasing ascent located over the Central
Plains over into the Corn Belt. At the surface, the aforementioned
cold front will slow its progression to the southeast and fan out
with an alignment from southwest to northeast, matching the mean
flow between 850-300mb. A nocturnal LLJ enhancement will occur over
the Mid-Mississippi Valley, extending into the vicinity of the
front leading to enhanced low-level convergence and modest low-
level frontogenesis across the Corn Belt back into the Missouri
River Valley. Expectation is for a rapid development of convection
across the the corridor of KS/NE, expanding to the east with a
centroid of the heaviest rainfall and convective coverage over
southwestern to central IA. This has been a signature that has
grown with time as the event has approached with the latest HREF
able to capture the entirety of the D1 within its temporal range.
The results of this evenings CAMs output depicted a more prolific
heavy rain threat for the above area with the HREF blended mean QPF
running between 3-5" over the area encompassing Des Moines and
points south and southwest. Associated neighborhood and EAS
probabilities are running generally hot for the setup with the
former producing a resounding 60-80% probability for >3" across the
aforementioned area, even depicting a 25-30% prob for >5" in the
same location. The EAS probabilities for >2" are upwards of 60-70%
in the area near Des Moines, a signature typically seen during more
appreciable setups with strong agreement from the CAMs suite. FFG
exceedance probabilities are also elevated with 3hr exceedance
probs firmly between 50-70% noting the potential widespread
impacts increasingly likely over that area of IA.
There is still a bit of uncertainty for how far back west the
heaviest rainfall potential extends with some CAMs noting
significant 3+ inch totals back into southeastern NE as well, but
the EAS probs are not as keen on this area, noting less overlap in
the CAMs overall. At this juncture, considering a strong confidence
in the CAMs given the EAS signal, as well as FFG's running between
1.5-2.5" for 3-hr exceedance, and in coordination with the Des
Moines WFO, a small Moderate Risk was introduced for the D1 ERO to
cover for the forecast threat. Locally significant rainfall between
3-6" is forecast over the area outlined with the main concerns
being urban footprints and those low-water crossing locations
located south of I-80 in IA. A broad SLGT still encompasses much of
the Midwest from the Door Peninsula down through eastern NE and
points in-between. Expectation is for at least scattered flash
flooding to occur with this setup with an expectation for heavy
rainfall to linger into the early morning hours Tuesday.
...Southwest...
The Southwestern U.S. will remain locked into prolonged southerly
flow aloft as the region sits on the western fringes of a broad
ridge axis further east. This will maintain a prominent moisture
advection pattern over the area with PWAT anomalies firmly in the
+2 to +3 standard deviations range, coincident with PWATs
encroaching on the 95-99th percentile over eastern AZ up through
much of NM into southern CO. Coupled with a suitable diurnal heat
flux leading to SBCAPE signatures between 1000-2500 J/kg over the
area, scattered to widespread showers and thunderstorms will
materialize over the above area leading to scattered flash flood
concerns for the afternoon and evening hours. A strong 60-90%
neighborhood probability for >1" exists over a large portion of NM
into eastern AZ and southwestern CO, coinciding with an array of
complex terrain features and remnant burn scars noted for flash
flooding in any stronger convective environments. The signal for
>2" maintains a modest signature as well, with the greatest signal
residing in southeastern AZ within the forecast thermodynamic max
(SBCAPE >2000 J/kg). The environmental factors and widespread
nature of the convection are suitable for a broad SLGT risk over
the region with the primary target currently aimed west of the I-25
corridor.
Kleebauer
Day 1 threat area:
www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
340 AM EDT Mon Sep 14 2026
Day 2
Valid 12Z Tue Sep 15 2026 - 12Z Wed Sep 16 2026
...THERE ARE SLIGHT RISKS FOR EXCESSIVE RAINFALL OVER PORTIONS OF
THE CENTRAL PLAINS, MISSOURI VALLEY, AND SOUTHWEST U.S...
...Central U.S...
The D2 period will continue to exhibit the threat for heavy
rainfall across portions of the Central U.S. with the area located
from northeastern KS up through southeastern NE and northwestern MO
as the primary area of impact. Cold front will slowly sag southward
with the aid of a high pressure building in from the Canadian
Prairies, edging southward with the push of cooler, more stable
continental air leading to the threat of heavy rain over much of IA
to cut off by Tuesday afternoon. The setup is a bit similar to the
previous period with increasing convergence in vicinity of the
front with the main time frame of interest centered over Tuesday
evening with the additional LLJ element. Forecast soundings from
various NWP indicate a prevailing wind field aloft that would align
parallel to the boundary leading to another round of training
convection from KS to points east-northeast. PWAT anomalies will
remain around +2 to +3 deviations with true values hovering around
that 2" marker. There's a general consensus on a swath of 2-3" of
rainfall over that area of northeastern KS and points eastward with
much of the global deterministic solidly in the 2-4" range which
agrees with the latest ML outputs. This agreement among models is a
solid signal for at least scattered flash flood prospects as the
environmental conditions favor areas of 1-2"/hr rates as convection
motions over the area. A high-end SLGT is forecast for this region
of the CONUS with a chance at a higher risk pending future
forecasts. We are just outside the full temporal range of the CAMs
for entire D2 period, so its plausible to see a higher risk added
if the CAMs indicate a higher risk for 3+ inches of rainfall. Until
then, maintained continuity from the previous forecast.
...Southwest U.S...
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 scattered 1+
inch totals depicted across much of the global deterministic. This
will be the 4th day in a row with this pattern persistence leading
to some areas becoming more and more vulnerable for flash flood
prospects. Continue to see the 18-06z period as the time range of
interest which is coincident with the diurnal instability maximum.
A broad SLGT remains positioned over the aforementioned areas with
an emphasis on eastern AZ and the western half of NM.
Kleebauer
Day 2 threat area:
www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
340 AM EDT Mon Sep 14 2026
Day 3
Valid 12Z Wed Sep 16 2026 - 12Z Thu Sep 17 2026
...THERE ARE SLIGHT RISKS FOR EXCESSIVE RAINFALL OVER PORTIONS OF
THE CENTRAL PLAINS, MIDWEST, & SOUTHWESTERN U.S...
...Central Plains & Midwest...
Our multi-day setup across the Central U.S. continues through mid-
week with the pattern shifting back north into the Corn Belt and
adjacent areas of the Midwest with the synoptic evolution entailing
another approach of our quasi-stationary front, although this time
from the south as the high pressure to the north slides eastward
and brings back return flow to the Plains. Aloft, a strengthening
250mb jet streak will situate itself over the Upper Midwest and
Great Lakes providing excellent RER jet dynamics under the
influence of a 120kt speed max centered over the northern tier of
the CONUS. The next wave of convection will likely generate with
the addition of yet another prominent LLJ development, this one
likely to be with more vigor as the jet has influence from the
return flow regime on the western side of the surface ridge to the
northeast. Deep moisture plume will advect poleward leading the
convergent pattern to materialize, once again, for the area between
northeast KS, eastern NE, through much of IA for Wednesday evening.
This area is increasingly likely to see a broad axis of 2-3" as an
areal average with embedded maxima likely to breach 4" when looking
at the different global deterministic outputs and 90th percentile
ensemble means. This setup is favorable for overlap with some areas
that will be impacted on D1 in the region of IA which could very
well lead to more widespread flash flood concerns for the period.
As of now, elected to maintain the broad SLGT risk over the Midwest
back into portions of the Central Plains, however a high-end SLGT
is now forecast for much of IA, especially areas along and south of
I-80 between Council Bluff to Davenport. There is a potential for
an upgrade in future updates, so stay tuned for the latest forecast
over the next 48hrs.
...Southwest U.S...
Another period of scattered to widespread convective activity is
forecast for areas of the Southwestern U.S. with the general axis
aligned over eastern AZ into NM and southern CO. Wednesday is
leaning towards the peak of impacts, however, as a more robust
shortwave ejection out of Mexico will likely provide further mid
and upper level ascent that can exacerbate an already formidable
environment. PWAT anomalies will remain in the +2 to +3 standard
deviation range which is already an asset to more appreciable
rainfall potential when you couple with a primed thermodynamic
environment. Ensemble means are aggressive for Wednesday afternoon
into early Thursday morning with some models printing out 2-3" in
spots across 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 the state. This threat has led to an introduction of higher
end SLGT risk wording with a chance for even an upgrade further if
the models show more appreciable rainfall forecasts in the coming
days.
Unlike previous periods, there is more of a threat further west
with this evolution leading to an extension of a MRGL back into
southwestern and southern UT to cover for the threat of flash
flooding within the slot canyon regions of the west. SLGT risk
expands west through the Mogollon Rim, as well, thanks to the
surge in PWATs and added forcing.
Kleebauer
Day 3 threat area:
www.wpc.ncep.noaa.gov/qpf/99epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
340 AM EDT Mon Sep 14 2026
Day 4 and Day 5
Valid 12Z Thu Sep 17 2026 - 12Z Sat Sep 19 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE SOUTHWEST U.S, CENTRAL PLAINS, MISSOURI VALLEY, AND INTO THE UPPER
MIDWEST...
The Days 4-5 period (Thu. Sept 17 - Fri. Sept 18) can be
summarized 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 West makes its way from the West Coast
towards the Northern Rockies. 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 both Days 4
and 5. The ECMWF SATs show >90th climatological percentile IVTs
aimed at the Great Lakes and Northeast on Day 4, which combined
with increasing instability and a nearby frontal boundary present,
could lead to scattered thunderstorms capable of producing
localized flash flooding.
By Day 5, 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, 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 pair of Slight Risks are in place over parts of the
North Central U.S. for both Thursday and Friday to cover this
prolonged window of excessive rainfall.
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 through the end of the week. A Slight Risk
remains in place for Day 4 (Thursday) while a large Marginal
encompasses an area that extends from southern NM and western TX,
to northern AZ and the Central Rockies.
Mullinax
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
340 AM EDT Mon Sep 14 2026
Day 4 and Day 5
Valid 12Z Thu Sep 17 2026 - 12Z Sat Sep 19 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE SOUTHWEST U.S, CENTRAL PLAINS, MISSOURI VALLEY, AND INTO THE UPPER
MIDWEST...
The Days 4-5 period (Thu. Sept 17 - Fri. Sept 18) can be
summarized 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 West makes its way from the West Coast
towards the Northern Rockies. 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 both Days 4
and 5. The ECMWF SATs show >90th climatological percentile IVTs
aimed at the Great Lakes and Northeast on Day 4, which combined
with increasing instability and a nearby frontal boundary present,
could lead to scattered thunderstorms capable of producing
localized flash flooding.
By Day 5, 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, 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 pair of Slight Risks are in place over parts of the
North Central U.S. for both Thursday and Friday to cover this
prolonged window of excessive rainfall.
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 through the end of the week. A Slight Risk
remains in place for Day 4 (Thursday) while a large Marginal
encompasses an area that extends from southern NM and western TX,
to northern AZ and the Central Rockies.
Mullinax
